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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Methods and devices based on brillouin selective sideband amplification

Opto-electronic devices and techniques using Brillouin scattering to select a sideband in a modulated optical carrier signal for amplification. Two lasers respectively provide a carrier signal beam and a Brillouin pump beam which are fed into an Brillouin optical medium in opposite directions. The relative frequency separation between the lasers is adjusted to align the frequency of the backscattered Brillouin signal with a desired sideband in the carrier signal to effect a Brillouin gain on the sideband. This effect can be used to implement photonic RF signal mixing and conversion with gain, conversion from phase modulation to amplitude modulation, photonic RF frequency multiplication, optical and RF pulse generation and manipulation, and frequency-locking of lasers.

Yao, X. Steve↗
NASA NTRS1976

Observation of stimulated Brillouin backscattering from an underdense plasma

Observations of stimulated Brillouin scattering from an underdense plasma in a magnetic field are reported. The observed shifts correspond to those expected from a plasma with the measured temperature. Scattering with twice the Brillouin shift was observed when the fundamental Brillouin reflectivity approached 5%.

Massey, R.↗
NASA NTRS1983

Stimulated Rayleigh-Brillouin gain spectroscopy in pure gases

Stimulated Rayleigh-Brillouin gain spectra of pure gases are reported. Stimulated Rayleigh scattering is now clearly distinguishable from stimulated Brillouin scattering without the aid of induced absorption. As examples, spectral line shapes of Ar and SF6 at various pressures and the associated gain asymmetry are discussed. Potential applications of coherent Rayleigh-Brillouin spectroscopy are suggested.

She, C. Y.↗
NASA NTRS1991

Rayleigh-Brillouin scattering for high-pressure gas temperature measurements

An experiment was set up to evaluate the feasibility of using Rayleigh-Brillouin scattering as a diagnostic technique for measuring gas temperature in high pressure environments, such as the Space Shuttle Main Engine (SSME) Preburner. A high pressure furnace is used as the scattering chamber. Either nitrogen or hydrogen may be used. An argon ion laser beam is focused into the furnace. Light backscattering from the gas in the furnace is collected and analyzed with a 5-pass scanning Fabry-Perot interferometer and photon counting electronics. The multi-pass configuration provides the high frequency selectively needed to measure the Brillouin peaks in the presence of large amounts of spuriously scattered light at the laser frequency. Preliminary measurements were made at room temperature in nitrogen at pressures up to 2000 psia. The free spectral range of the interferometer and frequency separation of the Brillouin peaks are determined from measured spectra. Temperature measurements are then obtained using the simple continuum theory with low frequency values of specific heat ratio and shear viscosity. The measured temperatures are within 10 percent of the true value.

Seasholtz, Richard G.↗
DOE OSTI2025

Brillouin Sensing with PCA, and PCA-Based Neural Networks for Efficient Temperature Monitoring

This work explores peak estimation techniques in Brillouin Optical Time Domain Analysis (BOTDA), emphasizing both accuracy and efficiency. Euclidean distance measurement method is applied to principal components derived from Brillouin Gain Spectrum data. It offers a major speed advantage being 180 170 times faster than traditional curve fitting methods such as Lorentzian curve fitting, while maintaining similar accuracy. Additionally, a PCA- based neural network model shows significant reduction of peak estimation time compared to Lorentzian fitting. Results show Brillouin frequency shift errors lie under 0.75 MHz in both Euclidean distance-based and neural network-based methods, both of which utilize PCA components. For large data sets and long length fibers, PCA- assisted neural network for peak estimation would be an efficient solution.

Distributed optical fiber sensing↗
NASA NTRS1975

Brillouin-scattering measurements of the acoustic absorption coefficient in liquid CS2

High-resolution Brillouin spectra were recorded for light scattered at small angles from liquid CS2. The use of a single-mode He-Ne laser, locked in frequency to a Fabry-Perot interferometer, permitted measurements of line widths of the order of 10 MHz for frequencies in the range 300-1000 MHz. These measurements extend previous Brillouin line-width measurements at higher frequencies into the region where relaxation effects are dominant and connect the optical measurements with lower-frequency acoustical data.

Coakley, R. W.↗
NASA NTRS1979

The applicability of Brillouin scattering to flow field diagnostics

To fill the void between turbulence theory and experiment; particularly in the flow fields consisting of monatomic gases, for example in wind tunnels, means of measuring fluctuating quantities are needed. In the area of density fluctuation measurement, the optical method of Brillouin scattering was suggested. This was based on the theory, that the Brillouin scattered intensity is proportional to a function of density. In this investigation the potential of this method as a diagnostic tool was studied. Here the density fluctuations in gases were sought. Continuous wave lasers and interferometers were used as the primary illuminating source and scattered light filters respectively.

Laiosa, J.↗
NASA NTRS1992

Rayleigh-Brillouin scattering to determine one-dimensional temperature and number density profiles of a gas flow field

Rayleigh-Brillouin spectra for heated nitrogen gas were measured by imaging the output of a Fabry-Perot interferometer onto a CCD array. The spectra were compared with the theoretical 6-moment model of Rayleigh-Brillouin scattering convolved with the Fabry-Perot instrument function. Estimates of the temperature and a dimensionless parameter proportional to the number density of the gas as functions of position in the laser beam were calculated by least-squares deviation fits between theory and experiment.

Lock, James A.↗
NASA NTRS1996

Robust, Brillouin Active Embedded Fiber-Is-The-Sensor System in Smart Composite Structures

Extensive review of our proposed sensing scheme, based mainly on the forward Guided Acoustic Wave Brillouin Scattering (GAWBS) with backward stimulated Brillouin scattering (sBs) as an auxiliary scheme for system fault tolerance has been completed during this project period. This preliminary study is conducted for a number of reasons. The most significant reasons lie in the essential capability of the system to measure temperature and pressure. These two measurands have been proposed to be sensed by sBs in our proposal. Temperature and pressure/strain are important measurands in structural monitoring, so that the effectiveness of sensing by sBs needs to be further examined. It has been pointed out initially that sBs shift will be dependent on temperature and pressure/strain simultaneously. The shift versus temperature or strain is linear. Now, the question is how can these two measurands be separated when sBs is used to sense an environment, in which both temperature and strain are changing simultaneously. Typical sBs shift plotted versus strain and varying temperature is shown in Fig. 1. As is clear, a fiber initially stressed will relax with rising temperature. This is verified by a displacement to the right with rising temperature of the sBs shift vs strain curves in the figure. A way to circumvent this ambiguity is by employing two fibers, one pre-stressed and the other is a free fiber. The latter will measure temperature and subtracting data in the latter fiber from those of the former will give us net strain readings. This is a laborious approach, since it involves the use of two identical fibers, and this is hard to accomplish, especially when many sensors are needed. Additional multiplexing of the data stream for data subtraction becomes a necessity.

Yu, Chung↗
NASA NTRS2024

Brillouin Asymmetric Spatial Heterodyne Oceanographic Lidar Receiver for Profiling Temperature, Salinity, and Sound Velocity

A lidar receiver employing a proposed Brillouin asymmetric spatial heterodyne (BASH) spectrometer to measure depth resolved profiles of near surface ocean temperature, salinity, and sound velocity from aircraft is conceptualized. A BASH spectrometer can have high throughput, can be designed for any wavelength and, importantly, can be field widened, allowing accurate, high spectral resolution of the Brillouin spectrum within diffuse scatter from depth. Temperature and salinity are measured independently with no assumptions about one or the other and the measurements are unbiased by the presence of particulate or elastic scatter. A sensitivity analysis and lidar simulations show the expected performance.

John A Smith↗
NASA NTRSDate not supplied

Brillouin Asymmetric Spatial Heterodyne Oceanographic Lidar Receiver for Profiling Temperature, Salinity, and Sound Velocity

No sensor today is capable of remotely sensing temperature and salinity at depth in oceanic waters, yet the physics to do so exists. Blue-green light (450-550 nm) can penetrate 10’s of meters into the water and interacts with water by the Brillouin scatter process. Temperature and salinity can be determined by analyzing the spectrum of Brillouin scatter. A host of scientific and operational drivers exist for such a sensor, from improved hurricane and red tide forecasting to studies of ocean fronts, eddies, and freshwater lenses. A low flying airborne light detection and ranging (lidar) instrument concept that exploits this physics is presented, along with simulation tools that potential data users can use to model its measurement performance, determine suitability for their application, and assess its implications.

John Anthony Smith↗
DOE OSTI2025

Low spontaneous Brillouin scattering in anti-resonant hollow-core fibers in GHz frequency range

Brillouin light scattering (BLS) is a powerful experimental tool that can be used to gain insights into the fundamental and applied properties of matter, like dispersions of quasiparticles in a solid, as well as their spatiotemporal dynamics. Many applications of light scattering favor the use of optical fibers in place of free-space optics. In this study, we compare the performance of anti-resonant hollow core fibers to that of conventional solid core fused silica fibers for BLS experiments in the GHz frequency range. Conventional fibers are barely suitable for low-noise measurements because of the spontaneous scattering of photons on various phononic modes present in the core and cladding. In the case of the hollow-core fiber, we identify a range of discrete phononic modes and associate them with the various acoustic modes of the structure surrounding the hollow core using finite-element numerical simulations. The measured relative intensity of the spontaneous BLS signal from these modes is orders of magnitude smaller than that of a solid-core fiber, making anti-resonant hollow-core fibers one of the best solutions for the single-mode light guidance for BLS and potentially other low-noise photonic experiments.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Repartitioning the Hamiltonian in many-body second-order Brillouin–Wigner perturbation theory: Uncovering new size-consistent models

Second-order Møller-Plesset perturbation theory is well-known as a computationally inexpensive approach to the electron correlation problem that is size-consistent with a size-consistent reference but fails to be regular. On the other hand, the less well-known many-body version of Brillouin-Wigner perturbation theory has the reverse properties: it is regular but fails to be size-consistent when used with the standard MP partitioning. Consequently, its widespread use remains limited. In this work, we analyze the ways in which it is possible to use alternative non-MP partitions of the Hamiltonian to yield variants of BW2 that are size-consistent as well as regular. We show that there is a vast space of such BW2 theories and also show that it is possible to define a repartitioned BW2 theory from the ground state density alone, which regenerates the exact correlation energy. We also provide a general recipe for deriving regular, size-consistent, and size-extensive partitions from physically meaningful components, and we apply the result to small model systems. The scope of these results appears to further set the stage for a revival of BW2 in quantum chemistry.

Ab initio perturbation↗
NASA NTRS1997

Brillouin Amplification--A Powerful New Scheme for Microwave Photonic Communications

We introduce the Brillouin selective sideband amplification technique and demonstrate many important applications of this technique in photonic microwave systems, including efficient phase modulation to amplitude modulation conversion, photonic frequency multiplication, photonic signal mixing with gain, and frequency multiplied signal up conversion.

systems Stimulated Brillouin Scattering (SBS) side↗