This PDF file contains the front matter associated with SPIE Proceedings Volume 8993, including the Title Page, Copyright information, Table of Contents, Invited Panel Discussion, and Conference Committee listing.

Smart Sensors is a technique developed in the 70’s when the processing capabilities, based on readout integrated with signal processing, was still far from the complexity needed in advanced IR surveillance and warning systems, because of the enormous amount of noise/unwanted signals emitted by operating scenario especially in military applications. The Smart Sensors technology was kept restricted within a close military environment exploding in applications and performances in the 90’s years thanks to the impressive improvements in the integrated signal read-out and processing achieved by CCD-CMOS technologies in FPA. In fact the rapid advances of “very large scale integration” (VLSI) processor technology and mosaic EO detector array technology allowed to develop new generations of Smart Sensors with much improved signal processing by integrating microcomputers and other VLSI signal processors. inside the sensor structure achieving some basic functions of living eyes (dynamic stare, non-uniformity compensation, spatial and temporal filtering). New and future technologies (Nanotechnology, Bio-Organic Electronics, Bio-Computing) are lightning a new generation of Smart Sensors extending the Smartness from the Space-Time Domain to Spectroscopic Functional Multi-Domain Signal Processing. History and future forecasting of Smart Sensors will be reported.

Ultrasensitive detection of methane, isotopic carbon dioxide, carbon monoxide, formaldehyde, acetylene and ethylene is performed in the spectral range 2.5 - 5 μm using intracavity spectroscopy inside a broadband optical parametric oscillator (OPO). The two separate OPOs were operated near degeneracy and were synchronously pumped either by a mode-locked erbium (1560 nm) or thulium (2050 nm) fiber laser. A large instantaneous bandwidth of up to 800 cm^-1 allowed for simultaneous detection of several gases. We observed an effective path length enhancement due to coherent interaction inside the OPO cavity and achieve part-per-billion sensitivity levels.

Within the ambitious quest for an electrically pumped version of the optical parametric oscillator (OPO), we demonstrate the first near-infrared integrated OPO in a direct gap semiconductor. This nonlinear device is based on a selectively oxidized GaAs/AlAs heterostructure, the same “AlOx” technology that is at the heart of VCSEL fabrication. The heterostructure and waveguide design allows for type-I form-birefringent phase matching, with a TM₀₀ pump around 1 μm and TE₀₀ signal and idler around 2 μm. Relying on the high non-resonant χ⁽²⁾ of GaAs, relatively weak guided-wave optical losses, and monolithic SiO₂/TiO₂ dichroic Bragg mirrors, we observe a threshold of 210 mW at degeneracy in the continuous-wave regime, with a single-pass-pump doubly resonant scheme. Further improvement can be achieved by adopting a double-pump-pass scheme and, in a more fundamental way, by further optimizing the waveguide optical losses. The latter are induced by a not entirely mastered AlAs oxidation process and are of two distinct types: Rayleighlike scattering at signal and idler wavelength (α ≤ 1cm^-1), due to the interface roughness between GaAs and AlOx layers; and absorption at pump wavelengths (α ≈ 3cm^-1), due to volume defects in the GaAs layers adjacent to the aluminum oxide. This result marks a milestone for integrated nonlinear photonics and represents a significant step toward the goal of a broadly tunable coherent light source on chip.

Many advances have been made recently in mid-wave infrared and long-wave infrared quantum cascade lasers (QCLs) technologies, and there is an increasing demand for these laser sources for ever expanding Naval, DoD and homeland security applications. We will discuss in this paper a portfolio of various Naval Air Warfare Weapons Division’s current and future small business innovative research programs and efforts on significantly improving QCLs’ performance, affordability, and reliability.

Polariton Lasers do not rely on stimulated emission of photons, a criterion that sets stringent conditions on the threshold current in a conventional laser. Therefore, they have the capability to outperform photon lasers in the weak coupling regime in terms of the threshold power consumption. We present the first successful realization of an electrically pumped polariton laser based on a GaAs/AlAs distributed Bragg reflector cavity. We have furthermore identified the system’s response to an applied magnetic field as a sensitive tool to distinguish a polariton laser from a standard VCSEL device in the weak light-matter coupling regime

We demonstrate random lasing emission in an active planar slab of AlGaAs/GaAs randomly perforated with subwavelength circular holes. Spectrally-resolved imaging of both the diffusion in the passive regime together with the lasing emission allows identifying exteneded lasing modes in the weakly diffusive regime.

Monolithic semiconductor passively mode locked lasers (MLL) are very attractive components for many applications including high bit rate telecommunications, microwave photonics and instrumentation. Owing to the three dimensional confinement of the charge carriers, quantum dot based mode-locked lasers have been the subject of intense investigations because of their improved performance compared to conventional material systems. Indeed, the inhomogeneous gain broadening and the ultrafast absorption recovery dynamics are an asset for short pulse generation. Moreover, the weak coupling of amplified spontaneous emission with the guided modes plus low loss waveguide leads to low timing jitter. Our work concentrates on InAs quantum dash nanostructures grown on InP substrate, intended for applications in the 1.55 μm telecom window. InAs/InP quantum dash based lasers, in particular, have demonstrated efficient mode locking in single section Fabry-Perot configurations. The flat optical spectrum of about 12 nm, combined with the narrow RF beat note linewidth of about 10 kHz make them a promising technology for optical frequency comb generation. Coherence between spectral modes was assessed by means of spectral phase measurements. The parabolic spectral phase profile indicates that short pulses can be obtained provided the intracavity dispersion can be compensated by inserting a single mode fiber.

Whispering gallery optical parametric oscillators (WGR OPOs) are monolithic sources for tunable coherent and non-classical light. They are based on total internal reflection. Since reflection losses are negligible, their oscillation threshold can be far below one milliwatt. With sub-millimeter diameters, they are the most compact OPOs demonstrated so far. Recent experimental results demonstrate that WGR OPOs emit coherent light tunable over hundreds of nanometers. Operation in the visible as well as in the near-infrared has been demonstrated with up to 30 % conversion efficiency. These results indicate a great potential of WGR OPOs for spectroscopic and sensing applications.

By introducing coupled microstrip antennas on THz Distributed Feedback (DFB) Quantum Cascade Lasers (QCLs), the radiation efficiency of each feedback aperture is greatly enhanced. Single mode emission ~3 THz from a 31-period antenna-coupled third-order DFB laser yields ~4 times improvement in output power comparing with a corrugated thirdorder device fabricated on the same gain medium. This 31-period device has ~15×25° beam divergence and 4 mW pulsed power (4%) at 10 K with maximum lasing temperature (Tmax) at 134 K (pulsed). When phase matching condition is met, emissions from 81 apertures (4-mm long) are coherently combined to form a narrow beam with 12.5° divergence. Further experiment demonstrated the new device at 4 THz (25-period, ~18 μm×1-mm long. The 4 THz device reaches >8 mW pulsed power (10%) at 12 K with Tmax 109 K (pulsed) and >77 K (cw). The slope efficiency is 450 mW/A with 0.57% wall-plug. It is worth pointing out although the antennas would be excited differently, similar enhancement in out-coupling efficiency can also be observed in second-order surface-emitting THz DFB lasers. Begin the abstract two lines below author names and addresses.

THz electromagnetic waves resonantly excite plasmons in the two dimensional electron gas (2DEG) of high electron mobility transistors (HEMTs) via grating-gate couplers. These excitations can induce measureable photoresponse. Biasing the grating gate tunes the photoresponse via control of 2DEG carrier density. Plasmons are investigated here in an InGaAs/InP HEMT with a 9 μm period grating gate at 78 and 106 GHz free-space radiation and 4K sample temperature. The dependence of the photoresponse on applied Source-Drain bias is also investigated. The minimum noise equivalent power (NEP) is estimated to be 113 pW/Hz^1/2 , with maximum responsivity of 200 V/W. Such plasmonic alterations in channel conductance provide a means for voltage-tunable THz and sub-THz detectors or filters.

We are studying on terahertz-quantum cascade lasers (THz-QCLs) using III-nitride semiconductor, which is a material having potentials for realizing wide frequency range of QCL, i.e., 1-15 THz and 1-10 μm, including an unexplored terahertz frequency range from 5 to 12 THz. GaN-based QCLs also have potential to realize room temperature operation of THz-QCL. The merit of using an AlGaN-based semiconductor in comparison with GaAs or InP is that it has much higher longitudinal optical phonon energies (E_LO) (> 90meV) than those of conventional GaAs-based materials (~ 36 meV). We designed a GaN/AlGaN QCL that can operates in THz frequency range, and fabricated the GaN/AlGaN QCL devices by using molecular beam epitaxy (MBE). We demonstrated dramatic improvement of structural properties of QC stacking layers by introducing a novel growth technique "a droplet elimination by thermal annealing (DETA) method". We have observed inter-subband spontaneous emissions under current injection with peak frequencies from 1.4 to 2.8 THz from GaN/AlGaN QCL devices. The intensity of the emission was much improved by fabricating them on a low threading dislocation density (TDD) AlN/AlGaN template prepared by metal-organic chemical-vapor epitaxy (MOCVD) on a sapphire substrate.

Recent experiments have generated great interest in combined wavlength (WDM) and spatial (SDM) divison multiplexing using optical angular momentum (OAM) at data rates orders of magnitude better than current telecommunication standards. We discuss here a class of novel fiber optic devices that induce mode coupling along the optical axis of the fiber by sinusoidally varying the refractive index. Using the analogy between the wave equation for weakly guiding fibers and the paraxial equation, we review fibers that support Laguerre-Gauss modes and, motivated by these works, demonstrate that similar fibers with different core shapes support Hermite-Gauss modes in the same regime. Finally, we utilize these relations to demonstrate how one might generate different orbital angular momentum states using induced coupling between Hermite-Gauss modes, motivated by the works of many previous authors. We further describe a class of devices that could generate either a mode with a defined orbital angular momentum, and support its propagation along a fiber, or create a superposition of modes from a single modal input. Previous efforts focused on the generation of OAM states in a fiber have required extremely exotic refractive index profiles, and we present here a method based on already developed refrative index profiles and manipulation techniques, specifically using fiber bragg gratings to drive modal coupling in a fiber, in an effort to generate states with well defined OAM.

High index contrast periodic structures can be exploited to perform an arbitrarily adjustable spatio-temporal molding of light at the wavelength scale. This tight control of photons is obtained through a shaping of resonant modes and a suitable adjustment of their coupling with propagative modes. In this talk, surface addressable (or above the light line) Bloch modes in photonic crystal membranes (PCMs) will be investigated. The concepts governing the properties of these modes will be first presented. It will be demonstrated that simple models can be considered to understand their behavior and, more specifically, their ability to capture photons during the desired lifetime. Bloch modes with a very large band width or a very high Q factor can be easily designed this way. The wide application range of these PCMs will be illustrated by different devices. Low Q Bloch modes will be first used as efficient and broadband reflectors and exploited to realize compact and efficient vertical cavity lasers with unprecedented functionalities. In addition, it will be shown that this kind of mirrors can be bent in order to confine photons in the 3 directions even in low index materials, opening the way to a new class of emitters and sensors. Finally, the exploitation of high Q Bloch modes to design highly directional thermal emitters with wavelength selectivity will be presented.

In this paper we present the design and applications of flexible photonic membranes. We discuss their use as versatile photonic layers in the framework of lab-on-fibre applications, specifically focusing on the design of angular robust spectral filters. We also show alternative routes to their fabrication, highlighting the opportunities and limitations associated to each approach. Finally we present our preliminary results on the all-optical control over flexible membranes, as a potential method to fine-tune their opto-mechanical properties to the required application.

In this work, we perform spectroscopic studies of AlGaAs/InGaAs quantum cascade laser structures that demonstrate frequency mixing using strain-compensated active regions. Using a three-quantum well design based on diagonal transitions, we incorporate strain in the active region using single and double well configurations on various surface planes (100) and (111). We observe the influence of piezoelectric properties in molecular beam epitaxy grown structures, where the addition of indium in the GaAs matrix increases the band bending in between injector regions and demonstrates a strong dependence on process conditions that include sample preparation, deposition rates, mole fraction, and enhanced surface diffusion lengths. We produced mid-infrared structures under identical deposition conditions that differentiate the role of indium(strain) in intracavity frequency mixing and show evidence that this design can potentially be implemented using other material systems.

There have been limited choices of optical materials in the Mid-Infrared for polarization control and subsequent isolation. We show several combinations of existing materials and optics that could realize polarization control and isolation for quantum cascade lasers in the MIR. Improvements in signal to noise ratio in MIR laser spectroscopy, as well as saturated absorption spectroscopy utilizing the isolation achieved, will be discussed.

Measurements characterizing spatial mode filtering of mid-infrared (mid-IR) laser beams using hollow core fiber optics are presented. The mode filtering depends strongly on the fiber diameter, with effective mode filtering demonstrated with bore diameters of d = 200 μm and 300 μm. In addition to mode filtering, beam profile measurements also demonstrate the strong dependence of the mode quality on the fiber coupling conditions. As predicted, optimal coupling is achieved using relatively slow optics that produce focused spots that nearly fill the fiber diameter. Examples of the utility of using hollow fibers for mode-filtering to improve molecular spectroscopy experiments are also discussed.

Fraunhofer IAF can look back on many years of expertise in developing high-performance infrared photodetectors. Since pioneering the InAs/GaSb type-II superlattice detector development, extensive capabilities of epitaxy, process technology, and device characterization of single element detectors and camera arrays for the mid- and longwave infrared (MWIR and LWIR) have been established up to the level of small-scale production. Bispectral MWIR/MWIR and MWIR/LWIR cameras based on type-II superlattices or HgCdTe are key topics at Fraunhofer IAF. Moreover, the development of InGaAs-based short-wave infrared (SWIR) photodetectors for low-light-level applications has recently been initiated. In this contribution, we report on the status of recent photodetector development activities at IAF, covering detector design, epitaxial growth, process technology, and most recent electro-optical characterization results of focal plane arrays as well as single element detectors especially for the SWIR based on InGaAs material system.

The material properties of p-type InAs/InAsSb superlattices are of interest for infrared photodiodes, but InAs/InAsSb superlattices are residually n-type and p-type superlattices have not been investigated thus far. This study examines the material properties of a mid-wavelength infrared InAs/InAsSb superlattice design doped with Be concentrations from 0.5-7x10¹⁶ cm^-3. High-resolution x-ray diffraction revealed slight structural variation throughout the ~500 nm thick superlattice layer, but the RMS surface roughness was reasonable. Hall Effect measurements, taken at 10 K to remove any conduction effects from the undoped GaSb substrate, revealed the superlattice converting from ntype to p-type at Be:3x10¹⁶ cm^-3. The maximum hole mobility achieved at the two highest Be doping levels was ~24,000 cm²/Vs, which is high for mid-wavelength infrared superlattices. The doped superlattices all had photoluminescence (PL) peaks 12 - 34 meV lower in energy than the undoped sample, and the PL peak FWHMs increased as the average superlattice mismatch increased, as expected. Comparing the photoresponse to the PL allowed the Be acceptor binding energy in the superlattice (13 meV) to be determined, which agreed with the reported Be acceptor binding energy in InAs.

In this study optical modulation response and photoluminescence spectroscopy were used to study mid-wave Ga-free InAs/InAsSb superlattices. The minority carrier lifetimes in the different samples varied from 480 ns to 4700 ns, partly due to different background doping concentrations. It was shown that the photoluminescence intensity can be used as a fast non-destructive tool to predict the material quality. It was also demonstrated that it is crucial to use a low excitation power in the photoluminescence measurements in order to get a good correlation between the photoluminescence intensity and the minority carrier lifetime.

In this communication, we examine the influence of the SL period of InAs/GaSb superlattice (SL), with diverse InAs to GaSb thickness ratio, on the material and device properties of midwave infrared pin photodiodes. Three SL devices made of three different periods, but exhibiting the same cut-off wavelength at 5 μm at 77K, were grown by molecular beam epitaxy on p-type GaSb substrates. Optical and electrical characterizations (photoluminescence, current-voltage, capacitance-voltage, and photoresponse measurements) were performed and analyzed in order to explain the results obtained. Our investigations show the strong influence of the SL composition on both the material and photodetector properties, such as residual doping concentration, shape of the response spectra and dark current values.

Quantum-engineered multiple stage photovoltaic (PV) devices are explored based on InAs/GaSb/AlSb interband cascade (IC) structures. These ICPV devices employ multiple discrete absorbers that are connected in series by widebandgap unipolar barriers using type-II heterostructure interfaces for facilitating carrier transport between cascade stages similar to IC lasers. The discrete architecture is beneficial for improving the collection efficiency and for spectral splitting by utilizing absorbers with different bandgaps. As such, the photo-voltages from each individual cascade stage in an ICPV device add together, creating a high overall open-circuit voltage, similar to conventional multi-junction tandem solar cells. Furthermore, photo-generated carriers can be collected with nearly 100% efficiency in each stage. This is because the carriers travel over only a single cascade stage, designed to be shorter than a typical diffusion length. The approach is of significant importance for operation at high temperatures where the diffusion length is reduced. Here, we will present our recent progress in the study of ICPV devices, which includes the demonstration of ICPV devices at room temperature and above with narrow bandgaps (e.g. 0.23 eV) and high open-circuit voltages.

Polycrystalline lead salt photoconductive (PC) detectors have been widely used for applications in the 1-5μm spectral range because of their low cost, room temperature operation and high detectivity. However, the physical mechanism of such detectors had not been un-ambiguously understood. In order to improve the performance, we proposed a charge separation junction (CSJ) model to analyze and guide our material synthesis process, which has led to PbSe PC detectors with record high detectivity. On the other hand, the performance of photovoltaic (PV) detectors using Pb-salt epitaxial films on Si substrates has been limited by their high defect density even though the ideal performance of the PbSe PV detector was theoretically proven to be higher than the most popular HgCdTe PV detectors at near room temperature, due to its low Auger recombination property. Inspired by the high material quality of self-assembled lead salt microcrystals, we developed a novel method to produce PV detectors using PbSe micro-crystals based on our studies on the PC detector research that showed promising preliminary results.

InSb pin photodiodes and nBn photodetectors were fabricated by Molecular Beam epitaxy (MBE) on InSb (100) n-type substrate and characterized. MBE Growth conditions were carefully studied to obtain high quality InSb layers, exhibiting in pin photodiode design dark current density values as low as 13nA.cm^-2 at -50mV and R0A product as high as 6x10⁶ WΩcm² at 77K. Then, a new unipolar nBn InSb/InAlSb/InSb detector structure on InSb substrate were designed in order to suppress generation-recombination dark current. The first InSb nBn devices were fabricated and preliminary electrical characterizations are reported.

In this communication, the potentiality of InSb material as an avalanche photodiode (APD) device is investigated. Current density-voltage (J-V) characteristics at 77K of InSb pin photodiodes were simulated by using ATLAS software from SILVACO, in dark conditions and under illumination. In order to validate parameter values used for the modeling, theoretical J-V results were compared with experimental measurements performed on InSb diodes fabricated by molecular beam epitaxy. Next, assuming a multiplication process only induced by the electrons (e-APD), different designs of separate absorption and multiplication (SAM) APD structure were theoretically investigated and the first InSb SAM APD structure with 1μm thick multiplication layer was then fabricated and characterized.

In this paper we discuss silicon-based photonic integrated circuit technology for applications beyond the telecommunication wavelength range. Silicon-on-insulator and germanium-on-silicon passive waveguide circuits are described, as well as the integration of III-V semiconductors, IV-VI colloidal nanoparticle films and GeSn alloys on these circuits for increasing the functionality. The strong nonlinearity of silicon combined with the low nonlinear absorption in the mid-infrared is exploited to generate picosecond pulse based supercontinuum sources and optical parametric oscillators that can be used as spectroscopic sensor sources.

Tunable Laser Absorption Spectroscopy in the mid-infrared wavelength region, especially between 3 and 6 µm, is of great interest for high performance gas sensing applications. Interband Cascade Lasers can provide monomode continuous wave (cw) emission above room temperature in this wavelength range. We present the simulation, design and manufacturing of application-grade distributed feedback laser devices based on this concept. The fabricated devices successfully target specific, technologically relevant, wavelengths in cw operation above room temperature with low energy consumption. Output powers above 5 mW, high Side Mode Suppression Ratio around 30 dB and tuning ranges of up to13 nm were achieved.

Mid-infrared spectral region (2-4 μm) is gaining significant attention recently due to the presence of numerous enabling applications in the field of gas sensing, medical, environmental and defense applications. Major requirement for these applications is the availability of laser sources in this spectral window. Type-I GaSb-based laser diodes are ideal candidates for these applications being compact, electrically pumped, power efficient and able to operate at room temperature in continuous-wave. Moreover, due to the nature of type-I transition these devices have characteristic low operation voltage, typically below 1 V, resulting in low power consumption, and high-temperature of operation. In this work, we present recent progress of 2.1 μm wavelength single-spatial mode GaSb type-I laser diode development at Brolis Semiconductors. Experimental device structures were grown by solid-source multi-wafer MBE, consisting of an active region with 2 compressively strained (~1.3 %) GaInAsSb quantum wells. Epi-wafers were processed into a narrow-ridge (3-5 μm) devices and mounted p-side up on CuW heatsink. Devices exhibited very low CW threshold powers of < 30 mW, and single spatial mode (TE00) operation with room-temperature output powers up to 200 mW in CW mode with a far-field fast axis divergence angle of ~ 57 degrees.

In this presentation we discuss application of broadband terahertz (THz) time-domain spectroscopy for probing subwavelength (micrometer) size objects. The problem of weak coupling between THz waves and sub-wavelength objects, which limits the use of THz spectroscopy to large samples, is mitigated by employing surface plasmon waves. In one implementation, THz surface waves, excited on a broad-band planar THz bow-tie antenna, are used to enhance the interaction with a small particle placed on the antenna surface. The surface field distribution near the particle is mapped with an integrated sub-wavelength aperture THz near-field probe. We demonstrate that imaging and probing of the subwavelength size dielectric particles (TiO₂ and SrTiO₃) can be realized using the enhanced THz field between the antenna and the probe. We also discuss THz wave confinement using two sharp metallic needles. We demonstrate that in the near-field region of the needle tips, the electric field of THz pulses is concentrated to a volume smaller than (10 μm)³ without limiting the THz pulse bandwidth. Application of both methods for high spatial resolution imaging and spectroscopy will be discussed.

Achieving high spatial resolutions for imaging with terahertz (THz) waves requires near-field probes, such as a sub-wavelength aperture probe. Bethe’s theory of transmission through a sub-wavelength aperture of size a predicts that the transmitted electric field scales as Eαa³. This strong dependence limits the size of apertures that can be employed and hence the spatial resolution. This dependence however changes for the evanescent field components in very close proximity (~1μm for THz waves) to the aperture, as shown by electromagnetic simulations. To exploit this effect in a THz near-field probe, we developed a photoconductive THz near-field detector structure, which incorporates a thinned photo-conductive detector region and a distributed Bragg reflector between the detector and the aperture plane. Near-field probes are manufactured with different aperture sizes to investigate transmission of THz pulses through apertures as small as 3μm. The experimental results confirm that the transmitted field amplitude, and therefore the sensitivity, increases by about one order of magnitude for the new probes. A 3μm aperture probe with a spatial resolution of λ/100 at 1THz is demonstrated.

Photodiodes based on the GaInAs/InP material system responding in the 1.3-1.7 μm wavelength range are of interest in a wide range of applications, from optical power and channel monitors in telecommunication systems through to advanced night vision imaging using large format focal plane type detectors for defense and security applications. Here we report on our results of GaInAs PIN photo detector structures grown on 2”, 3” and 4” InP substrates by low pressure Metalorganic Chemical Vapor Deposition (MOCVD) in both standard and new larger volume format reactor configurations. High quality, lattice matched InP/GaInAs epitaxial layers were grown and we demonstrate that when moving to larger platen configurations, high degree of thickness uniformity (<3%, FTIR), lattice mismatch (<0.1%, XRD) and compositional uniformity (<2 nm, PL) can be maintained. The surface quality of epitaxial wafers will be assessed by various surface analytical techniques. We also make comparisons with the performance of 2”, 3” and 4” photodetector structures grown, this demonstrating that MOCVD production processes have been successfully scaled. We conclude by discussing the material requirements for large area infrared focal plane array photodetectors and describe how MOCVD growth technology will address industry’s requirements for increasing device sizes with improved performance.

In this paper we report on an industry first; the growth and characterization of 6” diameter indium antimonide (InSb) substrates that are suitable for use in the fabrication of MWIR focal plane infrared detectors. Results will be presented on the production of single crystal 6” InSb ingots grown by the Czochralski (Cz) technique. We will also assess the electrical quality of new 6” InSb crystals and present uniformity information on Hall mobility, resistivity and carrier level from which we will infer comparisons on the relative dark current performance of the material grown. High quality, epitaxy-ready type surfaces have been prepared and we will demonstrate how the key surface quality characteristics of roughness (< 0.5 nm rms), oxide thickness (<100 Å) and flatness (<7 μm TTV) have been maintained across production processes that scale 4” to 6” wafer formats. We conclude by presenting our road map for the development of large area InSb substrates and describe how developments in Czochralski crystal growth and surface finishing technology will support industry’s requirements to deliver higher performance, large format IR focal plane array type devices.

Photoacoustic (PA) effect is a sensitive spectroscopic technique for chemical sensing. In recent years, with the development of quantum cascade lasers (QCLs), significant progress has been achieved for PA sensing applications. Using high-power, tunable mid-IR QCLs as laser sources, PA chemical sensor systems have demonstrated parts-pertrillion- level detection sensitivity. Many of these high sensitivity measurements were demonstrated locally in PA cells. Recently, we have demonstrated standoff PA detection of isopropanol vapor for more than 41 feet distance using a quantum cascade laser and a microphone with acoustic reflectors. We also further demonstrated solid phase TNT detections at a standoff distance of 8 feet. To further calibrate the detection sensitivity, we use nerve gas simulants that were generated and calibrated by a commercial vapor generator. Standoff detection of gas samples with calibrated concentration of 2.3 ppm was achieved at a detection distance of more than 2 feet. An extended detection distance up to 14 feet was observed for a higher gas concentration of 13.9 ppm. For field operations, array of microphones and microphone-reflector pairs can be utilized to achieve noise rejection and signal enhancement. We have experimentally demonstrated that the signal and noise spectra of the 4 microphone/4 reflector system with a combined SNR of 12.48 dB. For the 16-microphone and one reflector case, an SNR of 17.82 was achieved. These successful chemical sensing demonstrations will likely create new demands for widely tunable QCLs with ultralow threshold (for local fire-alarm size detection systems) and high-power (for standoff detection systems) performances.

Our objective is to enhance quantification of stable carbon and oxygen isotope ratios to better than 1‰ relative isotope precision for sample sizes < 1 pico-mole. A newer variant Capillary Absorption Spectrometer (CAS) is described using a proprietary linear-taper hollow waveguide in conjunction with wavelength and frequency modulation techniques of tunable laser absorption spectrometry. Previous work used circular capillaries with uniform 1 mm ID to measure ¹³C/¹²C ratios with ≥ 20 pico-mole samples to ≤ 10 ppm (1‰ precision against standards) [1]. While performing fairly well, it generated residual modal noise due to multipath propagation in the hollow-waveguides (HWGs). This system has been utilized with laser ablation-catalytic combustion techniques to analyze small resolution (~ 25 μm spot diameter) laser ablation events on solids. Using smaller ID capillary waveguides could improve detection limits and spatial resolutions. Reducing an IR compatible hollow waveguide’s inner diameter (ID) to < 300 μm, reduces modal noise significantly for mid-IR operation, but feedback noise with high gain semiconductor lasers can become problematic. A proprietary linear-taper small waveguide (mean ID = 0.35 mm, L = 1 m) was tested to understand whether modal noise and optical feedback effects could be simultaneously reduced. We see better mode filtering and, significant reductions of feedback noise under favorable coupling of a multi-spatial mode QC laser to the smaller ID of the linear-tapered HWG. We demonstrate that better modal coupling operation is consistent with Liouville’s theorem, where greater suppression of feedback from spurious scatter within the HWG occurs by injecting the laser into the smaller ID port. Our progress on developing lighter weight, potentially fieldable alternatives to Isotope Ratio Mass Spectrometers (IRMS) with a small volume (≤ 0.1 cm³) CAS system will be discussed and compared to other competitive systems.

In this paper, the scheme for both reproducing vibration waveform and locating disturbed places in the OTDR based distributed optical fiber vibration sensing systems is proposed and demonstrated. Based on the sampling law, the vibration waveform is reproduced from the detecting pulses including original sensing signals by denoising selectively, adjusting bias voltage and band-pass filtering. The vibrations at the frequencies of 500Hz and 1000Hz have been experimentally located and reproduced, respectively, and the highest frequency of 1 kHz for reproducing vibration waveform is realized at the repeat frequency of 2 kHz for the laser.

We employed a broadly tunable pulsed external cavity (EC)-QC laser with a spectral tuning range from 1030 cm^-1 to 1230 cm^-1 and a tuning speed of 166 cm^-1/s for direct absorption spectroscopy of aqueous solutions. The laser offered spectral power densities of up to four orders of magnitude higher than available with a conventional FTIR spectrometer. Therefore, a portable demonstration system with a large optical path length transmission flow cell (165 μm) could be realized preventing clogging of the flow cell. In pulsed mode an EC-QC laser provides significantly higher peak power levels than in continuous-wave mode, but pulse-to-pulse intensity variations, intra-pulse mode hops and mechanical imperfections of the scanning mechanism significantly impair the quality of resulting absorbance spectra. This article reports on measures which we found appropriate to reduce the initially high noise level of EC-QC laser absorbance spectra. These measures include a spectral self-referencing algorithm that makes use of the inherent structure of the EC-QC laser's gain curve to correct laser instabilities, as well as Fourier filtering, among others. This enabled us to derive infrared spectra which were finally useful for quantitative analysis in blood plasma samples. Finally, with the appropriate measures in place and using partial least squares regression analysis it was possible to simultaneously quantify 6 blood analytes from a single physical measurement of a 200 μL blood sample. This proves the potential of EC-QC lasers for practical application in clinical point of care analysis.

In our development of a field deployable infrared isotope ratio spectrometer (IR2) for compound specific isotope analysis (CSIA), the IR2‘s accuracy and stability have reached a stage that small fractionation in reference gas pulses generated as standard are observed easily and repeatedly. Such fine fractionation is often difficult to observe in regular Isotope Ratio Mass Spectrometer (IRMS) due to instrument drift on the order of 10s of minutes. After careful design of reference pulse sequences and long period of data collection, such fractionations are also verified in a commercial continuous flow CSIA-IRMS. Implications of the fractionation and observation process are discussed.

A quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor system was developed for the sensitive detection of hydrogen peroxide (H₂O₂) using its absorption transitions in the v6 fundamental band near 7.73 μm. The recent availability of distributed-feedback quantum cascade lasers (DFB-QCLs) provides convenient access to a strong H₂O₂ absorption line located at 1295.55 cm^-1. Sensor calibration was performed by means of a water bubbler that generated titrated average vapor concentrations. A minimum detection limit of 75 parts per billion (ppb) was achieved at a pressure of 80 torr for a 1 sec data acquisition time. The long-term repeatability and stability of the sensor was investigated by measuring time-varying H₂O₂ mixtures for ~2 hrs. An Allan deviation analysis was performed to investigate the long-term performance of the QEPAS sensor system, indicating the feasibility of a minimum detection limit of 12 ppb using the optimum data averaging time of 100 sec.

We report on an innovative quartz enhanced photoacoustic (QEPAS) gas sensor operating in the THz spectral range, employing a custom quartz tuning fork (QTF) with the two prongs spaced by ~800 μm. To test our sensor we employed a quantum cascade laser light source and selected a methanol rotational absorption line falling at 131.054 cm^-1 (~3.93 THz), with line-strength S = 4.28•10^-21 cm. The sensor operated at 10 Torr pressure on the QTF first flexion resonance frequency at 4245 Hz. We achieved a QEPAS normalized noise-equivalent absorption of 2•10^-10 W·cm^-1•Hz^-1/2 comparable with the best result of mid-IR QEPAS systems.

We report on a novel intracavity quartz enhanced photoacoustic (I-QEPAS) gas sensing technique taking advantage from both the high Q-factor of standard tuning forks and the power build-up of a high-finesse optical resonator. This first prototype employs a distributed feedback quantum cascade laser operating at 4.3 μm. CO₂ has been selected as gas target. Preliminary results demonstrate an improved sensitivity, close to the cavity enhancement factor (500) times the optical coupling efficiency (about 0.5), with respect to standard QEPAS technique. The detection limit was pulled from 7 ppm (obtained with standard QEPAS) down to 32 ppb, corresponding to normalized noise-equivalent absorption in the 10^-9 W•cm^-1•Hz^-1/2 range.

Step by step, US and European legislations enforce the further reduction of atmospheric pollution caused by automotive exhaust emissions. This is pushing automotive development worldwide. Fuel efficient diesel engines with SCRtechnology can impede NO₂-emission by reduction with NH₃ down to the ppm range. To meet the very low emission limits of the Euro6 resp. US NLEV (National Low Emission Vehicle) regulations, automotive manufacturers have to optimize continuously all phases of engine operation and corresponding catalytic converters. Especially nonstationary operation holds a high potential for optimizing gasoline consumption and further reducing of pollutant emissions. Test equipment has to cope with demanding sensitivity and speed requirements. In the past Fraunhofer IPM has developed a fast emission analyzer called DEGAS (Dynamic Exhaust Gas Analyzer System), based on cryogenically cooled lead salt lasers. These systems have been used at Volkswagen AG‘s test benches for a decade. Recently, IPM has developed DEGAS-Next which is based on cw quantum cascade lasers and thermoelectrically cooled detectors. The system is capable to measure three gas components (i.e. NO, NO₂, NH₃) in two channels with a time resolution of 20 ms and 1 ppm detection limits. We shall present test data and a comparison with fast FTIR measurements.

We discuss the possibility of building a matter wave interferometer using thermal (i.e. non condensed) cold atoms trapped in the vicinity of an atom chip for quantum sensing of acceleration and gravity fields with reduced mean-field effects. To maintain a satisfactory level of coherence, a high degree of symmetry is required between the two arms of such an interferometer. We discuss this point quantitatively, and describe the experimental protocol we are developing for this purpose, based on internal state labeling and on the use of two parallel coplanar waveguides deposited on top of the atom chip to selectively address the potential of each internal state through microwave dressing. We also report our recent experimental work demonstrating the possibility of achieving a magneto-optical trap with some of the beams passing through the chip.

In this theoretical work, we report on voltage-controllable hybridization of electromagnetic modes arising from strong interaction between graphene plasmons and molecular vibrations. Compared with the strong light-matter interaction platforms based on noble metals, graphene offers much tighter plasmonic field confinement thus smaller effective mode volume and higher quality-factor due to longer carrier relaxation time in midinfrared regime, leading to Rabi splitting and hybridized polaritonic modes at 3 orders of magnitude lower molecular densities. Electrostatically tunable carrier density in graphene allows for dynamic control over the interaction strength. In addition, the flat dispersion band arising from the deep confinement of the polaritonic modes gives rise to the omni-directional excitation. Our approach is promising for practical implementations in infrared sensing and detection.

This paper reviews recent advances in graphene active plasmonics and their applications to terahertz lasers and sensors. We theoretically discovered and experimentally manifested that when the carrier population in graphene is inverted the excitation of graphene plasmons results in propagating surface plasmon polaritons with giant gain in a wide THz range. Furthermore, when graphene is patterned in a microribbon array by grating gate metallization, the structure provides super-radiant plasmonic lasing with giant gain as well as ultrahigh sensitive detection at the plasmon modes in a wide THz frequency range.

Properties of graphene can be tuned electrically and chemically, providing a promising system for application in terahertz (THz) devices. Graphene response can be enhanced even further by means of coupling electromagnetic waves into plasmon modes, frequency of which is controlled by geometrical parameters. To probe excitation of confined plasmon modes and surface wave excitation, epitaxial graphene and its structures are investigated using THz near-field microscopy. Detected near-field images suggest excitation of THz surface waves occurring at graphene edges, similar to that observed at metallic edges, and excitation of confined plasmon modes. We will also discuss the impact of graphene inhomogeneity on local THz transmission properties on the sub-wavelength scale.

We experimentally demonstrated graphene plasmon resonant absorption in mid-IR by utilizing an array of graphene nanoribbon resonators on SiO2 substrate. By tuning resonator width we probed the graphene plasmons with λ_p ≤ λ0/100 and plasmon resonances as high as 0.240 eV (2100 cm^-1) for 40 nm wide nanoresonators. Resonant absorption spectra revealed plasmon dispersion as well as plasmon damping due to the interaction of graphene plasmons with the surface polar phonons in SiO₂ substrate and intrinsic graphene optical phonons. Graphene nanoribbons with varying widths enabled us to identify the damping mechanisms of graphene plasmons and much reduced damping was observed when the plasmon resonance frequencies were close to the substrate polar phonon frequencies. Then, by direct ebeam exposure of graphene nanoresonators, we effectively changed the carrier density and caused red-shift of the plasmon spectra. This work will provide insight into light-sensitive, frequency-tunable photodetectors based on graphene’s plasmonic excitations.

Recently there has been considerable effort to develop photon-counting detectors for the near-infrared wavelength range (up to 1700 nm). However, a practical detector, which can be employed in many real applications and has both high count rates and low noise, is still not available. Here we show a novel technique to operate InGaAs/InP single-photon avalanche diodes (SPADs) in a free-running equivalent mode at high count rate. The photodetector is enabled with a 915 MHz sinusoidal gate signal: by keeping the SPAD gate signal unlocked from the synchronization reference of the optical waveform to be reconstructed, a free-running equivalent mode is obtained, that we called gate-free. An extensive experimental characterization has shown how the SPAD performance improves compared with a classical square-wave gating scheme, especially for non-periodic high-throughput applications. The resulting single-photon detector achieves a maximum count rate of 100 Mcount/s, an afterpulsing probability below 0.3 %, a photon detection efficiency of 3 % at 1550 nm, a temporal resolution of 150 ps (Full-Width Half Maximum) and a dark count rate below 2000 count/s (the SPAD is cooled at 220 K).

The Time Correlated Single Photon Counting (TCSPC) technique has reached a prominent position among analytical methods employed in a great variety of fields, from medicine and biology (fluorescence spectroscopy) to telemetry (laser ranging) and communication (quantum cryptography). Nevertheless the development of TCSPC acquisition systems featuring both a high number of parallel channels and very high performance is still an open challenge: to satisfy the tight requirements set by the applications, a fully parallel acquisition system requires not only high efficiency single photon detectors but also a read-out electronics specifically designed to obtain the highest performance in conjunction with these sensors. To this aim three main blocks have been designed: a gigahertz bandwidth front-end stage to directly read the custom technology SPAD array avalanche current, a reconfigurable logic to route the detectors output signals to the acquisition chain and an array of time measurement circuits capable of recording the photon arrival times with picoseconds time resolution and a very high linearity. An innovative architecture based on these three circuits will feature a very high number of detectors to perform a truly parallel spatial or spectral analysis and a smaller number of high performance time-to-amplitude converter offering very high performance and a very high conversion frequency while limiting the area occupation and power dissipation. The routing logic will make the dynamic connection between the two arrays possible in order to guarantee that no information gets lost.

We present a compact time-resolved spectrometer suitable for optical spectroscopy from 400 nm to 1 μm wavelengths. The detector consists of a monolithic array of 16 high-precision Time-to-Digital Converters (TDC) and Single-Photon Avalanche Diodes (SPAD). The instrument has 10 ps resolution and reaches 70 ps (FWHM) timing precision over a 160 ns full-scale range with a Differential Non-Linearity (DNL) better than 1.5 % LSB. The core of the spectrometer is the application-specific integrated chip composed of 16 pixels with 250 μm pitch, containing a 20 μm diameter SPAD and an independent TDC each, fabricated in a 0.35 μm CMOS technology. In front of this array a monochromator is used to focus different wavelengths into different pixels. The spectrometer has been used for fluorescence lifetime spectroscopy: 5 nm spectral resolution over an 80 nm bandwidth is achieved. Lifetime spectroscopy of Nile blue is demonstrated.