This PDF file contains the front matter associated with SPIE Proceedings Volume 12430, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

The application space for GaN devices is expanding. During our study of Vertical GaN device technology for power electronics, one of the phenomenal advancements was achieving a high-voltage, robust avalanche in p-n diodes. A high-quality p-n junction, although superficially simple, can be fundamentally limited in offering a uniform avalanche. Uniformity of avalanche is a critical parameter that is often overlooked during device designs and other metrics.

GaN-based high-electron mobility transistors are widely recognized for their exceptional performance at RF and microwave frequencies, and are increasingly being explored for millimeter-wave amplifier applications. An additional application that is critical for future systems is signal switching and routing at millimeter-wave frequencies; this is essential for enabling millimeter-wave wireless communication systems (e.g. 6G and beyond) that require frequency agility and reconfigurability. For this type of RF and mm-wave switch applications, the high carrier concentration and high 2DEG mobility of III-N HEMTs leads to low on resistance and low insertion loss. However, the isolation is limited by off-state capacitance, and nonlinearity of the HEMT limits the power handling capabilities. We have observed that the inclusion of a ferroelectric gate dielectric (using ALD-deposited Hf_0.5Zr_0.5O₂) in the device can significantly enhance performance. By combining polarization engineering of the III-N HEMT with the hysteretic and dispersive polarization characteristics of the ferroelectric gate stack, substantial improvements in the switch figure of merit (FOM=1/2π(R_onC_off)) can be achieved. The reduced effective off-state capacitance enabled by ferroelectrics integrated with GaN-based transistors has led to switches with FOM of 2.5 THz. Combining this with advanced processing (e.g. regrowth of source and drain ohmic contacts, gate length scaling), further improvements in performance are expected.

Frequency combs based on mid-infrared cascade lasers have been studied both experimentally and theoretically in recent years. So far only FM combs with quasi-cw output have been reported for interband cascade lasers (ICLs). We discuss the parameters that need to be achieved to realize passive mode locking in ICLs. The results are obtained from a comprehensive numerical model based on the wavevector-resolved Bloch equations coupled to the one-dimensional wave equation. We find that the design of the saturable absorber, in particular the carrier extraction time and length, is very important, while passive mode locking should already be achievable for the experimentally demonstrated values of group velocity dispersion. The leakage into the high-index GaSb substrate should also be controlled via the waveguide design.

Interband cascade lasers (ICLs) constitute a new class of semiconductor lasers allowing lasing emission in the 3– 7 μm wavelength region. Their structure presents similarities and differences with respect to both standard bipolar semiconductor lasers and quantum cascade lasers (QCLs). In contrast to QCLs, the stimulated emission of ICLs relies on the interband transition of type-II quantum wells while the carrier-to-photon lifetime ratio is similar to conventional bipolar lasers. ICLs can be classified into class-B laser systems like common quantum well lasers, and they exhibit a multi-GHz relaxation oscillation frequency that is related to the maximum modulation/chaos bandwidth achievable by these lasers. Moreover, ICLs take advantage of a cascading mechanism over repeated active regions, which allows us to boost the quantum efficiency and, thus, the emitted optical power. On top of that, the power consumption of ICLs is one or two orders of magnitude lower than their QCL counterparts whereas high-power of few hundreds of milliWatts can be achieved. Here, we report some recent results on the dynamic and nonlinear properties of ICLs. In particular, we demonstrate the generation of fully-developed chaos under external optical feedback. We show that ICLs exhibit some peculiar intensity noise features with a clear relaxation oscillation frequency. Together, these properties are of paramount importance for developing long-reach secure free-space communication, random bit generator, and remote chaotic LiDAR systems. Lastly, we also predict that ICLs are preferable devices for amplitude-noise squeezing because large amplitude noise reduction is attainable through inherent high quantum efficiency and short photon and electron lifetimes.

There is a general need to detect and measure the concentration of multiple hydrocarbon species in a gas. In this work, we have developed a tunable external cavity interband cascade laser (EC-ICL) that covers the wavelength range λ = 3216 to 3479 nm (Δ λ = 263 nm) in continuous wave (CW) mode. The EC-ICL provides a versatile broadband source for hydrocarbon detection and measurements. To demonstrate this capability, we incorporated the EC-ICL into an absorption spectroscopy sensor that includes a detector, data acquisition electronics, and software for data processing and spectral fitting. The AR/HR-coated laser with 3 mm cavity length is mounted epi-up on a heat spreader with a TEC. The external cavity is formed by a ruled diffraction grating in a Littman-Metcalf configuration to achieve broad tuning. The wavelength is tunable across the entire range with speed exceeding 15 Hz and effective system spectral resolution of approximately Δν = 0.7 cm^-1 in a broad tuning mode. In addition, we developed and demonstrated mode-hop-free (MHF) tuning capability of the system for up to 0.4 cm^-1 tuning range around an arbitrary user selected central wavelength with estimated spectral resolution significantly lower than Δν = 0.01 cm^-1. Using the EC-ICL, we demonstrated direct absorption measurements of mixtures of methane, ethane, and propane inside an absorption cell. Furthermore, we demonstrated high resolution MHF measurements for methane in a low pressure fiber gas cell. The EC-ICL technology demonstrated in this work is appropriate for a variety of tunable laser applications spanning λ = 3 – 6 μm.

We present a tunable nonlinear QCL structure that uses an external-cavity lens-coupled Cherenkov waveguide, where a silicon lens is closely coupled to the device substrate to provide greatly enhanced THz coupling efficiency and considerable performance enhancements over existing devices. A source operating at room temperature outputs a peak power of 0.2 mW at 1.5 THz. Additionally, device tuning over an operating frequency range from 420 GHz up to 2 THz was demonstrated. The operating frequency of 420 GHz is the lowest reported operating frequency for room-temperature QCL sources.

In this talk, we highlight our progress towards scalable quantum-tech solutions. We demonstrate hybrid integration of single InAs quantum dots on a Si₃N₄ optical waveguide platform and show that the hybridization process does not degrade the single emitter properties, and can even enhance them.

This talk is focused on using the intelligent aspects of machine learning (ML) for both the understanding of the subtle properties of nanophotonic devices and their inverse design to achieve a desired response. It will be shown that by reducing the dimensionality of the problem using manifold learning techniques and simplifying the resulting networks using pruning, the computation complexity of the underlying artificial intelligence (AI) algorithms will be considerably reduced. Furthermore, by optimally defining the loss function (or the metric) for AI algorithms, priceless information about the properties of photonic nanostructures can be uncovered while facilitating the better visualization of the input-output relationship in these nanostructures. In addition, the resulting manifold-learning algorithms can be optimally trained to facilitate the inverse design of such nanostructures while minimizing the structural complexity. This talk will provide the foundation for both knowledge discovery and design in photonic nanostructures using manifold learning and metric learning and their application to the highly desired metaphotonic structures as an example platform.

We review the latest results on the physical cause for the degradation of heterogeneous and quantum-dot based infrared laser diodes. Such devices are a fundamental building block of photonic integrated circuits for silicon photonics applications. One of the most critical fabrication steps is the integration of the III-V semiconductors active device and the silicon-on insulator wafer providing the waveguiding and additional electronic components. One option is to achieve heterogeneous integration by bonding the two wafers together. Devices fabricated in this way do not suffer from bonding-related reliability issues; degradation is mainly related to long-term performance drift caused by generation and/or diffusion of non-radiative recombination centers. The second possible option is the epitaxial growth of active optical devices directly on top of the SOI wafer, used as a substrate. In this case, quantum-dot devices are preferable, since they limit the degradation caused by the highly defective heteroepitaxial material. In these devices the main degradation processes are related to the high dislocation density through a recombination-enhanced defect reaction (REDR) climb and/or growth. Operation in excited state versus ground state can also accelerate degradation, since it lowers the effective barrier for carrier escape from the quantum dots to the quantum wells, a region where the defect reaction process is taking place.

Quantum technology promises to deliver quantum computers, unbreakable communication and ultra-sensitive sensors. Quantum photonics is one of the prominent platforms of quantum technology which utilizes photons – often called flying qubits. Entanglement generated from a photon-pair source is a crucial resource for many quantum photonic implementations, for example, an entanglement-based global quantum network and metrology beyond classical limits. Here, we will discuss our recent results of chip-scale photon-pair sources in silicon photonics. These results are focused on improving brightness, spectral purity and indistinguishability of the photon-pair sources, for example, by engineering photonic structures and temporal pulse shaping. We have found that both methods have trade-offs among brightness, spectral purity and indistinguishability. Additionally, we have observed that generating a high-fidelity quantum state using a quantum photonic circuit requires sufficient isolation between the nonlinear photon-pair sources and the linear photonic circuit. It is crucial to remove the nonlinear effect of the strong pump both before and after the sources to limit the spurious photon-pair generation which contaminates the target quantum state.

Microlenses replicated on front-illuminated single-photon avalanche diodes (SPAD) or back-illuminated CMOS image sensor are found to be stable to temperature variations, exposure to humidity, mechanical shocks and vibrations, as well as irradiation by gamma rays (for space applications). They highly improve the effective fill-factor, on front-illuminated SPAD-based image sensors, and the parasitic light sensitivity on a back-illuminated CMOS image sensor. Their broad transmission spectrum from NUV to NIR, combined with the wide geometrical space available to fabricate microlenses on various active substrates (wafer or die down to 2×2 mm²), make them suitable to a wide range of quantum photonics applications.

We review our efforts in integrating optical hardware for quantum key distribution onto photonic chips and in engineering the first standalone photonic integrated QKD system. Our approach tackles various system integration challenges related to packaging, optoelectronic design and power consumption. The quantum hardware is assembled in pluggable interconnects that guarantee efficient thermal management and forward compatibility of a same host electronics with successive generations of chips. Autonomous operation and long-term stability are demonstrated in realistic operation conditions. Our work offers new pathways for practical implementations of QKD and its viable deployment at large scales.

Multi-stage infrared (IR) photodetectors with discrete absorbers can circumvent the diffusion length limitation compared to the conventional detector with a continuous absorber. In this multi-stage detector architecture, the absorber in each stage is designed with a thickness that is thinner than the carrier diffusion length so that photo-generated carriers can be collected efficiently and quickly. Among them, interband cascade IR photodetectors (ICIPs) based on type-II heterostructures with unipolar (electron and hole) barriers are the most promising for high temperature and high-speed operation. In this paper, a comprehensive theory on signal, noises and detectivities in ICIPs will be reviewed and discussed to gain improved understanding of multi-stage IR detectors. Also, a formula is derived to correctly evaluate the detectivity for conventional photodetectors under reverse bias.

Colloidal semiconductor quantum dots/graphene (QD/Gr) heterojunction nanohybrids have recently emerged as a promising candidate for broadband photodetection. The QD/Gr nanohybrids are quantum sensors that take advantages of the quantum confinement in QDs for spectral tunability and that in graphene for superior charge mobility, leading high photoconductive gains. Therefore, the QD/Gr nanohybrids allows design of broadband photodetectors and the intrinsic high gain could lead to high detectivity (D*). This presentation reports the result in a recent research on QD/Gr nanohybrids for short-wave to middle-wave infrared (SWIR-MWIR) detectors. The focus of the study is to identify key performance limiting factors on responsivity, D* and response speed through an understanding of the underlying physics. Specifically, we have investigated the origin of the noise in the QD/Gr and found the intrinsic quantum limit of the noise could be achieved by tuning the Fermi energy of the graphene. Furthermore, the charge transfer between QD and graphene, which impacts the responsivity and response speed, has been found to be dictated by the QD surface states and QD/Gr interface. Through development of atomic-scale surface and interface engineering approaches to reduce or eliminate charge traps, efficient charge transfer across the QD/Gr interface can be achieved, leading to high uncooled D* at SWIR-MWIR wavelengths at room temperature approaching that of the cooled counterparts. This result illustrates the QD/Gr nanohybrids could provide a promising low-cost, scalable scheme for uncooled infrared detection and imaging.

An ensemble Monte Carlo framework is used to compare the impact ionization behavior important to avalanche photodiode (APD) performance in a band-engineered InAlAs/InAsSb type-II superlattice with same-energy gap bulk InAs and HgCdTe at 250 K. Impact ionization rates are computed directly from the electronic band structures. The same stochastic transport kernel is used for each material for consistency. A realistic treatment of impact ionization initial and final carrier states is employed in the transport simulations that considers energy and crystal momentum conservation. The major effects of band features on carrier states, transit path lengths between impact ionization events, and impact ionization coefficients support the role of band engineering in materials selection for high-performance APDs.

We have realized a compact radiofrequency spectrum analyzer based on nitrogen-vacancy (NV) color centers in diamond. The RF spectral components are spatially encoded by means of a Zeeman shift of the NV resonances induced by a magnetic field gradient. The fluorescence of the NV centers is imaged on a CMOS detector array using a gradient index lens. The spectral components of the signal are revealed by the appearance of dark lines in the image. We observed frequencies up to 10 GHz, with a resolution of a few MHz and a RF sensitivity of the order of 100 μW.

The interaction between light and biological matter can be exploited as a useful tool in various fields of science and technology. Indeed the optical behavior of living cells can permit to use them as micro-lenses for imaging, as photonic micro-resonators or waveguides, and also as advanced probes in holographic optical tweezers for manipulating the matter at nanoscale, and even bio-probes of localized fluorescence at sub-wavelength scale have been demonstrated. Here, we present an overview of these new insights about biological lenses. Theoretical modelling of the lensing effect of living cells will be discussed in details in case of Red Blood Cells. Digital holography in microscopy configuration is the tool that allow the experimental verification of this modelling thanks to the numerical refocusing capability. Applications of such new paradigm range from anemia diagnostics to bio-lithography.

Infrared laser spectroscopy allows the sensitive detection of gaseous substances. We present a novel gas sensing approach based on photothermal common-path interferometry that offers parts-per-billion sensitivity in microliter volumes: The thermal lens distortion pattern imprinted onto a near-infrared probe beam by the absorption of an infrared pump laser serves as signal for the sensing of low trace substance concentrations in the ppb range. Next to high specific sensitivity, additional focus lies on a tiny measurement volume and a compact overall setup. The advantages of this approach are discussed at the example of real-time measurements of breath N₂O.

The LinoSPAD2 camera combines a 512×1 linear single-photon avalanche diode (SPAD) array with an FPGA-based photon-counting and time-stamping platform, to create a reconfigurable sensing system capable of detecting single photons. The read-out is fully parallel, where each SPAD is connected to a different FPGA input. The hardware can be reconfigured to achieve different functionalities, such as photon counters, time-to-digital converter (TDC) arrays and histogramming units. Time stamping is performed by an array of 64 TDCs, with 20 ps resolution (LSB), serving 256 channels by means of 4:1 sharing. At sensor level, the pixel pitch is 26.2 μm with a fill factor of 25.1%. The median dark count rate of each SPAD at room temperature is below 100 cps at 6V excess bias, the single-photon timing resolution (SPTR) of each channel is 50 ps FWHM, and the peak photon detection probability reaches ~50% at 510 nm at the same excess bias. The fill factor can be increased by 2.3× by means of microlenses, with good spatial uniformity and flat spectral response above 400 nm. At system level, the average instrument response function (IRF) is 135 ps FWHM. The LinoSPAD2 camera enables a wide range of time-of-flight and time-resolved applications, including 3D imaging, fluorescence lifetime imaging microscopy (FLIM), heralded spectroscopy, and compressive Raman imaging, to name a few. Thanks to its features, LinoSPAD2 is a novel generation of reconfigurable single-photon image sensors capable of adapting their read-out and processing to match application-specific requirements, and combining SPAD arrays with advanced, massively-parallel computational functionalities.

We propose a nonlinear optical crystal-based compact terahertz (THz) - microfluidic chip with a few arrays of metaatoms for the ultra-trace sensing of solutions. We design the meta-atom array to induce natural evolutional resonance with a point THz source. The point THz source is locally generated by optical rectification at the irradiation spot of a femtosecond pulse laser beam in the single meta-atom, which induces a tightly electric field confinement mode. The generated THz waves resonate with surrounding meta-atoms in the time domain. We employed various types of metaatom structures and were able to detect minute changes in the concentration of trace amounts of ethanol and glucose water solutions by monitoring the shift in the resonance frequencies. This technique contributes compactification of the THzmicrofluidic chip with high sensitivity and accelerates the developments of future microfluidics integrated with THz technology, such as lab-on-a-chip devices and THz micro total analysis systems.

We investigate the possibility of realizing telecommunication wavelength (1.3 – 1.55 μm) single photon emitters based on quantum dots. We take two approaches to fabricate these emitters. The first approach is based on the growth of InAs on InP that results in both quantum dots and dashes. The second approach involves the growth of GaSb on GaAs to realize strained and unstrained quantum dots. The growth mode observed for InAs on InP follows a Stranski-Krastanov (SK) growth mode with a planar phase followed by a three-dimensional growth phase. However, unlike the growth of InAs on GaAs where a wetting layer is initially formed, followed by three-dimensional island growth, InAs on InP (100) results in a much thicker muti-monolayer planar phase followed by a three-dimensional island growth that has a preferential elongation along the (1-10) direction. These quantum dashes however do not show single dot/dash behavior and instead appear to have quantum well like characteristics. To achieve individual quantum dots we grow on (311)B InP substrates which clearly show single dot emission. The GaSb on GaAs system also has the possibility of longer wavelength quantum dots. This material system offers the option of both the coherently strained SK growth mode and also a strain-free island growth mode characterized by the presence of interfacial misfit dislocation arrays at the GaSb/GaAs interface. There is however the issue of band-alignment in the GaSb/GaAs system which is believed to be a type-II configuration. In addition, the capping of the GaSb quantum dots with GaAs also presents some unique challenges due to interdiffusion between the GaSb island and GaAs matrix.

We demonstrate both second harmonic generation (with a normalized efficiency of 0.20 %W⁻¹ cm⁻² ) and, to our knowledge, the first degenerate χ ⁽²⁾ optical parametric amplifier (with an estimated normalized gain of 0.6 dBW^−1/2 cm⁻¹ ) using silicon-on-insulator waveguides fabricated in a CMOS-compatible commercial foundry.

We investigate the characteristics of the quaternary alloy In_xGa_1−xAs_ySb_1−y as a viable alternative to extended InGaAs for sensing in short wavelength infrared. In_xGa_1−xAs_ySb_1−y p-i-n photodetectors with 0 < x < 0.3 have been grown on GaSb substrates in the wavelength region between 1 - 3 µm. Absorption coefficient up to ∼ 10⁴ cm⁻¹ compares well with that of InGaAs, increasing for samples with narrower bandgaps. Capacitance measurements shed light on the intrinsic unintentional doping levels, which are up to an order of magnitude lower than in typical bulk GaSb, due to a reduction in native defects of the material. Current density initially decreases with addition of small fractions of In/As to GaSb, then proceeds to increase once again towards higher alloy fractions as the bandgap narrows.

A 512-element lidar sensor equipped with a 30-micron-pitch linear-mode InGaAs APD array was developed for scanned time-of-flight lidar at 1550 nm. In a demonstration, the sensor was scanned in azimuth, using an optical system resulting in 0.067-degree angular resolution over 34.2 degrees of elevation; the scan rate was chosen to result in similar resolution over 120 degrees of azimuth. The sensor supports frame rates greater than 30 Hz at this image resolution. The sensor collects pulse return intensity data in addition to time-of-flight data, resulting in reflected intensity images analogous to conventional imagery in addition to "point cloud" range images.

We report on the development of Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) technology to detect 8 different air pollutants, namely CH₄, NO₂, CO₂, N₂O, CO, NO, SO₂ and NH₃, with the same acoustic detection module and interchangeable laser sources, to prove the modularity of the technique as well as the adaptability to different lasers. For each gas species, the fine structure of the infrared absorption bands has been simulated by using HITRAN database. Each gas species was detected with an ultimate detection limit well below their typical natural abundance in air even with signal integration time as low as 0.1 s.

Achieving higher operating temperatures is a key-point in the current infrared photodetection research. One promising way to achieve this goal is through the reduction of the thickness of the active region and the use of optical resonators to compensate the consequent loss of absorption. Herein we present simulation results of the absorption in a thin LWIR T2SL photodetector, capped with heavily doped semiconductors nanostructures and the benches used to measure their properties.

A 128-channel linear array photodetector, with 25 μm pixel pitch, connected to a readout integrated circuit (ROIC) was developed for mid-infrared spectroscopic applications that use a wavelength-variable quantum cascade laser (QCL). The detector is composed of III-V semiconductor InAsSb, has sensitivity in the mid-infrared region, and is operated at room temperature. The photovoltaic type of MIR detectors has a low shunt resistance, which causes high dark current. Therefore, a multi-series detector, which has a high total shunt resistance, is generally used for uncooled operation. However, in our newly developed detector array, a single element is employed as each channel’s detector to achieve high signal sensitivity. Also, a DC feedback (DCFB) mechanism is applied to the ROIC to draw out the detector’s high dark current. The detector’s performance is evaluated using a pulsed QCL with an emission wavelength of 7-10 μm at room temperature. A reverse voltage is applied to the detector to improve the detector’s characteristics and allow it to respond to a QCL’s pulse width of 100 nsec. Although the reverse voltage increases the detector’s dark current, the DC feedback draws out the dark current up to 1 mA. The detector’s sensitivity is 1.5 A/W at 7 μm, the TIA’s gain is designed to be 1k ohm, so the total trans gain obtained is 1.5 V/mW. The detector’s noise input equivalent power is 200 nW. Therefore, a high signal-to-noise ratio can be achieved because the pulsed QCL can output a peak power higher than several tens of milliwatts.

Mesa-based depleted passivation InGaAs photodetectors have a lower dark current than classical mesa type photodetectors due to in-device passivation. However, the in-device passivation layer’s depleted state induces electrical crosstalk. High electric field distribution between the pixels originating from the depleted state is the main reason for increased electrical crosstalk. An additional thin crosstalk-block layer in the modified depleted passivation InGaAs photodetectors manipulates this electric field distribution between the pixels and improves inter-pixel crosstalk while dark current suppression is preserved.

Conventional mid-wave infrared (MWIR) band photodetectors based on HgCdTe material typically require external cooling to achieve sufficient sensing performance. The development of a scalable, low cost, low power, and room temperature operating MWIR detector technology capable of high spatial resolution IR imaging can greatly augment space and satellite sensing capabilities such as remote sensing and earth observation. By integrating bilayers of p ⁺ -doped graphene to function as a high mobility channel enhancing recombination of photogenerated carriers, a graphene-enhanced photodetector comprising HgCdTe absorbing material can provide higher performance uncooled detection over the 2-5 μm MWIR band. This high performance MWIR band detector technology consists of graphene bilayers on Si/SiO₂ substrates doped with boron using a spin-on dopant (SOD) process, and subsequently transferred onto HgCdTe substrates. Boron doping levels and structural properties of the graphene bilayers were analyzed using Raman spectroscopy, Xray photoelectron spectroscopy (XPS), and secondary-ion mass spectroscopy (SIMS) throughout various stages of the development process including undoped, boron-doped, and following transfer onto HgCdTe/CdTe substrates. The developed room-temperature operating graphene-enhanced HgCdTe MWIR detectors have demonstrated through device modeling and optical and electrical characterization enhanced MWIR detection performance for NASA Earth Science, defense, and commercial applications.

Quartz Enhanced Photoacoustic Spectroscopy (QEPAS) is a sensitive trace gas detection technique employing Quartz Tuning Forks (QTF) as sensitive elements. Usually, a transimpedance amplifier is used as QTF front-end electronic, with a 10 MΩ feedback resistor. With a low-pass filter time constant of 100 ms, the thermal noise of the QTF intrinsic resistance (~100 kΩ) represents the main noise contribution. For real-time applications, shorter time constants need to be employed. In this work, we studied different amplifier structures with the aim to reduce the QTF thermal noise and improve the signalto- noise ratio when the QTF is used in QEPAS sensors.

Here we report on the application of multivariate analysis on optical sensors for gas detection based on Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) technique, focused on the analysis of complex gas mixtures. In real-world applications the effects of spectral and non-spectral interference occurring within the gas samples cannot be neglected in order to increase sensors selectivity and accuracy. In this work, Partial Least Squares Regression (PLSR) is selected as regression technique and tested on different gas samples for different applications. PLSR is able to retrieve analytes concentrations filtering out both: i) spectral contributions of analytes characterized by strongly overlapping features; ii) correlation effects due to the interaction among the sample’s components, i.e., matrix effects characterizing the photoacoustic detection.

Hydrogen sulfide (H₂S) is a harmful gas whose emissions are associated to natural gas leaks. Laser-based spectroscopy techniques have been demonstrated to be well suited for real time gas monitoring, providing high sensitivity and selectivity. Quartz enhanced photoacoustic spectroscopy (QEPAS) helped in developing of compact sensors. In the QEPAS sensor here presented, a distribute feedback diode laser emitting around 2.6 μm and a T-shaped quartz tuning fork coupled with acoustic resonator tubes were used to detect H₂S in methane-based matrix. The realized QEPAS sensor is a ready-to use solution for H₂S leaks monitoring in presence of methane (CH₄) at the percent scale.

Meta-optics allow the realization of new optical functions that are increasingly complex to realize and characterize locally. This is why we propose an interferometric method of systematic wavefront metrology of the meta-elements constituting a metasurface. This technique will allow the design of a library of nano-antennas, characterized in phase and amplitude. Once constituted, this library will allow the design of more complex optical functions. Tested for MIM (Metal-Isolating-Metal) metasurfaces, this technique can be applied to all metasurfaces.

We present an investigation on the electrical and optical properties of tapered quantum cascade lasers emitting at 14-15 μm, based on the InAs/AlSb system. In tapered lasers the active zone volume is increased to obtain higher optical power outputs without degrading the beam quality. Devices with three different taper angles of 1°, 2° and 3° were examined in terms of electrical, optical, and spectral properties and were compared with conventional ridge waveguide lasers.

Colloidal quantum dots (QDs) are increasingly emerging as efficient single-photon emitters (SPEs) for quantum applications. In this work, we report on the manipulation of single-photon signals of CdSe/CdS core/shell QDs by placing them precisely at desired positions in the polymeric submicropillars structures using a simple, inexpensive technique called low one-photon absorption direct laser writing. Thanks to the evanescent wave coupling effect, the fabricated submicropillars play the roles of directional couplers that guide both excitation laser and single-photon emission signals. Using a single conventional confocal system, we have successfully captured the combined emission signal from multiple SPEs based on polymeric submicropillars structures and thus experimentally tested its antibunching behaviors. Two architectural configurations have been proposed. Our approach offers a wide range of possibilities in integrated devices based on solid-state quantum emitters.

Maintaining the heart's health is one of the largest challenges in medicine due to the proclivity of life-threatening cardiovascular diseases, such as myocardial infarctions. When the heart experiences an infarction, a scar begins forming within an hour of the event, which will continue to grow and weaken the heart’s ability to contract. The myocardium after an infarction will increase in stiffness as the tissue becomes fibrotic; the influx of collagen dampens the flexion of the ventricles and reduces the cardiac output. The nature of the tissue stiffness is vital to understand not only at the tissue level but also at the mesoscopic domain. It is necessary to specify how the primary structural tissue components at the subcellular level contribute to the mechanical behavior of the muscle. To investigate this, we produced a procedure for mapping the mechanical nature of fresh myocardium: using atomic force microscopy to measure the mechanical properties of each structural component imaging determined by our second harmonic generation (SHG) microscopy. To coregistered AFM and SHG image, which has not been accomplished previously, we developed a convenient means of marking PDMS to be visible in SHG at 830 nm. Our research draws the line between the macroscopic mechanical behavior of the tissue to the nanoscopic structures.

The presence of micro and nano plastics in the environment and their impact on the various life forms within it are of principle concern around the globe. However, whilst a considerable amount of work has been done on the detection of microplastics, many challenges remain in the development of analytical techniques for nanoplastics due to their inherent ultra-small size and ubiquitous shapes. Here, a simple technique is reported based on surface enhanced Raman spectroscopy (SERS) and salt (NaCl) induced aggregation of gold nanoparticles that has been used to detect 100 nm diameter polystyrene (PS) beads. The gold nanoparticles (AuNPs) were synthesized and stabilized by negatively charged sodium citrate. When the PS beads present in a water sample were introduced into the solution of colloidal AuNPs, they interact to each other via hydrophobic interactions and other weak forces (i.e. hydrogen, ionic, and Van der waals forces). Upon an addition of NaCl, the negatively charged ions around the AuNPs are shielded and disturbed, resulting in their aggregation around the PS beads. As a consequence, strong SERS signal enhancement produced by the aggregated AuNPs was observed, and also demonstrated in numerical modelling. Concentrations of 100 nm PS beads as low as 1 part per million (ppm) were measured, and to the best of the author’s knowledge, this is the lowest concentration detected for nanoplastics of that size or smaller by such a simple technique that has been reported.

Many sub-wavelength structures have been used to enhance the infrared fingerprint of molecules in order to develop sensitive and versatile infrared spectroscopy molecular detection tools. Helmholtz-like optical resonators have the ability to strongly enhance electric fields in relatively large volumes and show good angular stability while their fabrication process is well mastered, what makes them interesting for an application to surface enhanced infrared absorption (SEIRA) spectroscopy. The overcoupled configuration shows new advantages compared to other coupling regimes: it can enhance the signature of vibrational modes of poly(methyl methacrylate) (PMMA) up to 70% over 5 μm wide wavelength range with a unique resonator. This study presents the behaviour of this promising structure compared to the original Helmholtz optical resonator and the application of different coupling regimes to SEIRA spectroscopy of PMMA, underlining the advantages of the overcoupling regime previously demonstrated.

We have developed a quantum memory using quantum dots with a photon echo method for the storage of ultraweak femtosecond pulses. This quantum memory has a large bandwidth of 7.2 THz, which can be achieved due to the large inhomogeneous broadening of quantum dots. We successfully demonstrated femtosecond timebin pulse transfer to photon-echo-based quantum memory using quantum dots. We also succeeded in measuring the retrieved time-bin pulses as a photon echo from the quantum memory using a pulse-pumped frequency upconversion single-photon detector (UCSPD) with a temporal resolution of 429 fs. It is found that the retrieved time-bin photon echo pulse maintains the sub-picosecond time duration and the relative phase.

We describe the electrical characteristics of graphene by chemical vapor deposition and oxidized using a solution of KMnO₄/H₂SO₄. It was possible to successfully oxidize graphene without any pores or substrate separation. The electrical resistance of the oxidized graphene (OG) rose when the H₂SO₄ concentration was raised. Due to direct tunneling via the interfaces between the sp² and sp³ regions, OG in particular exhibits a nonlinear I-V curve resembling that of diode. The oxygen functional groups in the OG rose as the concentration of H₂SO₄ increased. Additionally, it was discovered that the average distance between faults in the OG had decreased.

The development of energy-efficient and ultrafast neuromorphic computing based on the dynamics of the ferromagnetic (FM) skyrmion on the nanotrack has attained considerable interest. In this work, FM skyrmion based artificial neuron device is proposed. The perpendicular magnetic anisotropy (PMA) gradient is created on a thin film ferromagnetic (FM) layer by voltage control-PMA effect (VC-PMA). The anisotropy is directly co-related with the strength of 𝑚_𝑧 that affects the size of skyrmion meaning that in the region with larger PMA, the skyrmion size is smaller and hence, more energy. However, the skyrmions have the tendency to move in the direction to minimize the energy. Hence, the skyrmion move towards the lower PMA. This behavior of skyrmion on a nanotrack with PMA gradient corresponds to the leaky-integrate-fire (LIF) functionality of the neuron device. Hence, the suggested energy-efficient artificial neuron opens up the path for developing for energy-efficient neuromorphic computing.

Spintronics has attracted considerable interest for next-generation nano-devices because of their low power consumption, unlimited endurance, and non-volatility. Although spin-transfer-torque and spin-orbit-torque are widely used magnetization switching mechanisms, they are still limited by high power consumption and low switching speed. On the other hand, optically assisted magnetization switching using ultrashort laser pulses is able to achieve sub-picosecond switching operation. However, ferromagnetic materials require multiple laser pulses to switch their magnetization, that leads to higher energy consumption as compared to ferrimagnetic materials. In this paper, optically assisted magnetization dynamics in Ho-Fe-Co ferromagnetic nanostructure has been investigated using atomistic spin and monte carlo simulations. Ho has a relatively high magnetic moment and enhances magnetic anisotropy in Ho-Fe-Co nanostructure to achieve single shot and energy-efficient magnetization switching at room temperature.

Random-distribution antireflective metasurfaces suppress specular reflection by selectively scattering light into the forward axial direction. These surfaces have been shown to produce broadband, polarization independent transmission enhancement in the visible and IR wavelength bands. Rigorous full-wave solvers of light scatter from aperiodic surfaces can be computationally intensive, therefore alternative methods are desired to predict and analyze bi-directional surface scatter. Using a transfer function approach, an approximation of far-field light scatter can be modeled based on surface statistics. Random rough surfaces, which are generally globally isotropic and polarization insensitive, are well-modeled by Gaussian statistics, making them ideal candidates for a surface transfer function approach of surface scatter analysis. For this study, Si windows were processed to have statistically random nanofeatures which were optimized to enhance transmission throughput in the MWIR (3-5 μm). Optical performance of structured samples was verified using FTIR spectrophotometry. Bidirectional scattering distribution function of processed substrates was measured at selected angles of incidence using a 3.39-μm-wavelength polarized-laser scatterometer. Surface statistics were obtained via non-contact profilometric methods and used as input for calculation of surface feature diffractive effects by the Generalized Harvey-Shack scatter theory. Scatter distributions predicted using a Gaussian approximation of a random surface and structured surface metrology data were compared to the measured scatter data for assessment of the transfer function model validity within the bandlimit of interest.

In this work, mathematical models of surface plasmon resonance (SPR) biosensors are proposed. The proposed sensor with transition metal dichalcogenides (such as PtSe₂) constructed of two-dimensional materials (BP and WS2). Traditional SPR biosensors are also discussed. In the field of SPR sensors, researchers have been very interested in 2-D materials. Figure of merit (F.O.M) and sensitivity are two important parts of SPR sensors, and it has been talked about with analyte ranges from 1.330 to 1.36. The proposed sensor was found to be most sensitive when it had just one layer of Platinum diselenide (PtSe₂) and two layers of black phosphorous (BP). Here, a heterostructure made of BK7 Prism/Ag/PtSe₂/WS₂/BP is proposed as a much sensitive SPR biosensor with a Kretschmann configuration at a wavelength of 633 nm. The attenuated total reflection (ATR) method is used to measure the sensors' sensitivity, figure of merit (F.O.M.), Minimum reflections (R_min) and detection accuracy (D.A). The proposed sensor has many uses in biomedical, chemical, and bio-sensing fields.

Losses due to reflection of radiation off substrates and optical components often substantially inhibit the performance of detector and imaging systems. A novel means of enhancing transmission for improved detector and system performance involves the growth of nanostructured optical layers offering tunable refractive index properties, enabling broadband and omnidirectional suppression of light reflection/scattering while increasing transmission. These nanostructured antireflection (AR) coatings can be custom designed for specific wavebands from the ultraviolet (UV) to infrared (IR) for many potential optical applications, particularly when maximizing electro-optic and IR radiation transmission onto the surface of detectors is required to increase their sensitivity over various bands. The optimized AR nanostructured coatings were fabricated using a proprietary deposition process for high broadband AR performance. We have developed and advanced the AR coatings on GaSb, Si and various other substrate types particularly for IR band sensing applications. These nanostructured coatings provide substantial improvements over more conventional thin film AR coating technologies such as quarter wavelength stacks by further minimizing reflection losses and increasing transmission over a wide range of light incidence angles on optical detector and imaging devices. In this paper we review the latest developments in the high-performance nanoengineered AR coating technology for advancing NASA Earth Science sensing and imaging for various IR bands.

Integration of ridge array and Talbot cavity is an effective method for semiconductor laser optical power amplification. However, it is difficult for such designs to work stably in the fundamental supermode, resulting in the inability to achieve phase locking among the ridge arrays. Here, we report a phase-locked scheme that significantly increases the waveguide loss of high-order supermodes by adjusting the absorption boundary width of the ridge array, making the Talbot devices work stably in the fundamental supermode. Compared with the first-generation devices, the output power of the designed device is increased from 286 mW to 359 mW, and the central brightness is increased by twice. The demonstrated phase-locked high-brightness terahertz (THz) laser sources will have great application potential in THz spectroscopy and imaging.