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SPIE Defense + Commercial Sensing, 2021, Online Only, The performance of optical and electronic detectors and sensors are affected by surface and bulk impurities. In some cases, nanoscale thin films are used as detectors and their life cycle is significantly decreased. In the case of conformal shapes, surfaces with different polishing, decoration and geometries exhibit unusual wetting and nucleation characteristics for impurities and this requires continuous attention for cleaning. The situation for space borne components and vehicles surfaces exposed to wetting liquids requires remote cleaning. In the present paper, we report the effect of surface topographies of substrates with nanoengineered titanium oxide and copper oxide nanoparticles embodied in polystyrene and study the effect of the composites to create different hydrophobic characteristics with great potential for detectors and sensors operating in ultra-violet and infrared regions.

The understanding of the surface behavior, interaction, wettability, and topographies of surfaces with fluids is very important to remove impurities from the devices and components and to develop washing fluids to clean large area surfaces. We synthesized nano particle filled composites by wet and semi-wet techniques to achieve hydrophobicity and hence the lotus effect. Nanocomposites with different composition of polymers doped with titania nanoparticles were studied to evaluate effects on wettability. Light scattering methods were used to study the absorptions and particle size. The contact angle and hydrophobic characteristics were very composition dependent in thin film composites. At certain compositions, we observed that material showed very high anisotropy in droplet shapes which diminished with loadings of nanoparticles. These composites did not show any change in hydrophobic characteristics when exposed with ultraviolet radiation.

In this paper, the development of a three-beam aerosol backscatter correlation (ABC) lidar to measure wind characteristics for wake vortex and plume tracking applications is discussed. This is a direct detection elastic lidar that uses three laser transceivers, operating at 1030 nm wavelength with ~10 kHz pulse repetition frequency and nanosec class pulse widths, to directly obtain three components of wind velocities. By tracking the motion of aerosol structures along and between three near-parallel laser beams, three-component wind speed profiles along the field-of-view of laser beams are obtained. With three 8-inch transceiver modules, placed in a near-parallel configuration on a two-axis pan-tilt scanner, the lidar measures wind speeds up to 2 km away. Optical flow algorithms have been adapted to obtain the movement of aerosol structures between the beams. Aerosol density fluctuations are cross-correlated between successive scans to obtain the displacements of the aerosol features along the three axes. Using the range resolved elastic backscatter data from each laser beam, which is scanned over the volume of interest, a 3D map of aerosol density in a short time span is generated. The performance of the ABC wind lidar prototype, validated using sonic anemometer measurements, is discussed.

Heavy metal selenides have shown very good properties including wavelength conversion in MWIR and LWIR regions, acousto-optic and great potential for radiation detection. We have extensively studied thallium-based compounds for variety of applications. Studies were performed for crystal growth, fabricability and radiation detection characteristics of ternary congruent compounds of thallium mercury iodide system from the melt by Bridgman method. The congruency and phase transition was studied by DTA. Material melts congruently between 300-400 0C and do not show any other phases between room temperature and melting point. Crystal slabs were fabricated as bulk detector to demonstrate good characteristics for detectivity of X-ray and gamma-rays. Effect of impurities on performance were evaluated by using source materials of different purity for synthesis. Crystals with high purity source materials and mixed by vibrating method were determined for resistivity in range of 1012ohm-cm.

In this paper, the development of a novel picosecond pulsewidth direct detection lidar for velocimetry and hard target imaging applications is discussed. The lidar system comprises of a high-speed fiber coupled laser, novel interleaved three-dimensional (3D) scanner, fiber coupled receiver with optical pre-amp module and a high-speed digitizer. The laser is a pulsed Erbium-doped fiber laser that operates at 1.55 microns wavelength, 10 MHz PRF, 60 picosecond pulse width and 8 W of output average power. The scanner is a multi-faceted polygon type that operates at scan speeds of 10000 lines per second. The system utilizes a state-of-the art 40 GS/s digitizer. The picosecond lidar allows high resolution volumetric measurement of temporally and spatially resolved 3D airspeeds in wind tunnels for capturing a 3D time-accurate map of aerosols or other seeding particles in the airflow using elastic backscatter from a rapidly scanned lidar beam with a narrow field-of-view. Preliminary testing inside wind tunnel has generated promising results for aerodynamic applications including visualizing flow characteristics around test targets. The lidar provided dynamic measurements of complex flow, including the downstream evolution of a wing tip vortex. A 3D image processing algorithm was used to correlate the motion of aerosol features between successive frames and to extract 3D airflow profiles. In this paper, details of lidar instrumentation configuration is discussed followed by results of high-speed 3D hard target imaging of various test targets.

Uncooled focal plane arrays (FPA) with reduced size, weight, and power consumption (SWaP) features and coupled with enhanced characteristics have the potential to significantly benefit a wide range of imaging applications including space surveillance from terrestrial and space-based platforms and planetary composition mapping for space exploration missions. Recently, an innovative, uncooled Photon-Sensing Integrated Circuit (PSIC) hetero-junction phototransistor (HPT) device has been developed. This InGaAs based PSIC HPT device is a room temperature detector and imager that is of 320 x 256 pixel format with 30 micron pixels, and operates in the short-wave infrared (SWIR) spectral region of 0.9 to 1.7 microns. It is a continuously operating (i.e., zero recovery time), zero-excess-noise and linear-mode (i.e., capable of representing photon numbers) photon-sensing detector and imager. Enabled by its hetero-junction phototransistor (HPT) amplification instead of the conventional avalanche multiplication mechanism, this InGaAs HPT simultaneously exhibits signal amplification gain of >1000, namely, >20 x higher gain, and

We are developing a semi-classical model to explain the physical processes behind the origin of the statistical variations in the photoelectron current pulses that we register for different kinds of light. They are: super-Poissonian thermal light, Poissonian laser light and sub-Poissonian nonlinearly generated light. Einstein’s photoelectron equation is an energy balancing equation. It does not incorporate the E-vector stimulation process before the quantum mechanically bound electrons can be released, which constitutes a key objective of physics. To introduce physics, we postulate that the photons are hybrid entities. They are discrete packets of energy hνmn at the moment of emission. Then they immediately evolve into spatially spreading diffractive wave packets to accommodate Huygens-Fresnel principle. HF principle has been behind the sustained progress in classical optics and photonics engineering. Thus a spatially spread out single wave-packet cannot any more deliver the necessary quantum cupful of energy hνmn to Angstrom-size detecting atoms. We need simultaneous stimulation of the same quantum entity by multiple wave packets. This model of physical interaction process naturally brings into play the significance of the degree of mutual coherence between different photon wave packets, along with their time varying amplitudes that are simultaneously stimulating the detecting quantum entities during any time-interval selected for the detection system. The superposition effects on the detector due to these phase and amplitude fluctuations are the physics-reasons behind the generation of different statistical variations in the photoelectron counts due to different kinds of sources even though the original photons are released randomly by all quantum sources.

In this paper, we describe a novel interleaved scanner for an eye-safe 3D scanning lidar system to measure aerodynamic phenomena in a wind tunnel using elastic backscatter from seeding particles. The scanner assembly consists of a rotating polygon scanner for line scanning along the fast axis, a galvanometer (galvo) scanner for scanning along the slow axis, angular position sensors, and motor controllers. The polygon scanner sweeps the lidar beam at up to 10,000 lines/s across a 27 deg angular field of regard in the fast axis, while the galvo scanner covers an angular range of 20 deg in the slow axis. Using this scanner, the lidar can perform nonintrusive flow visualization, velocimetry, and hard target mapping at millimeter-scale spatial resolution to a standoff range of 5 m at an update rate of 50 Hz for the full field of regard. An interleaved scanning methodology for the acquisition of two snapshots of 3D lidar intensity data with a 100 µs time offset is discussed. The design of the control and data acquisition electronics is described. The effects of rapid scanning on the response of a narrow field-of-view lidar are addressed. The design of the scanner is scalable and can be tailored to meet the requirements of other applications by increasing or decreasing the standoff range, angular field of regard, and scan rate.

In order to realize high-throughput roll-to-roll manufacturing of flexible perovskite solar cells, low-temperature processing of all device components must be realized. However, the most commonly used electron transporting layer in high-performance perovskite solar cells is based on TiO2 thin films processed at high temperature (>450 °C). Here, we demonstrate room temperature solution processing of the TiOx layer that performs as well as the high temperature TiO2 layer in perovskite solar cells, as evidenced by a champion solar cell efficiency of 16.3%. Using optical spectroscopy, electrical measurements, and X-ray diffraction, we show that the room-temperature processed TiOx is amorphous with organic residues, and yet its optical and electrical properties are on par with the high-temperature TiO2. Flexible perovskite solar cells that employ a room-temperature TiOx layer with a power conversion efficiency of 14.3% are demonstrated.

Superhydrophobic polymer films are a material of interest for aircraft deicing fluids to achieve the selfcleaning lotus effect. Hydrophobic polymer films were obtained by a solvent selective method composed of hydrophilic polymethylmethacrylate (PMMA) and hydrophobic polystyrene (PS) and hydrophilic titania nanoparticles. The addition of titania nanoparticles changed the surface of the thin films from an anisotropic morphology to a spherical isotropic surface due to hydrophobic and hydrophilic repulsion. Irradiation of UV responsive titania nanoparticles retained the same surface morphology. Water contact angle measurements will be completed to determine the hydrophobic nature of the polymer films.

Sensors are measuring tools. In any measurement, we have at least two different kinds of interactants. We never know all there are to know about any one of these interactants and the interaction processes that are mostly invisible. Yet, our engineering innovation driven evolution is persisting for over five million years. It is then important to articulate explicitly our Interaction Process Mapping Thinking, or IPMT, which we keep applying in the real world without formally recognizing it. We present how the systematic application of IPMT removes century old wave-particle duality by introducing a model of hybrid photon. It seamlessly bridges the quantum and the classical worlds. Photons are discrete energy packets only at the moment of emission; then they evolve diffractively and propagate as classical waves. We apply IPMT to improve the photoelectric equation & we obtain Non-Interaction of Wave, or NIW. NIW was recognized by Huygens when postulating his secondary spherical wavelets, which is now integrated into Huygens-Fresnel diffraction integral, a staple for modern optical science and engineering. Maxwell wave equation accepts HF integral as its solution. Systematic application of IPMT to our causal and working mathematical equations, along with NIW in interferometric experiments, reveal that Superposition Effects can emerge only when the interacting material dipoles respond, whether classically or quantum mechanically, to the joint stimulations due to all the simultaneously superposed waves. This indicates the non-causality of our belief that a single indivisible photon can interfere by itself. We would not have a causally evolving universe had any stable elementary particle were to change itself through self-interference. Further, our working superposition equations always contain two or more terms representing two or more independently evolving entities., 13 pages. Six figures. To be presented at the 2019 SPIE Photonics West Conference

Tellurium dioxide is the most widely used uniaxial crystal for acousto-optic devices. Acousto-optic tunable filters based on this material can cover spectral range from UV to MWIR in a non-collinear configuration. The diffracted narrow band output beams have orthogonal linear polarizations, propagating in different directions, allowing the filter to act as polarizing beam splitter/analyzer as well. To achieve full electronic tuning, two liquid crystal variable retarders are used to measure all six polarization states used in the calculation of Stokes vector. We will present the design of the instrument, test results, and performance considerations.

We report on the development of an acousto-optic tunable filter (AOTF) based novel, high speed spectropolarimeter system operating over the visible and near-IR spectral bands to extract Stokes and Mueller matrices. Developed primarily for planetary composition and analysis applications, the wavelength tunable polarimetric system is configured with tellurium dioxide based AOTF and liquid crystal based variable retarders (LCVR) with no movable mechanical parts. Fitted with a standard silicon camera for operation up to 900 nm and a Mercury Cadmium Telluride (MCT) camera for operation up to 2500 nm, the spectropolarimetric system is currently configured for passive operation. The operation of this spectropolarimetric system is fully automated with an interactive and user friendly graphical user interface, and accordingly provides a snapshot polarimetric measurement capability in minutes.

The transition metal oxide embodied organic composites have great promise for high energy radiation detection. The interaction of high energy radiation such as γ-rays with the organic composite can generate photoelectric responses, Compton scattering and electron hole pairs, which can provide favorable properties to enhance the radiation detectivity of the composite. These effects along with changes of oxidation state of metal oxides, provide significant change in the electrical characteristics of composites due to radiation exposure. We have developed nickel oxide (NiO2) nanoparticles embodied urea composite (urea-NiO2), and determined effect of γ-radiation on the current – voltage characteristics in the frequency range of 100 Hz to 100,000Hz. In this paper, we describe the results of effect of additional oxidizing agent MnO2 (urea-NiO2-MnO2) on the morphology, processing and current voltage characteristics due to exposure of Cs-137 γ-radiation. It was observed that addition of MnO2 in urea-NiO2 composite decreases the sensitivity of detection. However, urea-NiO2-MnO2 composite recovers to original properties after irradiation much faster than urea-NiO2 composite.

We have developed ultra-low noise quadrant InGaAs photoreceivers for multiple applications ranging from Laser Interferometric Gravitional Wave Detection, to 3D Wind Profiling. Devices with diameters of 0.5 mm, 1mm, and 2 mm were processed, with the nominal capacitance of a single quadrant of a 1 mm quad photodiode being 2.5 pF. The 1 mm diameter InGaAs quad photoreceivers, using a low-noise, bipolar-input OpAmp circuitry exhibit an equivalent input noise per quadrant of

The hexagonal apatite single crystals have been investigated for their applications as laser host materials. Czochralksi and flux growth methods have been utilized to obtain single crystals. For low temperature processing (

We present a mathematical approach to appreciate that short pulse characterization requires recognizing inseparability of the measurements of the amplitude envelope-correlation and spectral measurements and then use a suitable iterative approach to derive the real characteristics. We will use a standard Michelson interferometer, as usual, to introduce the autocorrelation function of a pulse containing single and multiple frequencies. In the process, we also underscore that detectors play the key role in generating measurable Superposition Effects (SE), recognized as fringes after the detectors carry out the square modulus operation. Simple mathematical summation of amplitude factors, the Superposition Principle (SP), is not directly observable. We underscore this by mentioning that we present EM waves as classical and detectors as quantum mechanical. This semi-classical approach has been established by Lamb and Jaynes, which is indirectly supported by Glauber’s comment, “A photon is what a detector detects”. The semi-classical approach helps us separate the phenomenological difference between the absorbed detected energy by a detector (SE) from the energy supplied by the simultaneously present multiple wave amplitudes (SP). As in atomic and molecular physics, we use the detector’s dipolar stimulation as the product of its linear dipolar polarizability multiplied by all the EM fields stimulating it simultaneously. The analysis also demonstrates that for a pulse containing multiple frequencies, the two-beam autocorrelation function becomes a product of the traditional amplitude correlation factor and a frequency-comb correlation factor. Hence, the spectral interpretation of a short pulse and two-beam autocorrelation are inseparable. Therefore, the detailed characterization would require iterative computational approach by guessing the most plausible functional forms. This deeper understanding can be applied to rapid re-calibration of pulsed lasers that need to be maintained at single mode but has the tendency to move to multimode behavior. If the newly measured autocorrelation function differs from the original amplitude correlation factor, then one should check for the spectral characteristics first, before assuming that only the pulse shape has changed.

In order to realize high-throughput roll-to-roll manufacturing of flexible perovskite solar cells, low-temperature processing of all device components must be realized. However, the most commonly used electron transporting layer in high-performance perovskite solar cells is based on TiO

We demonstrate experimentally the detection of detailed human cardiac mechanical activity in a remote, non-contacting, and non-ionizing manner using a pulsed laser vibrometer. The highly sensitive pulsed laser vibrometer allows the detection of the temporally-phased mechanical events occurring in individual cardiac cycles even from the surface of clothing-covered extremities of the subjects. Fine structures of the detected cardiac traces are identified with their meanings assigned and corroborated using accelerometer and electrocardiogram measurements obtained concurrently with the pulsed laser vibrometer studies.

Deep space radiations pose a major threat to the astronauts and their spacecraft during long duration space exploration missions. The two sources of radiation that are of concern are the galactic cosmic radiation (GCR) and the short lived secondary neutron radiations that are generated as a result of fragmentation that occurs when GCR strikes target nuclei in a spacecraft. Energy loss, during the interaction of GCR and the shielding material, increases with the charge to mass ratio of the shielding material. Hydrogen with no neutron in its nucleus has the highest charge to mass ratio and is the element which is the most effective shield against GCR. Some of the polymers because of their higher hydrogen content also serve as radiation shield materials. Ultra High Molecular Weight Polyethylene (UHMWPE) fibers, apart from possessing radiation shielding properties by the virtue of the high hydrogen content, are known for extraordinary properties. An effective radiation shielding material is the one that will offer protection from GCR and impede the secondary neutron radiations resulting from the fragmentation process. Neutrons, which result from fragmentation, do not respond to the Coulombic interaction that shield against GCR. To prevent the deleterious effects of secondary neutrons, targets such as Gadolinium are required. In this paper, the radiation shielding studies that were carried out on the fabricated sandwich panels by vacuum-assisted resin transfer molding (VARTM) process are presented. VARTM is a manufacturing process used for making large composite structures by infusing resin into base materials formed with woven fabric or fiber using vacuum pressure. Using the VARTM process, the hybridization of Epoxy/UHMWPE composites with Gadolinium nanoparticles, Boron, and Boron carbide nanoparticles in the form of sandwich panels were successfully carried out. The preliminary results from neutron radiation tests show that greater than 99% shielding performance was achieved with these sandwich panels. Moreover, the mechanical testing and thermo-physical analysis performed show that core materials can preserve their thermo-physical and mechanical integrity after radiation.

Recently, a mercury-cadmium-telluride (MCT) linear array detection system that is capable of rapidly capturing (~1-5 second) a broad spectrum of atomic and molecular laser-induced breakdown spectroscopy (LIBS) emissions in the longwave infrarμed region (LWIR, ~5.6 to 10 μm) has been developed. Similar to the conventional Ultraviolet (UV)-Visible (Vis) LIBS, a broad band emission spectrum of condensed phase samples covering the entire 5.6 to 10 μm region can be acquired from just a single laser-induced micro-plasma or averaging a few single laser-induced micro-plasmas. This setup has enabled probing samples “as is” without the need for extensive sample preparation and also offers the possibility of a simultaneous UV-Vis and LWIR LIBS measurement. A Martian regolith simulant (JSC Mars-1A) was studied with this novel Vis + LWIR LIBS array system. A broad SiO2 vibrational emission feature around 9.5 μm and multiple strong emission features between 6.5 to 8 μm can be clearly identified. The 6.5 to 8 μm features are possibly from biological impurities of the simulant. JSC Mars-1A samples with organic methyl salicylate (MeS, wintergreen oil) and Dimethyl methyl-phosphonate (DMMP) residues were also probed using the LWIR LIBS array system. Both molecular spectral signature around 6.5 μm and 9.5 μm of Martian regolith simulant and MeS and DMMP molecular signature emissions, such as Aromatic CC stretching band at 7.5 μm, C-CH3O asymmetric deformation at 7.6 μm, and P=O stretching band at 7.9 μm, are clearly observed from the LIBS emission spectra in the LWIR region.

This paper describes an innovative, compact and eyesafe coherent lidar system developed for use in wind and wake vortex sensing applications. This advanced lidar system is field ruggedized with reduced size, weight, and power consumption (SWaP) configured based on an all-fiber and modular architecture. The all-fiber architecture is developed using a fiber seed laser that is coupled to uniquely configured fiber amplifier modules and associated photonic elements including an integrated 3D scanner. The scanner provides user programmable continuous 360 degree azimuth and 180 degree elevation scan angles. The system architecture eliminates free-space beam alignment issues and allows plug and play operation using graphical user interface software modules. Besides its all fiber architecture, the lidar system also provides pulsewidth agility to aid in improving range resolution. Operating at 1.54 microns and with a PRF of up to 20 KHz, the wind lidar is air cooled with overall dimensions of 30” x 46” x 60” and is designed as a Class 1 system. This lidar is capable of measuring wind velocities greater than 120 +/- 0.2 m/s over ranges greater than 10 km and with a range resolution of less than 15 m. This compact and modular system is anticipated to provide mobility, reliability, and ease of field deployment for wind and wake vortex measurements. The current lidar architecture is amenable for trace gas sensing and as such it is being evolved for airborne and space based platforms. In this paper, the key features of wind lidar instrumentation and its functionality are discussed followed by results of recent wind forecast measurements on a wind farm.

Nanostructured thermoelectric powders can be produced using a variety of techniques. However, it is very challenging to build a bulk material from these nanopowders without losing the nanostructure. In the present work, nanostructured powders of the bismuth telluride alloy system are obtained in kilogram quantities via a gas atomization process. These powders are characterized using a variety of methods including scanning electron microscopy, transition electron microscopy, and x-ray diffraction analysis. Then the powders are consolidated into a dense bulk material using a shock-wave consolidation technique whereby a nanopowder-containing tube is surrounded by explosives and then detonated. The resulting shock wave causes rapid fusing of the powders without the melt and subsequent grain growth of other techniques. We describe the test setup and consolidation results.

Recently, Non- Interaction of Waves or the NIW property has been proposed as a generic property of all propagating electromagnetic waves by one of the authors (CR). In other words, optical beams do not interact with each other to modify or re-distribute their field energy distribution in the absence of interacting materials. In this paper, path taken to re-create CR's original demonstration of the NIW-property as an on-site tabletop experiment is discussed. Since 1975, when the NIW demonstration was first reported, several advances in lasers and optical component design architecture have occurred. With the goal of using low cost components and having agility in setting up on non-conformable platforms for general viewing, a compact arrangement for demonstrating the NIW property was envisioned. In our experimental arrangement, a beam multiplier element was utilized to generate a set of spatially separate parallel beams out of an incident laser beam. The emerging parallel beams from the beam multiplier element were then focused on a one-sided ground glass, the flat side being towards the beam multiplier. This flat side reflects off all the incident focused beams as fanning out independent laser beams, remaining unperturbed even though they are reflecting out of a common superposed spot. It is clear that there is neither "interference between different photons", nor "a photon interferes with itself", even within a region of superposed beams. In contrast, the ground glass surface (same silica molecules but granular or lumpy) was anticipated to generate a set of crisp spatial fringes on its surface as in the original experiment. The fringes are due to granulated individual silica lumps responding simultaneously to the local resultant E-vectors due to all the superposed beams and are scattering energy proportional to the square modulus of the sum of all the simultaneous dipolar amplitude stimulations. The dark fringe locations imply zero resultant amplitude stimulation and hence no scattering. Due to multi-longitudinal mode nature of laser module, the fringes appeared washed out at the backside of the ground glass plate. Experimental refinements followed by our views on whether the fundamental physics behind the generation of superposition fringes by photo detectors different from those due to a ground glass are briefly discussed.

This paper discusses an innovative, compact and eyesafe coherent lidar system developed for wind and wake vortex sensing applications. With an innovative all-fiber and modular transceiver architecture, the wind lidar system has reduced size, weight and power requirements, and provides enhanced performance along with operational elegance. This all-fiber architecture is developed around fiber seed laser coupled to uniquely configured fiber amplifier modules. The innovative features of this lidar system, besides its all fiber architecture, include pulsewidth agility and user programmable 3D hemispherical scanner unit. Operating at a wavelength of 1.5457 microns and with a PRF of up to 20 KHz, the lidar transmitter system is designed as a Class 1 system with dimensions of 30"(W) x 46"(L) x 60"(H). With an operational range exceeding 10 km, the wind lidar is configured to measure wind velocities of greater than 120 m/s with an accuracy of +/- 0.2 m/s and allow range resolution of less than 15 m. The dynamical configuration capability of transmitted pulsewidths from 50 ns to 400 ns allows high resolution wake vortex measurements. The scanner uses innovative liquid metal slip ring and is built using 3D printer technology with light weight nylon. As such, it provides continuous 360 degree azimuth and 180 degree elevation scan angles with an incremental motion of 0.001 degree. The lidar system is air cooled and requires 110 V for its operation. This compact and modular lidar system is anticipated to provide mobility, reliability, and ease of field deployment for wind and wake vortex measurements. Currently, this wind lidar is undergoing validation tests under various atmospheric conditions. Preliminary results of these field measurements of wind characteristics that were recently carried out in Colorado are discussed.

The search for improved thermoelectric materials is driven in part by the desire to convert otherwise wasted low-temperature heat into useful electricity. In this work, we demonstrate a new path towards materials having higher overall zT, and consequently improved capacity to obtain more electrical power from a given content of heat. We produced alloys of (Bi,Sb) 2 Te 3 using a special gas atomization process that is capable of producing source powder material having nanometer-scale grain size. When impulse-compacted by shockwave consolidation, the obtained dense solid will retain its nanostructure because insufficient time and temperature are available for the kinetics of any appreciable grain growth to proceed. However, if there is initial non-uniformity in the properties of the source powder, or if there is stress non-symmetries during shockwave consolidation, then the obtained consolidated material may have locally inhomogeneous properties distributed throughout the material. Thermoelectric property measurements from selected regions within the consolidated sample indicate a wide distribution of properties. For example, the thermal conductivity at room temperature ranged from as low as 1.30 Watts/m-K in one region to higher than 3.00 Watts/m-K in a neighboring region. The electrical resistivity showed similar variation from as low as 0.5 m : -cm to as high as 1.5 m : -cm. Individually, those regions exhibited thermoelectric material figure- of-merit, zT values ranging between 0.3 and 0.4. However, when combined into a dense nanocomposite, the overall ensemble zT approaches 0.7 which is nearly a factor of 2 higher.

A great deal of research has been performed on developing room temperature mid wave infrared (MWIR) and long wave infrared (LWIR) detectors to replace very costly mercury cadmium telluride based detectors. Among the more studied materials for high operating temperature detectors, PbSe and PbSe-type heavy metal selenides have been grown in the bulk, thin film and nano crystal morphologies. To better understand the effects of the substrate on the properties of these thin films, we have deposited lead selenide by physical vapor transport (PVT) method on highresistivity Si substrates and studied the characteristics of the film. Growth on silicon and glass substrates showed different morphologies compared to pure lead selenide material. It was seen that materials grown on a glass substrate possessed different morphology after annealing. FTIR was used to calculate bandgap information comparison with undoped PbSe. We will describe the details of the growth method, effect of substrate on nucleation and morphology of the pure and lead selenide material and band gap comparisons between substrates.

The mid-wave IR (MWIR) spectral band extending from 3 to 5 microns is considered to be a low loss atmospheric window. The MWIR wavelengths are eye safe and are attractive for several free-space applications including remote sensing of chemical and biological species, hard target imaging, range finding, target illumination, and free-space communications. Due to the nature of light-matter interaction characteristics, MWIR wavelength based systems can provide unique advantages over other spectral bands for these applications. The MWIR wavelengths are found to effectively penetrate natural and anthropogenic obscurants. Consequently, MWIR systems offer increased range performance at reduced power levels. Free-space, line-of-sight optical communication links for terrestrial as well as space based platforms using MWIR wavelengths can be designed to operate under low visibility conditions. Combined with high-bandwidth, eye-safe, covert and jam proof features, a MWIR wavelength based optical communication link could play a vital role in hostile environments. A free-space optical communication link basically consists of a transmitter, a receiver and a scheme for directing the beam towards a target. Coherent radiation in the MWIR spectral band can be generated using various types of lasers and nonlinear optical devices. Traditional modulation techniques are applicable to these optical sources. Novel detector and other subcomponent technologies with enhanced characteristics for a MWIR based system are advancing. Depending on the transmitter beam characteristics, atmospheric conditions may adversely influence the beam propagation and thereby increasing the bit error rate. For satisfactory transmission over a given range, the influence of atmosphere on beam propagation has to be analyzed. In this chapter, salient features of atmospheric modeling required for wavelength selection and performance prediction is presented. Potential optical sources and detectors for building a practical MWIR communication link are surveyed. As an illustration, the design configuration and experimental results of a recently demonstrated free-space, obscurant penetrating optical data communication link suitable for battlefield applications is discussed. In this case, the MWIR wavelength was derived using an all solid-state, compact, optical parametric oscillator device. With this device, weapon codes pertaining to small and large weapon platforms were transmitted over a range of 5 km. Furthermore, image transmission through light fog, accomplished using this hardware, is also presented. Advances in source and detector technologies are contributing to the development of cost effective systems compatible with various platforms requirements. In coming years, MWIR wavelengths are anticipated to play a vital role in various human endeavors.

Lead selenide (PbSe) has been studied as a promising material for room temperature midwave infrared detection. We have investigated pure PbSe, as well as tin (Tn) and cadmium (Cd)-doped PbSe, nanocrystalline materials produced using physical vapor transport methods on glass and high-resistivity silicon substrates. The morphologies were investigated by scanning electron microscopy and energy-dispersive x-ray analysis. Pure PbSe layers consisted of nanocrystals that change into cubes and cuboids upon annealing. Cuboids generally grew in [100] orientation and ultimately developed in nanorods. Growth on silicon and glass substrates showed different morphologies of pure PbSe material. Parabolic and elongated morphologies resulted in nanowires on the top of thin layers of PbSe nanofilm, which acted as the substrate. Under low gradient annealing conditions (

Nanotechnology based thermoelectric materials are considered attractive for developing highly efficient thermoelectric devices. Nano-structured thermoelectric materials are predicted to offer higher ZT over bulk materials by reducing thermal conductivity and increasing electrical conductivity. Consolidation of nano-structured powders into dense materials without losing nanostructure is essential towards practical device development. Using the gas atomization process, amorphous nano-structured powders were produced. Shockwave consolidation is accomplished by surrounding the nanopowder-containing tube with explosives and then detonating. The resulting shock wave causes rapid fusing of the powders without the melt and subsequent grain growth. We have been successful in generating consolidated nano-structured bismuth telluride alloy powders by using the shockwave technique. Using these consolidated materials, several types of thermoelectric power generating devices have been developed. Shockwave consolidation is anticipated to generate large quantities of nanostructred materials expeditiously and cost effectively. In this paper, the technique of shockwave consolidation will be presented followed by Seebeck Coefficient and thermal conductivity measurements of consolidated materials. Preliminary results indicate a substantial increase in electrical conductivity due to shockwave consolidation technique.

The objective of the Materials International Space Station Experiment (MISSE) is to study the performance of novel materials when subjected to the synergistic effects of the harsh space environment for several months. MISSE missions provide an opportunity for developing space qualifiable materials. Several laser and lidar components were sent by NASA Langley Research Center (LaRC) as a part of the MISSE 7 mission. The MISSE 7 module was transported to the international space station (ISS) via STS 129 mission that was launched on Nov 16, 2009. Later, the MISSE 7 module was brought back to the earth via the STS 134 that landed on June 1, 2011. The MISSE 7 module that was subjected to exposure in a space environment for more than one and a half years included fiber laser, solid-state laser gain materials, detectors, and semiconductor laser diode. Performance testing of these components is now progressing. In this paper, the results of performance testing of a laser diode module sent by NASA Langley Research Center on MISSE 7 mission will be discussed. This paper will present the comparison of pre-flight and post-flight performance of two different COTS acousto-optic modulator (AOM) devices. Post-flight measurements indicate that these two devices did not undergo any significant performance degradation.

In this paper, we describe the development of a three-beam elastic lidar that utilizes aerosol backscatter correlation to measure three-component wind profiles for detecting and tracking aircraft wake vortices; turbulence intensity and wind shear profiles. High-resolution time-resolved wind information can currently be obtained with ultrasonic or hot-wire anemometers suitable for local point measurements, or with Doppler wind lidars that only measure line-of-sight wind speeds and have to be scanned over large measurement cone angles for obtaining three-component winds. By tracking the motion of aerosol structures along and between three near-parallel laser beams, our lidar obtains three-component wind speed profiles along the field of view (FOV) of the lidar beams. Our prototype lidar wind profiler (LWP) has three 8-inch transceiver modules placed in a near-parallel configuration on a two-axis pan-tilt scanner to measure winds up to 2km away. Passively q-switched near-infrared (1030nm) Yb:YAG lasers generate 12 - 18ns wide pulses at high repetition rate (about 10KHz) that are expanded and attenuated to eye-safe levels. Sensitive low noise detection is achieved even in daytime using a narrow FOV receiver, together with narrowband interference filters and single photoncounting Geiger-mode Si detectors. A multi-channel scaler retrieves the lidar return with 7.8ns bins (∼1.2m spatial resolution) and stores accumulated counts once every 50ms (20 profiles/sec). We adapted optical flow algorithms to obtain the movement of aerosol structures between the beams. The performance of our prototype LWP was validated using sonic anemometer measurements.

In-band core-pumped Ho3+-doped ZBLAN fiber lasers at the 1.2 μm region were investigated with different gain fiber lengths. A 2.4 W 1190 nm all-fiber laser with a slope efficiency of 42% was achieved by using a 10 cm long gain fiber pumped at a maximum available 1150 nm pump power of 5.9 W. A 1178 nm all-fiber laser was demonstrated with an output power of 350 mW and a slope efficiency of 6.5%. High Ho3+ doping in ZBLAN is shown to be effective in producing single-frequency fiber lasers and short-length fiber amplifiers immune from stimulated Brillouin scattering.

The vertical profile of atmospheric temperature is a principal state variable to study atmospheric stability. A lidar system, constructed using a 355 nm Nd:YAG laser transmitter, measures the temperature profile using the rotational Raman technique. In comparison with traditional Raman lidar, the major innovations are the use of a low peak power and high repetition rate laser to achieve eye-safe operation in a compact reliable instrument and the use of an angle tuning filter to select operating wavelengths. We demonstrate the capability of both nighttime and daytime measurements as a step toward a future stand-alone capability for routine measurements of important meteorological properties in the lower atmosphere.

Holmium-doped ZBLAN fiber has proven to be an efficient high gain material in the 1.2 μm region. In this paper, single-mode fiber lasers and amplifiers at 1178 nm, 1190 nm, and 1200 nm are reported. Over 2 watts of continuous wave output power was achieved with a 10-cm long gain fiber.

Optical beam alignment in a coherent lidar (or ladar) receiver system plays a critical role in optimizing its performance. Optical alignment in a coherent lidar system dictates the wavefront curvature (phase front) and Poynting vector) matching of the local oscillator beam with the incoming receiver beam on a detector. However, this alignment is often not easy to achieve and is rarely perfect. Furthermore, optical fibers are being increasingly used in coherent lidar system receivers for transporting radiation to achieve architectural elegance. Single mode fibers also require stringent mode matching for efficient light coupling. The detector response characteristics vary with the misalignment of the two pointing vectors. Misalignment can lead to increase in DC current. Also, a lens in front of the detector may exasperate phase front and Poynting vector mismatch. Non-Interaction of Waves, or the NIW property indicates the light beams do not interfere by themselves in the absence of detecting dipoles. In this paper, we will analyze the extent of misalignment on the detector specifications using pointing vectors of mixing beams in light of the NIW property.

The NIW (non-interaction of waves) property has been proposed by one of the coauthors. The NIW property states that in the absence of any "obstructing" detectors, all the Huygens-Fresnel secondary wavelets will continue to propagate unhindered and without interacting (interfering) with each other. Since a coherent lidar system incorporates complex behaviors of optical components with different polarizations including circular polarization for the transmitted radiation, then the question arises whether the NIW principle accommodate elliptical polarization of light. Elliptical polarization presumes the summation of orthogonally polarized electric field vectors which contradicts the NIW principle. In this paper, we present working of a coherent lidar system using Jones matrix formulation. The Jones matrix elements represent the anisotropic dipolar properties of molecules of optical components. Accordingly, when we use the Jones matrix methodology to analyze the coherent lidar system, we find that the system behavior is congruent with the NIW property.

The objective of the Materials International Space Station Experiment (MISSE) is to study the performance of novel materials when subjected to the synergistic effects of the harsh space environment for several months. MISSE missions provide an opportunity for developing space qualifiable materials. Several laser and lidar components were sent by NASA Langley Research Center (LaRC) as a part of the MISSE 7 mission. The MISSE 7 module was transported to the international space station (ISS) via STS 129 mission that was launched on Nov 16, 2009. Later, the MISSE 7 module was brought back to the earth via the STS 134 that landed on June 1, 2011. The MISSE 7 module that was subjected to exposure in space environment for more than one and a half year included fiber laser, solid-state laser gain materials, detectors, and semiconductor laser diode. Performance testing of these components is now progressing. In this paper, the results of performance testing of a laser diode module sent by NASA Langley Research Center on MISSE 7 mission will be discussed. This paper will present the comparison of pre-flight and post-flight performance curves and discuss the effect of space exposure on the laser diode module. Preliminary findings on output power measurements show that the COTS laser diode characteristics did not undergo any significant performance degradation.

We report on recent progress made in the development of highly compact, single mode, distributed feedback laser (DFB) seed laser modules for lidar and spectroscopy applications from space based platforms. One of the intended application of this technology is in the NASA's Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) mission. The DFB laser modules operating at 1571 nm and 1262 nm have advanced current and temperature drivers built into them. A combination of temperature and current tuning allows coarse and fine adjustment of the diode wavelengths.

Studies were performed to carry out semi-empirical validation of a new measurement approach we propose for molecular mixing ratios determination. The approach is based on relative measurements in bands of O2 and other molecules and as such may be best described as cross band relative absorption (CoBRA). . The current validation studies rely upon well verified and established theoretical and experimental databases, satellite data assimilations and modeling codes such as HITRAN, line-by-line radiative transfer model (LBLRTM), and the modern-era retrospective analysis for research and applications (MERRA). The approach holds promise for atmospheric mixing ratio measurements of CO2 and a variety of other molecules currently under investigation for several future satellite lidar missions. One of the advantages of the method is a significant reduction of the temperature sensitivity uncertainties which is illustrated with application to the ASCENDS mission for the measurement of CO2 mixing ratios (XCO2). Additional advantages of the method include the possibility to closely match cross-band weighting function combinations which is harder to achieve using conventional differential absorption techniques and the potential for additional corrections for water vapor and other interferences without using the data from numerical weather prediction (NWP) models.

We implemented single-photon detector in 1500-nm band based on frequency up-conversion in nonlinear waveguide at pump wavelength of 1920 nm. Ultralow dark count rate and signal photon detection rate are 20 s−1 and 56.8 s−1.

We describe a new approach for molecular mixing ratio measurements based on spectral lines matching of various molecules with oxygen resulting in substantial reductions of temperature and pressure induced errors and close weighting functions matching.

We have carried out comparative simulation studies to establish the advantages and limitations of alternative spectral regions and measurement wavelengths being investigated by different groups for the sensing of CO 2 and O 2 for potential use in the ASCENDS mission implementation. Our studies are based on the lidar modeling framework we developed specifically for ASCENDS which may be further applied to similar missions relying on the active sensing approach from space or aircraft. The modeling framework performs standard lidar sensitivity calculations, and also includes analysis of weighting functions and the effects of laser wavelength instabilities. As such, the factors considered in the analysis include the general LIDAR sensitivity, shapes of the weighting functions, as well as the added error due to the laser wavelength jitter in the selected spectral bands and wavelength regions. In particular, the studies were performed for the 1.26 – 1.27 micron and the A-band of oxygen, as well as the 1.57 and 2.06 micron bands of carbon dioxide. Additionally, the analysis is based on a range of satellite datasets and models to also take into account a variety of spacial and temporal variations in surface and atmospheric parameters. The results of our comparative studies for alternative spectral bands will be presented including the quantitative estimates of required constraints on selected system parameters to achieve the desired accuracy of ~0.3% in XCO 2 measurements.

A single-frequency (SF) fiber laser at 1200 nm was developed with a distributed Bragg reflector (DBR) configuration by splicing a 22 mm long highly holmium-doped ZBLAN (ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF) fiber with a pair of silica fiber Bragg gratings. The linewidth was estimated to be less than 100 kHz based on the measured frequency noise. The relative intensity noise was measured to be110 dB/Hz at the relaxation oscillation peak and the polarization extinction ratio was measured to be19 dB. Our results highlight the exciting prospect that wavelength coverage of SF DBR fiber lasers can be expanded significantly by using rare-earth-doped ZBLAN fibers.