Active resonators based on semiconductor gain media encompass a large optical nonlinearity that arises from gain saturation and enables bright soliton generation. The ability to operate these resonators below the lasing threshold as tunable passive devices –– filters, modulators, phase shifters –– opens up an untapped potential of seamlessly integrated reconfigurable devices for both generation of multimode mid-infrared (4 – 12 μm) light and its manipulation.
The global defense community requires new approaches for standoff detection of chemical, biological, radiological, nuclear and explosive (CBRNE) threats. Such standoff detection methods must be capable of discriminating the target hazardous materials from the environmental background. Therefore these sensors must exhibit high selectivity. High selectivity detection of CBRNE threats can be accomplished using infrared (IR) spectroscopy, which produces a unique spectral “fingerprint” of the target chemical, enabling discrimination of the target chemical from other chemicals in the background. Standoff detection using IR spectroscopy however requires that enough of the incident source light may be collected at the detector; therefore a high-power source is needed. Commercially available quantum cascade laser (QCL) sources are capable of projecting high power, coherent laser light at targets down range from the source. In order to collect complete IR spectra throughout the entire fingerprint region, the output of multiple QCL modules are combined into a single exit aperture. This is typically achieved using mirrors and other optics which are susceptible to vibrational and temperature misalignments in field systems. In order to provide a more ruggedized solution to combining the beam output of multiple QCL modules, we developed a unique chalcogenide optical fiber beam combiner which combines the output of four commercial QCL modules. This allows for scanning across a spectral range from 6.01 – 11.20 μm encompassing parts of both the IR functional groups and fingerprint regions. We demonstrate the ability of this QCL system to generate high quality IR spectra of hazardous materials.
Quantum cascade laser (QCL) systems are mature and at the vanguard of a new generation of products that support military applications such as Infrared Countermeasures (IRCM) and targeting. The demanding product requirements for aircraft platforms that include reduced size, weight, power consumption and cost (SWaP-C) extends to portable, battery powered handheld products. QCL technology operates throughout the mid-wave (MWIR) and long-wave (LWIR) infrared to provide new capabilities that leverage existing thermal imaging cameras. In addition to their suitability for aircraft platforms, QCL products are a natural fit to meet operator demands for small, lightweight pointer and beacon capabilities. Field-testing of high power, lightweight, battery operated devices has demonstrated their utility across a range of air and ground applications. This talk will present an overview of QCL technology and the Defense and Security products and capabilities that are enabled by it. This talk will also provide an overview of the extensive environmental and performance testing associated with products based on QCL technology.
Daylight Solutions has pioneered the development and commercialization of quantum cascade laser (QCL) technology
for commercial and military markets. Multi-Watt, multi-wavelength QCL-based systems have been manufactured and
tested against harsh military environmental requirements for military applications. These self-contained, turn-key
systems have been designed to comply with modular open system architecture (MOSA) principles, and have been
proven in several different system geometries. This paper will highlight the environmental requirements imposed upon,
and performance from, QCL-based laser systems for example military applications.
Micro- and nano-technologies (MNT) have opened up the mid-infrared (IR) spectral region to room temperature
techniques that are enabling new applications in chemical imaging. The mid-IR is rich in wavelength specific
absorptions that can be used to identify different chemicals and materials. It is only in the last decade, however, that mid-
IR cameras and tunable, intense mid-IR laser sources have become available that are compact and operate at room
temperature. MNT has allowed these developments; micro-bolometer arrays are now routinely fabricated with 25 μm
resolution and the ability to sense mid-IR radiation from 7 to 14 um. Quantum cascade (QC) lasers fabricated with
exquisite control of semiconductor layers and waveguides serve as the gain media for tunable mid-IR lasers, some even
tuned with MEMS feedback elements. The current state of mid-IR imaging and illumination is discussed, and specific
examples of its use in chemical imaging are presented. First, passive mid-IR imaging is considered, along with its ability
to be used for chemical identification. The use of tunable mid-IR lasers as an illumination source is then considered.
Technical aspects of illumination and detection paradigms are presented, with a consideration of how spectroscopic
information gathered in both stimulated thermal emission and reflectance modes can be analyzed to determine chemical
composition in an image. Finally, specific examples of QC laser assisted chemical imaging are presented.
Commercially available quantum cascade semiconductor materials continue to mature. When integrated into external
cavity quantum cascade laser (ECqcL™) geometries, these laser systems are now providing near-continuous coverage
throughout the entire 3 - 13 μm regime. Such coverage enables molecular detection systems to enjoy high sensitivity
and selectivity. Individual lasers have been demonstrated to provide > 320 wavenumbers of tuning. Wide tuning ranges
have also been demonstrated at wavelengths in the 3 - 4 μm regime. In addition, phase continuous (mode-hop-free)
tuning allows for extremely high resolution spectroscopy to be performed throughout the mid-IR. Daylight Solutions
will review the most up-to-date results regarding wavelength coverage, tuning range and power levels achieved from
ECqcL™ systems. Daylight will also provide recent results in sensitivity and coverage from their multi-species Swept
Sensor™ and photoacoustic detection platforms.
Commercially available quantum cascade gain media has been integrated with advanced coating and die attach
technologies, mid-IR micro-optics and telecom-style assembly and packaging to yield cutting edge performance. When
combined into Daylight's external-cavity quantum cascade laser (ECqcL) platform, multi-Watt output power has been
obtained. Daylight will describe their most recent results obtained from this platform, including high cw power from
compact hermetically sealed packages and narrow spectral linewidth devices. Fiber-coupling and direct amplitude
modulation from such multi-Watt lasers will also be described. In addition, Daylight will present the most recent results
from their compact, portable, battery-operated "thermal laser pointers" that are being used for illumination and aiming
applications. When combined with thermal imaging technology, such devices provide significant benefits in contrast and
identification.
Recent advances in commercially available quantum cascade semiconductor materials providing laser gain in the 3-
12μm regime have been developed. This enables wavelength tunable, narrow linewidth external cavity quantum cascade
laser (ECqcL) sources operating above room temperature to be realized with high yield. Daylight has combined these
materials with advanced coating and attach technologies, mid-IR micro-optics and telecom-style packaging to yield
compact, hermetically-sealed lasers. In addition, ultra-broad tuning ranges (>250 wavenumbers) have been demonstrated
from a commercially available product platform. Meanwhile, phase continuous tuning capabilities have been achieved to
provide the ability to perform wavelength modulation spectroscopy in the mid-IR from similar commercial platforms.
When integrated and optimized with new room temperature mid-IR detectors and modern low power embedded digital
signal processing electronics, the resulting sensor platform can provide significant advantages. These include multispecies
fingerprint identification at real-time update rates (10 Hz). Daylight will review the most recent progress in
ECqcL devices as well as describe their portable, battery-operated Swept SensorTM technology based upon this platform.
Daylight Solutions has integrated commercially available quantum cascade gain media with their advanced coating and
die attach technologies, mid-IR micro-optics and telecom-style assembly and packaging to yield cutting edge
performance. When orchestrated together into Daylight's external-cavity quantum cascade laser (ECqcL) platform,
significant performance has been achieved. These ECqcL modules have now be
Daylight Solutions is currently developing field deployable, high power, wavelength agile, external cavity quantum
cascade lasers (EC-QCLs). These devices are finding uses as IR sources for applications such as remote gas sensing,
imaging, and illumination. Progress in three specific areas of development will be discussed: (i) miniaturization of a fast
tunable, moderate resolution, pulsed QCL for gas sensing, (ii) demonstration of high power mod hop free tunable CW
QCL's for high resolution spectroscopy, and (iii) progress in development of battery powered high efficiency fixed
wavelength EC-QCL light sources for molecular imaging and detection.
Terrorists both with IEDs and suicide bombers are targeting civilian infrastructures such as transportation systems.
Although explosive detection technologies exist and are used effectively in aviation, these technologies do not lend
themselves well to protecting open architecture soft targets, as they are focused on a checkpoint form factor that limits
throughput. However, remote detection of explosives and other chemicals would enable these kinds of targets to be
protected without interrupting the flow of commerce.
Tunable mid-IR laser technology offers the opportunity to detect explosives and other chemicals remotely and quickly.
Most chemical compounds, including explosives, have their fundamental vibrational modes in the mid-infrared region
(3 to 15μm). There are a variety of techniques that focus on examining interactions that have proven effective in the
laboratory but could never work in the field due to complexity, size, reliability and cost. Daylight Solutions has solved
these problems by integrating quantum cascade gain media into external tunable cavities. This has resulted in
miniaturized, broadly tunable mid-IR laser sources. The laser sources have a capability to tune to +/- 5% of their center
wavelength, which means they can sweep through an entire absorption spectrum to ensure very good detection and false
alarm performance compared with fixed wavelength devices. These devices are also highly portable, operate at room
temperature, and generate 10's to 100's of mW in optical power, in pulsed and continuous wave configurations.
Daylight Solutions is in the process of developing a variety of standoff explosive and chemical weapon detection
systems using this technology.
We provide a general technique for evaluating the performance of an optical sensor for the detection of chemical warfare agents (CWAs) in realistic environments and present data from a simulation model based on a field deployed discretely tunable 13CO2 laser photoacoustic spectrometer (L-PAS). Results of our calculations show the sensor performance in terms of usable sensor sensitivity as a function of probability of false positives (PFP). The false positives arise from the presence of many other gases in the ambient air that could be interferents. Using the L-PAS as it exists today, we can achieve a detection threshold of about 4 ppb for the CWAs while maintaining a PFP of less than 1:106. Our simulation permits us to vary a number of parameters in the model to provide guidance for performance improvement. We find that by using a larger density of laser lines (such as those obtained through the use of tunable semiconductor lasers), improving the detector noise and maintaining the accuracy of laser frequency determination, optical detection schemes can make possible CWA sensors having sub-ppb detection capability with <1:108 PFP. We also describe the results of a preliminary experiment that verifies the results of the simulation model. Finally, we discuss the use of continuously tunable quantum cascade lasers in L-PAS for CWA and TIC detection.
We present an analytical model evaluating the suitability of optical absorption based spectroscopic techniques for detection of chemical warfare agents (CWAs) and toxic industrial chemicals (TICs) in ambient air. The sensor performance is modeled by simulating absorption spectra of a sample containing both the target and multitude of interfering species as well as an appropriate stochastic noise and determining the target concentrations from the simulated spectra via a least square fit (LSF) algorithm. The distribution of the LSF target concentrations determines the sensor sensitivity, probability of false positives (PFP) and probability of false negatives (PFN). The model was applied to CO2 laser based photoacosutic (L-PAS) CWA sensor and predicted single digit ppb sensitivity with very low PFP rates in the presence of significant amount of interferences. This approach will be useful for assessing sensor performance by developers and users alike; it also provides methodology for inter-comparison of different sensing technologies.
We report sensitive and selective detection of Diisopropyl methylphosphonate (DIMP) - a decomposition product of Sarin and a common surrogate for the nerve gases - in presence of several gases expected to be interferences in an urban setting. By employing photoacosutic spectroscopy with broadly tunable CO2 laser as a radiation source we demonstrate detection sensitivity for DIMP in the presence of these interferences of better than 0.5 ppb in 60 second long measurement time, which satisfies most current homeland and military security requirements and validates the photoacoustic spectroscopy as a powerful technology for nerve gas sensing instrumentation.
A novel trace-gas sensor system has been developed based on resonant photoacoustics, wavelength modulation spectroscopy, near-infrared diode lasers and optical fiber amplifiers that can achieve parts-per-billion sensitivity with a ten centimeter long sample cell and standard commercially-available optical components. An optical fiber amplifier with 500 mW output power is used to increase the photoacoustic signal by a factor of 25, and wavelength modulation spectroscopy is used to minimize the interfering background signal from window absorption in the sample cell, thereby improving the overall detection limit. This sensor is demonstrated with a diode laser operating near 1532 nm for detection of ammonia that achieves an ultimate sensitivity of less than 6 parts-per-billion. The minimum detectable fractional optical density, αminl, is 1.8x10-8, the minimum detectable absorption coefficient, αmin, is 9.5x10-10 cm-1, and the minimum detectable absorption coefficient normalized by power and bandwidth is 1.5x10-9 Wcm-1/&sqrt; Hz. These measurements represent the first use of fiber amplifiers to enhance photoacoustic spectroscopy, and this technique is applicable to all other species that fall within the gain curves of optical fiber amplifiers.
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