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NASA NTRS1983

Multiwavelength analyzer for the determination of diffusion lengths

The minority carrier diffusion length Ln in the base or substrate region is an important parameter which governs a solar cell's performance. The present investigation is concerned with the development of a multiwavelength analyzer (MWA) technique for the nondestructive spatial testing of polycrystalline solar cells. The MWA method is based on the utilization of the short-circuit current generated by two or more light-emitting diodes (LEDs) operating at different wavelengths and modulated 180 deg out-of-phase. For a determination of Ln by the MWA technique, it is necessary to know the value of the absorption coefficient.

Stafsudd, O. M.↗

NASA NTRS1991

Two-Dimensional Acousto-Optical Spectrum Analyzer

State-of-the-art two-dimensional acousto-optical spectrum analyzer processes input radio-frequency signal in real time into components in any number of spectral channels up to about 10(Sup5). Input radio-frequency signal to be analyzed launched via transducer into acousto-optical device along x axis. Acousto-optical device becomes Bragg cell. Pulsed plane waves of light from laser aimed at Bragg cell, which spatially modulates phases of plane waves and diffracts waves according to pattern of acoustic signal.

Ansari, Homayoon↗

NASA NTRS1994

Optically Driven Q-Switches For Lasers

Optically driven Q-switches for pulsed lasers proposed, taking place of acousto-optical, magneto-optical, and electro-optical switches. Optical switching beams of proposed Q-switching most likely generated in pulsed diode lasers or light-emitting diodes, outputs of which are amplitude-modulated easily by direct modulation of relatively small input currents. Energy efficiencies exceed those of electrically driven Q-switches.

Hemmati, Hamid↗

NASA NTRS1993

General technique for discrete retardation-modulation polarimetry

The general theory and rigorous solutions of the Stokes parameters of light of a new technique in time-resolved ellipsometry are outlined. In this technique the phase of the linear retarder is stepped over three discrete values over a time interval for which the Stokes vector is determined. The technique has an advantage over synchronous detection techniques, as it can be implemented as a digitizable system.

Saxena, Indu↗

NASA NTRS1980

A 5.57 hr modulation in the optical counterpart of 2S 1822-371

A periodic 5.57 hr modulation has been observed in the optical counterpart of the X-ray source 2S 1822-371. Two alternative periods are consistent with the data: P = 0.232114d and P = 0.232191d, with statistical uncertainties of 0.000015d in each case. Minimum light occurred at JD 2,444,105.668 + or - 0.005. The amplitude of the modulation is about 1 mag, independent of UBV color, and no variability exceeding the 2% level other than the 5.57 hr effect is found on time scales down to a few seconds. The light curve of the star can be understood in terms of a highly inclined close binary system which contains a relatively large, luminous accretion disk that is periodically occulted by a companion star and an associated gas stream. On the assumption that the companion is a main-sequence star, the distance of the system is found to be more than 600 pc, based on the absence of color variations commensurate with the 5.57 hr intensity cycle.

Mason, K. O.↗

NASA NTRS1991

Illuminance and luminance distributions of a prototype ambient illumination system for Space Station Freedom

Preliminary results of research conducted in the late 1970's indicate that perceptual qualities of an enclosure can be influenced by the distribution of illumination within the enclosure. Subjective impressions such as spaciousness, perceptual clarity, and relaxation or tenseness, among others, appear to be related to different combinations of surface luminance. A prototype indirect ambient illumination system was developed which will allow crew members to alter surface luminance distributions within an enclosed module, thus modifying perceptual cues to match crew preferences. A traditional lensed direct lighting system was compared to the prototype utilizing the full-scale mockup of Space Station Freedom developed by Marshall Space Flight Center. The direct lensed system was installed in the habitation module with the indirect prototype deployed in the U.S. laboratory module. Analysis centered on the illuminance and luminance distributions resultant from these systems and the implications of various luminaire spacing options. All test configurations were evaluated for compliance with NASA Standard 3000, Man-System Integration Standards.

Mullican, R. C.↗

NASA NTRS2012

Design and Analysis of Modules for Segmented X-Ray Optics

Future X-ray astronomy missions demand thin, light, and closely packed optics which lend themselves to segmentation of the annular mirrors and, in turn, a modular approach to the mirror design. The modular approach to X-ray Flight Mirror Assembly (FMA) design allows excellent scalability of the mirror technology to support a variety of mission sizes and science objectives. This paper describes FMA designs using slumped glass mirror segments for several X-ray astrophysics missions studied by NASA and explores the driving requirements and subsequent verification tests necessary to qualify a slumped glass mirror module for space-flight. A rigorous testing program is outlined allowing Technical Development Modules to reach technical readiness for mission implementation while reducing mission cost and schedule risk.

McClelland, Ryan S.↗

NASA NTRS2010

Selectivity enhancement in photoacoustic gas analysis via phase-sensitive detection at high modulation frequency

A method for detecting a target fluid in a fluid sample comprising a first fluid and the target fluid using photoacoustic spectroscopy (PAS), comprises a) providing a light source configured to introduce an optical signal having at least one wavelength into the fluid sample; b) modulating the optical signal at a desired modulation frequency such that the optical signal generates an acoustic signal in the fluid sample; c) measuring the acoustic signal in a resonant acoustic detector; and d) using the phase of the acoustic signal to detect the presence of the target fluid.

Kosterev, Anatoliy↗

NASA NTRS2007

Electro-Optical Modulator Bias Control Using Bipolar Pulses

An improved method has been devised for controlling the DC bias applied to an electro-optical crystal that is part of a Mach-Zehnder modulator that generates low-duty-cycle optical pulses for a pulse-position modulation (PPM) optical data-communication system. In such a system, it is desirable to minimize the transmission of light during the intervals between pulses, and for this purpose, it is necessary to maximize the extinction ratio of the modulator (the ratio between the power transmitted during an "on" period and the power transmitted during an "off" period). The present method is related to prior dither error feedback methods, but unlike in those methods, there is no need for an auxiliary modulation subsystem to generate a dithering signal. Instead, as described below, dither is effected through alternation of the polarity of the modulation signal. The upper part of Figure 1 schematically depicts a Mach-Zehnder modulator. The signal applied to the electro-optical crystal consists of a radio-frequency modulating pulse signal, VRF, superimposed on a DC bias Vbias. Maximum extinction occurs during the off (VRF = 0) period if Vbias is set at a value that makes the two optical paths differ by an odd integer multiple of a half wavelength so that the beams traveling along the two paths interfere destructively at the output beam splitter. Assuming that the modulating pulse signal VRF has a rectangular waveform, maximum transmission occurs during the "on" period if the amplitude of VRF is set to a value, V , that shifts the length of the affected optical path by a half wavelength so that now the two beams interfere constructively at the output beam splitter. The modulating pulse signal is AC-coupled from an amplifier to the electro-optical crystal. Sometimes, two successive pulses occur so close in time that the operating point of the amplifier drifts, one result being that there is not enough time for the signal level to return to ground between pulses. Also, the difference between the optical-path lengths can drift with changes in temperature and other spurious effects. The effects of both types of drift are suppressed in the present method, in which one takes advantage of the fact that when Vbias is set at the value for maximum extinction, equal-magnitude positive and negative pulses applied to the electro-optical crystal produce equal output light pulses.

Farr, William↗

NASA NTRS1990

Optical Modulation Via The Photorefractive Effect

Rotation of polarization and use of analyzer yield large variations in intensity. Experiments show one beam of light used to change intensity of another beam via photorefractive effect in GaAs. Each beam causes polarization of other beam to rotate. Rotation detected by passing modulated beam through analyzer. Results agree closely with predictions of theory of photorefractive effect. Modulation scheme works with other photorefractive materials of similar crystallographic symmetry.

Cheng, Li-Jen↗

NASA NTRS2011

Feasibility of Ultraviolet Light Emitting Diodes as an Alternative Light Source for Photocatalysis

The objective of this study was to determine whether ultraviolet light emitting diodes (UV-LEDs) could serve as an alternative photon source efficiently for heterogeneous photocatalytic oxidation (PCO). An LED module consisting of 12 high-power UV-A LEDs was designed to be interchangeable with a UV-A fluorescent black light blue (BLB) lamp in a Silica-Titania Composite (STC) packed bed annular reactor. Lighting and thermal properties were characterized to assess the uniformity and total irradiant output. A forward current of (I(sub F)) 100 mA delivered an average irradiance of 4.0 m W cm(exp -2), which is equivalent to the maximum output of the BLB, but the irradiance of the LED module was less uniform than that of the BLB. The LED- and BLB-reactors were tested for the oxidization of 50 ppmv ethanol in a continuous flow-through mode with 0.94 sec space time. At the same irradiance, the UV-A LED reactor resulted in a lower PCO rate constant than the UV-A BLB reactor (19.8 vs. 28.6 nM CO2 sec-I), and consequently lower ethanol removal (80% vs. 91%) and mineralization efficiency (28% vs. 44%). Ethanol mineralization increased in direct proportion to the irradiance at the catalyst surface. This result suggests that reduced ethanol mineralization in the LED- reactor could be traced to uneven irradiance over the photocatalyst, leaving a portion of the catalyst was under-irradiated. The potential of UV-A LEDs may be fully realized by optimizing the light distribution over the catalyst and utilizing their instantaneous "on" and "off' feature for periodic irradiation. Nevertheless, the current UV-A LED module had the same wall plug efficiency (WPE) of 13% as that of the UV-A BLB. These results demonstrated that UV-A LEDs are a viable photon source both in terms of WPE and PCO efficiency.

Levine, Langanf H.↗

NASA NTRS1991

SIRTF stray light analysis

The Space Infrared Telescope Facility (SIRTF) is a 1-meter cryogenic infrared telescope. Stray light is kept below the natural background by restrictions on sun, Earth, and moon off-axis angles; by conservative baffle design; by the use of advanced diffuse black coatings; and by superfluid helium cooling. The aperture stop is located at the primary mirror rather than at the secondary mirror to increase the aperture and reduce the central obscuration. Stray light from off-axis sources is greater with the aperture stop at the primary than with the aperture stop at the secondary, but the modulation of the signal produced by tilting of the secondary mirror for chopping is less. Stray light from telescope thermal emission is lower with the aperture stop at the primary.

Elliott, David G.↗

NASA NTRS1973

Ultrasonic signal enhancement by resonator techniques

Ultrasonic resonators increase experimental sensitivity to acoustic dispersion and changes in attenuation. Experimental sensitivity enhancement line shapes are presented which were obtained by modulating the acoustic properties of a CdS resonator with a light beam. Small changes in light level are made to produce almost pure absorptive or dispersive changes in the resonator signal. This effect is due to the coupling of the ultrasonic wave to the CdS conductivity which is proportional to incident light intensity. The resonator conductivity is adjusted in this manner to obtain both dispersive and absorptive sensitivity enhancement line shapes. The data presented verify previous thoretical calculations based on a propagating wave model.

Heyman, J. S.↗

NASA NTRS1980

Spacelab's interface to payload experiments

The Spacelab Payload Standard Modular Electronics (SPSME) program has been designed to provide a standardized set of space-qualified low-power electronic modules from which an experimenter may economically implement a command and data management system. SPSME is based on the Computer Automated Measurement and Control (CAMAC) interface standards. To the system of CAMAC, SPSME adds Spacelab interface modules, a flight qualified system crate, and an efficient light-weight power supply to produce a system compatible with the Spacelab environments, the Spacelab Command and Data Management System interface, and any experiment.

Golemon, W. F.↗

NASA NTRS1991

Ginga observation of an AM Herculis type source H0538 + 608

Results from a Ginga observation of the AM Her type object H0538 + 608 are presented. During the first half of the observation (pulsing state) the source showed periodic modulations caused by the white dwarf rotation, and the modulation profile was characterized by a flat top and a flat bottom. During the second half, the source was in a remarkable flaring state and the periodic modulation disappeared. The dramatic change of the X-ray light curve is interpreted in terms of a change of accretion pattern between an eclipsing spot and a noneclipsing spot. The spectrum is well described throughout by a thin thermal model including an iron K-line with equivalent width of some hundred eV, supporting the standard model for the hard X-ray emission region. The temperature in the pulsing state was found to change with the spin phase of the white dwarf. In the flaring state, the temperature showed a positive correlation with the source luminosity.

Ishida, M.↗

NASA NTRS1994

The ASCA PV phase observation of FO Aquarii

We report on a approximately 1-day Advanced Satellite for Cosmology and Astrophysics (ASCA) observation of the intermediate polar FO Aquarii. We find two distinctive spectral components, one unabsorbed and the other strongly absorbed; the observed 2-10 keV flux severely underestimates the total system luminosity, due to this strong absorption intrinsic to the binary. The absorbed component is dominant in terms of luminosity, and its light curve is simple. The unabsorbed component accounts for approximately 2% of the luminosity, and shows a much more complicated light curve. As the dominant component predominantly shows a sinusoidal modulation at the white dwarf spin period, it provides a strong evidence for a partial accretion disk in the system.

Mukai, Koji↗

NASA NTRS1999

STS-93 Post Flight Presentation

An overview of Flight STS-93 is presented. The primary objective of the STS-93 mission was to deploy the Advanced X-Ray Astrophysics Facility (AXAF), also known as the Chandra X-ray Observatory. The mission flew on the Columbia Shuttle, on July 22, 1999. This facility is the most sophisticated X-ray observatory ever built. Other payloads on STS-93 were: (1) the Midcourse Space Experiment (MSX), (2) Shuttle Ionospheric Modification with Pulsed Local Exhaust (SIMPLEX), (3) Southwest Ultraviolet Imaging System (SWUIS), (4) Gelation of Sols: Applied Microgravity Research (GOSAMR), Space Tissue Loss-B (STL-B), (5) Light Weight Flexible Solar Array Hinge (LFSAH), (6) Cell Culture Module (CCM), and (7) the Shuttle Amateur Radio Experiment-II (SAREX-II), (8) EarthKam, (9) Plant Growth Investigations in Microgravity (PGIM), (10) Commercial Generic Bioprocessing Apparatus (CGBA), (11) Micro-Electrical Mechanical System (MEMS), and (12) the Biological Research in Canisters (BRIC). The crew was: Eileen M. Collins, Mission Commander, the first female shuttle commander; Jeffrey S. Ashby, Pilot; Steven A. Hawley , Mission Specialist; Catherine G. Coleman, Mission Specialist; Michel Tognini (CNES), Mission Specialist. The video contains views of life aboard the space shuttle. This mission featured both a night launching and a night landing at the Kennedy Space Center.

Source record↗

NASA NTRS2010

FPGA Coprocessor Design for an Onboard Multi-Angle Spectro-Polarimetric Imager

A multi-angle spectro-polarimetric imager (MSPI) is an advanced camera system currently under development at JPL for possible future consideration on a satellite-based Aerosol-Cloud-Environ - ment (ACE) interaction study. The light in the optical system is subjected to a complex modulation designed to make the overall system robust against many instrumental artifacts that have plagued such measurements in the past. This scheme involves two photoelastic modulators that are beating in a carefully selected pattern against each other. In order to properly sample this modulation pattern, each of the proposed nine cameras in the system needs to read out its imager array about 1,000 times per second. The onboard processing required to compress this data involves least-squares fits (LSFs) of Bessel functions to data from every pixel in realtime, thus requiring an onboard computing system with advanced data processing capabilities in excess of those commonly available for space flight. As a potential solution to meet the MSPI onboard processing requirements, an LSF algorithm was developed on the Xilinx Virtex-4FX60 field programmable gate array (FPGA). In addition to configurable hardware capability, this FPGA includes Power -PC405 microprocessors, which together enable a combination hardware/ software processing system. A laboratory demonstration was carried out based on a hardware/ software co-designed processing architecture that includes hardware-based data collection and least-squares fitting (computationally), and softwarebased transcendental function computation (algorithmically complex) on the FPGA. Initial results showed that these calculations can be handled using a combination of the Virtex- 4TM Power-PC core and the hardware fabric.

Pingree, Paula J.↗