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The dissertation presented here describes advancements made in adaptive polymer lens design and implementation. Singlets and doublets lenses were constructed for visible, short- wavelength infrared (SWIR), and middle-wavelength infrared (MWIR)applications. The lenses are implemented in a variety of tactical imaging systems to demonstrate their performance. A process was developed that defines the allowable fabrication variables, first for APL singlets and then for APL doublets. A first-order finite element model is described that enables going from an optical design to APL fabrication. This model was then extended to the design of fluidic doublets, which are equivalent to their two-element glass counter-parts. Two constant volume fluidic chambers were enclosed by three flexible membranes resulting in a variable focal length doublet. Chromatic focal shift was then used to compare numerical modeling to experimentally measured results. These same tools, methodology, and process were lastly used in the definition and fabrication of the SWIR and MWIR adaptive polymer lens for tactical systems. vi Imaging and illumination systems are presented, based on these lensesnotably an adaptive zoom imaging system, in the MWIR. This is the first known instance of such a system in this band.

This paper is focused on analyzing the impact of a two-dimensional metal hole array structure integrated to the back-illuminated quantum dots-in-a-well (DWELL) infrared photodetectors. The metal hole array consisting of subwavelength-circular holes penetrating gold layer (2D-Au-CHA) provides the enhanced responsivity of DWELL infrared photodetector at certain wavelengths. The performance of 2D-Au-CHA is investigated by calculating the absorption of active layer in the DWELL structure using a finite integration technique. Simulation results show that the performance of the DWELL focal plane array (FPA) is improved by enhancing the coupling to active layer via local field engineering resulting from a surface plasmon polariton mode and a guided Fabry-Perot mode. Simulation method accomplished in this paper provides a generalized approach to optimize the design of any type of couplers integrated to infrared photodetectors. Experimental results demonstrate the enhanced signal-to-noise ratio by the 2D-Au-CHA integrated FPA as compared to the DWELL FPA. A comparison between the experiment and the simulation shows a good agreement., Published in Optics Express, v21 n4 p4709-4716, 25 Feb 2013.

The antimonide based vertical external cavity surface emitting lasers (VECSELs) operating in the 1.8 to 2.8 μm wavelength range are typically based on InGaSb/AlGaSb quantum wells on AlAsSb/GaSb distributed Bragg reflectors (DBRs), grown latticematched on GaSb substrates. In this work the ability to grow such antimonide VECSEL structures on GaAs substrates is explored. The growth of such III-Sb VECSELs on GaAs substrates is non-trivial due to the 7.78% lattice mismatch between the antimonide based active region and the GaAs/AlGaAs DBR. The challenge is therefore to reduce the threading dislocation density in the active region without a very thick metamorphic bu\u21b5er and this is achieved by inducing 90! interfacial misfit dislocation arrays between the GaSb and GaAs layers. In this work cross section transmission electron microscopy is used to analyze a variety of approaches to designing and growing III-Sb VECSELs on GaAs substrates to achieve a low threading dislocation density. The failure mechanisms in such growths and the extent to which the threading dislocations permeate a thick active region are also analyzed. Finally, growth strategies and techniques to enable low-defect density III-Sb VECSEL active regions on GaAs are discussed.

Blue???emitting and green???emitting laser heterostructures were grown by molecular beam epitaxy, incorporating InGaN/GaN quantum dots as the active medium, with a measured quantum efficiency of 60% on n???GaN bulk substrates. These quantum dots exhibit no S???shape in the photoluminescence peak wavelength as a function of temperature, as typically found in comparable quantum well devices. The lasers were characterized by a threshold current density, J th , of 930 A/cm 2 under pulsed bias, with a differential efficiency of 13.9%, and a wall plug (power conversion) efficiency of 0.4% at 1050 A/cm 2 . Green???emitting quantum dot lasers have J th = 935 A/cm 2 . The lasers were also characterized by their modal properties through near field imaging (?? 2013 WILEY???VCH Verlag GmbH & Co. KGaA, Weinheim)

The first and second generations of infrared detectors—developed from the 1950s to the 1990s—were dominated by single pixel, linear, and staring small format, containing from 1 Kpixels to 100 Kpixels. In the past decade, the third-generation systems presented (a) large format (1 Mpixels to 16 Mpixels), (b) higher operating temperature (200 K to 250 K for MWIR, and 120 K to 150 K for LWIR), and (c) multicolor operation. The emphasis demanded for the next generation of devices is the incorporation of an enhanced functionality in the imagers—preferably at the pixel level—such as color, polarization, and dynamic range control, leading to a dramatic reduction in the size, complexity, and cost of infrared imaging systems. In this work, a new 96 x 96 pixel, 30 um pitch mixed-signal readout-integrated circuit (ROIC) with a pixel-level tunable bias control is demonstrated. The new ROIC is capable of providing a large-bias voltage in both polarities on each individual pixel, independently. These enhanced functionalities are achieved by modifying a capacitive transimpedance amplifier (CTIA) CMOS ROIC architecture. The unit cell electronic circuit was designed using 15 transistors and four capacitors and consists of the CTIA integrator—a two-stage, seven-transistor operational amplifier—one analog memory, one address selector, one reference recover switch, a sample-and-hold stage, an output buffer, and an output multiplex switch. Several test structures of individual devices and complete circuits were implemented on the test chip to characterize each one and to reconstruct the unit cell with discrete components, if necessary. Intending to test, characterize, and control the ITP-ROIC, an FPGA-based hardware and GUI software were developed to generate four analog and 26 digital output signals, with 87 adjustable parameters. In addition to the hardware, chip interconnection techniques were developed to grant nondestructive, flexible, quick inter

This dissertation contains three major parts: (1) demonstration of the algorithmic spectrometry in the mid-IR sensing regime using spectrally tunable quantum dots-in-a-well (DWELL) IR detector without employing any spectral filters; (2) further demonstration of the spectral-classification capability of tunable DWELL IR focal-plane array (FPA), again without using any spectral filters; and (3) development of a generalized filter-free data-compressive spectral sensing paradigm using the DWELL detector that enables arbitrarily specified MS sensing (e.g., spectral matched filtering, slope sensing, multicolor sensing, etc.) without using any spectral filters and possibly under constrained acquisition times.

Infrared (IR) detectors today are being utilized for a variety of imaging applications such as medical diagnostics, navigation instruments of automobiles and aircrafts, meteorological imaging, night-vision and fog/smoke imaging, surveillance, target acquisition and astronomical/space imaging. These wide ranging implementations have given rise to varied design requirements for these devices such as the required sensitivity, operating temperature, spectral sensitivity, peak wavelength and cost. Type-II band aligned InAs/Ga(In)Sb strained layer superlattice (SLS) material system proposed for the IR detection in the 1970s has been considered in recent years as an interesting alternative to the present day IR detection technologies. Type-II SLS technology possesses mature growth technologies able to achieve uniformity over large areas along with band-gap tunability which results in IR detectors in mid wave (MW), long-wave (LW) and very long-wave infrared (VLWIR) ranges. The large electron effective mass in SLS help in reducing inter-band tunneling and hence allow for longer-wavelength operation in these IR detectors. Large splitting between heavy-hole and light-hole valence subbands due to strain in the SLSs contributes to the suppression of Auger recombination and this enables significantly higher operating temperatures. The commercialization of type-II SLS technology has been hindered by material defects that promote excess dark currents in the bulk and on detector surfaces. During SLS device fabrication the mesa delineation leads to discontinuity of the periodic crystal structure which results in formation of unsatisfied chemical bonds on the etched surfaces and hence enhancing the surface leakage currents. More-over, with the scaling of single pixel dimensions, the performance of focal plane arrays is strongly dependent on surface effects due to the large pixels surface to volume ratio. Hence the reduction of surface leakage currents in LWIR detectors has become a te

This paper reports the radio frequency (RF) performance of InAs nanomembrane transistors on both mechanically rigid and flexible substrates. We have employed a self-aligned device architecture by using a T-shaped gate structure to fabricate high performance InAs metal-oxide-semiconductor field effect transistors (MOSFETs) with channel lengths down to 75 nm. RF measurements reveal that the InAs devices made on a silicon substrate exhibit a cutoff frequency (f t) of approx. 165 GHz, which is one of the best results achieved in III-V MOSFETs on silicon. Similarly, the devices fabricated on a bendable polyimide substrate provide a f(t) of approx. 105 GHz, representing the best performance achieved for transistors fabricated directly on mechanically flexible substrates. The results demonstrate the potential of III-V -on-insulator platform for extremely high-frequency (EHF) electronics on both conventional silicon and flexible substrates., Published in the Journal of Nano Letters, v12 n8 p4140-4145, 2012. Supported in part by DARPA, DOE and AFOSR Grant no. FA9550-10-1-0113.

This report was developed under a SBIR contract for topic AF08-BT02. Polaris Sensor and UNM developed a growth optimized DWELL FPA and a novel ROIC which allows the bias voltage of individual pixels to be controlled independently. In one mode of operation, the bias voltages of neighboring pixels can be varied such that two or more IR color images are interlaced, much in the way a color camera employing Bayer color filters interlaces Red, Green and Blue colored images., The original document contains color images.

The performance of a long-wave infrared type-II InAs/GaSb superlattice photodetector with a 50% cut-off wavelength of approximately 8.7 micrometer is presented. The ability to lower dark current densities over traditional P-type-Intrinsic-N-type diodes is offered by way of hetero-structure engineering of a pBiBn structure utilizing superlattice p-type (p) and n-type (n) contacts, an intrinsic (i) superlattice active (absorber) region, and unipolar superlattice electron and hole blocking (B) layers. The spectral response of this pBiBn detector structure was determined using a Fourier transform infrared spectrometer, and the quantum efficiency was determined using a 6250 nm narrow band filter and a 500 K blackbody source. A diode structure designed, grown, and fabricated in this study yielded a dark current density of 1.05 x 10(-5) A/cm2 at a reverse bias of -50 mV and a specific detectivity value of greater than 10(11) Jones at 77 K. Theoretical fittings of the diode dark currents at 77 K were used in this study to help isolate the contributing current components observed in the empirical dark current data. A variable temperature study (80 to 300 K) of the dark current is presented for a diode demonstrating diffusion-limited dark current down to 77 K., Published in Optical Engineering, v51 n12 p124001-1/124001-8, December 2012.

The goal of this project was to realize multicolor detectors using InAs/GaSb/AlGaSb strain layer superlattices (SLS). The program has been very successful both on the technical aspects of the projects and the personnel aspects of the projects. Several publications including one in Nature and one in Nature Communications have been published using funding from this project. One doctoral student, Dr. Arezou Khoshakhlagh, has defended her PhD and is now a full time staff member at NASA Jet Propulsion Laboratory. One more student, Mr. Vince Cowan, who works at the Air Force Research Laboratory is completing his PhD on barrier devices based on Type II superlattices., The original document contains color images.

Quantum Dot Infrared Photodetector (QDIP) Focal Plane Arrays (FPAs) have been proposed as an alternative technology for the 3rd generation FPAs. QDIPs are emerging as a competitive technology for infrared detection and imaging especially in the midwave infrared (MWIR) and longwave infrared (LWIR) regime. These detectors are based on intersubband transitions in self-assembled InAs quantum dots (QDs) and offer several advantages such as normal incidence detection, low dark currents and high operating temperatures, while enjoying all the benefits of a mature GaAs fabrication technology. However, due to Stranski-Krastanov (SK) growth mode and the subsequent capping growth, the conventional SK QDs are pancake shaped' with small height to base ratio due to interface diffusion. Thus they cannot fully exploit the 3D 'artificial atom' properties. This dissertation work investigates two approaches for shape engineered QDs: (1) Selective capping techniques of Stranski-Krastanov QDs, and (2) Growth of Sub-Monolayer (SML) QDs. Using Molecular Beam Epitaxy (MBE) growth, engineered QDs have been demonstrated with improved dot geometry and 3D quantum confinement to more closely resemble the 3D 'artificial atom'. In SK-QDs, the results have demonstrated an increased dot height to base aspect ratio of 0.67 compared with 0.23 for conventional SK-QD using Transmission Electron Microscope (TEM) images, enhanced s-to-p polarized spectral response ratio of 37% compared with 10% for conventional SK-QD, and improved SK-QDIP characterization such as: high operating temperature of 150K under background-limited infrared photodetection (BLIP) condition, photodetectivity of 1x109 cmHz1/2/W at 77K for a peak wavelength of 4.8 μm, and photoconductive gain of 100 (Vb=12V) at 77 K. In SML-QDs, we have demonstrated dots with a small base width of 4~6 nm, height of 8 nm, absence of wetting layer and advantage optical property than the SK-QDs. SML-QD shows adjustable dot height to base aspect rati

A mid wave infrared type-II superlattice focal plane array with 320x256 pixels, 30 mu m pitch and 90 % fill factor was fabricated in house, using a conventional homojunction p-i-n photodiode design and the ISC9705 readout circuit. High-quality imaging up to 110 K is demonstrated with the substrate fully removed. The absorber is 2 mu m thick, and no antireflection coating was used, so there is still room for significant improvement of the quantum efficiency, which is in the 40 % range. Studies of the dark current vs. temperature behavior indicate that the device is limited by Shockley-Read-Hall generation from the depletion region. The activation energy of this dark current component is 0.13 eV, suggesting an unidentified recombination center positioned halfway into the 0.24 eV bandgap. Furthermore, we report on detectors with 100 % cut-off at 13 mu m. The dark current density at 60 K and -50 mV bias is 2x10(-4) A/cm(2). Quantum efficiency, NETD and BLIP temperature are also calculated. Position-sensitive photocurrent measurements on mesa-etched superlattice material were made at low temperatures using a focused laser spot. The lateral diffusion length for holes was extracted and is reported., QC 20190312

The focus of this dissertation is to design, optimize and build an efficient high power multi kilowatt thin-disk laser system. We improve the thin-disk beam quality by eliminating thermally induced lensing and disk bowing. The characteristics and performance of a ceramic and single crystal Yb:YAG thin disk (TD) lasers are analyzed both experimentally and theoretically. We perform these experiments at room and at cryogenic temperatures. Novel composite substrate materials are explored for thermal management. Thermal and stress computations are modeled in detail using the finite element analysis COMSOL software. Geometrical and physical optics models, employing ZEMAX and other numerical techniques, are used to evaluate beam quality. Theoretical modeling results are combined to further explain physical mechanisms that influence a high power output laser beam. An analytical amplified spontaneous emission (ASE) model in thin-disk laser is developed. Experimental data includes: thermal measurements of thin-disk and output couplers; small signal gain; wavefront; spectrum; lifetime and fluorescence measurements. Most importantly, for the first time, thin-disk laser performance at room and cryogenic temperatures using a novel two phase boiling cooling system is investigated. Our unique setup allows us to directly compare the same material performance at these two temperatures. Our cryogenic results show that operating the laser as a four level system could be the key in achieving very high output power with less complicated system since there is a higher cross-section, and a fewer number of pump bounces is required. Thin-disks for cryogenic operation do not have to be as thin, which also makes it easier to manufacture them. Techniques developed in these experiments are of fundamental importance in future work related to high power solid state lasers; material science, particularly ceramic lasers, and composite materials manufacturing; and cryogenic operation lasers. A thorou

Type-II InAs/GaSb Strained Layer Superlattice (T2SL) is an emerging technology for infrared detection. They are being seen as a threat to 50 years old incumbent technology based on Mercury-Cadmium-Telluride (MCT) system. T2SL have been theoretically predicted to outperform MCTs. This dissertation has been aimed at improving the physical understanding and detector performance of T2SL detectors. This work has been focused on the bandstructure simulation, molecular beam epitaxy (MBE) growth optimization, physical understating, and heterojunction barrier engineering of T2SL, in midwave infrared (MWIR, 3-5\uf06dm) and longwave infrared (LWIR, 8-12\uf06dm) regimes. The bandstructure of InAs/GaSb/AlSb superlattices has been simulated in this work using empirical pseudopotential method. The simulation results have been used extensively in the later part of this work for designing heterojunction T2SL photodetectors. The interfaces between the individual layers (InAs and GaSb) in T2SL have been optimized for improving the detector performance. Performance of different interface structures were evaluated using variable temperature photoluminescence response, and with the use of detector performance parameters such as responsivity, detectivity and dark current. It was concluded that supporting InSb' type bonds at both the interfaces resulted in the best performance. This was achieved by using Sb2 soak time on 'InAs on GaSb' interface and growing thin InSb layer on 'GaSb on InAs' interface. This also helps in strain balancing the system. This interface scheme has been subsequently used in the high performance LWIR pBiBn devices as well as the HOT MWIR cascade devices, giving lattice matched T2SL in these structures. Physical properties of T2SL system are not very well understood, for example the nature of minibands. Polarization sensitive photocurrent spectroscopy measurements were carried out on MWIR and LWIR T2SL material, and experimental results were correlated with the theo

We have increased the ratio of s-polarization (normal incidence) to p-polarization photocurrent to 50% in a quantum dot-in-a-well based infrared photodetector form the typical s-p polarization ratio about 20%. This improvement was achieved by engineering the dot geometry and the quantum confinement via post growth capping materials of the Stranski Krastanov growth mode quantum dots (QDs). The TEM images show that the height to base ratio of shape engineered QDs was increased to 8 nm/12 nm from the control sample's ratio 4 nm/17 nm. The dot geometry correlates with the polarized photocurrent measurements of the detector. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4764905]