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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Dual-Band Optical Bench for Terahertz Radiometer for Outer Planet Atmospheres (TROPA)

We have developed a wide-band dual frequency spectrometer for use in deep space planetary atmospheric spectroscopy. The instrument uses a dual-band architecture, both to be able to observe spectral lines from a wide range of atmospheric species, and to allow a higher precision retrieval of temperature/pressure/partial pressure and wind profiles. This dual-band approach requires a new design for the optical bench to couple both frequencies into their respective receivers.

submillitmeter↗
NASA NTRS2011

System and method for tuning adjusting the central frequency of a laser while maintaining frequency stabilization to an external reference

A method and system for stabilizing a laser to a frequency reference with an adjustable offset. The method locks a sideband signal generated by passing an incoming laser beam through the phase modulator to a frequency reference, and adjusts a carrier frequency relative to the locked sideband signal by changing a phase modulation frequency input to the phase modulator. The sideband signal can be a single sideband (SSB), dual sideband (DSB), or an electronic sideband (ESB) signal. Two separate electro-optic modulators can produce the DSB signal. The two electro-optic modulators can be a broadband modulator and a resonant modulator. With a DSB signal, the method can introduce two sinusoidal phase modulations at the phase modulator. With ESB signals, the method can further drive the optical phase modulator with an electrical signal with nominal frequency OMEGA(sub 1) that is phase modulated at a frequency OMEGA(sub 2)

Livas, Jeffrey↗
NASA NTRS1988

Study of optical output couplers for submillimeter wavelength backward-wave oscillators (BWO's)

The machining of slow wave structures for high frequency backward-wave oscillators (BWO) is extremely difficult beyond 1 THz. Recently a microfabrication technique using photolithography and ion-beam assisted etching has been used to construct a prototype BWO operating at 200 to 265 GHz. The output coupler for such tubes remains a problem. Waveguides do not exist or are very lossy at the frequencies of interest (300 to 2000 GHz). This paper discusses several scaled experiments of optical output couplers for submillimeter BWOs. Various designs of planar antennas (Vivaldi horns) and lens-feed systems (Hyperhemispherical lens) were constructed and tested between 20 and 100 GHz using a spectrum analyzer. The lens system was also tested at 337 GHz using a CO2 pumped FIR laser.

Cook, Jerry D.↗
NASA NTRS1994

Nonadiabatic nonradial p-mode frequencies of the standard solar model, with and without helium diffusion

The nonadiabatic frequencies of a standard solar model and a solar model that includes helium diffusion are discussed. The nonadiabatic pulsation calculation includes physics that describes the losses and gains due to radiation. Radiative gains and losses are modeled in both the diffusion approximation, which is only valid in optically thick regions, and the Eddington approximation, which is valid in both optically thin and thick regions. The calculated pulsation frequencies for modes with l less than or equal to 1320 are compared to the observed spectrum of the Sun. Compared to a strictly adiabatic calculation, the nonadiabatic calculation of p-mode frequencies improves the agreement between model and observation. When helium diffusion is included in the model the frequencies of the modes that are sensitive to regions near the base of the convection zone are improved (i.e., brought into closer agreement with observation), but the agreement is made worse for other modes. Cyclic variations in the frequency spacings of the Sun as a function of frequency of n are presented as evidence for a discontinuity in the structure of the Sun, possibly located near the base of the convection zone.

Guenther, D. B.↗
NASA NTRS1965

Electro-optic crystals and their use for light modulation

Several methods of modulating a beam of light, which have been described in the literature, utilizing the influence of an electrical signal on the birefringence of certain crystals, will be reviewed. These employ optics which respond to the state of polarization of a light beam, and include intensity modulation, position modulation, and the possibility of an electrically tuned optical filter. The influence of the piezo-optic, or strain contribution to the total electro-optic response in the design of an optoelectronic device will be discussed. Current experimental work in our laboratory in which the strain contribution is separated from the direct effect will be described. The strain-free effect is measured by applying a step voltage to the crystal, and observing the initial response. The electro-optical transient response can be observed with nanosecond time resolution. An electronic sampling technique is used to extract the desired response from photon noise. The stress-free or low-frequency effect is measured similarly but at low audio frequencies. Single crystal tetragonal BaT10 3 has been investigated in detail with the result that the strain-optic contribution to the low frequency effect r_(c) = r_(33)—r_(13) is about 80% of the total, where it is only 10% in KDP and 45% in ADP. The magnitudes of the electro-optic effect, dielectric constant, and other related properties are compared for several materials potentially useful as electro-optic modulators, and some comments are made about the practical problems of building a modulator.

ELECTRO-OPTICS↗
NASA NTRS1992

Doppler lidar wind measurement with the edge technique

The edge technique is a new and powerful method for measuring small frequency shifts. Range resolved lidar measurements of winds can be made with high accuracy and high vertical resolution using the edge technique to measure the Doppler shift of an atmospheric backscattered signal from a pulsed laser. The edge technique can be used at near-infrared or visible wavelengths using well developed solid state lasers and detectors with various edge filters. In the edge technique, the laser frequency is located on the steep slope of the spectral response function of a high resolution optical filter. Due to the steep slope of the edge, very small frequency shifts cause large changes in measured signal. The frequency of the outgoing laser pulse is determined by measuring its location on the edge of the filter. This is accomplished by sending a small portion of the beam to the edge detection setup where the incoming light is split into two channels - an edge filter and an energy monitor channel. The energy monitor signal is used to normalize the edge filter signal for magnitude. The laser return backscattered from the atmosphere is collected by a telescope and directed through the edge detection setup to determine its frequency (location on the edge) in a similar manner for each range element. The Doppler shift, and thus the wind, is determined from a differential measurement of the frequency of the outgoing laser pulse and the frequency of the laser return backscattered from the atmosphere. We have conducted simulations of the performance of an edge lidar system using an injection seeded pulsed Nd:YAG laser at 1.06 microns. The central fringe of a Fabry-Perot etalon is used as a high resolution edge filter to measure the shift of the aerosol return.

Korb, C. Laurence↗
NASA NTRS1992

Modulation characteristics of a high-power semiconductor Master Oscillator Power Amplifier (MOPA)

A semiconductor master oscillator-power amplifier was demonstrated using an anti-reflection (AR) coated broad area laser as the amplifier. Under CW operation, diffraction-limited single-longitudinal-mode powers up to 340 mW were demonstrated. The characteristics of the far-field pattern were measured and compared to a two-dimensional reflective Fabry-Perot amplifier model of the device. The MOPA configuration was modulated by the master oscillator. Prior to injection into the amplifier, the amplitude and frequency modulation properties of the master oscillator were characterized. The frequency response of the MOPA configuration was characterized for an AM/FM modulated injection beam, and was found to be a function of the frequency detuning between the master oscillator and the resonant amplifier. A shift in the phase was also observed as a function of frequency detuning; this phase shift is attributed to the optical phase shift imparted to a wave reflected from a Fabry-Perot cavity. Square-wave optical pulses were generated at 10 MHz and 250 MHz with diffraction-limited peak powers of 200 mW and 250 mW. The peak power for a given modulation frequency is found to be limited by the injected power and the FM modulation at that frequency. The modulation results make the MOPA attractive for use as a transmitter source in applications such as free-space communications and ranging/altimetry.

Cornwell, Donald Mitchell, Jr.↗
NASA NTRS1983

Efficient Distribution of Frequency-Standard Signals

Low power system distributes precise frequency standard signal to network of remote stations. Reference frequency at phase angle modulates transmitter at master transmitter/receiver circuit and recovers at remote circuit. Two circuits continuously transmit on microwave or optical signals 100 MHz apart to effect synchronization of reference frequency and phase.

Meyer, R. F.↗
NASA NTRS1995

Two Optical-Beam-Forming Concepts For Array Antennas

Two optical-beam-forming concepts selected for development of phased-array antennas. Involve use of novel combinations of optical and electronic techniques to distribute radio-frequency signal to or from antenna elements in array: phase and amplitude of radio-frequency signal traveling to or from each element controlled in such way to cause array as whole to transmit or receive signal in desired spatial pattern, steered, narrowed, broadened, or otherwise varied. Techniques result in compact, lightweight beam-steering antennas. Potential applications include steered-beam or quasi-optical microwave antennas in communication and radar systems, remote control of antennas in general, and photonic communication. With some modifications, transmitting and receiving configurations incorporated into single system.

Wu, Te-Kao↗
NASA NTRS1996

Efficient, Narrow-Pass-Band Optical Filters

Optical filters with both narrow pass bands and high efficiencies fabricated to design specifications. Offer tremendous improvements in performance for number of optical (including infrared) systems. In fiber-optic and free-space communication systems, precise frequency discrimination afforded by narrow pass bands of filters provide higher channel capacities. In active and passive remote sensors like lidar and gas-filter-correlation radiometers, increased efficiencies afforded by filters enhance detection of small signals against large background noise. In addition, sizes, weights, and power requirements of many optical and infrared systems reduced by taking advantage of gains in signal-to-noise ratios delivered by filters.

Sandford, Stephen P.↗
NASA NTRS2009

Ground Vibration Test of the Aerostructure Test Wing 2

The Aerostructures Test Wing (ATW) was developed to test unique concepts for flutter prediction and control synthesis. A follow-on to the successful ATW, denoted ATW2, was fabricated as a test bed to validate a variety of instrumentation in flight and to collect data for development of advanced signal processing algorithms for flutter prediction and aviation safety. As a means to estimate flutter speed, a ground vibration test (GVT) was performed. The results of a GVT are typically utilized to update structural dynamics finite element (FE) models used for flutter analysis. In this study, two GVT methodologies were explored to determine which nodes provide the best sensor locations: (i) effective independence and (ii) kinetic energy sorting algorithms. For measurement, ten and twenty sensors were used for three and 10 target test modes. A total of six accelerometer configurations measured frequencies and mode shapes. This included locations used in the original ATW GVT. Moreover, an optical measurement system was used to acquire data without mass effects added by conventional sensors. A considerable frequency shift was observed in comparing the data from the accelerometers to the optical data. The optical data provided robust data for use of the ATW2 finite element model update.

Herrera, Claudia↗
NASA NTRS2019

A Black Hole X-ray Binary at ~100 Hz: Multiwavelength Timing of MAXI J1820+070 with HiPERCAM and NICER

We report on simultaneous sub-second optical and X-ray timing observations of the low-mass X-ray binary black hole candidate MAXI J1820+070. The bright 2018 outburst rise allowed simultaneous photometry in five optical bands (ugrizs) with HiPERCAM/GTC (Optical) atf rame rates over 100 Hz, together with NICER/ISS observations (X-rays). Intense (factor of2) red flaring activity in the optical is seen over a broad range of time-scales down to∼10 ms. Cross-correlating the bands reveals a prominent anticorrelation on time-scales of ∼seconds, and a narrow sub-second correlation at a lag of≈+165 ms (optical lagging X-rays). This lag increases with optical wavelength, and is approximately constant over Fourier frequencies of∼0.3–10 Hz. These features are consistent with an origin in the inner accretion flow and jet base within∼5000 Gravitational radii. An additional∼+5 s lag feature may be ascribable to disc reprocessing. MAXI J1820+070 is the third black hole transient to display a clear∼0.1 s optical lag, which may be common feature in such objects. The sub-second lag variation with wavelength is novel, and may allow constraints on internal shock jet stratification models.

J A Paice↗
NASA NTRS2009

Ultra-Broad-Band Optical Parametric Amplifier or Oscillator

A concept for an ultra-broad-band optical parametric amplifier or oscillator has emerged as a by-product of a theoretical study in fundamental quantum optics. The study was originally intended to address the question of whether the two-photon temporal correlation function of light [in particular, light produced by spontaneous parametric down conversion (SPDC)] can be considerably narrower than the inverse of the spectral width (bandwidth) of the light. The answer to the question was found to be negative. More specifically, on the basis of the universal integral relations between the quantum two-photon temporal correlation and the classical spectrum of light, it was found that the lower limit of two-photon correlation time is set approximately by the inverse of the bandwidth. The mathematical solution for the minimum two-photon correlation time also provides the minimum relative frequency dispersion of the down-converted light components; in turn, the minimum relative frequency dispersion translates to the maximum bandwidth, which is important for the design of an ultra-broad-band optical parametric oscillator or amplifier. In the study, results of an analysis of the general integral relations were applied in the case of an optically nonlinear, frequency-dispersive crystal in which SPDC produces collinear photons. Equations were found for the crystal orientation and pump wavelength, specific for each parametric-down-converting crystal, that eliminate the relative frequency dispersion of collinear degenerate (equal-frequency) signal and idler components up to the fourth order in the frequency-detuning parameter

Strekalov, Dmitry↗
NASA NTRS1977

Extragalactic sources with strong millimeter-wave emission

Observations at 90 GHz of a sample of 38 sources chosen to have flat or rising spectra between 0.318 and 5 GHz are reported. Roughly 25% of the sources were found to have flat or rising spectra between 5 and 90 GHz. The optical magnitude of each of the sources from the E print of the Palomar Sky Survey has also been estimated. Evidence is found for a correlation between the 90-GHz flux density and the optical magnitude, suggesting a relationship between the emission processes at these frequencies. Little evidence is found for a correlation between the low- and high-frequency spectral indices of the sources. This suggests that the sources tend to be opaque at centimeter wavelengths and optically thin at millimeter wavelengths. The properties of two of the more interesting sources are also discussed. Evidence is presented that strong millimeter activity may be generally associated with the BL Lac phenomenon.

Owen, F. N.↗
NASA NTRS2016

Deep Space Optical Link ARQ Performance Analysis

Substantial advancements have been made toward the use of optical communications for deep space exploration missions, promising a much higher volume of data to be communicated in comparison with present -day Radio Frequency (RF) based systems. One or more ground-based optical terminals are assumed to communicate with the spacecraft. Both short-term and long-term link outages will arise due to weather at the ground station(s), space platform pointing stability, and other effects. To mitigate these outages, an Automatic Repeat Query (ARQ) retransmission method is assumed, together with a reliable back channel for acknowledgement traffic. Specifically, the Licklider Transmission Protocol (LTP) is used, which is a component of the Disruption-Tolerant Networking (DTN) protocol suite that is well suited for high bandwidth-delay product links subject to disruptions. We provide an analysis of envisioned deep space mission scenarios and quantify buffering, latency and throughput performance, using a simulation in which long-term weather effects are modeled with a Gilbert -Elliot Markov chain, short-term outages occur as a Bernoulli process, and scheduled outages arising from geometric visibility or operational constraints are represented. We find that both short- and long-term effects impact throughput, but long-term weather effects dominate buffer sizing and overflow losses as well as latency performance.

optical space communications↗
NASA NTRS1988

High energy efficient solid state laser sources

Recent progress in the development of highly efficient coherent optical sources is reviewed. This work focusses on nonlinear frequency conversion of the highly coherent output of the Non-Planar Ring Laser Oscillators developed earlier in the program, and includes high efficiency second harmonic generation and the operation of optical parametric oscillators for wavelength diversity and tunability.

Byer, Robert L.↗