This PDF file contains the front matter associated with SPIE Proceedings Volume 10111, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

The last two decades have seen tremendous progress in the design and performance of mid-wavelength infrared (MWIR) type-II superlattices (T2SL) for detectors. The materials of focus have evolved from the InAs/(In)GaSb T2SL to include InAs/InAsSb T2SLs and most recently InGaAs/InAsSb SLs, with each materials system offering particular advantages and challenges. InAs/InAsSb SLs have the longest minority carrier lifetimes, and their best nBn dark current densities are <5X Rule ’07 at high temperatures, while those of InAs/GaSb SLs and InGaAs/InAsSb SLs are <10X Rule ’07. The quantum efficiency of all three SL detectors can still be improved, especially by increasing the diffusion length beyond the absorber length at low temperatures. Evidence of low temperature carrier localization is greatest for the two SLs containing ternary layers; however, the interface intermixing causing the localization is present in all three SLs. Localization likely does not affect the high temperature detector performance (>120 K) where these SL unipolar barrier detectors are diffusion-limited and Auger-limited. The SL barrier detectors remain diffusion-limited post proton irradiation, but the dark current density increases due to the minority carrier lifetime decreasing with increased displacement damage causing an increase in the trap density. For these SL detectors to operate in space, the continued understanding and mitigation of point defects is necessary.

Global efforts to mitigate climate change have largely focused on reducing emissions of carbon dioxide (CO₂), which is responsible for 55-60% of current anthropogenic radiative forcing on warming impact. Because of its long lifetime (~130 years [1]) in the atmosphere, long-lasting CO₂ will remain the primary driver of long-term temperature rise even if new CO₂ emissions dropped to zero. A "fast-action" climate mitigation strategies is therefore strongly needed to provide more sizeable short-term benefits than CO₂ reductions by reducing emission of short-lived climate pollutants (SLCPs), having atmospheric lifetimes of less than 20 years [2], which would allow for short-term drops in atmospheric concentrations and hence slow climate change over the next several decades. Monitoring of climatically and environmentally active SLCPs is important not only for policy-based reporting, but also for basic process-based understanding of climate related processes in the atmosphere. In this talk, we will overview our recent progress in the developments and applications of laser-based optical instruments for the measurements of environmental and livestock emitted methane (CH₄), as well as the measurement of black carbon (BC) absorption. The experimental detail, the preliminary measurement results, the corresponding data processing and analysis will be presented.

A quantum cascade laser-based gas analyzers with table-top size are developed for the acetone and isotope of carbon dioxide. The precision of 0.1 ppm and 0.3 ‰ in delta notation are achieved respectively.

We report here on the realization of a single-tube on-beam quartz-enhanced photoacoustic (QEPAS) spectroscopy sensor employing a custom-made quartz tuning fork (QTF) with a large prong spacing. The prongs of the QTF have been designed in order to provide a quality factor twice higher when the QTF operates in the first overtone flexural mode than in the fundamental mode. The influence of the microresonator tube on the main parameters characterizing the sensing performance of the QEPAS spectrophone, including the quality factor, the magnitude of the QEPAS signal and the associated background noise was investigated in detail.

Nitrogen oxides (NO_x), including nitric oxide (NO) and nitrogen dioxide (NO₂) play important roles in determining the photochemistry of the ambient atmosphere, controlling the production of tropospheric ozone, affecting the concentration levels of the hydroxyl radical, and forming acid precipitation. A sensor system capable of simultaneous measurements of NO and NO₂ by using a commercial 76 m astigmatic multi-pass gas cell (MPGC) was developed in order to enable fastresponse NOx detection. A continuous wave (CW), distributed-feedback (DFB) quantum cascade laser (QCL) and a CW external-cavity (EC) QCL were employed for targeting a NO absorption doublet at 1900.075 cm^-1 and a NO₂ absorption line at 1630.33 cm^-1, respectively. Both laser beams were combined and transmitted through the MPGC in an identical optical path and subsequently detected by a single mid-infrared detector. A frequency modulation multiplexing scheme was implemented by modulating the DFB-QCL and EC-QCL at different frequencies and demodulating the detector signal with two Labview software based lock-in amplifiers to extract the corresponding second-harmonic (2f) components. Continuous monitoring of NO and NO2 concentration levels was achieved by locking the laser frequencies to the selected absorption lines utilizing a reference cell filled with high concentrations of NO and NO₂. The experimental results indicate minor performance degradation associated with frequency modulation multiplexing and no cross talk between the two multiplexed detection channels. The performance of the reported sensor system was evaluated for real time, sensitive and precise detection of NO and NO₂ simultaneously.

We report on a novel quantum cascade laser (QCL) capable of operating in pure amplitude or wavelength modulation configuration thereby allowing the acquisition of background-free gas absorption-line profiles using quartz-enhanced photoacoustic spectroscopy (QEPAS). The QCL is composed of three electrically independent sections: Gain, Phase (PS) and Master Oscillator (MO). The non-uniform pumping of these three QCL sections allows laser wavelength tuning with constant optical power and vice-versa. Pure QEPAS amplitude modulation operating conditions were obtained by modulating the PS current, while pure wavelength modulation was obtained by modulating the MO section and slowly scanning the PS current.

Reliable standoff detection of traces of explosives is still a challenging task. Imaging MIR backscattering spectroscopy has been shown to be a promising technique for non-contact detection of traces of explosives on various surfaces. This technique, which is eye-safe, relies on active imaging with MIR laser illumination at various wavelengths. Recording the backscattered light with a MIR camera at each illumination wavelength, the MIR backscattering spectrum can be extracted from the three-dimensional data set recorded for each point within the laser illuminated area. Applying appropriate image analysis algorithms to this hyper-spectral data set, chemically sensitive and selective images of the surface of almost any object can be generated. This way, residues of explosives can be clearly identified on the basis of characteristic finger print backscattering spectra and separated from the corresponding spectra of the underlying material. To achieve a high selectivity, a large spectral coverage is a key requirement. Using a MIR EC-QCL with a tuning range from 7.5 μm to 9.5 μm, different explosives such as TNT, PETN and RDX residing on different background materials, such as painted metal sheets, cloth and polyamide, could be clearly detected and identified. 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. During the European FP7 projects EMPHASIS and HYPERION several field tests were performed at the test site of FOI in Sweden. During these tests realistic scenarios were established comprising test detonations of IEDs. We could demonstrate the potential of QCL-based imaging backscattering spectroscopy for the detection of trace amounts of hazardous substances in such scenarios.

We are developing a technology for standoff detection of chemicals on surfaces based on active broadband infrared imaging spectroscopy. This approach leverages one or more IR quantum cascade lasers (QCL), 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 response upon laser illumination. The broadband IR signal is processed as a hyperspectral image cube comprised of spatial, spectral and temporal dimensions as vectors within a detection algorithm. Such standoff spectroscopic imaging applications place stringent stability requirements on the wavelength, power, pulse width and spatial beam profile that pose a challenge for broadly tunable IR QCL. In this manuscript, we discuss methods to mitigate these challenges, including extensive calibration and active feedback stabilization. These mitigation methods should benefit many applications of IR QCL, including those for standoff detection, spectroscopy and imaging.

We report here an analysis of the performance of a quartz-enhanced photoacoustic (QEPAS) system operating in a pulsed mode by employing a quantum cascade laser (QCL). The QEPAS system is based on a quartz tuning fork (QTF) having fundamental resonance frequency of 4.2 kHz and a first overtone resonance of 25.4 KHz. Water vapor was used as a target gas by selecting its absorption line falling at 1296.5 cm^-1 with a line strength of 1.69⋅10^-22 cm/molecule. The QEPAS signal was investigated, while varying the QCL duty-cycle from continuous wave operation, down to 5%, which corresponds to a laser power consumption of 0.17 mW and a pulse-width of 4 μs.

We present mid-infrared vibrational spectroscopy and imaging at the nanoscale of individual cell membranes deposited on ultraflat gold substrate by use of resonantly-enhanced mechanical photoexpansion technique. This platform allows one to measure the energy absorbed by the sample by monitoring its local thermal expansion with a nanometer atomic force microscope tip. The observed Amide-I and Amide-II bands of proteins in the spectrum acquired on individual purple membrane flakes, filled with bacteriorhodopsin (bR) molecules, are in good agreement with the far-field infrared spectrum collected on large numbers of membranes. Differences among the relative intensity of the two Amide bands in the near- and far-field spectra are attributed to different orientation of bR protein molecules in the two samples. Strong vibrational contrast imaging at the Amide-I of proteins with a lateral resolution of around 50 nm is reported for individual flakes of both purple membranes and artificial lipid vesicles loaded with channelrhodospin molecules.

Only recently, a novel type of intensity autocorrelator in the time-domain has been reported for the Terahertz frequency range. The technique is based on fast electro-optic sampling in a double beam configuration and its temporal resolution is ultra-fast, as short as only few hundreds of femtoseconds. In particular, the self-referencing character of the technique is suitable for any type of source, including free-running sources. These unique characteristics enable therefore the investigation of the output profile of Terhertz Quantum Cascade Laser based Frequency Combs, with typical roundtrip times of few tens of picoseconds. The output dynamics of such devices have been investigated theoretically by Maxwell-Bloch equations and experimentally using Shifted Wave Interference Fourier Transform Spectroscopy. In this work, we present the results of the direct measurement of intensity autocorrelations of a Terahertz comb around 2.5 THz, when operated in the comb and high-noise regime, with radio-frequency beatnotes of 800 Hz and few MHz, respectively. We find the laser to be both amplitude- and frequency-modulated in both regimes, with a modulation ratio of the intensity of roughly 90 percent.The technique might come to use in future for the measurement of free-running pulses at Terahertz frequencies with high temporal resolution.

Plasmonic nanoantenna designs are quickly evolving in the direction of practical molecular sensing applications hence their wavelength range is being extended from the visible towards the mid-infrared. The problem of obtaining, in the mid-infrared, the same degree of plasmonic confinement obtained with gold in the visible range is related to the perfect conductor behavior of metals at long wavelengths. Here we fabricated bow-tie nanoantennas made of bottom-up assembled “metallic germanium” with free electron density of the order of 10²⁰ cm^-3 and therefore short plasma wavelength of 4.5 μm. We demonstrate the existence in the antenna gaps of confined hotspots with radius of the order of 100 nm, which we imaged by near-field photoexpansion microscopy at a wavelength of 5.8 μm in order to provide a clear proof of strong field confinement in the mid-infrared.

While much of the previous work on interband cascade lasers (ICLs) has been limited to the 3-4 μm spectral range, it was recently demonstrated at NRL and elsewhere that the low threshold current and power densities characteristic of ICLs can be extended to longer wavelengths. Here we report on the performance of ICLs operating in the 4.6-6.1 μm spectral range. The pulsed threshold current density at room temperature for an ICL emitting at λ = 4.8 μm is 220 A/cm², the lowest ever reported for a semiconductor laser at such a long emission wavelength. Broad-area devices emitting in the 4.6-4.9 μm range are observed to maintain pulsed external differential quantum efficiencies (EDQEs) of 11-17% when operating at 375 K. An ICL emitting at λ = 5.7 μm exhibits a threshold current density of 450 A/cm² and EDQE of 27% at room temperature. The Auger coefficients extracted from these thresholds indicate a systematic increase with wavelength, with the value at 6 μm being 3-4 times higher than that at λ = 3.5 μm.

In this work we present latest achievements on gain chips as sources for single-frequency tunable laser absorption spectroscopy and sensing. External cavity lasers based on Brolis Semiconductors (2.05 – 2.45) μm wavelengths GaSb gain chips exhibited single mode laser emission with linewidths <100 kHz and output powers of <5 mW in the entire tuning range of <100 nm per chip. Continuous current tuning of 60 GHz and mode-hop free piezo tuning of 26 GHz were demonstrated. Additionally, we report on extended wavelengths range by demonstrating low spectral modulation 850 nm GaAs-based gain chips. Finally, experimental results on GaSb-based gain chip integration with silicon photonics are presented.

Interband cascade lasers (ICLs) are a promising light source for the mid-infrared (mid-IR) spectral range. However, for certain applications such as spectroscopic techniques for chemical sensing and non-invasive disease diagnostics, a broadband incoherent radiation source such as an LED may be more desirable. Here we investigate both ICLs and interband cascade light emitting devices (ICLEDs). The ICLEDs follow the example of ICLs by cascading multiple active stages in series to improve efficiency and increase output power, but without an optical cavity to provide feedback. In this work we will present studies of these devices using high hydrostatic pressure techniques to determine the key efficiency limiting processes so that they might be mitigated. The application of hydrostatic pressure causes reversible changes to the band structure, increasing the energy of the conduction band gamma point and moving other key points in the band structure. This makes it a useful technique to probe recombination processes that depend on band gap and offsets, independently of temperature. For a laser dominated by CHCC Auger recombination, as is typical in narrow band gap devices for the mid-IR, one would expect a decrease in threshold current with increasing pressure, as the Auger process decreases with increasing band gap. However, the lasers studied here exhibit an increase in threshold current with pressure, indicating that other processes also play a significant role. We will discuss the relative contributions from Auger recombination and other processes such as defect-related recombination and carrier leakage in these devices, with respect to relevant modelling.

The family of interband cascade (IC) IR devices includes: interband cascade lasers (ICLs), interband cascade IR photodetectors (ICIPs), and thermophotovoltaics (ICTPVs). To date, developments at the component level have resulted in power-efficient mid-IR ICLs with CW operation at room temperature and above as well as uncooled mid-IR low-noise and high-speed ICIPs. However, there has been little effort to integrate these devices on a single chip for an IR photonic system. Since an appropriately designed ICL can operate as an IR photodetector at zero bias, ICLs and ICIPs can be grown and fabricated on a single chip, enabling the on-chip integration of IR lasers and photodetectors for mid- and long-IR wavelengths. We report the first demonstration of monolithically integrated mid-IR IC devices operating at room temperature. The unit consists of a monolithically integrated ICL and ICIP fabricated using focused ion beam (FIB) milling. The base structure is a type-I ICL with quaternary GaInAsSb active regions. The laser peak emission wavelength is 3.1 μm at 20 ◦C and the 10% cut-off wavelength of the corresponding ICIP is 3.3 μm, which ensures sufficient photon absorption at the lasing wavelength. For a laser/detector unit (at 20 ◦C) with a 12 μm gap between laser mirror and detector, the open-circuit voltage of the ICIP is 1.06 V and its short-circuit current is 106 μA, resulting from the laser emission (2.6 mW/facet). These preliminary results demonstrate the practical application of integrated IC devices for high-temperature, high-bandwidth and power-efficient on-chip sensors and optical communication mid-IR photonic systems.

Narrow gap semiconductors and superlattices relevant to optoelectronics often host multiple conducting species, such as electrons and holes, requiring a mobility spectral analysis (MSA) method to separate contributions to the conductivity. Building on the Fourier-domain MSA (FMSA) method proposed previously by the authors, we introduce a background subtraction step prior to FMSA to more accurately extract the spectral mobilities below what is normally considered the low mobility threshold μth = 1/B_max, where B_max is the maximum magnetic field of the experimental data under analysis. This preliminary step subtracts a linear background from the magnetotransport data and enables a more accurate fit in the low mobility range by several orders of magnitude. Background subtraction extends the useful low-mobility limit by a factor of 5 to μ_min = 1/5Bmax, and can be easily applied in other MSA techniques where low mobilities are of interest.

We demonstrate sub-wavelength electromagnetic resonators operating in the THz spectral range, whose resonant properties and optical response can be engineered using lumped elements, similarly to what is done in electronic circuits and antennas. We discuss the device concept, and we experimentally study the tuning of the resonant frequency as a function of variable capacitances and inductances. The advantages of this ‘circuit-tunable’ platform to realize novel THz meta-devices featuring an ultra-small semiconductor core are then discussed. As an application, we show that these micro-resonators have a strong potential for ultra-fast THz detection, when combined to a tiny quantum well photodetector active core.

Plasmonic terahertz (THz) resonators provide a promising route for exploring strong light-matter coupling phenomena. Double-metal resonator designs in particular enable strong enhancement of the THz field and provide well-defined field orientation and confinement within a sub-wavelength size volume. The strong field confinement however limits access to the internal fields essential for investigations of light-matter coupling. We propose and investigate a method for mapping and spectroscopic analysis of the internal fields in double-metal plasmonic THz resonators. We use aperture-type scanning near-field THz microscopy to access strongly confined fields with sub-wavelength spatial resolution of ~5 μm (~λ/100). Combined with the THz time-domain spectroscopy technique, the near-field method allows us to perform spectroscopic studies and investigate the field evolution inside the resonator. This experimental method opens doors to studies of strong light-matter coupling at THz frequencies in individual plasmonic resonators.

Terahertz quantum cascade lasers (THz QCL) are a very promising source for efficient frequency comb generation at terahertz frequencies. They do not only provide an output power of the order of milliwatts but are also covering a large spectral bandwidth. Octave spanning devices have recently been reported by our group. They provide a very low intrinsic dispersion due to the flat gain curve and the flat losses of the resonator. This allows frequency comb operation up to more than 600 GHz bandwidth with standard broadband metal-metal waveguide Fabry-Pérot QCLs. Frequency combs at terahertz frequencies are especially interesting for spectroscopic applications employing the powerful dual-comb setup. Such a setup requires a fast detector which is difficult to get with a sufficient sensitivity at terahertz frequencies. We present here an alternative approach, which does not need a fast detector but rather uses one of the two THz QCL frequency combs as an ultrafast multiheterodyne detector integrating local oscillator (LO) and detector in one single device. Two laser ridges are fabricated on the same chip at a distance of 500 um. Part of the light from the sample laser is coupled into the LO laser via the metallic ground plane. The downconverted multiheterodyne beatnote can be measured through the laser power supply line with a bias Tee. The obtained dual-comb covers a bandwidth of 630 GHz with a central frequency of 2.5 THz. The frequency comb spacing was analysed using frequency counting techniques revealing an accuracy down to _frep=fcarrier 10^(-12) at the carrier frequency of 2.5 THz.

Silicon photonics is being considered as the future photonic platform for low power consumption optical communications. However, silicon is a centrosymmetric crystal, i.e. silicon doesn’t have Pockels effect. Nevertheless, breaking the crystal symmetry of silicon can be used to overcome this limitation. This crystal modification is achieved by depositing a SiN high-stress overlayer. In this work, we present recent developments on the subject taking into account parasitic effects including plasma dispersion effect and fixed charge effect under an electric field. We theoretically and experimentally investigated Pockels effect in silicon waveguides and last results will be presented.

Ternary GaAsP nanowires (NWs) have gained great attention due to their structure-induced novel properties and band gap that can cover the working wavelength from green to infrared. However, the growth and hence applications of selfcatalyzed GaAsP NWs are troubled by the difficulties in controlling P and the complexities in growing ternary NWs. In this work, self-catalyzed core-shell GaAsP NWs were successfully grown and demonstrated almost stacking-fault-free zinc blend crystal structure. By using these core-shell GaAsP NWs, single NW solar cells have been fabricated and a single NW world record efficiency of 10.2% has been achieved. Those NWs also demonstrated their potential application in water splitting. A wafer-scale solar-to-hydrogen conversion efficiency of 0.5% has been achieved despite the low surface coverage. These results open up new perspectives for integrating III−V nanowire photovoltaics on a silicon platform by using self-catalyzed GaAsP core−shell nanowires.

Gallium Nitride (GaN) materials are the backbone of emerging solid state lighting. To date, GaN research has been primarily focused on hexagonal phase devices due to the natural crystallization. This approach limits the output power and efficiency of LEDs, particularly in the green spectrum. However, GaN can also be engineered to be in cubic phase. Cubic GaN has a lower bandgap (~200 meV) than hexagonal GaN that enables green LEDs much easily. Besides, cubic GaN has more isotropic properties (smaller effective masses, higher carrier mobility, higher doping efficiency, and higher optical gain than hexagonal GaN), and cleavage planes. Due to phase instability, however, cubic phase materials and devices have remained mostly unexplored. Here we review a new method of cubic phase GaN generation: Hexagonal-to-cubic phase transition, based on novel nano-patterning. We report a new crystallographic modelling of this hexagonal-to-cubic phase transition and systematically study the effects of nano-patterning on the GaN phase transition via transmission electron microscopy and electron backscatter diffraction experiments. In summary, silicon-integrated cubic phase GaN light emitters offer a unique opportunity for exploration in next generation photonics.

SHG is used in many practical applications such as a substance diagnostics, and imaging of various processes as well as for frequency conversion. Well known that the frequency doubling is used also for a generation of tripled frequency wave due to mixing of optical radiation at basic frequency with optical radiation at doubled frequency. In this case an important role plays a relation between phases of interacting waves with basic frequency and doubled frequency. Therefore, a derivation of the corresponding law for phase evolutions is an urgent problem. Below we provide such derivation for a SHG of high intensive femtosecond pulse with taking into account an influence of a cubic nonlinear response on the frequency doubling. Using the frame-work of long pulse duration approximation and plane wave approximation as well as an original approach we derive the solution of Schrodinger equations describing the SHG for femtosecond pulse without using the basic wave energy non-depletion approximation. It should be stressed, that the frequency conversion in conditions under consideration possesses multi-stability: there are many modes of SHG efficiency. We write a wave phase evolution for each of the modes. The derived formulas are verified by computer simulation based on using the corresponding Schrodinger equations.

We studied the Ga-free InAs/InAsSb type-II superlattice (T2SL) period, thickness and antimony composition, in order to define an optimized structure suitable for detection of the full mid-wavelength infrared domain (MWIR). The SL structures were fabricated by MBE on n-type GaSb substrates and exhibited cut-off wavelengths between 5μm and 5.5μm at 150K. The growth procedure used to achieve strain-balanced structures is reported and first structural and optical results, made of high-resolution Xray diffraction pattern, AFM image scan, photoluminescence (PL) and time resolved photoluminescence measurements (TRPL), are presented and analyzed.

High temperature operation of long wavelength interband cascade infrared photodetectors (ICIPs) has been demonstrated with a working temperature above 300 K. We conducted a comparison study of three sets of ICIP structures, which comprise single absorber barrier detectors and multi-stage ICIPs with four, six and eight discrete absorbers. The 90% cutoff wavelength of these detectors was between 7.5 and 11.5 μm from 78 to 340 K. Advantages of the multi-stage ICIPs over the one-stage devices are demonstrated in terms of lower dark current density, higher detectivity (D*) and higher operating temperatures. Multiple stage ICIPs were able to operate at temperatures up to 340 K with a monotonically increasing bias-independent responsivity up to 280 K, while the one-stage detectors operated at temperatures up to 250 K with the responsivity decreased at 200 K with bias dependence. The D* values for these ICIPs at 200 and 300 K were higher than 1.0×10⁹ and 1.0×10⁸ cmˑHz^1/2/W at 8 μm, respectively, which is more than a factor of two higher than the corresponding values for photovoltaic HgCdTe detectors with similar cutoff wavelengths. Interestingly, negative differential conductance (NDC) was observed in these detectors at high temperatures. The underlying physics of the NDC was investigated and correlated with the number of cascade stages and electron barriers. With enhanced electron barriers in the multiple-stage ICIPs, the NDC was reduced, and the device performance, in terms of D*, was improved.

We investigated a novel approach to extend a cut-off wavelength of Sb-based nBn detectors. We incorporated a series of single InSb monolayer into InAsSb bulk that allowed to realize a digital alloy absorber with an extended cut-off wavelength of λ = 4.6 μm at T = 200 K. The cut-off wavelength extension to 4.6μm is technologically important for realization of detectors covering CO₂ absorption line at 4.26μm.

In the short wavelength infrared (SWIR) region, InGaAs/GaAsSb type-II quantum well absorption structures are proposed as an attractive material for realizing low dark current. Recently QVGA format (array size 320×256) focal plane array (FPA) with cutoff-wavelength of 2.35 μm was demonstrated for commercial use by our group. We succeeded in extending cut-off wavelength of FPA consisting of InGaAs/GaAsSb type-II quantum well up to 2.5 μm. The 250-pairs InGaAs/GaAsSb quantum well structure lattice matched to InP substrate was grown by metal organic vapor phase epitaxy (MOVPE). The p-n junction of each pixel was formed by selective zinc diffusion method. Dark current of pixel showed the diffusion current limited mode and slightly better than that of HgCdTe with a same cutoff-wavelength. We present the electrical and optical characteristics of InGaAs/GaAsSb type-II quantum well FPA with cutoff-wavelength of 2.5 μm.

Midwave-midwave dual color detection has been successfully demonstrated by using pixel filters fabricated on top of InAs/GaSb focal plane arrays (FPAs). The pixel filters used in these FPAs were designed to transmit infrared radiation in the 3.5 - 4.1 μm wavelength region and to completely block light shorter than 3.5 μm. By comparing the signals of filtered and unfiltered pixels, excellent contrast between the two bands were obtained. This design concept offers a great flexibility to tailor the transmission window to any wavelength range within the 3-5 μm wavelength region. In particular, this dual color detector concept has been used for gas detection of volatile organic compounds which have main absorption peaks at 3.3 μm.

Timely technology transition with minimal risk requires an understanding of fundamental and technology limitations of material synthesis, device operation and design controllable parameters. However, this knowledge-based approach requires substantial investment of resources in the Science and Technology (ST) stage of development. For low volume niche semiconductor technologies of Department of Defense (DoD) relevance, there is little drive for industry to expend their limited resources towards basic research simply because there is no significant return on investment. As a result, technology transition from ST to product development is often delayed, expensive and carries risks. The Army Research Laboratory (ARL) is addressing this problem by establishing a Center for Semiconductor Modeling of Materials and Devices (CSM) that brings together government, academia, and industry in a collaborative fashion to address research opportunities through its Open Campus initiative. This Center leverages combined core competencies of partner organizations, which include a broad knowledge base in modeling, and its validation; sharing of computational, characterization, materials growth and device processing resources; project continuity; and ‘extension of the bench’ via exchange of researchers between affiliated entities. A critical DoD technology is sensing in the infrared (IR) spectrum, where understanding of materials, devices and methods for sensing and processing IR information must continually improve to maintain superiority in combat. In this paper we focus on the historical evolution of IR technology and emphasize the need for understanding of material properties and device operation to accelerate innovation and shorten the cycle time, thereby ensuring timely transition of technology to product development and manufacturing. There are currently two competing IR technologies being pursued, namely the incumbent II-VI Hg₁- _xCd_xTe technology and the III-V Type 2 Superlattices (SLs) technology. A goal of the CSM is to develop physics based models for Type 2 SLs with the capability to timely understand the knowledge gap between what is built and what is designed.

HgCdTe avalanche photodiodes offers a new horizon for observing spatial or temporal signals containing only a few infrared (IR) photons, enabling new science, telecommunication and defence applications. A large number of HgCdTe APD based detectors have been developed at CEA LETI to address the increasing number of applications in which a faint photonic information needs to be extracted from the noise of the proximity electronics used to sample the signal. The performance of HgCdTe APDs is directly related to the multiplication process and the dark current generation in the APDs. The impact of these parameters is presented as a function of the Cd composition and geometry of the APDs. The obtained and expected performance of HgCdTe APD detectors is reported for applications ranging from very low flux observations with long observations times to high data rate telecommunications with up to single photon resolution.

Type II Strained-Layer Superlattice detectors are currently being incorporated into hybridized infrared camera focal plane arrays for commercial applications. The detectors offer significant advantages over InSb and MCT detectors for certain application spaces, particularly high-speed imaging for industrial purposes, and military test ranges. The advantage over MWIR InSb sensors is driven by blackbody physics, which results in much higher emitted photon radiance values for target temperatures around ambient, as well as increased temperature dynamic range as a result of the lower thermal derivative in the LWIR band relative to the MWIR band.

Type II superlattices (T2SLs) based on alternating layers of InAs and GaSb exhibit rather unique properties, including a zero band gap at a critical value of the layer thicknesses. In this respect, T2SLs bear a close relationship to the alloy, Hg_1-xCd_xTe (“MCT”), where the band gap vanishes at a critical value of the composition parameter, x. A 15 μm pitch T2SL Long Wave Infrared array detector has recently been developed by SCD, based on a new XBp barrier architecture and a new and robust passivation process. This detector is made entirely from III-V materials and exhibits performance comparable to high quality MCT detectors. The SCD T2SL XBp detector contains both an InAs/GaSb active layer (AL) and an InAs/AlSb barrier layer. A k • p simulation method is described which can predict both the quantum efficiency and dark current with reasonable precision, from a basic definition of the superlattice period and the AL stack thickness. Results are compared with simulations for type I HgTe/CdTe superlattices. The method introduces a number of novel features including the use of an interface matrix, and a way of calculating the Luttinger parameters from standard reference values. For layer thicknesses greater than the critical values, both InAs/GaSb/AlSb and HgTe/CdTe superlattices undergo a transition to a Topological Insulator (TI) phase. The TI phase exhibits unusual spin polarized transport and optical properties which may be useful in future spintronic and THz devices.

This paper reports studies on spatial characteristics of Mid Wave InfraRed (MWIR) InAs/GaSb superlattices (T2SL) photodetectors. Modulation Transfer Function (MTF) measurements on commercial T2SL MWIR Focal Plane Array (FPA) are reported, using a Continuously Self Imaging Grating (CSIG). We find that measurements of the pixel size can be reliably achieved thanks to a new approach of data processing. Next, a new class of radiometric characterization, called "correctability", or ability for FPA pixels to durably keep the same behavior when exposed to a given radiometric flux, has been investigated on. Gain and offset corrections and Residual Fixed Pattern Noise (RFPN) measurements have also been made. The results obtained confirm the potentiality of high performance T2SL infrared photodetectors.

The knowledge of carrier concentration of doped or non-intentionally doped layer structures grown by Molecular Beam Epitaxy (MBE) is crucial to fabricate and manage design of new advanced photodetectors called "barrier structures". This communication reports on capacitance-voltage (C-V) study on MOS structure. Simulation to define specific MOS design, allowing doping layer concentration extraction by measurements, is performed. MOS structures based on InAs/GaSb Longwave infrared (LWIR) superlattice have been fabricated and characterized. Results obtained were analyzed and compared with simulations.

Time-Correlated Single Photon Counting (TCSPC) is acknowledged as one of the most effective techniques for measuring weak and fast optical signals, since it provides very high temporal resolution and sensitivity. Nevertheless, the long acquisition time needed to perform a measurement it’s still the main drawback. To overcome this limitation, multidimensional TCSPC systems have been developed, but they still suffer for a strong trade-off between performance and number of channels: the higher the number of channels, the poorer the performance. In this work we present the design of a complete TCSPC acquisition system which is meant to overcome this trade-off. Since the best state-of-the-art detectors and sensing circuits developed so far are designed with different technologies, following the same approach those circuits will be designed onto different chips to achieve the best performance from both sides. Through Silicon Vias (TSVs) will be investigated as a possible solution for connecting a custom technology SPAD array to a CMOS pick-up circuit. Since a high number of detectors will cause the count rate to saturate due to the limited transfer rate of a PC, the target throughput has been set to 10 Gb/s, well beyond the state of the art. Consequently, the number of acquisition chains has been tailored on the affordable throughput, and a dynamic-routing logic connects the detectors to this lower number of acquisition channels. Five fast Time-to-Amplitude Converters (TACs), able to reach 80 Mconv/s, have been designed to get high temporal resolution along with low dead time.

Nanoparticles composed of high refractive index semiconductors can support strong localized Mie-type resonances of electric and magnetic multipolar character that can be tuned by the nanoresonator geometry [1]. In addition, such semiconductor nanoresonators can exhibit very low absorption losses at optical frequencies. Based on these unique optical properties, semiconductor nanoresonators represent versatile building blocks of functional photonic nanostructures with tailored optical properties. This talk will provide an overview of our recent advances in controlling the generation and propagation of light with dielectric nanostructures composed of silicon or other high-index semiconductor nanoresonators. First, I will focus on passive and linear silicon metasurfaces designed to impose a spatially variant phase shift onto an incident light field, thereby providing control over its wave front. Based on the simultaneous excitation of electric and magnetic dipole resonances, silicon nanoresonators can be tailored to emulate the behaviour of the forward-propagating elementary wavelets known from Huygens’ principle [2]. This concept allows for the realization of various wave front shaping devices with high transmittance efficiency, full phase coverage, and a polarization insensititve response [3,4]. I will then discuss how we can utilize semiconductor nanoresonators for tailoring spontaneous emission from nanoscale light sources as well as for the manipulation of nonlinear effects in semiconductor nanoparticles. [1] I. Staude et al., ACS Nano 7, 7824 (2013). [2] M. Decker et al., Adv. Opt. Mater. 3, 813 (2015). [3] K. E. Chong et al., Nano Lett. 15, 5369–5374 (2015). [4] K. E. Chong et al., ACS Photonics 3, 514-519 (2016).

We demonstrate monolithic aluminum gallium arsenide (AlGaAs) optical nanoantennas for enhanced second harmonic generation (SHG) at telecom wavelengths. From measurements on nanocylinders of 400 nm height and varying radius pumped with femtosecond pulses delivered at 1554-nm wavelength, we estimated a peak conversion efficiency exceeding 10⁻⁵. Our measurements are in excellent agreement with frequency-domain numerical simulations, revealing the microscopic nature of the SHG process in our nanoresonators.

Plasmonic nano-antennas provide broadband spontaneous emission control by confining light on highly sub-wavelength volumes. We realize a plasmonic patch antenna by positioning a emitter within a ultrathin slab of dielectric limited by an optically thick gold layer and a thin gold patch. A single CdSe/CdS colloidal quantum dot is deterministically located just in the center of the antenna by an original in situ optical lithography protocol [1]. Depending on the dimension of the patch antenna and the emitter orientation, different Purcell factors could be achieved leading to different optical properties. For moderate Purcell factors, patch nanoantennas are plasmonic directive single photon sources. For higher Purcell factors, the spontaneous emission acceleration makes the multiexciton radiative recombination more efficient than Auger non radiative recombination. Emission of photons due to multiexcitons recombination could be observe at very short time scale. Such antennas can be very efficiently excited. Such antenna appear to be extremely bright as their luminescence exceed by more than one order of magnitude the one of single nanocrystals. References: [1] Dousse, A. et al. Controlled light-matter coupling for a single quantum dot embedded in a pillar microcavity using far-field optical lithography. Phys. Rev. Lett. 101, 267404 (2008). [2] C. Belacel, B. Habert, F. Bigourdan, F. Marquier, J-P. Hugonin, S. Michaelis de Vasconcellos, X. Lafosse, L. Coolen, C. Schwob, C. Javaux, B. Dubertret, J-J. Greffet, P. Senellart, A. Maître, Controlling spontaneous emission with plasmonic optical patch antennas, Nanoletters 13 1516 (2013)

Epsilon-Near-Zero (ENZ) metamaterials (MMs), whose dielectric permittivity approaches zero at specific wavelengths, exhibit exotic physical properties and promising optoelectronic applications. Here we exploit the effective medium approach to obtain the ENZ condition by stacking metal and dielectric materials, with individual subwavelength thickness. Based on this configuration, we investigate optical activity (dichroism and circular birefringence) of 1D chiral MMs enhanced by the ENZ effect and the all-optical transition of ENZ MMs, from metallic to dielectric, as a function of the pumping optical power.

Metal nanoantennas make it possible to manipulate the light, and in particular to control its absorption. According to Kirchhoff's law, emissivity equals absorptivity and nanoantennas may become light sources operating by thermal emission. These sources exhibit properties that deviate from those of the ideal blackbody described by Planck's law. We will show that it is possible to develop a metasurface based on metal-insulator-metal nanoantennas, wherein each antenna has dimensions smaller than the wavelength, and acts as a transmitter at given polarization state and wavelength of light, independent of the adjacent antennas. It is thus possible to obtain spatial, spectral and polarization control of the emitted light, and thus to encode complex images. Other nanoantennas concepts will be presented, such as optical Helmholtz resonators.

In this work, we take advantage of the resistive losses induced by plasmons excited at optical frequencies to design, fabricate and characterize a metal grating based CMOS-compatible light detector. A change of resistance is caused by increased electron scattering introduced by localized and delocalized surface plasmons in an applied current. We realize a spectral and polarization dependent detector that can be read out electronically. The optical response of the sensor can be tuned from the visible to IR regime by changing the geometry of the metal grating, which enables a variety of applications for an on-chip ultra-wideband plasmonic detector.

Invited abstract. The extreme light confinement provided by nanophotonic structures pushes toward revisiting the photodetector design. On the other hand introducing absorbing layers in nano-resonators demands dedicated electromagnetic design. This context opens the way for performance improvements and new functionalities, introducing the fourth generation of photo-detectors with promising features such as ultra-thin absorbing layers, device area much smaller than its optical cross-section and carved optical response. In this talk, I present a GMR InGaAs photo-detector dedicated for FPA applications, illustrating this global design and the cross-linked properties of the optical and semiconductor structures. In this "guided mode resonator", the semiconductor stack works as an optical guide. Its bottom part is structured in order to generate the first order diffraction modes in the semiconductor. Adjusting the coupling between the optical modes of the guide and those of the grating, allows optimizing this structure for various applications as optimum absorption at 1.55 μm or in the SWIR band [M. Verdun et al, Appl. Phys. Lett. 108 053501 (2016)]. The photodiode is based on an InP/InGaAs double heterojunction. The small thickness of the InGaAs absorbing layer (100 – 200 nm) allows suppressing the diffusion currents as well as reducing the generation-recombination currents in the space charge layer. It will be shown that the minimum value of the dark current is not necessarily reached for the thinnest absorbing layers. As a result, experimental data show at λ = 1.55 μm an external quantum efficiency of 75% and a specific detectivity of up to 1013 cm.√Hz.W-1.

Wavelength conversion via quadratic optical nonlinearity in AlGaAs waveguiding devices will be presented. Devices reported in this article include periodically inverted quasi-phase matching (QPM) devices and thin- rectangular high-index-contrast birefringence phase matching devices. Special emphasis will be placed on GaAs/AlGaAs QPM waveguides fabricated based on epitaxial growth technique (sublattice reversal epitaxy) we have developed for growing spatially inverted semiconductors. We have succeeded in demonstrating QPM second-harmonic generation and difference-frequency generation with reasonably high efficiencies.

Optical frequency combs currently represent enabling components in a wide number of fast-growing research fields, from frequency metrology to precision spectroscopy, from synchronization of telecommunication systems to environmental and biomedical spectrometry. As recently demonstrated, quadratic nonlinear media are a promising platform for optical frequency combs generation, through the onset of an internally pumped optical parametric oscillator in cavity enhanced second-harmonic generation systems. We present here a proposal for quadratic frequency comb generation in AlGaAs waveguide resonators. Based on the crystal symmetry properties of the AlGaAs material, quasi-phase matching can be realized in curved geometries (directional quasi-phase matching), thus ensuring efficient optical frequency conversion. We propose a novel design of AlGaAs waveguide resonators with strongly reduced total losses, compatible with long-path, high-quality resonators. By means of a numerical study, we predict efficient frequency comb generation with threshold powers in the microwatt range, paving the way for the full integration of frequency comb synthesizers in photonic circuits.

Antibacterial items are one of the major queries from the medical community in the fight against medical infections. Indeed, bacteria are resistant and their multiplication and biofilm formation on devises are one of the major causes of infections. Finding antibacterial surfaces, which are biocompatible, cost-effective, not toxic, and spreadable over large and irregular surfaces, is not easy. However, we created an antibacterial cloak by laser printing of Graphene Oxide (GO) hydrogels by mimicking the Cancer Pagurus carapace. This surface provides up to 90% reduction of bacteria cells through a bacteriostatic and bactericidal effect. Indeed, Laser treating allows GO sheets gel to cut and wrap microorganisms. Our findings are confirmed by a theoretical active matter model. This new technology based on antibiotic-free biomimetic Graphene Oxide gels opens untrodden roads to the fight against infections in biomedical applications and chirurgical equipment.

From latest nanotechnology advances, low-dimensional matter confinement delivered by nanostructuration or few-layer stacking offer new opportunities for ultimate light absorption performances. In this field, semiconducting 2D materials and photonic crystals have already demonstrated promising flexible optical properties from monoatomic to bulk structuration covering visible to IR spectral range. Today, these emerging materials such as Phosphorene, allow reconsideration of some physical effects such as photoconductivity. Indeed, its exploitation in integrated planar structures become c in terms of efficient local contactless control with a high degree of tunability by optics in association with high dark resistivity, fast carrier dynamics, and sub-wavelength light coupling solutions compatibility. Multiscale modeling and design tools implementing material anisotropic parameters from atomic configuration up to mesoscale, in complement with multiscale optical characterization in a large frequency bandwidth opens routes to new microwave signal processing functionalities such as switching, generation, amplification and emission over a large frequency bandwidth, that could not be achieved by full electronic solutions. This paper will report on latest demonstrations of high performance photoconductive structures for high frequency applications and review state-of-the-art research work in this area, with a specific focus on latest demonstrations for airborne applications.

This paper reviews recent advancement on the research toward graphene-based terahertz (THz) lasers. Optical and/or injection pumping of graphene can enable negative-dynamic conductivity in the THz spectral range, which may lead to new types of THz lasers. A forward-biased graphene structure with a lateral p-i-n junction was implemented in a distributed-feedback (DFB) dual-gate graphene-channel FET and observed a single mode emission at 5.2 THz at 100K. The observed spectral linewidth fairly agrees with the modal gain analysis based on DFB-Fabry-Perrot hybrid-cavitymode modeling. Although the results obtained are still preliminary level, the observed emission could be interpreted as THz lasing in population-inverted graphene by carrier-injection.

A prototypical experiment in cavity quantum electrodynamics involves controlling the light-matter interaction by tuning the frequency of a cavity mode in- and out-of resonance with the frequency of a quantum emitter,^1-3 while the field amplitude is generally unaltered. The opposite situation, where one perturbs the spatial pattern of a cavity mode without changing its frequency, has been considered only recently in a few works.^{4, 5} Changing the amplitude of the field at the emitter's position has important applications, at it allows a real-time control of the light-matter coupling rate, and therefore a direct control of processes such as spontaneous emission and Rabi oscillations. In view of this large potential, in this paper we discuss general design principles that allow obtaining large variations of the electromagnetic field, without change of the frequency, upon an external perturbation of the cavity. We showcase the application of these rules to two photonic structures, a single Fabry-Perot cavity and a coupled three-cavity system. As showed by our analysis and by the examples provided, a small frequency spacing between the modes of the unperturbed cavity is an important requirement to obtain large field variations upon small perturbations. In this regard, a coupled-cavity system, where the frequency spacing is controlled by the interaction rates between the single cavities, constitutes the most promising system to achieve large modulations of the field amplitude.

Optical resonators have enabled the label-free measurement of nanoparticles suspended in liquids, down to the resolution of individual viruses and large molecules, but are only able to quantify optical properties (refractive index, scattering, fluorescence). Additionally, these sensors are fundamentally limited by the random diffusion of particles to the sensing region, and thus only measure a tiny fraction of the analyte. We have developed a microfluidic optomechanical resonator capable of sensing freely flowing nanoparticles using the action of phonons that are coupled to light. The phonon mode of the system casts a nearly perfect net for measuring density, viscoelasticity, and compressibility of the particles that flow through, without being limited by random diffusion. Information on the mechanical properties of the particles is encoded in the light scattered from the thermal fluctuations of the phonon mode. We have also developed a new electro-opto-mechanical method for improving the sensing speed achievable with this technique. We demonstrate real-time particle transit measurements as fast as 400 microseconds, without any post-processing. We discuss how this novel technique can be used for ultra-high throughput analysis of mechanical properties of biological particles in liquids, enabling a new form of flow cytometry. (invited by Prof. Giuseppe Leo)

First, we will provide some recent advances on low-frequency phononic and acoustic insulators based on metasurfaces. We will introduce a new concept of acoustic absorption based on the coiling-up space design which exhibits extreme acoustic properties. A new acoustic absorber operating at 125Hz with deep-subwavelength thickness (~ λ/230) acting as an “acoustic sink” is designed and its functionalities are discussed. Second, as we are dealing with how to reduce or to absorb low-frequency sound/noise, we will explore a novel idea on the use in a positive manner these noises as a source of energy. We theoretically and numerically show the properties of a novel acoustic energy harvester resulting from the confinement and conversion of low-frequency acoustic/noise disturbances to electrical energy. We indeed present preliminary results showing a metamaterial structure producing an electrical power density of 0.54μw/cm³ for one confined frequency, which presents a very good value compared the others acoustic energy harvesting approaches.

Mid-infrared detection with semiconductor based pixel arrays attracted constant research interest over the past years. Remaining challenges for intersubband detectors are high device performance at elevated temperatures in combination with cost effective scalability to large pixel counts needed for applications in remote sensing and high resolution infrared imaging. In this field, quantum cascade detectors may offer promising advantages such as photovoltaic room temperature operation at a designable operation wavelength with compatibility to stable material systems and growth technology. We present a high performance InGaAs/InAlAs quantum cascade detector design suitable for pixel devices. The design is based on a vertical optical transition and resonant tunneling extraction. The 20 period active region is optimized for a high device resistance and thereby high detectivity up to room temperature. The pixels are fully compatible with standard processing technology and material growth to provide scalability to large pixel counts. An enhanced quantum cascade detector simulator is used for design optimization of the resistance and extraction efficiency while maintaining state of the art responsivity. The device is thermo-compression bonded to a custom read out integrated circuit with substrate bottom side illuminated pixels utilizing a metal grating coupling scheme. The operation wavelength is designed to align with the strong CO2 absorption around 4.3µm. A room temperature responsivity of 16mA/W and a detectivity of 5∙10^7 cm√Hz/W was achieved in good agreement with our simulation results. Device packaging and thermo-electric cooling in an N2 purged 16 pin TO-8 housing has been investigated.

A high photoresponse in a room-temperature quantum cascade detector (QCD) based on a coupled quantum-well design is demonstrated with a peak detection wavelength of 5.4 μm. In this design, forward electron transfer is engineered to be five times as large as relaxation back to ground level. In this situation, the coupled quantum-well QCD indicates a high responsivity of 22 mA/W as well as a specified detectivity (D*) of 8.0×10⁷ cmW^-1Hz^1/2, both at room-temperature with commonly used 45° wedge configuration. Applying a waveguide configuration for the proposed QCD, an elevated responsivity of ~130 mA/W with a D* of 1.1×10⁸ cmW^-1Hz^1/2 was obtained at room-temperature. A laser absorption spectroscopy for N₂O gas with proposed QCD and a distributed feedback quantum cascade laser has been also demonstrated.

Bi-functional active regions, capable of light generation and detection at the same wavelength, allow a straightforward implementation of the mid-infrared quantum cascade technology for integrated photonics. Different parts of the chip can be used for laser and for photodetectors. Potential applications are on-chip integrated sensors or lasers with integrated power monitoring capabilities. In the first bi-functional designs, wavelength matching was achieved using thicker barriers and reduced energy splitings between the extraction levels, but with the drawback of a reduced laser performance. The following introduction of the horizontal-vertical extraction scheme was a significant step towards high performance laser operation. In this work, we combine our design experience with optimized, laterally overgrown waveguides and refined bandstructure modelling. The device was designed for emission at 8 μm to show that wavelength matching can also be achieved at longer wavelengths, where it becomes increasingly difficult due to the smaller ratio between photon energy and LO-phonon energy. Graded interfaces were used in the bandstructure design to consider the behaviour of the MOVPE growth. In pulsed mode a threshold current density of 1.3 kA/cm 2 and a total wallplug efficiency of over 10% was achieved. In continuous-wave operation, the device emits 80mW output power in an episide-up configuration. A much higher performance can be expected after episide-down mounting on AlN substrates. In detector operation the device has a responsivity at the emission wavelength of about 20mA/W.