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At least 127 records · Page 7

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NASA NTRS1992

Injection seeded single mode alexandrite ring laser for lidar applications

Along with many spectroscopic applications, atmospheric lidar measurements require a tunable, narrow band laser with a very high degree of spectral purity. A standing wave pulsed alexandrite laser tuned by injection seeding with an AlGaAs laser diode has demonstrated high stability. The standing wave cavity, however, poses several difficulties in light of the single mode operation and efficient seeding beam into the cavity. In order to overcome these problems and to operate the high power alexandrite laser in a single axial mode with a high spectral purity, a new ring laser system is being developed. The design features of the ring laser and some measurements of the laser characteristics are presented.

Lee, H. Sang↗

NASA NTRS2002

Laboratory Studies of the Photochemistry of Peroxynitric Acid

Observations of odd hydrogen radicals at high SZA in the lower stratosphere have demonstrated that our understanding of the HO(x) chemistry is incomplete [Wennberg et al., 1994a; Salawitch et al., 1994; Wennberg et al., 1999]. In particular, the concentrations of the HO(x) radicals are significantly larger than expected under weak photolytic conditions. Donaldson et al. [1997] have speculated that excitation of overtones of the OH stretching frequency in molecules such as HNO3 and HO2NO2 may be significant sources of HO(x) under these conditions. Although weak, vibrationally mediated photolysis may be important because it occurs in the near IR and visible and can provide energy in excess of the dissociation energy (D(o)): HONO2 + hv yields OH + NO (D(o) approx. 600 nm) and HOONO2 + hv yields OH + NO3 (D(o) approx. 735 nm) HOONO2 + hv yields HO2 + NO2 (D(o) approx. 1250 nm). In this project we developed instrumentation to characterize the photodissociation yields of hydroxyl containing compounds in the visible and near IR. This effort has involved coupling a tunable photolysis optical parametric oscillator (OPO) laser system with precise determination of the hydroxyl radical. The OPO system [Wu et al., 1997] was developed with support from the NSF Major Research Instrumentation Fund in a proposal entitled "Development of Novel, Compact Light Sources for Advanced Spectroscopy in Atmospheric Science and Materials Research" (Geoffrey A. Blake, P.I. California Institute of Technology).

Wennberg, Paul O.↗

NASA NTRS1993

Solid state laser

A wavelength-tunable, injection-seeded, dispersion-compensated, dispersively-pumped solid state laser includes a lasing medium; a highly reflective mirror; an output coupler; at least one isosceles Brewster prism oriented to the minimum deviation angle between the medium and the mirror for directing light of different wavelengths along different paths; means for varying the angle of the highly reflective mirror relative to the light from at least one Brewster angle for selecting a predetermined laser operating wavelength; a dispersion compensation apparatus associated with the lasing medium; a laser injection seeding port disposed between the dispersion compensation apparatus and one of the mirror and coupler and including a reflective surface at an acute non-Brewster angle to the laser beam for introducing a seed input; a dispersion compensation apparatus associated with the laser medium including opposite chirality optical elements; the lasing medium including a pump surface disposed at an acute angle to the laser beam to define a discrete path for the pumping laser beam separate from the pumped laser beam.

Rines, Glen A.↗

NASA NTRS2011

Pulsed Lidar for Measurement of C02 Concentrations for the ASCENDS Mission - Update

We have been developing a laser-based sounding technique for the remote measurement of the tropospheric CO2 concentrations from orbit for NASA is ASCENDS mission. The mission's goals are to provide measurements of tropospheric CO2 abundance with global-coverage, a few hundred km spatial and monthly temporal resolution. These are needed to better understand CO2 fluxes and the processes that regulate CO2 storage by the land and oceans. For the lIP, we are developing and demonstrating the lidar techniques and key lidar technology that will permit measurements of the CO2 column abundance in the lower troposphere from aircraft. Our final goal is to demonstrate the key capabilities needed for a space lidar and mission approach for the ASCENDS mission. We use a pulsed lidar technique, which is much less sensitive to errors from cloud and atmospheric scattering and to noise from solar background. It allows continuous measurements of CO2 mixing ratio in the lower troposphere during day and night. Our approach uses the 1570nm CO2 band and a two-wavelength laser absorption spectrometer, which continuously measures at nadir from a circular polar orbit. It directs the narrow co-aligned laser beams from the instrument's lasers toward nadir, and measures the energy of the laser echoes reflected from land and water surfaces. It uses a pair of tunable laser transmitters, which allowing measurement of the extinction from a single selected CO2 absorption line in the 1570 nm band and from a line pair in the Oxygen A-band near 765 nm. These regions have temperature insensitive absorption lines are free from interference from other gases. The lasers pulse at 10KHz, use tunable diode seed lasers followed by laser amplifiers, and have MHz spectral widths. During the measurement the lasers are stepped across the selected lines at a kHz rate. The receiver uses a 1-m class telescope and photon sensitive detectors and measures the background light and energies of the laser echoes from the surface. The extinction and column densities for the CO2 and O2 gases are estimated from the ratio of the on and off line echo pulse energies via the integrated path differential absorption (IPDA) technique. Our technique exploits the atmospheric pressure broadening of the lines to weight the measurement sensitivity to the atmospheric column below 5 km. Pulsed laser signals, time gated receiver are used to isolate the surface laser echo signals and to exclude photons scattered from clouds and aerosols. We have successfully demonstrated many key aspects of the approach and lidar technology in the laboratory. We have demonstrated CO2 column measurements in airborne flights during the summers of 2009 and 2010. These included measurements from 3-l3 km altitudes made over a variety of surfaces and through thin and broken clouds. We demonstrated initial airborne measurements of O2 column density to 10 km altitudes during the summer 2010 flights. More details approach, key technologies, and demonstration measurements will be given in the presentation.

Abshire, James↗

NASA NTRS2004

Novel Biomedical Device Utilizing Light-Emitting Nanostructures Developed

Sketches and chemical diagrams of state-of-the-art device and novel proposed device are presented. Current device uses a diode laser that emits into a fluorescent fluid only one wavelength and a photodetector diode that detects only one wavelength. Only one type of bacteria can be detected. The proposed device uses a quantum dot array that emits into a fluorescent fluid multiple wavelengths and an NIR 512 spectrometer that scans 0.8- to 1.7-mm wavelengths. Hundreds of different bacteria and viruses can be detected. A novel biomedical device is being developed at the NASA Glenn Research Center in cooperation with the University of Michigan. This device uses nano-structured quantum dots that emit light in the near-infrared (IR) region. The nanostructured quantum dots are used as a source and excite fluorochrome polymers coupled with antibodies that seek out and attach to specific bacteria and viruses. The fluorochrome polymers/antibodies fluoresce at specific wavelengths in the near-IR spectrum, but these wavelengths are offset from the excitation wavelength and can be detected with a tunable spectrometer. The device will be used to detect the presence of viruses and bacteria in simple fluids and eventually in more complex fluids, such as blood. Current state-of-the-art devices are limited to single bacteria or virus detection and a considerable amount of time and effort is required to prepare samples for analysis. Most importantly, the devices are quite large and cumbersome, which prohibits them from being used on the International Space Station and the space shuttles. This novel device uses nanostructured quantum dots which, through molecular beam epitaxy and highly selective annealing processes, can be developed into an illumination source that could potentially generate hundreds of specific wavelengths. As a result, this device will be able to excite hundreds of antibody/fluorochrome polymer combinations, which in turn could be used to detect hundreds of bacteria and viruses in fluids. A novel sample preparation technique that exploits micromembrane filtration and centrifugation methods has been developed for this device. The technique greatly reduces the time required to prepare the sample and the amount of sample needed to perform an accurate and comprehensive analysis. Last, and probably most important, because of the nano-light-emitting source and the novel sample preparation technique, the overall size of the device could be reduced dramatically. This device will serve as a nanoscale lab-on-a-chip for in situ microorganism detection and will enable tests to be performed on a time scale of minutes rather than days. Thus, it is ideally suited for monitoring the environmental conditions onboard the International Space Station and the space shuttles, thereby enhancing the safety of the astronauts. In addition, the device has important commercial applications, such as detecting the presence of bacteria and viruses in water at food- and beverage-processing centers, water treatment plants, and restaurants. Also, this technology has the potential to be used to detect bacteria and viruses in more complex fluids, such as blood--which in all likelihood would revolutionize blood analysis as it is performed today. This project was made possible through the Director's Discretionary Fund and is ongoing. In addition, this project provides funding to Dr. Rachel Goldman of the University of Michigan for the research and development of nanostructured quantum dots.

Scardelletti, Maximilian C.↗

NASA NTRS2017

Miniature Tunable Laser Spectrometer for Detection of a Trace Gas

An open-path laser spectrometer (OPLS) for measuring a concentration of a trace gas, the OPLS including an open-path multi-pass analysis region including a first mirror, a second mirror at a distance and orientation from the first mirror, and a support structure for locating the mirrors, a laser coupled to the analysis region and configured to emit light of a wavelength range and to enable a plurality of reflections of the emitted light between the mirrors, a detector coupled to the analysis region and configured to detect a portion of the emitted light impinging on the detector and to generate a corresponding signal, and an electronic system coupled to the laser and the detector, and configured to adjust the wavelength range of the emitted light from the laser based on the generated signal, and to measure the concentration of the trace gas based on the generated signal.

Christensen, Lance E.↗

NASA NTRS1990

Airborne water vapor DIAL system development

A differential absorption lidar (DIAL) system developed at NASA Langley Research Center for the remote measurement of atmospheric H2O and aerosols from an aircraft is briefly discussed. This DIAL system utilizes a Nd:YAG laser-pumped dye laser as the off-line transmitter and a narrowband, tunable Alexandrite laser as the on-line transmitter. A 1-m monochromator and a multipass absorption cell are used to position the on-line laser to the center of the H2O line. The receiver system has a 14-in. diameter, f/7 Celestron telescope to collect the backscattered laser light and focus in into the detector optics. Return signals are converted to electrical signals by the optical detector and are digitalized and stored on magnetic tape. The results of fligh tests of the system are shown.

Higdon, Noah S.↗

NASA NTRS1994

Resonance lamp absorption technique for simultaneous determination of the OH concentration and temperature at 10 spatial positions in combustion environments

A rugged, easy to implement, line-of-sight absorption instrument which utilizes a low pressure water vapor microwave discharge cell as the light source, has been developed to make simultaneous measurements of the OH concentration and temperature at 10 spatial positions. The design, theory, and capability of the instrument are discussed. Results of the measurements obtained on a methane/air flat flame burner are compared with those obtained using a single-frequency, tunable dye laser system.

Shirinzadeh, B.↗

NASA NTRS2012

High Absorptance Coatings for THz Applications

High absorptance materials find application throughout the electromagnetic spectrum as radiation terminations, calibration standards, and glint reduction coatings. Successful use of materials at millimeter through submillimeter wavelengths requires an accurate knowledge and control over their thermal, mechanical, and electromagnetic properties in order to achieve the desired response while minimizing mass and volume. In practice, the achieved blackness is intimately linked to the material properties and geometry. Here, we summarize the characteristics of a variety of tunable artificial dielectric mixtures appropriate for THz applications at room and cryogenic temperatures. Theoretical guidelines for their application will be provided in the context of the effective-medium mean-field-approximation. The performance of these coatings as elements of reflectance standards, radiometric flux calibrators, passive thermal radiators, and stray light suppression baffles for imaging systems will be reviewed.

Wollack, Edward J.↗

NASA NTRS1983

Guidance and control of MIR TDL radiation via flexible hollow metallic rectangular pipes and fibers for possible LHS and other optical system compaction and integration

Flexible hollow metallic rectangular pipes and infrared fibers are proposed as alternate media for collection, guidance and manipulation of mid-infrared tunable diode laser (TDL) radiation. Certain features of such media are found to be useful for control of TDL far field patterns, polarization and possibly intensity fluctuations. Such improvement in dimension compatibility may eventually lead to laser heterodyne spectroscopy (LHS) and optical communication system compaction and integration. Infrared optical fiber and the compound parabolic coupling of light into a hollow pipe waveguide are discussed as well as the design of the waveguide.

Yu, C.↗

NASA NTRS1993

Measured optical performance of three Fabry-Perot interferometers for use in a tunable ultraviolet filter

A narrowband ultraviolet (UV) filter would allow the first monochromatic two-dimensional images of astrophysical plasmas to be obtained in UV emission lines. The high etendue and spectral resolving power of the Fabry-Perot (FP) interferometer make it an excellent candidate for use in a tunable UV filter, provided that adequate optical performance can be obtained. Laboratory measurements of three UV FP interferometers with progressively greater dielectric mirror reflectances are described. The measurements demonstrate the adequate reflectivity, absorption, and small-scale smoothness of currently available coatings and substrates for UV interferometry. The measurements are conducted at 228.8 nm utilizing a cadmium hollow cathode light source. The best performing interferometer has a finesse of 41 and maximum transmittance of 0.38 over a coating-performance-dominated 3-mm-diam subaperture and a finesse of 26 and maximum transmittance of 0.32 over a parabolic-defect-dominated 30-mm-diam aperture. This interferometer is well suited for use in a UV filter system.

Korendyke, Clarence M.↗

NASA NTRS1990

Field induced gap infrared detector

A tunable infrared detector which employs a vanishing band gap semimetal material provided with an induced band gap by a magnetic field to allow intrinsic semiconductor type infrared detection capabilities is disclosed. The semimetal material may thus operate as a semiconductor type detector with a wavelength sensitivity corresponding to the induced band gap in a preferred embodiment of a diode structure. Preferred semimetal materials include Hg(1-x)Cd(x)Te, x is less than 0.15, HgCdSe, BiSb, alpha-Sn, HgMgTe, HgMnTe, HgZnTe, HgMnSe, HgMgSe, and HgZnSe. The magnetic field induces a band gap in the semimetal material proportional to the strength of the magnetic field allowing tunable detection cutoff wavelengths. For an applied magnetic field from 5 to 10 tesla, the wavelength detection cutoff will be in the range of 20 to 50 micrometers for Hg(1-x)Cd(x)Te alloys with x about 0.15. A similar approach may also be employed to generate infrared energy in a desired band gap and then operating the structure in a light emitting diode or semiconductor laser type of configuration.

Elliott, C. Thomas↗

NASA NTRS1990

Laboratory measurements of NO2 line parameters near 1600/cm for the interpretation of stratospheric spectra

Tunable diode laser laboratory measurements of infrared spectral parameters of selected NO2 lines near 1600/cm have been made to assess the contribution of uncertainties in these parameters to stratospheric measurements of NO2 made using the Balloon-Borne Laser In-Situ Sensor (BLISS) tunable diode laser spectrometer. Relative line intensities are measured to accuracies of better than 2 percent, with a root-sum-squared uncertainty in the absolute linestrengths of 4.5 percent. Air-broadening coefficients have been determined from measurements at total pressures in the range 20-100 Torr, at temperatures of 293 K and 214 K. These results are also discussed in the light of the discrepancies between infrared instruments flown in the 1982 and 1983 Balloon Intercomparison Campaigns.

May, R. D.↗

NASA NTRS1995

Stress Tuning of Laser Crystals

The topic of stress tunable laser crystals is addressed in this study with the purpose of determining the piezo-optic coefficients of a new laser material. This data was collected using a quadruple pass birefringence technique because of its high degree of sensitivity relative to the other methods examined including fringe shift analysis using a Mach-Zender interferometer. A green He-Ne laser was passed through a light chopper and Glan-Thompson prism before entering a crystal of Erbium doped Yttrium Aluminum Garnet (Er:YAG) (used in order to validate the experimental technique). The Er:YAG crystal is mounted in a press mechanism and the laser is quadruple passed through test specimen before being returned through the prism and the orthogonally polarized portion of the beam measured with a optical sensor. At a later stage, the Er:YAG crystal was replaced with a new crystal in order to determine the piezo-optic coefficients of this uncharacterized material. The applied load was monitored with the use of a 50 lb. load cell placed in line with the press. Light transmission readings were taken using a lock-in amplifier while load cell measurements were taken with a voltmeter from a 5 volt, 0.5 amp power supply. Despite the fact that an effective crystal press damping system was developed, size limitations precluded the use of the complete system. For this reason, data points were taken only once per full turn so as to minimize the effect of non uniform load application on the collected data. Good correlation was found in the transmission data between the experimentally determined Er:YAG and the previously known peizo-optic constants of non-doped crystal with which it was compared. The variation which was found between the two could be accounted for by the aforementioned presence of Erbium in the experimental sample (for which exact empirical data was not known). The same test procedure was then carried out on a Yttrium Gallium Aluminum garnet (YGAG) for the purpose of establishing values of its unknown piezo-optic constant tensor using experimentally collected transmission data. Significant variation between the piezo-optic constants of YAG and YGAG crystals was found however, the excellent data correlation of separate experimental runs carried out on the YGAG sample demonstrates the validity of these results. The data collected during the stressing of the YGAG was of high quality, however the amount of data collected was somewhat limited by a fracture of YGAG specimen which undoubted altered the crystalline lattice structure and hence precluded any further testing.

Carty, Atherton A.↗

NASA NTRSDate not supplied

A Vacuum-Compatible, Spectrally Tunable, Flat Panel Uniform Source for Testing Large Aperture Earth Observation Systems

Labsphere, Inc. in conjunction with NASA GSFC and Genesis Engineering Solutions Inc., has developed an innovative, vacuum compatible, calibration spectro-radiometric illumination source with a highly uniform large-area rectangular flat panel active area. This device features a uniquely shaped diffuse integration geometry to achieve high uniformity over a large active output area while maintaining a smaller and more robust overall form-factor when compared to previous designs or integrating spheres. A new liquid-cooled hybrid quartz-tungsten (QT) and light emitting diode (LED) source module has been engineered to provide direct-in-vacuum reference illumination over the full dynamic range and spectrum of the VIIRS instrument’s optical bands during pre-launch testing. The first unit has been demonstrated to meet its requirements using ambient technology and a fully-vacuum-compatible second unit is planned to allow testing in thermal vacuum (TVAC) campaigns. This technology is flexible and capable of meeting the needs of many other instruments/missions requiring this type of test/calibration capability.

Jeffrey Holt↗

NASA NTRS1992

POLARIS-II - An acousto-optic imaging spectropolarimeter for ground-based astronomy

A compact, acousto-optic tunable filter (AOTF) imaging spectropolarimeter for ground based astronomy from 400-1100 nm has been constructed at NASA/GSFC. The key components of this instrument are a TeO2 non-collinear AOTF, CCD camera, and an all-reflective optical relay assembly which uses a single elliptical mirror to produce side-by-side orthogonally polarized spectral images. The instrument was used at the Lowell Observatory 42-inch telescope for 'first light' planetary imaging and measurements of photometric standard stars. Narrow-band images of Saturn near 700 nm appear to show polarization effects which result from multiple scattering by aerosols. The instrument has recently been upgraded in order to integrate the RF drive electronics and eliminate contamination by scattered light. Design of the instrument and some initial results are presented.

Glenar, D. A.↗

NASA NTRS1992

JPL activities on development of acousto-optic tunable filter imaging spectrometer

Recent activities of JPL in the development of a new type of imaging spectrometers for earth observation and planetary exploration are reported. This instrument uses the acousto-optic tunable filter (AOTF) as high resolution and fast programmable bandpass filter. AOTF operates in the principle of acousto-optic interaction in an anisotropic medium. This filter can be tuned in sequential, random, and multiwavelength access modes, providing observational flexibility. The diffraction process in the filter generates two diffracted monochromatic beams with polarization orthogonal to each other, creating a unique capability to measure both polarimetric and spectral properties of the incoming light simultaneously with a single instrument. The device gives wide wavelength operations with reasonably large throughput. In addition, it is in a compact solid-state structure without moving parts, providing system reliability. These attractive features give promising opportunities to develop a new generation of airborne/spaceborne and ground, real-time, imaging spectrometer systems for remote sensing applications.

Cheng, Li-Jen↗

NASA NTRS1995

Linear operating region in the ozone dial photon counting system

Ozone is a relatively unstable molecule found in Earth's atmosphere. An ozone molecule is made up of three atoms of oxygen. Depending on where ozone resides, it can protect or harm life on Earth. High in the atmosphere, about 15 miles up, ozone acts as a shield to protect Earth's surface from the sun's harmful ultraviolet radiation. Without this shield, we would be more susceptible to skin cancer, cataracts, and impaired immune systems. Closer to Earth, in the air we breathe, ozone is a harmful pollutant that causes damage to lung tissue and plants. Since the early 1980's, airborne lidar systems have been used for making measurements of ozone. The differential absorption lidar (DIAL) technique is used in the remote measurement of O3. This system allows the O3 to be measured as function of the range in the atmosphere. Two frequency-doubled Nd:YAG lasers are used to pump tunable dye lasers. The lasers are operating at 289 nm for the DIAL on-line wavelength of O3, and the other one is operated at 300 nm for the off-line wavelength. The DIAL wavelengths are produced in sequential laser pulses with a time separation of 300 micro s. The backscattered laser energy is collected by telescopes and measured using photon counting systems. The photon counting system measures the light signal by making use of the photon nature of light. The output pulse from the Photo-Multiplier Tube (PE), caused by a photon striking the PMT photo-cathode, is amplified and passed to a pulse height discriminator. The peak value of the pulse is compared to a reference voltage (discrimination level). If the pulse amplitude exceeds the discrimination level, the discriminator generates a standard pulse which is counted by the digital counter. Non-linearity in the system is caused by the overlapping of pulses and the finite response time of the electronics. At low count rates one expects the system to register one event for each output pulse from the PMT corresponding to a photon incident upon the photocathode, however, at higher rates the limitations of the discrimination/counting system will cause the observed count rate to be non-linear with respect to the true count rate. Depending on the pulse height distribution and the discriminator level, the overlapping of pulses (pulse pile-up) can cause count loss or even an additional apparent count gain as the signal levels increase. Characterization of the system, including the pulse height distribution, the signal to noise ratio, and the effect of the discriminator threshold level, is critical in maximizing the linear operating region of the system, thus greatly increasing the useful dynamic range of the system.

Andrawis, Madeleine↗