This PDF file contains the front matter associated with SPIE Proceedings Volume 7467, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

NASA Goddard Space Flight Center has launched four space based laser instruments for Earth and planetary sciences. Three out of four are single beam laser altimeter systems. We are transitioning into multi-beam swath mapping altimeter systems for high-resolution mapping. This paper will discuss the system approach and enabling technologies for swath mapping laser altimetry.

This work has sought to develop distributed feedback (DFB) diode-laser concepts and technologies necessary to facilitate NASAs upcoming Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) mission. Specifically, a modified-COTS DFB laser module, incorporating a low-noise variable laser bias current supply and low-noise variable temperature control circuit, has been developed. Prototype hardware has been built and tested.

Dust contamination is a serious problem for equipment and vehicles for space mission applications. The lunar regolith is chemically composed of several elements and compounds and lunar "weathering" has left the lunar soil with a relatively fine texture as illustrated by the grain-size distribution on soil taken from a mare region on Apollo 11. Previous investigations by NASA indicated a lunar regolith deposition rate of about 0.3 percent coverage per day, but the deposition rate is expected to be both geographically variable and also to vary from time to time. Dust gathers on photonic sensors inhibiting motion and data gathering. In addition, devices that require transparency to light for maximum efficiency such as solar photovoltaic power systems, video cameras and optical or infrared detectors will suffer from the dust accumulation. Another potential hazard is the unintentional capture of extraterrestrial bacteria or spores on the surfaces of the equipment, to the extent that can be anticipated, that might bring inadvertent and possibly catastrophic contamination of human habitats. This presentation will discuss the properties, as a function of ionizing radiation, temperature and space contamination effects, of a new type of self-cleaning and anti-contamination photonic coating for space mission applications.

For applications in space systems, devices based on novel nanomaterials offer significant advantages over traditional technologies in terms of light-weight and efficiency. Examples of such novel devices include quantum dot (QD) based solar cells and photodetectors. However, the response of these devices to radiation effects is not well understood, and radiation effects modeling tools are not yet available. In this paper we review our numerical models and experimental investigation of radiation effects in quantum dot based solar cells. In the natural, high-radiation environment of space all solar cells suffer from degradation. Although some studies have been conducted, and test data collected, on the performance of solar cells in a radiation environment, the mechanisms of radiation-induced degradation of quantum dot superlattices (QDS) has yet to be established. We have conducted proton irradiation experiments to provide a direct comparison of radiation hardness of quantum dot based cells and regular solar cells. An approach to the development of Nano-scale Technology Computer Aided Design (NanoTCAD) simulation software for simulation of radiation effects in QDS-based photovoltaic (PV) devices is presented. The NanoTCAD tools are based on classical drift-diffusion and quantum-mechanical models for the simulation of QD PV cells.

The radiation resistance of organic electro-optic and optoelectronic materials of different conjugation lengths for space applications is receiving increased attention. Earlier investigation reported that guest-host (G-H) poled polymer EO modulator devices composed of a phenyltetraene bridge-type chromophore in amorphous polycarbonate (CLD/APC) did not exhibit a decrease in EO response (i.e., an increase in modulation-switching voltage- V_π) following irradiation by low dose [10-160 krad(Si)] ⁶⁰Co gamma-rays. In this work, the post-irradiation responses of ⁶⁰Co gamma-rays on CLD1/APC thin films are examined by various chemical and spectroscopic methods including: a solubility test, thin-layer chromatography, proton nuclear magnetic resonance spectroscopy, UV-vis absorption, and infra-red absorption. The results indicate that CLD1 and APC did not decompose under gamma-ray irradiation at dose levels ranging from 66-274 krad(Si) and from 61-154 krad(Si), respectively which support the previously reported data. A comparison with an in situ proton irradiated DRI/PMMA material is also presented.

Optical limiters are nonlinear optical devices that limit the amount of power or energy transmitted. They function through either optically-induced nonlinear absorption or refraction or a combination of the two. At low incident optical power or pulse energy, the transmission of the system is high enough to allow nominal operation of the system. At high incident optical power or pulse energy, the transmission decreases to protect sensitive components such as optical receivers or transmitters. The interest in optical power limiters (OPL) for use in the space environment is due to the increasingly large number of space based missions and applications that require laser protection. Temperature and space radiation-induced effects in optical and electronic materials are well known and they can cause disruption in OPL functions, or in the worst case, failure of the sensor. Therefore, designing materials that can withstand the space environment has been an area of intense exploration in recent years. Some of the best-performing optical limiters are materials containing chromophores that work via reverse saturable absorption, multiphoton absorption or nonlinear scattering mechanisms; however, such materials are difficult to prepare and have problems with long-term stability. In this paper, a novel type of polymeric OPL materials based on a multi-chromophore approach is described. The origin of the OPL properties in these materials and preliminary results of their effects of radiation on the OPL properties are discussed.

Polymers are receiving considerable attention as components in novel optical systems because of the tailored functionality, ease of manufacturing, and relatively low cost. The processing of layered polymeric systems by coextrusion is a method to produce films comprising hundreds to thousands of alternating layers in a single, one-step roll-to-roll process. Several layered polymer optical systems have been fabricated by coextrusion, including gradient refractive index lenses, tunable refractive index elastomers, photonic crystals, and mechanically tunable photonic crystals. Layered polymeric optical systems made by coextrusion can also incorporate active components such as photoreactive additives for multilayered patterning and laser dyes for all-polymer laser systems. Coextrusion is a process which allows for the flexible design of polymeric optical systems using layers with thickness spanning the nanoscale to the microscale.

A new type of ferrofluid was synthesized and characterized by Faraday rotation. The ferrofluid is composed of ironoxide nanoparticles that are stabilized by covalently attached polyethylene glycol chains. This material shows great promise as magnetic sensing material.

Faraday rotation for magnetic field sensing can find applications in satellite altitude monitoring. Enhancing and tuning Faraday rotation is demonstrated in hybrid magnetic photonic crystals, based on an independent nanoscale engineering of two different materials (silica and iron oxide) at different length scales (< 20 and > 200 nm). An engineering approach towards combined photonic band gap properties and magnetic functionalities, based on independent nanoscale engineering of two different materials at different length scales, is conceptually presented, backed by simulations, and experimentally confirmed. Large (> 200 nm) monodisperse nanospheres of transparent silica self-assemble into a photonic crystal with a visible band gap, which is retained upon infiltration of small (< 20 nm) nanoparticles of magnetic iron oxide. Enhancing and tuning Faraday rotation in photonic crystals is demonstrated.

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. Two lasers and a few optical components from NASA Lnagley Research Center (LaRC) were included in the MISSE 6 mission for long term exposure. MISSE 6 items were characterized and packed inside a ruggedized Passive Experiment Container (PEC) that resembles a suitcase. The PEC was tested for survivability due to launch conditions. MISSE 6 was transported to the international Space Station (ISS) via STS 123 on March 11. 2008. The astronauts successfully attached the PEC to external handrails of the ISS and opened the PEC for long term exposure to the space environment. The current plan is to bring the MISSE 6 PEC back to the Earth via STS 128 mission scheduled for launch in August 2009. Currently, preparations for launching the MISSE 7 mission are progressing. Laser and lidar components assembled on a flight-worthy platform are included from NASA LaRC. MISSE 7 launch is scheduled to be launched on STS 129 mission. This paper will briefly review recent efforts on MISSE 6 and MISSE 7 missions at NASA Langley Research Center (LaRC).

As the minimum feature size of integrated circuits has decreased, it has produced a pressing need for a low cost method of protecting commercial off-the-shelf integrated circuits from naturally occurring thermal neutrons. The limitations of materials and manufacturing methods currently utilized pose major design and cost constraints in this area. Metalized Polyhedral Oligomeric Silsesquioxanes, can be utilized to provide efficient radiation absorptive materials. The primary advantage of using the nanoscopic metalized POSS technology is to disperse individual metal atoms at the 1.5 nm level within a low density and easily applied polymeric carrier. Calculations and experimental data on the shielding effectiveness of the metalized POSS conformal coating against thermal neutrons, warm X-rays, and gamma radiation are presented.

We present our recent theoretical studies of surface plasmon polariton analogues of the Goos-Hanchen effect and of Young's double-slit experiment.

The Air Force Research Laboratory (AFRL) is studying the application and utility of various ground-based and space-based optical sensors for improving surveillance of space objects in both Low Earth Orbit (LEO) and Geosynchronous Earth Orbit (GEO). This information can be used to improve our catalog of space objects and will be helpful in the resolution of satellite anomalies. At present, ground-based optical and radar sensors provide the bulk of remotely sensed information on satellites and space debris, and will continue to do so into the foreseeable future. However, in recent years, the Space-Based Visible (SBV) sensor was used to demonstrate that a synthesis of space-based visible data with ground-based sensor data could provide enhancements to information obtained from any one source in isolation. The incentives for space-based sensing include improved spatial resolution due to the absence of atmospheric effects and cloud cover and increased flexibility for observations. Though ground-based optical sensors can use adaptive optics to somewhat compensate for atmospheric turbulence, cloud cover and absorption are unavoidable. With recent advances in technology, we are in a far better position to consider what might constitute an ideal system to monitor our surroundings in space. This work has begun at the AFRL using detailed optical sensor simulations and analysis techniques to explore the trade space involved in acquiring and processing data from a variety of hypothetical space-based and ground-based sensor systems. In this paper, we briefly review the phenomenology and trade space aspects of what might be required in order to use multiple band-passes, sensor characteristics, and observation and illumination geometries to increase our awareness of objects in space.

Dualband infrared focal plane arrays (FPA), developed for multi-spectral imaging applications, have advantages over conventional multi-FPA sensor configurations in compactness and band-to-band pixel registration. These FPAs have also enabled hyperspectral applications that employ gratings used in two orders, allowing high efficiency hyperspectral imaging over very broad wavelength regions. As time progresses, multi-waveband FPAs are expected to provide an increase in spectral information at the pixel level without the need for external, dispersive optical elements. A variation on this approach, described here, uses detector material of fixed composition, with waveband sensitivity achieved as a function of depth, made possible by the spectral dependence of the absorption coefficient. An increase in the number of wavebands provides hyperspectral capability at the pixel level, hereafter denoted hyperspectral pixel. This technology may someday become possible through advanced detector array architectures, with photons of different wavelength continuously absorbed at different depths, and their resulting photocurrents isolated with a vertical grid of contacts or an equivalent mechanism for transporting depth-dependent signal photocurrent to a read-out circuit unit cell.

In space situational awareness scenarios, the objects needed to be characterized and identified are usually quite far away and quite dim. Thus, optical detectors need to be able to sense these very dim optical signals. Quantum interference in a three-level system can lead to amplification of optical signals. If we put a three-level system into a cavity tuned to the frequency of an incoming optical signal, we anticipate the amplification possibilities should be increased proportional to the quality factor of the cavity. Our vision is to utilize quantum dots in photonic crystal cavities, but as a stepping stone we first investigate a simple three-level system in a free-space optical cavity. We investigate quantum interference and classical interference effects when a three-level system interacts with both a cavity field mode and an external driving field mode. We find that under certain circumstances the cavity field evolves to be equal in magnitude to, but 180° out-of-phase with the external pump field when the pump field frequency equals the cavity frequency. At this point the resonance fluorescence from the atom in the cavity goes to zero due to a purely classical interference effect between the two out-of-phase fields. This is quite different from the quantum interference that occurs under the right circumstances, when the state populations are coherently driven into a linear combination that is decoupled from any applied field - and population is trapped in the excited states, thus allowing for a population inversion and an amplification of incoming optical signals.

We have formulated a theory to help us investigate the conditions which are needed to achieve stronger plasmon instability leading to emission in the terahertz (THz) regime for semiconductor quantum wells (QWs). The surface response function is calculated for a bilayer two-dimensional electron gas (2DEG) system in the presence of a metal grating placed on the surface which modulates the electron density. The 2DEG layers are coupled to surface plasmons arising from excitations of free carriers in the bulk region between the layers. A current is passed through one of the 2DEG layers and is characterized by a drift velocity υ_D. With the use of the surface response function, the plasmon dispersion equation is obtained as a function of frequency ω, the in-plane wave vector q_ll = (q_x, q_y) and reciprocal lattice vector nG where n = 0,±1,±2, ... with G = 2π/d and d denoting the period of the grating. The dispersion equation, which yields the resonant frequencies, is solved in the complex ω-plane for real wave vector q_ll. It is ascertained that the imaginary part of ω is enhanced with decreasing d, and with increasing the doping density of the free carriers in the bulk medium for fixed grating period.

We report on our development of both detectors and lasers in the terahertz (THz) region. For detection, we focus on the approach based on the extension of the celebrated quantum well infrared photodetectors (QWIPs); whereas the quantum cascade lasers (QCLs) provide the source. We show our preliminary demonstration of free space communication using our detectors and lasers. An all photonic THz communication link operating at 3.8 THz using a QCL and quantum well photodetector has been demonstrated. The link consists of a quantum cascade laser transmitter and a quantum well photodetector receiver. The link was used to transmit audio through two meters of room air. Carrier strength at the photodetector was 100 times above the noise level measured. THz free space communication may be of interest in satellite based systems.

Gate-voltage tunable plasmon resonances in the two dimensional electron gas of high electron mobility transistors (HEMT) fabricated from the InGaAs/InP and AlGaN/GaN materials systems are reported. Gates were in the form of a grating to couple normally incident THz radiation into 2D plasmons. Narrow-band resonant absorption of THz radiation was observed in transmission for both systems in the frequency range 10 - 100 cm^-1. The fundamental and harmonic resonances shift toward lower frequencies with negative gate bias. Calculated spectra based on the theory developed for MOSFETs by Schaich, Zheng, and McDonald (1990) agree well with the GaN results, but significant differences for the InGaAs/InP device suggest that modification of the theory may be required for HEMTs in some circumstances.

Jet Propulsion Laboratory is actively developing the III-V based infrared detector and focal plane arrays (FPAs) for NASA, DoD, and commercial applications. Currently, we are working on multi-band Quantum Well Infrared Photodetectors (QWIPs), Superlattice detectors, and Quantum Dot Infrared Photodetector (QDIPs) technologies suitable for high pixel-pixel uniformity and high pixel operability large area imaging arrays. In this paper we report the first demonstration of the megapixel-simultaneously-readable and pixel-co-registered dual-band QWIP focal plane array (FPA). In addition, we will present the latest advances in QDIPs and Superlattice infrared detectors at the Jet Propulsion Laboratory.

Type-II InAs/GaSb Superlattice (SL), a system of multi interacting quantum wells was first introduced by Nobel Laureate L. Esaki in the 1970s. Since then, this low dimensional system has drawn a lot of attention for its attractive quantum mechanics properties and its grand potential for the emergence into the application world, especially in infrared detection. In recent years, Type-II InAs/GaSb superlattice photo-detectors have experienced significant improvements in material quality, structural designs and imaging applications which elevated the performances of Type-II InAs/GaSb superlattice photodetectors to a comparable level to the state-of-the-art Mercury Cadmium Telluride. We will present in this talk the current status of the state-of-the-art Type II superlattice photodetectors and focal plane arrays, and the future outlook for this material system.

We report on surface passivation using SU-8 for type-II InAs/GaSb strained layers superlattice (SLS) detectors with a PIN design operating in mid-wave infrared (MWIR) spectral region (λ_{50% cut-off} ~ 4.4 μm). Material growth and characterization, single pixel device fabrication and testing, as well as focal plane array (FPA) processing are described. High quality strain-balanced SLS material with FWHM of 1st SLS satellite peak of 36 arcsec is demonstrated. The electrical and optical performance of devices passivated with SU-8 are reported and compared with those of unpassivated devices. The dark current density of a single pixel device with SU-8 passivation showed four orders of magnitude reduction compared to the device without any passivation. At 77K, the zero-bias responsivity and detectivity are equal to 1.1 A/W and 4 x 10¹² Jones at 4μm, respectively, for the SU-8 passivated test pixel on the focal plane array.

We report on the performance of multi-stack quantum dots in a well (DWELL) detectors. Present-day QD detectors are limited by low responsivity and quantum efficiency (QE). This can be attributed to the low absorption efficiency of these structures due to the small number of QD stacks in the detector. In this paper we examine the effect of the number of stacks on the performance of the detector. In particular, we investigate the InAs/GaAs/AlGaAs D-DWELL (Dots-in-double-well) design, which has a lower strain per DWELL stack than the InAs/InGaAs/GaAs DWELLs thereby enabling the growth of many more stacks in the detector. The purpose of the study detailed in this paper is to examine the effects of varying the number of stacks in the InAs/InGaAs/GaAs/AlGaAs D-DWELL detector, on its device performance. The numbers of stacks grown using solid source molecular beam epitaxy (MBE), were 15, 30, 40, 50, and 60. Once fabricated as single pixel devices, we carried-out a series of device measurements such as spectral response, dark current, total current, responsivity along with computing the photoconductive gain and the activation energies. The goal of these experiments is to not only study the single pixel detector performance with varying number of stacks in a D-DWELL structure, but to also understand the effect of the transport mechanism in these devices.

Capacitance-voltage-frequency measurements on n⁺-GaN/Al_xGa_1-xN Heterojunction Interfacial Workfunction Internal Photoemission (HEIWIP) detectors were used to analyze the effects of Al fraction induced heterojunction barrier and its effect on the electrical characteristics at the heterointerface. The detector's IR threshold can be modified by changing the barrier Al concentration. A sample with an Al fraction of 0.1 shows a distinct capacitance step and capacitance hysteresis, which is attributed to N-vacancies and/or C-donor electron trap states located just above the Fermi level (200 meV) at the GaN/AlGaN interface, with activation energies of 149±1 and ~189 meV, respectively. A sample with an Al fraction of 0.026 showed negative capacitance and dispersion, indicating interface electron trap states located below the Fermi level (88 meV), most likely due to C-donor and/or N-vacancy with activation energies of 125±1 and 140±2 meV, respectively. Additional impurity related absorption centers were identified in both samples, however these shallow Si-donor sites (~30.9±0.2 meV) did not affect the capacitance as these states were located in the barrier layer and not in the vicinity of the Fermi level. The Al fraction in the barrier layer was found to significantly change the positions of the interface trap states relative to the Fermi level, resulting in the observed capacitance characteristics.