This PDF file contains the front matter associated with SPIE Proceedings Volume 9467, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Conceived in ~1971 [1,2] and first experimentally demonstrated in 1994 [3], quantum cascade lasers have become the most importance sources of infrared laser radiation in the 3.5 μm to >12 μm spectral region. With needs already identified at even longer wavelengths, QCLs are being pursued vigorously as sources of terahertz laser radiation. The mid wave infrared (MWIR) and the long wave infrared (LWIR) regions are, however, significantly more important because of a number defense, homeland security and commercial applications critically require the capabilities of QCLs. These capabilities include size, weight and power considerations (SWaP), which make QCLs unique among all other potential sources of laser radiation in this region including optical parametric oscillators, optically pumped semiconductors and optically pumped solids. In this presentation, I will summarize some of the key advances and status of QCL technology as well as defense and civilian applications of the MWIR and LWIR quantum cascade lasers.

As advanced as modern machines are, the building blocks have changed little since the industrial revolution, leading to rigid, bulky, and complex devices. Future machines will include electromechanical systems that are soft and elastically deformable, lending them to applications such as soft robotics, wearable/implantable devices, sensory skins, and energy storage and transport systems. One key step toward the realization of soft systems is the development of stretchable electronics that remain functional even when subject to high strains. Liquid-metal traces embedded in elastic polymers present a unique opportunity to retain the function of rigid metal conductors while leveraging the deformable properties of liquid-elastomer composites. However, in order to achieve the potential benefits of liquid-metal, scalable processing and manufacturing methods must be identified.

Conventional, rigid materials remain the key building blocks of most modern electronic devices, but they are limited in their ability to conform to curvilinear surfaces. It is possible to make electronic components that are flexible and in some cases stretchable by utilizing thin films, engineered geometries, or inherently soft and stretchable materials that maintain their function during deformation. Here, we describe the properties and applications of a micromoldable liquid metal that can form conductive components that are ultra-stretchable, soft, and shape-reconfigurable. This liquid metal is a gallium-based alloy with low viscosity and high conductivity. The metal develops spontaneously a thin, passivating oxide layer on the surface that allows the metal to be molded into non-spherical shapes, including films and wires, and patterned by direct-write techniques or microfluidic injection. Furthermore, unlike mercury, the liquid metal has low toxicity and negligible vapor pressure. This paper discusses the mechanical and electrical properties of the metal in the context of electronics, and discusses how the properties of the oxide layer have been exploited for new patterning techniques that enable soft, stretchable and reconfigurable devices.

Current developments on enhancing our smart living experience are leveraging the increased interest for novel systems that can be compatible with foldable, wrinkled, wavy and complex geometries and surfaces, and thus become truly ubiquitous and easy to deploy. Therefore, relying on innovative structural designs we have been able to reconfigure the physical form of various materials, to achieve remarkable mechanical flexibility and stretchability, which provides us with the perfect platform to develop enhanced electronic systems for application in entertainment, healthcare, fitness and wellness, military and manufacturing industry. Based on these novel structural designs we have developed a siliconbased network of hexagonal islands connected through double-spiral springs, forming an ultra-stretchable (~1000%) array for full compliance to highly asymmetric shapes and surfaces, as well as a serpentine design used to show an ultrastretchable (~800%) and flexible, spatially reconfigurable, mobile, metallic thin film copper (Cu)-based, body-integrated and non-invasive thermal heater with wireless controlling capability, reusability, heating-adaptability and affordability due to low-cost complementary metal oxide semiconductor (CMOS)-compatible integration.

Two-dimensional (2D) semiconductors with high carrier mobilities and sizeable bandgap are desirable for future high-speed and low power mechanically flexible nanoelectronics. In this work, we report encapsulated bottom-gated black phosphorus (BP) field-effect transistors (FETs) on flexible polyimide affording maximum carrier mobility of about 310cm²/V∙s and current on/off ratio exceeding 10³. Essential circuits of flexible electronic systems enabled by the device ambipolar functionality, high-mobility and current saturation are demonstrated in this work, including digital inverter, frequency doubler, and analog amplifiers featuring a voltage gain of ~8.7, which is the state-of-the-art value for flexible 2D semiconductor based amplifiers. In addition, we demonstrate the single FET based flexible BP amplitude-modulated (AM) demodulator, an active stage in radio receivers.

We report a simple, versatile, and wafer-scale water-assisted transfer printing method (WTP) that enables the transfer of nanowire devices onto diverse nonconventional substrates that were not easily accessible before, such as paper, plastics, tapes, glass, polydimethylsiloxane (PDMS), aluminum foil, and ultrathin polymer substrates. The WTP method relies on the phenomenon of water penetrating into the interface between Ni and SiO₂. The transfer yield is nearly 100%, and the transferred devices, including NW resistors, diodes, and field effect transistors, maintain their original geometries and electronic properties with high fidelity.

Flexible or stretchable electronic devices for healthcare technologies have attracted much attention in terms of usefulness to assist doctors in their operating rooms and to monitor patients’ physical conditions for a long period of time. Each device to monitor the patients’ physiological signals real-time, such as strain, pressure, temperature, and humidity, etc. has been reported recently. However, their limitations are found in acquisition of various physiological signals simultaneously because all the functions are not assembled in one skin-like electronic system. Here, we describe a skin-like, multi-functional healthcare system, which includes single crystalline silicon nanomembrane based sensors, nanoparticle-integrated non-volatile memory modules, electro-resistive thermal actuators, and drug delivery. Smart prosthetics coupled with therapeutic electronic system would provide new approaches to personalized healthcare.

This paper describes a novel, wearable, battery powered ultrasound applicator that was evaluated as a therapeutic tool for healing of chronic wounds, such as venous ulcers. The low frequency and low intensity (~100mW/cm²) applicator works by generating ultrasound waves with peak-to-peak pressure amplitudes of 55 kPa at 20 kHz. The device was used in a pilot human study (n=25) concurrently with remote optical (diffuse correlation spectroscopy - DCS) monitoring to assess the healing outcome. More specifically, the ulcers’ healing status was determined by measuring tissue oxygenation and blood flow in the capillary network. This procedure facilitated an early prognosis of the treatment outcome and – once verified - may eventually enable customization of wound management. The outcome of the study shows that the healing patients of the ultrasound treated group had a statistically improved (p<0.05) average rate of wound healing (20.6%/week) compared to the control group (5.3%/week). In addition, the calculated blood flow index (BFI) decreased more rapidly in wounds that decreased in size, indicating a correlation between BFI and wound healing prediction. Overall, the results presented support the notion that active low frequency ultrasound treatment of chronic venous ulcers accelerates healing when combined with the current standard clinical care. The ultrasound applicator described here provides a user-friendly, fully wearable system that has the potential for becoming the first device suitable for treatment of chronic wounds in patient's homes, which - in turn - would increase patients’ compliance and improve quality of life.

Developing new technologies that enable the repair or replacement of injured or diseased tissues is a major focus of regenerative medicine. This paper will discuss three ultrasound technologies under development in our laboratories to guide tissue regeneration both in vitro and in vivo. A critical obstacle in tissue engineering is the need for rapid and effective tissue vascularization strategies. To address this challenge, we are developing acoustic patterning techniques for microvascular tissue engineering. Acoustic radiation forces associated with ultrasound standing wave fields provide a rapid, non-invasive approach to spatially pattern cells in three dimensions without affecting cell viability. Acoustic patterning of endothelial cells leads to the rapid formation of microvascular networks throughout the volumes of three-dimensional hydrogels, and the morphology of the resultant microvessel networks can be controlled by design of the ultrasound field. A second technology under development uses ultrasound to noninvasively control the microstructure of collagen fibers within engineered tissues. The microstructure of extracellular matrix proteins provides signals that direct cell functions critical to tissue regeneration. Thus, controlling collagen microfiber structure with ultrasound provides a noninvasive approach to regulate the mechanical properties of biomaterials and control cellular responses. The third technology employs therapeutic ultrasound to enhance the healing of chronic wounds. Recent studies demonstrate increased granulation tissue thickness and collagen deposition in murine dermal wounds exposed to pulsed ultrasound. In summary, ultrasound technologies offer noninvasive approaches to control cell behaviors and extracellular matrix organization and thus hold great promise to advance tissue regeneration in vitro and in vivo.

The physiology of the vasculature in the central nervous system (CNS), which includes the blood-brain barrier (BBB) and other factors, complicates the delivery of most drugs to the brain. Different methods have been used to bypass the BBB, but they have limitations such as being invasive, non-targeted or requiring the formulation of new drugs. Focused ultrasound (FUS), when combined with circulating microbubbles, is a noninvasive method to locally and transiently disrupt the BBB at discrete targets. The method presents new opportunities for the use of drugs and for the study of the brain.

Therapeutic ultrasound is an established technique for biomodulation used by physical therapists. Typically it is used to deliver energy locally for the purpose of altering tissue plasticity and increasing local circulation. Access to ultrasound therapy has been limited by equipment and logistic requirements, which has reduced the overall efficacy of the therapy. Ultrasound miniaturization allows for development of portable, wearable, self-applied ultrasound devices that sidestep these limitations. Additionally, research has shown that the timescale of acoustic stimulation matters, and directly affects the quality of result. This paper describes a novel, long duration approach to therapeutic ultrasound and reviews the current data available for a variety of musculoskeletal conditions.

The development of advances in surgical techniques and pharmaceuticals have dramatically contributed to the improvement of global health. However, surgical procedures and pharmaceutical agents are costly and have the potential to create severe side effects and complications for patients. Interdisciplinary researchers are looking for non-pharmaceutical therapies and non-surgical interventions to provide effective treatment for a broad range of medical conditions. This presentation describes one of the most promising therapies-photobiomodulation.

After more than fifty (50) years of clinical use, no serious side effects or adverse reactions of using phototherapy as a medical treatment modality have been observed. Phototherapy affects the natural and basic mechanism of virtually all human cells and restores impaired function, triggering a subsequent cascade of positive therapeutic effects.

Phototherapy currently is being used in virtually every medical specialty including dermatology, plastic surgery, family medicine, vascular surgery, thoracic surgery, ophthalmology, ENT, gastroenterology, hematology, oncology, orthopedics, endocrinology, esthetics, urology, neurology and neurosurgery to name a few. In general, phototherapy serves to improve wound healing, cellular function, reduction of edema, healing of neurological injuries, increased microcirculation and provides intrinsic pain relief. More than 3,000 scientific archived references by the Swedish Laser Society report restorative, therapeutic and healing results from the use of photobiomodulation therapy.

As with all types of scientific work, new discoveries generate new questions. In spite of tremendous advances in the scientific understanding of the medical effects of light we still do not know all the optimal parameters. We also are still struggling as clinicians and scientists to understand the scientific term which best describes the medical effects of light on the modulation of human cell function.

Despite the fact that we are still learning the pathophysiology every day and searching to find the terminology to describe the effects that we are observing it is important to know that clinicians and researchers alike know enough to make phototherapy a mainstream clinical treatment modality. The application of phototherapy inducing photobiomodulation effects has changed the lives of hundreds of thousands of patients and will continue to grow as our understanding of the healing abilities of the application of light continues to improve.

In this preclinical study, we investigated the utility of antimicrobial blue light therapy for Candida albicans infection in acutely burned mice. A bioluminescent strain of C. albicans was used. The susceptibilities to blue light inactivation were compared between C. albicans and human keratinocyte. In vitro serial passaging of C. albicans on blue light exposure was performed to evaluate the potential development of resistance to blue light inactivation. A mouse model of acute thermal burn injury infected with the bioluminescent strain of C. albicans was developed. Blue light (415 nm) was delivered to mouse burns for decolonization of C. albicans. Bioluminescence imaging was used to monitor in real time the extent of fungal infection in mouse burns. Experimental results showed that C. albicans was approximately 42-fold more susceptible to blue light inactivation in vitro than human keratinocyte (P=0.0022). Serial passaging of C. albicans on blue light exposure implied a tendency for the fungal susceptibility to blue light inactivation to decrease with the numbers of passages. Blue light reduced fungal burden by over 4-log₁₀ (99.99%) in acute mouse burns infected with C. albicans in comparison to infected mouse burns without blue light therapy (P=0.015).

This invited paper reviews our research with scalp application of red/near-infrared (NIR) light-emitting diodes (LED) to improve cognition in chronic, traumatic brain injury 1. Application of red/NIR light improves mitochondrial function (especially hypoxic/compromised cells) promoting increased ATP, important for cellular metabolism. Nitric oxide is released locally, increasing regional cerebral blood flow. Eleven chronic, mTBI participants with closed-head injury and cognitive dysfunction received 18 outpatient treatments (MWF, 6 Wks) starting at 10 Mo. to 8 Yr. post-mTBI (MVA, sports-related, IED blast injury). LED therapy is non-invasive, painless, non-thermal (FDA-cleared, non-significant risk device). Each LED cluster head (2.1" diameter, 500mW, 22.2mW/cm²) was applied 10 min (13J/cm²) to 11 scalp placements: midline, from front-to-back hairline; and bilaterally on dorsolateral prefrontal cortex, temporal, and parietal areas. Testing performed pre- and post-LED (+1 Wk, 1 and 2 Mo post- 18th treatment) showed significant linear trend for LED effect over time, on improved executive function and verbal memory. Fewer PTSD symptoms were reported. New studies at VA Boston include TBI patients treated with transcranial LED (26J/cm²); or treated with only intranasal red, 633nm and NIR, 810nm diodes placed into the nostrils (25 min, 6.5mW, 11.4J/cm²). Intranasal LEDs are hypothesized to deliver photons to hippocampus. Results are similar to Naeser et al. (2014). Actigraphy sleep data show increased sleep time (average, +1 Hr/night) post-18th transcranial or intranasal LED treatment. LED treatments may be self-administered at home (Naeser et al., 2011). A shamcontrolled study with Gulf War Illness Veterans is underway.

Recently, layered 2D crystals of other materials similar to graphene have been realized which include insulating hexagonal-BN (band gap ~5.5 eV) and transition metal di-chalcogenides which display properties ranging from semiconducting, superconducting, metallic to insulating. The device applications of such van der Waals solids also show promising characteristics where MoS₂ transistors have been formed on flexible and transparent substrates, and transistors derived from 2D monolayers of MoS₂ show ON/OFF ratios many orders of magnitude larger than the best graphene transistors. In this paper, an overview of the novel properties of these layered 2D nanomaterials is provided that can enable their device applications in electronics, photonics, sensors and other related applications.

In this paper, we present an overview of the currently employed techniques to synthesize two-dimensional materials, focusing on MoS₂ and WSe₂, and summarize the progress reported to-date. Here we discuss the importance of controlling reactor geometries to improve film uniformity and quality for MoS₂ through a combination of modeling and experimental design. In addition, development of processes scalable to provide wafer scale uniformity is explored using synthesis of WSe₂ via metal-organic chemical vapor deposition. Finally, we discuss the impact of each of these processes for TMD synthesis on epitaxial graphene.

The record electronic properties achieved in monolayer graphene and related 2D materials such as molybdenum disulfide and hexagonal boron nitride show promise for revolutionary high-speed and low-power electronic devices. Heterogeneous 2D-stacked materials may create enabling technology for future communication and computation applications to meet soldier requirements. For instance, transparent, flexible and even wearable systems may become feasible. With soldier and squad level electronic power demands increasing, the Army is committed to developing and harnessing graphene-like 2D materials for compact low size-weight-and-power-cost (SWAP-C) systems. This paper will review developments in 2D electronic materials at the Army Research Laboratory over the last five years and discuss directions for future army applications.

In this paper, we present an overview of the current state-of-the-art in two-dimensional materials beyond graphene, and summarize device performance reported to-date. There is promise for these layered materials to be the foundation of a new area in low power and high frequency electronics, with early reports indicating 10s of gigahertz (GHz) operation without significant optimization of parasitic resistances or capacitances. In addition, we discuss the synthesis of transition metal dichalcogenides and the integration of as-grown material into heterostructures and electronic devices. Finally, we discuss the impact of surface preparation on the integration of dielectrics with MoS₂ required to achieve GHz performance.

The realization of the first Field Effect Transistors operating at room temperature, based on a single layer silicene channel, open up highly promising perspectives, e.g., typically, for applications in digital electronics. Here, we describe recent results on the growth, characterization and electronic properties of novel synthetic two-dimensional materials beyond graphene, namely silicene and germanene, its silicon and germanium counterparts.

During the past few years, 2D (two-dimensional) materials have found increasing attention in the electronic device community. The first 2D material studied in detail was graphene and many groups explored it as a material for transistors. During the early years of graphene research, the expectations on its impact on electronics have been extremely high. It soon turned out, however, that the missing bandgap of graphene causes problems for proper transistor operation and meanwhile the prospects of graphene are assessed less optimistic. Recently researchers have extended their work to 2D materials beyond graphene and the number of 2D materials under investigation is literally exploding. At present, about 500 2D materials are known and part of them is considered to be useful for electronic applications. A realistic assessment of the prospects of the 2D materials, however, is still missing. The present paper represents is a step in this direction. After introducing the major classes of 2D materials, we compose a short wish list of material properties desirable for transistor channels and examine to what extent the 2D materials fulfill the criteria of our wish list. We review the current state-of-the-art of 2D transistors, compare their performance to that of competing conventional transistors, and identify potential applications of 2D materials and transistors.

Super-resolution surface-enhanced Raman scattering (SERS) imaging is used to map out SERS hot spots in aggregated silver nanoparticles labeled with the electrochemically-active probe molecule Nile Blue. In super-resolution SERS, the diffraction-limited emission from a SERS-active nanoparticle aggregate is fit to a 2-dimensional Gaussian in order to localize the site of emission, or emission centroid, with 5-10 nm precision. This strategy typically involves working at or near the single molecule concentration level, in order to avoid the super-position of signals from multiple emitters, which leads to an ensemble-averaged centroid position and no spatial information about the location of individual emitters. We have proposed working above the single molecule concentration by using electrochemical control to transition the Nile Blue between its emissive (oxidized) and non-emissive (reduced) form, in order to spatially isolate individual Nile Blue molecules on the surface of aggregated silver nanoparticles. Using this electrochemical modulation strategy, SERS-active regions on nanoparticle aggregates can be mapped out by fitting the centroid location of the emitters as a function of applied potential. Interestingly, while the modulation of Nile Blue SERS intensity does not follow the expected on/off trend with applied potential, we find that we are still able to map out SERS hot spots even while working above the single molecule level.

We present the realization and optoelectronic characterization of p-n junctions based on two-dimensional semiconductors. Such junctions may be realized by lateral or vertical arrangement of atomically thin p-type and n-type materials. In particular, a WSe₂ monolayer p-n junction, formed by electrostatic doping using a pair of split gate electrodes, and a MoS₂/WSe₂ van der Waals type-II heterojunction are presented. Upon optical illumination, conversion of light into electrical energy occurs in both devices. Under forward bias, electrically driven light emission is achieved. Measurements of the electrical characteristics, the photovoltaic properties, and the gate voltage dependence of the photoresponse will be discussed.

Origami structures morph between 2D and 3D conformations along predetermined fold lines that efficiently program the form, function and mobility of the structure. The transfer of origami concepts to engineering design shows potential for many applications including solar array packaging, tunable antennae, and deployable sensing platforms. However, the enormity of the design space and the complex relationship between origami-based geometries and engineering metrics places a severe limitation on design strategies based on intuition. This motivates the development of design tools based on optimization to identify optimal fold patterns for geometric and functional objectives. The present work proposes a topology optimization method using mechanical analysis to distribute fold line properties within a reference crease pattern to achieve a target actuation. By increasing the fold stiffness, unnecessary folds are effectively removed from the design solution, which allows fundamental topologies for actuation to be identified. A series of increasingly refined reference grids were analyzed and several actuating mechanisms were predicted. The fold stiffness optimization was then followed by a node position optimization, which determined that only two of the predicted topologies were fundamental and the solutions from higher density grids were variants or networks of these building blocks. This two-step optimization approach provides a valuable check of the grid dependency of the design and offers an important step toward systematic incorporation of origami design concepts into new, novel and reconfigurable engineering devices.

Recent advances in laminate manufacturing techniques have driven the development of new classes of millimeter-scale sensorized medical devices, robots capable of terrestrial locomotion and sustained flight, and new techniques for sensing and actuation. Recently, the analysis of laminate micro-devices has focused more manufacturability concerns and not on mechanics. Considering the nature of such devices, we draw from existing research in composites, origami kinematics, and finite element methods in order to identify issues related to sequential assembly and self-folding prior to fabrication as well as the stiffness of composite folded systems during operation. These techniques can be useful for understanding how such devices will bend and flex under normal operating conditions, and when added to new design tools like popupCAD, will give designers another means to develop better devices throughout the design process.

HanaFlex is a new method for deployment from a compact folded form to a large array derived from the origami flasher folding pattern. One of the unique features of this model is that the height constraints of the stowed array do not limit the deployed diameter. Additional rings can be added to increase the deployed diameter while only minimally increasing the stowed diameter. Larger solar arrays may enable longer missions in space, manned missions to distant destinations, or clean energy sources for Earth. The novel folding design of the HanaFlex array introduces many new possibilities for space exploration. This paper demonstrates the performance of the HanaFlex array in four areas: deployed stiffness, deployed strength, stowed volume specific power, and mass specific power.

This short manuscript highlights the industry's first proven reservoir nanoagents' design and demonstrates a successful multi-well field trial using these agents. Our fundamental nanoparticles tracer template, A-Dots or Arab-D Dots, is intentionally geared towards the harsh but prolific Arab-D carbonate reservoir environment of 100⁺°C temperature, 150,000⁺ppm salinity, and an abundant presence of divalent ions in the connate water. Preliminary analyses confirmed nanoparticles' breakthrough at a producer nearly 500m from the injector at the reservoir level; thus, proving the tracer nanoparticles' mobility and transport capability. This is considered industry-first and a breakthrough achievement complementing earlier accomplishments in regard to the nanoagents' reservoir stability with the first successful single well test and ease of scale up with the synthesis of one metric ton of this material. The importance of this accomplishment is not in how sophisticated is the sensing functionalities of this design but rather in its stability, mobility, scalability, and field application potentials. This renders the concept of having active, reactive, and even communicative, in-situ reservoir nanoagents for underground sensing and intervention a well anticipated near-future reality.

This paper describes the development of autonomous electronic micro and nanoscale sensor systems for very harsh downhole oilfield conditions and provides an overview of the operational requirements necessary to survive and make direct measurements of subsurface conditions. One of several significant developmental challenges is selecting appropriate technologies that are simultaneously miniaturize-able, integrate-able, harsh environment capable, and economically viable. The Advanced Energy Consortium (AEC) is employing a platform approach to developing and testing multi-chip, millimeter and micron-scale systems in a package at elevated temperature and pressure in API brine and oil analogs, with the future goal of miniaturized systems that enable the collection of previously unattainable data. The ultimate goal is to develop subsurface nanosensor systems that can be injected into oil and gas well bores, to gather and record data, providing an unparalleled level of direct reservoir characterization. This paper provides a status update on the research efforts and developmental successes at the AEC.

This paper presents fiber optical gas sensors based on nano-porous metal oxide functional materials for high-temperature energy applications. A solution-based approach was used to produce nano-porous functional metal oxide and their dopant variants as sensing films, which was integrated on high-temperature stable FBGs in D-shaped silica fibers and sapphire fibers. The Bragg grating peaks were used to monitor the refractive index change and optical absorption loss due to the redox reaction between Pd-doped TiO₂ and hydrogen from the room temperature to 800°C. The experimental results show the sensor's response is reversible for hydrogen concentration between 0.1 vol.% to 5 vol. %. The response time of the hydrogen sensor is <8s.

A novel approach to the implementation of a fiber optic thermometer with high temperature capability is described. It utilizes a phosphor in the form of a microsphere. With this design, a fiber optic thermal probe having a useful range of 100-1,100 °C has been demonstrated using an LED as the excitation source. From previous work, we believe that it should be possible to extend the maximum operating temperature of such a device to at least 1,400 °C if a laser diode is employed as the excitation source.

The injection of CO₂ into deep aquifers can potentially affect the quality of groundwater supplies were leakage to occur from the injection formation or fluids. Therefore, the detection of CO₂ and/or entrained contaminants that migrate into shallow groundwater aquifers is important both to assess storage permanence and to evaluate impacts on water resources. Naturally occurring elements (i.e., Li, Sr) in conjunction with isotope ratios can be used to detect such leakage. We propose the use of laser induced breakdown spectroscopy (LIBS) as an analytical technique to detect a suite of elements in water samples. LIBS has real time monitoring capabilities and can be applied for elemental and isotopic analysis of solid, liquid, and gas samples. The flexibility of probe design and use of fiber optics make it a suitable technique for real time measurements in harsh conditions and in hard to reach places. The laboratory scale experiments to measure Li, K, Ca, and Sr composition of water samples indicate that the technique produces rapid and reliable data. Since CO₂ leakage from saline aquifers may accompany a brine solution, we studied the effect of sodium salts on the accuracy of LIBS analysis. This work specifically also details the fabrication and application of a miniature ruggedized remotely operated diode pumped solid state passively Q-switched laser system for use as the plasma excitation source for a real time LIBS analysis. This work also proposes the optical distribution of many laser spark sources across a wide area for widespread leak detection and basin monitoring.

This study reports on the temperature dependent behavior of absorption bands generated in optical fibers via hydrogen exposure at 800 °C. Hydrogen exposure at 800 °C resulted in the generation of two large absorption bands in the 1-2.5 μm wavelength range at ~1.4 μm and ~2.2 μm. These bands showed temperature dependent behavior when in the temperature range of 20–800 °C such that at higher temperatures the absorption intensity in these two bands was smaller than at room temperature. The temperature dependent behavior was shown to be reversible and repeatable under an array of testing conditions including thermal cycling and long periods of time without hydrogen exposure. The reversibility suggests that no chemical change is taking place while the repeatability suggests that no permanent structural change in the glass is taking place. Although both absorption bands are associated with hydroxyl groups and exhibited similar temperature dependence, variations were observed with respect to time and exposure environment. Therefore, we surmised that the observed behaviors were not exclusive to the hydroxyl bond and/or structural modifications. In this paper, we discuss the possible mechanisms responsible for the observed phenomena and, conversely, the conditions that would be necessary to induce the structural changes that would induce changes in the absorption intensities.

One mission of the Crosscutting Technology Research program at the National Energy Technology Laboratory is to develop a suite of sensors and controls technologies that will ultimately increase efficiencies of existing fossil-fuel fired power plants and enable a new generation of more efficient and lower emission power generation technologies. The program seeks to accomplish this mission through soliciting, managing, and monitoring a broad range of projects both internal and external to the laboratory which span sensor material and device development, energy harvesting and wireless telemetry methodologies, and advanced controls algorithms and approaches. A particular emphasis is placed upon harsh environment sensing for compatibility with high temperature, erosive, corrosive, and highly reducing or oxidizing environments associated with large-scale centralized power generation. An overview of the full sensors and controls portfolio is presented and a selected set of current and recent research successes and on-going projects are highlighted. A more detailed emphasis will be placed on an overview of the current research thrusts and successes of the in-house sensor material and device research efforts that have been established to support the program.

The successful operation of small unmanned aircraft systems (sUAS) in dynamic environments demands robust stability in the presence of exogenous disturbances. Flying insects are sensor-rich platforms, with highly redundant arrays of sensors distributed across the insect body that are integrated to extract rich information with diminished noise. This work presents a novel sensing framework in which measurements from an array of accelerometers distributed across a simulated flight vehicle are linearly combined to directly estimate the applied forces and torques with improvements in SNR. In simulation, the estimation performance is quantified as a function of sensor noise level, position estimate error, and sensor quantity.

In this paper, we summarize recent research enabling high-speed navigation in unknown environments for dynamic robots that perceive the world through onboard sensors. Many existing solutions to this problem guarantee safety by making the conservative assumption that any unknown portion of the map may contain an obstacle, and therefore constrain planned motions to lie entirely within known free space. In this work, we observe that safety constraints may significantly limit performance and that faster navigation is possible if the planner reasons about collision with unobserved obstacles probabilistically. Our overall approach is to use machine learning to approximate the expected costs of collision using the current state of the map and the planned trajectory. Our contribution is to demonstrate fast but safe planning using a learned function to predict future collision probabilities.

The neurophysiology of insects suggests that they are able to track conspecifics, which manifest as small targets, against a variety of backgrounds with ease. This perception occurs at the same stage as motion perception suggesting a role for optic flow in target discrimination. Optic flow also is an attractive method of perception for visual system design due to the possibility of parallel processing that lends itself to implementation in hardware acceleration. This paper investigates some of the limits for reliable target discrimination solely from an optic flow field which are dependent on algorithm parameters, the nature of the target, and imager noise properties.

Minimally-actuated palm-size robots are capable of running at speeds greater than 2 meters per second (20 body lengths per second), with leg stride rates of greater than 20 Hz. In this dynamic regime, passive stabilization is needed for roll-and-pitch instability. However, we have found that certain roll-oscillation modes can be used for continuous high speed turning. Other continuous turning modes have also been identified, such as modulating foot contact location through foot compliance, and controlling differential leg velocity. For the small minimally actuated robots examined, the dynamically enhanced roll-steer mode showed the best turning rate, of over 8 degrees per step, but only appears at certain running frequencies. Interstride phase and velocity control appears promising as a mode for in-plane maneuverability for under-actuated robots.

Measuring the stability of highly-dynamic bipedal locomotion is a challenging but essential task for more capable human-like walking. By discretizing the walking dynamics, we treat the system as a Markov chain, which lends itself to an easy quantification of failure rates by the expected number of steps before falling. This meaningful and intuitive metric is then used for optimizing and benchmarking given controllers. While this method is applicable to any controller scheme, we illustrate the results with two case demonstrations. One scheme is the now-familiar hybrid zero dynamics approach and the other is a method using piece-wise reference trajectories with a sliding mode control. We optimize low-level controllers, to minimize failure rates for any one gait, and we adopt a hierarchical control structure to switch among low-level gaits, providing even more dramatic improvements on the system performance.

Legged robots must traverse complex terrain consisting of particles of varying size, shape and texture. While much is known about how robots can effectively locomote on hard ground and increasingly on homogeneous granular media, principles of locomotion over heterogeneous granular substrates are relatively unexplored. To systematically discover how substrate heterogeneity affects ambulatory locomotion, we investigate how the presence of a single boulder (3D printed convex objects of different geometries) embedded in fine granular media affects the trajectory of a small (150 g) six legged robot. Using an automated system to collect thousands of locomotion trials, we observed that trajectories were straight before the interaction with the boulder, and scattered to different angles after the interaction depending on the leg-boulder contact positions. However, this dependence of scattering angle upon contact zone was relatively insensitive to boulder shape, orientation and roughness.¹ Inspired by this insensitivity, here we develop an anticipatory control scheme which uses the scattering information in coordination with a tail induced substrate jamming. Our scheme allows the robot to "envision" outcomes of the interaction such that the robot can prevent trajectory deviation before the scattering occurs. We hypothesize that (particularly during rapid running or in the presence of noisy sensors) appropriate substrate manipulation can allow a robot to remain in a favorable locomotor configuration and avoid catastrophic interactions.

Legged locomotion is a challenging regime both for experimental analysis and for robot design. From biology, we know that legged animals can perform spectacular feats which our machines can only surpass on some specially controlled surfaces such as roads. We present a concise review of the theoretical underpinnings of Data Driven Floquet Analysis (DDFA), an approach for empirical modeling of rhythmic dynamical systems. We provide a review of recent and classical results which justify its use in the analysis of legged systems.

Ultraspectral sensing has been investigated as a way to resolve terrestrial chemical fluorescence within solar Fraunhofer lines. Referred to as Fraunhofer Line Discriminators (FLDs), these sensors attempt to measure "band filling" of terrestrial fluorescence within these naturally dark regions of the spectrum. However, the method has challenging signal to noise ratio limitations due to the low fluorescence emission signal of the target, which is exacerbated by the high spectral resolution required by the sensor (<0.1 nm). To now, many Fraunhofer line discriminators have been scanning sensors; either pushbroom or whiskbroom, which require temporal and/or spatial scanning to acquire an image. In this paper, we attempt to quantify the snapshot throughput advantage in ultraspectral imaging for FLD. This is followed by preliminary results of our snapshot FLD sensor. The system has a spatial resolution of 280x280 pixels and a spectral resolving power of approximately 10,000 at a 658 nm operating wavelength.

Tunable lenses have attracted much attention due to their potential applications in such areas like machine vision, laser projection, ophthalmology, etc. In this work we present the design of a tunable opto-mechatronic system capable of focusing and to regulate the entrance illumination that mimics the performance made by the iris and the crystalline lens of the human eye. A solid elastic lens made of PDMS has been used in order to mimic the crystalline lens and an automatic diaphragm has been used to mimic the iris of the human eye. Also, a characterization of such system has been performed with standard values of luminosity for the human eye have been taken into account to calibrate and to validate the entrance illumination levels to the overall optical system.

The beam control system of a high energy laser (HEL) application can typically experience error amplification due to disturbance measurements that are associated with the non-common path of the optical train setup. In order to address this error, conventional schemes require offline identification or a calibration process to determine the non-common path error portion of a measured sequence that contains both common and non-common path disturbances. However, not only is it a challenging to model the properties of the non-common path disturbance alone but also a stationary model may not guarantee consistent jitter control performance and repeated calibration may be necessary. The paper first attempts to classify the non-common path error problem into two categories where the designer is only given one measurement or two measurements available for real-time processing. For the latter case, an adaptive correlated pre-filter is introduced here to provide in situ determination of the non-common path disturbance through an adaptive correlation procedure. Contrasting features and advantages of this algorithm will be demonstrated alongside a baseline approach of utilizing notch filters to bypass the non-common portion of the combined sequence.

Active remote sensing returns information of the highest value at the lowest cost when outgoing energy can be carefully shaped and directed to the task at hand. This paper presents results of lab and airborne testing of an Electronically Steerable Flash Lidar (ESFL) under continuing development by Ball Aerospace and Technologies Corp. The results highlight the adaptive nature of this and other active instruments having fine control of illumination, and show the benefits of combining lab simulation with flight testing in validation of algorithms and control design.

We describe the implementation of a self-heterodyne, tunable down converting RF-IF photonic link as a key component of a wideband microwave signal search and intercept system covering S to Ka bands. The presented architecture uses photomixing of two distributed feedback lasers injection locked to a master external cavity laser, allowing low phase to amplitude noise conversion and improved sensitivity. Coherent detection of the intermediate frequency allows unambiguous recovery of full time-domain information. The practical implementation of a packaged prototype system will be discussed, with emphasis on the system stabilization strategy and performance requirements.

RF photonic channelizers can overcome limitations of conventional electronic methods for analysis of wideband RF spectral content. Here, we will present a recent progress on the RF photonic channelizer systems that are based on optical parametric combs. These systems can analyze very wide RF bandwidths exceeding 100GHz, therefore providing essential capability for the applications demanding a wide-bandwidth spectral analysis. The RF channelizers being presented utilize parametric processes in the highly non-linear fiber mixers to generate a large number of RF signal copies in the optical domain. Two different implementations for generation of RF signal copies will be presented and compared: one using a parametric multicasting and another utilizing a direct comb modulation. Generation of optical combs spanning more than 10THz will be shown. We will also present two distinct system architectures for RF photonic channelizer system: one employing a periodic optical filter such as Fabry-Perot etalon to select channels from the signal comb, and another one utilizing a coherent detection between a frequency-locked signal comb and a parametrically generated local oscillator (LO) comb. The second scheme gives benefit of providing both in-phase and quadrature (I/Q) information on channelized intermediate frequency (IF) signals. We will present a system with 32 implemented channels using a filtered scheme and a 32-channel coherent system with a full-field detection implemented on one tunable channel. Sensitivity and dynamic range as well as benefits of both system architectures will be discussed.

The Navy is actively developing diverse optical application areas, including high-energy laser weapons and free- space optical communications, which depend on an accurate and timely knowledge of the state of the atmospheric channel. The Optical Channel Characterization in Maritime Atmospheres (OCCIMA) project is a comprehensive program to coalesce and extend the current capability to characterize the maritime atmosphere for all optical and infrared wavelengths. The program goal is the development of a unified and validated analysis toolbox. The foundational design for this program coordinates the development of sensors, measurement protocols, analytical models, and basic physics necessary to fulfill this goal.

The wireless, high-data-rate transmission of information is becoming increasingly important for undersea applications that include defense, environmental monitoring, and petroleum engineering. Free-space optical (FSO) communication addresses this need by providing an undersea high-data-rate link over moderate distances (up to 100s of meters). Light transmission through seawater is maximal in the blue-green part of the optical spectrum (475 nm–575 nm), but turbidity conditions, which are dynamic, strongly influence the actual maximum. We describe the development of a laser-wavelength auto-selection algorithm and system for optimized underwater FSO communications. The use of a passive corner cube retroreflector allows all transmitter and receiver electronics to be collocated, which will be beneficial for any fielded system. First, we describe the laser test bed and retroreflector system. Next, we describe the development of the algorithm and hardware. We then describe the creation of various water types (from clear to turbid) in the laboratory using particle suspensions and dyes, which will enable wavelength-dependent transmission tests. Finally, we show experimental results from water tube tests, demonstrating wavelength auto-selection within one minute.

Research into the development of advanced RF electronics and devices having high-Temperature Superconducting (HTS) circuitry is being carried out in the Cryogenic Exploitation of RF (CERF) laboratory at SPAWAR Systems Center (SSC) - Pacific. Recently, we have developed a novel annealing process wherein a film of YBa₂Cu₃O_x is produced having a gradient of oxygen composition along a given direction which we refer to as YBa₂Cu₃O_∇x. Such samples are intended for rapid experimental investigation of the evolution of electronic properties within the compound and in combination with structurally compatible functional oxide materials as integrated sensor devices. We present here an investigation as to the extent to which local oxygen content affects the ion milling process in the formation of Josephson junctions in the HTS compound YBa₂Cu₃O_∇x. We find an abrupt transition in the profile and depth of ion milled trenches at oxygen concentrations at and below the well ordered oxygen level, O_6.72. The method described here shows good potential for use in the fabrication of large numbers of uniform Josephson junctions in films of YBa₂Cu₃O_x, as either a complementary processing tool for grain boundary, step edge, or ion damaged formed JJs, or as a stand alone method for producing nano-bridge JJ’s.

Optical nonlinearities in semiconductors and semiconductor detectors have been widely investigated and exploited for many scientific and industrial applications. The correlation of optical and electronic characteristics in these detector materials under exposure of ultra-short laser pulses at high pulse repetition rates is still not very well known. These effects may be quite beneficial for many applications ranging from chemical and biological sensing to light-induced superconductivity. In this paper, we discuss the effect of extended bleaching in order to demonstrate sensing applications of such phenomenon as an example. Pump-probe measurements in bulk semiconductors will be presented to quantify the transient absorption dynamics and relate this to the electronic response of the detector devices. This effect is not limited semiconductors and may affect other matter states and electronic structures, like dielectrics.

Over past three decades ultrafast lasers have come a long way from the bulky, demanding and very sensitive scientific research projects to widely available commercial products. For the majority of this period the titanium-sapphire-based ultrafast systems were the workhorse for scientific and emerging industrial and biomedical applications. However the complexity and intrinsic bulkiness of solid state lasers have prevented even larger penetration into wider array of practical applications. With emergence of femtosecond fiber lasers, based primarily on Er-doped and Yb-doped fibers that provide compact, inexpensive and dependable fs and ps pulses, new practical applications have become a reality. The overview of current state of the art ultrafast fiber sources, their basic principles and most prominent applications will be presented, including micromachining and biomedical implementations (ophthalmology) on one end of the pulse energy spectrum and 3D lithography and THz applications on the other.

Conversion of plane waves to surface waves prior to detection allows key advantages in changes to the architecture of the detector pixels in a focal plane array. We have integrated subwavelength patterned metal nanoantennas with various detector materials to incorporate these advantages: midwave infrared indium gallium arsenide antimonide detectors and longwave infrared graphene detectors.

Nanoantennas offer a means to make infrared detectors much thinner by converting incoming plane waves to more tightly bound and concentrated surface waves. Thinner architectures reduce both dark current and crosstalk for improved performance. For graphene detectors, which are only one or two atomic layers thick, such field concentration is a necessity for usable device performance, as single pass plane wave absorption is insufficient. Using III-V detector material, we reduced thickness by over an order of magnitude compared to traditional devices.

We will discuss Sandia’s motivation for these devices, which go beyond simple improvement in traditional performance metrics. The simulation methodology and design rules will be discussed in detail. We will also offer an overview of the fabrication processes required to make these subwavelength structures on at times complex underlying devices based on III-V detector material or graphene on silicon or silicon carbide. Finally, we will present our latest infrared detector characterization results for both III-V and graphene structures.

Short channel field effect transistors can detect terahertz radiation. Such detection is enabled by the excitation of the plasma waves rectified due to the device nonlinearities. The resulting response has nanometer scale spatial resolution and can be modulated in the sub THz range. This technology could enable a variety of sensing, imaging, and wireless communication applications, including detection of biological and chemical hazardous agents, cancer detection, shortrange covert communications (in THz and sub-THz windows), and applications in radio astronomy. Field effect transistors implemented using III-V, III-N, Si, SiGe, and graphene have been used to detect THz radiation. Using silicon transistors in plasmonic regimes is especially appealing because of compatibility with standard readout silicon VLSI components.

Advances in infrared (IR) detector technologies over the last decade have led to compact low-cost thermal imaging systems that have become almost ubiquitous. They are now used in such market applications as automotive, security and construction. Terahertz (THz) imagers can take advantage of the state-of-the-art in the infrared domain to reduce their size and cost. Such an example is the IRXCAM-THz-384 Terahertz camera whose electronics core is based on the IRXCAM camera core and whose detector has been specifically designed and optimized for the THz. The 384 x 288 35- micron-sized pixel detectors of both cameras are uncooled microbolometers. A micro-electronics core is currently being developed for both platforms that will yield ultra-compact IR and THz cameras.

While IR systems are passive and thus do not require an illumination source, the THz system does. Thus, the THz source must be included when talking about overall imaging system size and cost. There are a wide variety of THz sources, from quantum cascade lasers on the optical side of the radiation spectrum to different types of diodes on the electromagnetic micro-wave side. When considering a source for a given application, the output wavelength, output power, size, weight and cost are primary factors that must be taken into account.

This paper presents a description of a compact real-time imaging system at 750 μm wavelength. An overview of the motivation for the wavelength choice is discussed, a description of the imaging components is given and finally image results are presented.

The goal in the design of an efficient and low-noise antenna coupled receiver is to achieve a maximal capture cross section for the incident electromagnetic radiation compared to the dimensions of the sub-wavelength sized sensor loading the antenna. Collection efficiency captures this concept of power output/input and is made up of several subefficiencies. In the ideal case all of the available, incident power is collected and transferred to the load. However, many of the fundamental limits of antennas are based on theory describing the transmitting mode, whereas certain questions remain open for receiving antennas. Textbook antenna theory predicts that only 50% of available incident power can be absorbed by an antenna, yet under specific conditions this limitation can be surpassed. Two considerations are presented; (1) fundamental limits on antenna absorption, and (2) practical participation of dissipative media in achieving impedance matching between antenna and load, and the associated performance compromise. Specifically we seek to determine whether antenna-coupled detectors can approach unity absorption efficiency under matched conditions. Further, we identify practical conditions that must be met in order to overcome fundamental limitations that inhibit total absorption. Then antenna loss is split into radiative and dissipative terms in order to identify trade-offs between impedance matching and radiation efficiency.

CMOS technology offers relatively low performance at mm-wave frequencies compared with other III-V technologies and the high levels of process variation further exacerbate design margins. This paper discusses several CMOS system-on-chips (SoCs) developed by JPL through collaboration with UCLA that use a self-healing approach to optimize mm-wave transceiver performance, as well as calibrate operation at runtime. Several applications will be discussed for mm-wave spectroscopy, radar, and communication systems, with SoCs demonstrated at V, W and D band.

MMW and THz sensors offer unique imaging capabilities and challenges. This paper will provide a brief discussion of illumination, propagation, and resolution in these and adjacent bands, followed by a discussion of some application areas for these sensors, in particular imaging in Degraded Visual Environments (DVE), stand-off screening and chemical detection, and surveillance and monitoring. Comparisons with other sensing modalities will be provided discussing some of the relative strengths and weaknesses of MMW and THz sensing compared to these other modalities.

We demonstrate video rate THz imaging in both reflection and transmission by frequency upconverting the THz image to the near-IR. In reflection, the ability to resolve images generated at different depths is shown. By mixing the THz pulses with a portion of the fiber laser pump (1064 nm) in a quasi-phase matched gallium arsenide crystal, distinct sidebands are observed at 1058 nm and 1070 nm, corresponding to sum and difference frequency generation of the pump pulse with the THz pulse. By using a polarizer and long pass filter, the strong pump light can be removed, leaving a nearly background free signal at 1070 nm. We have obtained video rate images with spatial resolution of 1mm and field of view ca. 20 mm in diameter without any post processing of the data.

In this paper we review our results on high power quantum cascade lasers in the mid- and long-wave infrared regions of the spectrum (4-12um). The specifications and characteristics of state-of-the-art QC lasers fabricated by MOCVD technology are illustrated, along with their key application requirements and potential issues for future improvements. Single emitter QC lasers in the Watt-class range are presented and analyzed. In addition, we explore the use of high power QCLs for THz generation at room temperature by non-linear mixing of high power mid-infrared beams in a monolithic intra-cavity design. The THz radiation so obtained is widely tunable by electrical injection. Experimentally, we demonstrate ridge waveguide single mode devices electrically tunable between 3.44 and 4.02 THz.

Mid- infrared ultrafast pulses are of interest in different applications ranging from vibrational spectroscopy, strong field physics (stable CEP) to detection of trace quantities of compounds. The traditional approach uses solid state lasers, i.e. mature but sensitive technology that is restricted to laboratory use due to its complexity. In real-world applications, ultrashort fiber lasers offer a more rugged, portable and scalable platform for the generation of tunable, brilliant mid-IR femtosecond pulses. This paper will cover approaches for the generation of high-intensity femtosecond pulses in the mid-IR region by means of DFG. The DFG technique also opens up new avenues for frequency comb applications and tunable absolute optical frequency sources. It can be used to set up intrinsically phase stable amplified laser systems as well. The power scalability of lasers with doped Thulium fibers made it possible to generate supercontinua in the mid-IR. Our mid-IR sources along with the availability of high power fiber optics, double clad doped gain fibers and LMA fibers for the 2μm and 1μm region enables "all fiber" compact and robust sources that can be man-portable.

At Waterloo, we are developing a high power, short pulse, two-color, Yb:fiber amplifier system to generate the long wavelength (<15μm) side of the molecular fingerprint spectral region, by difference frequency mixing the two colors. This spectral region is important for trace gas detection of explosives. As an example, it has been shown that the strong spectroscopic signatures of a peroxide-based explosive triacetone triperoxide (TATP) occur between 15 and 20 μm. To date, we have achieved a tuning range from 16 to 20 μm with a maximum average power of 1.7 mW. On the short wavelength side, the two colors would need to be pulled further apart, which requires a higher power seed to beat the amplified spontaneous emission that appears at the gain peak of the amplifiers between the two seed colors. On the long wavelength side, we are limited to 20 μm by the transparency region of the nonlinear crystals. We would like to find new nonlinear materials that have transparency from 1 to 30μm. If we could generate wavelengths from 15 to 30 μm with sufficient power, we could extend the spectral region to also cover 8 to 15μm by frequency doubling the longer wavelengths. We are currently working on replacing bulk optics in the system with fiber based optical elements to select the wavelengths as well as stretch and recompress the pulses in order to make the system compact and stable.

We report a novel design of CW Cr²⁺:ZnS/ZnSe laser systems and demonstrate record output powers of 27.5 W at 2.45 μm and 13.9 W at 2.94 μm with slope efficiencies of 63.7% and 37.4%, respectively. Power scaling of ultra-fast Cr²⁺:ZnS/ZnSe Kerr mode-locked lasers beyond 2 W level, as well as the shortest pulse duration of 29 fs, are also reported. New development of Fe:ZnSe laser with average output power > 35 W at 4.1 μm output wavelength and 100 Hz pulse repetition rate (PRR) was achieved in a nonselective cavity. With intracavity prim selector, wavelength tunability of 3.88-4.17 μm was obtained with maximum average output power of 23 W. We also report new results on Tm-fiber pumped passively and actively Q-switched Ho:YAG laser systems. High peak power actively Q-switched Ho:YAG laser demonstrates stable operation with pulse energy > 50 mJ, 12 ns pulse duration, and 100-1000 Hz PRR which correspondents to more than 4 MW peak power. The actively Q-switched Ho:YAG laser system optimized for high repetition rate delivers 40 W average output power at 10-100 kHz PRR. The Ho:YAG laser with passive Q-switcher demonstrates constant 5 mJ output energy from 200 Hz to 2.23 kHz PRR with optical slope efficiency with respect to Tm-fiber laser of ~43%.

Frequency-comb-based absorption spectroscopy in the molecular fingerprint part of the spectrum 2-12 μm has great potential for standoff chemical sensing because of massive parallelism of data acquisition. Especially attractive is the dual-comb Fourier transform spectroscopy, with two phase-locked sources, where full advantage is taken of temporal and spatial coherence of frequency combs as well as of their broadband nature. The promise is high speed (up to 1M spectral points in less than a second), broad spectral coverage (> one octave), superior sensitivity (< 1 part per billion in gas phase), high spectral resolution (~100 MHz), and the possibility of absolute frequency calibration of molecular resonances. Here we report a broadband frequency comb source based on a degenerate optical parametric oscillator (OPO) that allows extending frequency comb technology to the mid-IR range. The OPO uses, as gain element an orientation-patterned GaAs crystal (OP-GaAs), is pumped by a femtosecond Tm-fiber lasers at 2-μm wavelength, and is suitable for performing broadband dual-comb spectroscopy. High temporal coherence and broad instantaneous spectral coverage of 2.5 - 7.5 μm make this system promising for chemical detection and trace molecular sensing. Few examples of single- and dual-comb spectroscopic sensing are presented.

In this work we present a hyperspectral image sensor based on MIR-laser backscattering spectroscopy for contactless detection of explosive substance traces. The spectroscopy system comprises a tunable Quantum Cascade Laser (QCL) with a tuning range of 7.5 μm to 9.5 μm as an illumination source and a high performance MCT camera for collecting the backscattered light. The resulting measurement data forms a hyperspectral image, where each pixel vector contains the backscattering spectrum of a specific location in the scene. The hyperspectral image data is analyzed for traces of target substances using a state of the art target detection algorithm (the Adaptive Matched Subspace Detector) together with an appropriate background extraction method. The technique is eye-safe and allows imaging detection of a large variety of explosive substances including PETN, RDX, TNT and Ammonium Nitrate. For short stand-off detection distances (<3 m), residues of explosives at an amount of just a few 10 μg, i.e. traces corresponding to a single fingerprint, could be detected. For larger concentration of explosives, stand-off detection over distances of up to 20 m has already been demonstrated.

Mid-Infrared standoff spectroscopy using Quantum Cascade Lasers has been a focus of on-going research for many years. When attempting to detect trace analyte residues, the greatest challenge facing this technology is not in the lasers, but the difficulty in creating a spectroscopic background reference for an unknown surface. Such techniques as Differential Location Measurements fail when analyte concentrations are below 1 μg/cm². To overcome this challenge of unknown surface backgrounds, we propose a technique to alter the IR absorption peaks of a target analyte by exposing the surface to a high intensity, alternating electric field in a standoff fashion. The high intensity electric field generates ozone radicals from the local air, oxidizing organic compounds on the surface. A spectrum of the surface before and after the ozone radicals is obtained. The ozone altered spectrum acts as the reference background and is compared against the un-altered spectrum, generating a differential signal used to identify the target analyte.

The Army is investigating several spectroscopic techniques (e.g., infrared spectroscopy) that could allow for an adaptable sensor platform. Traditionally, chemical sensing platforms have been hampered by the opposing concerns of increasing sensor capability while maintaining a minimal package size. Current sensors, although reasonably sized, are geared to more classical chemical threats, and the ability to expand their capabilities to a broader range of emerging threats is uncertain. Recently, photoacoustic spectroscopy, employed in a sensor format, has shown enormous potential to address these ever-changing threats, while maintaining a compact sensor design. In order to realize the advantage of photoacoustic sensor miniaturization, light sources of comparable size are required. Recent research has employed quantum cascade lasers (QCLs) in combination with MEMS-scale photoacoustic cell designs. The continuous tuning capability of QCLs over a broad wavelength range in the mid-infrared spectral region greatly expands the number of compounds that can be identified. Results have demonstrated that utilizing a tunable QCL with a MEMS-scale photoacoustic cell produces favorable detection limits (ppb levels) for chemical targets (e.g., dimethyl methyl phosphonate (DMMP), vinyl acetate, 1,4-dioxane). Although our chemical sensing research has benefitted from the broad tuning capabilities of QCLs, the limitations of these sources must be considered. Current commercially available tunable systems are still expensive and obviously geared more toward laboratory operation, not fielding. Although the laser element itself is quite small, the packaging, power supply, and controller remain logistical burdens. Additionally, operational features such as continuous wave (CW) modulation and laser output powers while maintaining wide tunability are not yet ideal for a variety of sensing applications. In this paper, we will discuss our continuing evaluation of QCL technology as it matures in relation to our ultimate goal of a universal compact chemical sensor platform.

This manuscript describes the results of recent tests regarding standoff detection of trace explosives on relevant substrates using a mobile platform. We are developing a technology for detection based on photo-thermal infrared (IR) imaging spectroscopy (PT-IRIS). This approach leverages one or more microfabricated IR quantum cascade lasers, tuned to strong absorption bands in the analytes and directed to illuminate an area on a surface of interest. An IR focal plane array is used to image the surface thermal emission upon laser illumination. The PT-IRIS signal is processed as a hyperspectral image cube comprised of spatial, spectral and temporal dimensions as vectors within a detection algorithm. Increased sensitivity to explosives and selectivity between different analyte types is achieved by narrow bandpass IR filters in the collection path. We have previously demonstrated the technique at several meters of stand-off distance indoors and in field tests, while operating the lasers below the infrared eye-safe intensity limit (100 mW/cm²). Sensitivity to explosive traces as small as a single 10 μm diameter particle (~1 ng) has been demonstrated. Analytes tested here include RDX, TNT, ammonium nitrate and sucrose. The substrates tested in this current work include metal, plastics, glass and painted car panels.

Standoff detection and identification of chemical threats has been the "holy grail" of detection instruments. The advantages of such capability are well understood, since it allows detection of the chemical threats without contact, eliminating possible operator and equipment contamination and the need for subsequent decontamination of both. In the case of explosives detection, standoff detection might enable detection of the threat at safe distances outside the blast zone. A natural extension of this capability would be to also detect and identify biological threats in a standoff mode and there are ongoing efforts to demonstrate such capability.

In this work, we propose a novel Graphene field effect transistor (GFET) with ohmic Source/Drain contacts having capacitive extension towards the Gate. The ohmic contacts of the proposed GFET are used for DC biasing as like as conventional GFETs whereas their extended parts which are capacitively coupled to the channel reduce access region length as well as the access resistance and provide a low impedance route for the high frequency RF signal. Reduction of access resistance along with the paralleling of ohmic contact resistance and real part of capacitive impedance result in an overall lower Source/Drain resistance which eventually increases the current gain cut-off frequency, f_T. We have studied and compared the DC and RF characteristics of the baseline conventional GFET and proposed GFET using analytical and numerical techniques.

In this paper analysis of comb design for the sensing element MEMS accelerometer with longitudinal displacement of the inertial mass under the influence of acceleration to obtain the necessary parameters for the further construction of an electronic circuit for removal and signal processing has been done. Fixed on the stator the inertia mass has the ability to move under the influence of acceleration along the longitudinal structure. As a result the distance between the fixed and movable combs, and hence the capacitance in the capacitors have been changed. Measuring the difference of these capacitances you can estimate the value of the applied acceleration. Furthermore, managing combs that should apply an electrostatic force for artificial deviation of the inertial mass may be used for the initial sensitive elements culling. Also in this case there is a change of capacitances, which can be measured by the comb and make a decision about the spoilage presence or absence.

The research and development results along the characteristics of the micro-mirror element driven by thermal microactuator are presented. This work shows that for calculating micro-mirror element deflection is crucial for consideration the temperature distribution along the length of the micromirror element. The calculation of the superheat temperature is provided, along with the effective overheat temperature. Provided calculations are in good correlation with experimental data.

The state of art in shock resistant MEMS accelerometer design is to reduce the size of the proof-mass, thereby reducing the generated forces and moments due to shock loading. Physical stops are also provided to limit proof-mass motion to prevent damage to various moving components. The reduction of the proof-mass size reduces the sensor sensitivity. In addition, to increase the sensor dynamic response, proof-mass motion needs to be minimally damped, resulting in a significant sensor settling time after experiencing a high shock loading such as those experienced by gun-fired munitions during firing. The settling time is particularly important for accelerometers that are used in gun-fired munitions and mortars for navigation and guidance. This paper describes the development of a novel class of accelerometers that are provided with the means of locking the sensor proof-mass in its “null” position when subjected to acceleration levels above prescribed thresholds, thereby protecting the moving parts of the accelerometer. In munitions applications, the proof-mass is thereby locked in its null position during the firing and released during the flight to begin to measure flight acceleration with minimal settling time. Details of the design and operation of the developed sensors and results of their prototyping and testing are presented. The application of the developed technology to other types of inertial sensors and devices is discussed.

A microstructure along with a robust fabrication process is developed for measuring the thermal conductivity (K) of nanowires and thin films. The thermal conductivity of a thin-film material plays a significant role in the thermoelectric efficiency of the film and is usually considered the most difficult thermoelectric property to measure. The lower the K, the higher is the thermoelectric efficiency and hence a higher detectivity can be attained if utilized for infrared detection. We have previously shown high responsivity uncooled thermoelectric IR detectors [1] that utilize polysilicon as the thermoelectric material. To further improve the performance of these devices, it is required to understand how the wire dimensions and different deposition parameters affect the thermal conductivity of polysilicon.

The nanowires of this work are formed by patterning a thin layer of low-pressure chemical vapor deposited polysilicon using e-beam lithography. Consequently, the common pick-an-place process followed by deposition of metallic contacts is avoided. As a result a significant source of error in calculating the thermal conductivity is eliminated. Additionally, several serpentine nanowires are fabricated between the two thermally-isolated membranes so that a greater amount of heat, comparable to heat loss through the arms, is transported through the nanowires for a more accurate measurement while the serpentine shape of the wires improves their structural integrity. The K of polysilicon nanowires are measured for the first time and it is shown that for nanowires with a cross section of ~60nmx100nm, the K is ~3.5 W/m.K (a 10X reduction compared to the bulk value of ~30W/m.K [2]).

We have studied high speed optical logic utilizing ultrafast two-photon absorption (TPA) induced phase change in semiconductor optical amplifiers (SOA). Results show that this scheme can realize all-optical logic and encryption at data speeds to 250 Gb/s.