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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 1,063 records · Page 59

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NASA NTRS1983

Heterodyne applications of tunable semiconductor diode lasers

Infrared tunable diode lasers were developed in the 1960s and have been a valuable radiation source for high resolution laboratory and in situ spectroscopy. Use of Pb-salt Tunable Diode Lasers (TDL) in heterodyne applications impose stringent requirements on the TDL not normally required for laboratory spectroscopy. A review will be made of progress associated with TDLs in such heterodyne applications. Areas addressed will include such items as lifetime, operating temperature, and factors affecting excess noise. The review will emphasize the experience at Langley Research Center, but will include material from other users. The Langley information will include a description and current status of the Laser Heterodyne Spectrometer experiment and atmospheric solar absorption data obtained from a groundbased heterodyne system.

Sidney, B. D.↗

NASA NTRS1981

Spectroscopy of quasibound states formed by molecular collisions in the presence of a laser

A theory is reported which describes spectroscopic transitions between quasibound states formed during molecular collisions in a laser field. A preliminary calculation suggests that the shapes of absorption lines are sensitive to the shapes of the potentials; hence a method for determining the latter. The calculation also shows that respectable cross-sections for scattering can be obtained at low laser powers.

Hutchinson, M.↗

DOE OSTI2025

Open-source simulation program for extreme ultraviolet and soft x-ray sources based on high-harmonic generation

Light sources based on high-harmonic generation (HHG) underpin ultrafast spectroscopy experiments across a large range of photon energies, spanning from the extreme ultraviolet to the soft x-ray. To this day, their design, implementation, and improvement presens unique challenges, but can be aided by numerical tools. Here we present a new simulation program designed for this purpose, which takes both macroscopic and microscopic aspects of high-harmonic generation into account and is therefore applicable across the broad range of parameters which HHG based light sources are today utilized. The program is validated by comparison with published experimental results and by calculating harmonic emission in four common experimental configurations.

Femtosecond lasers↗

NASA NTRS1988

Mid-infrared solid-state lasers and laser materials

An account is given of NASA-Langley's objectives for the development of advanced lasers and laser materials systems applicable to remote sensing in the mid-IR range. Prominent among current concerns are fiber-optic spectroscopy, eye-safe solid-state lasers for both Doppler sensing and mid-IR wavelength-generation laser pumping, and nonlinear optics generating tunable mid-IR radiation. Ho:YAG lasers are noted to exhibit intrinsic advantages for the desired applications, and are pumpable by GaAlAs laser diodes with a quantum efficiency approaching 2.

Barnes, Norman P.↗

NASA NTRS1991

Tunable far infrared laser spectrometers

The state of the art in far infrared (FIR) spectroscopy is reviewed. The development of tunable, coherent FIR radiation sources is discussed. Applications of tunable FIR laser spectrometers for measurement of rotational spectra and dipole moments of molecular ions and free radicals, vibration-rotation-tunneling spectra of weakly bound complexes, and vibration-rotation spectra of linear carbon clusters are presented. A detailed description of the Berkeley tunable FIR laser spectrometers is presented.

Blake, G. A.↗

NASA NTRS1994

Near-IR diode laser absorption for measurement of tropospheric HO2

The possibility of using tunable lead salt diode lasers in the infrared for measurement of tropospheric HO2 has been frequently considered. Although the sensitivity of diode laser absorption has been improved through the use of high frequency detection techniques, nature has been unkind in that the HO2 absorption cross sections are weak. Even using the most optimistic assumptions about attainable path length and detectable absorbance, measurement of tropospheric HO2 by diode laser absorption in the mid-IR appears marginal. A possible alternative method for measuring HO2 is by absorption at near-infrared wavelengths. Several absorption bands of HO2 occur in the wavelength region between 1.2 and 1.6 micron due to electronic transitions and overtones of the fundamental vibrational modes. InGaAsP diode lasers operate in this wavelength region and can be used for high resolution spectroscopy in a manner analogous to the lead salt lasers. A diode laser system in the near-IR offers some advantages.

Stanton, Alan C.↗

DOE OSTI2025

Evaluating nonlocal heat transport in directly driven chromium spheres using x-ray spectroscopy

We report on experiments investigating heat transport in laser-generated plasmas using directly driven chromium spheres. The spheres are fielded at the OMEGA laser facility and are driven with laser intensities of 5×10 14 Wcm −2 . Plasma conditions in the corona and scattered light are measured experimentally and compared against predictions from two-dimensional (2D) radiation-hydrodynamic simulations using different heat transport models. Spectroscopic analysis of x-ray self-emission is used as an additional diagnostic. X-ray emission is integrated over a large region of the plasma, probing regions that are not observed by localized optical Thomson scattering. In particular, x-ray emission peaks near the plasma critical density, so emission from optically thin lines provides information on plasma conditions where nonlocal transport is most likely to be significant. Three common heat transport models are considered: local transport with flux limiters f = 0.15 and f = 0.03, and the nonlocal Schurtz–Nicolai–Busquet (SNB) model. Consistent with previous work, both the high-flux (f = 0.15) and SNB models show good agreement with experimentally measured plasma conditions in the corona despite overpredicting laser absorption, whereas the low-flux (f = 0.03) model fails to match any experimental data. Conditions inferred from x-ray self-emission line ratios support this conclusion during the period of laser peak power, although synthetic spectra for all models fail to match the experiment during the transient portions of the pulse. For these reasons, the low-flux model is again rejected.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1992

Tunable Electro-optic modulators for lidar systems and atmospheric applications

In global sensing applications using different types of lidars, the spectral range and fine frequency coverages are often limited because of the finite tunabilities of molecular lasers and the number of molecular species that are available. To overcome the above obstacle, we have proposed new broadband frequency tunable electro-optic (EO) modulators that can cover a wide range from the mid-infrared to the visible as lidar sources in atmospheric sensing applications such as high resolution atmospheric molecular spectroscopy, Differential Absorption Lidar (DIAL), and laser radar imaging. The configuration of the proposed new tunable EO modulators includes an electro-optic active crystal element surrounded by a ferrite tuning element which is placed inside a microwave waveguide. The tuning is provided by an external magnetic field, which is either longitudinal or transverse, and the modulator can be either single sideband type or a double sideband type depending on the application required for the spectral purity of the modulator output.

Eng, R. S.↗

DOE OSTI2022

Implementation of a portable diagnostic system for Thomson scattering measurements on an electrothermal arc source

To fulfill the increasing needs of diagnostic support for researchers in plasma technology, a portable diagnostic package (PDP) equipped for both laser Thomson scattering (TS) and optical emission spectroscopy has been designed and constructed at Oak Ridge National Laboratory (ORNL), aiming to measure the temperature and number density of electrons and temperatures of ions in plasma devices. The PDP has been initially implemented on a high density and low temperature electrothermal arc source (ET-arc) at ORNL to test its TS capability. TS from the plasmas in the ET-arc has been obtained using the PDP. The electron temperature and number density were determined from TS spectra. These results were then compared to measurements from previous studies on the ET-arc. The TS diagnostic measured 0.8 ± 0.1, 1.3 ± 0.2, and 0.7 ± 0.1 eV and (4.4 ± 0.5) × 1021, (5.9 ± 0.7) × 1021, and (4.3 ± 0.5) x 1021 m-3, respectively, from three lines of sight that transect the plasma column.

He, Z. (ORCID:0000000183159882)↗

DOE OSTI2021

Real-space Green's function approach for x-ray spectra at high temperature

There has been considerable interest in properties of condensed matter at high temperature, including nonequilibrium behavior and extreme conditions up to the warm dense matter regime. Such behavior is encountered, e.g., in experimental time-resolved x-ray absorption spectroscopy in the presence of intense laser fields. In an effort to simulate such behavior, we present an approach for calculations of high-temperature x-ray absorption spectra in arbitrary materials, using a generalization of the real-space Green's function formalism. Here, the method is incorporated as an option in the core-level x-ray spectroscopy code FEFF10. To illustrate the approach, we present calculations for several materials together with comparisons to experiment and with other methods.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Characterizing laser preheat for laser-driven magnetized liner inertial fusion using soft x-ray emission

Laser heating of a gas in a cylindrical liner held in by a thin foil window is a critical process in the MagLIF (magnetized liner inertial fusion) concept. Window burn-through and gas heating for OMEGA scale MagLIF cylinders as a function of time have been determined using spectrally integrated soft x-ray diagnostics. Window laser absorption is classified in terms of the emitted x-rays from the window plasma as a function of laser energy, and shows that laser energy absorbed is weakly dependent on incident intensity. Radiation-hydrodynamic simulations overestimate the amount of laser energy absorbed by the window as evidenced by the increase in x-ray radiation across several photon energy bands compared to experiments. Gas temperatures inferred from soft x-ray emission from the front 1 mm of the liner are shown to evolve in time in a similar manner to simulation predictions. In conclusion, soft x-ray emission from the gas within the region of the liner that is normally imploded is shown to meet the 100 eV requirements set by the initial point design for laser-driven MagLIF.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2023

Voltage scanning and technical upgrades at the Collinear Resonance Ionization Spectroscopy experiment

To optimize the performance of the Collinear Resonance Ionization Spectroscopy (CRIS) experiment at CERN-ISOLDE, technical upgrades are continuously introduced, aiming to enhance its sensitivity, precision, stability, and efficiency. Recently, a voltage-scanning setup was developed and commissioned at CRIS, which improved the scanning speed by a factor of three as compared to the current laser-frequency scanning approach. This leads to faster measurements of the hyperfine structure for systems with high yields (more than a few thousand ions per second). Additionally, several beamline sections have been redesigned and manufactured, including a new field-ionization unit, an electrostatic bend with a larger deflection angle, and improved ion optics. The beamline upgrades are expected to yield an improvement of at least a factor of 5 in the signal-to-noise ratio by avoiding the use of high-power lasers (which yield non-resonantly produced ions) and providing time-of-flight separation between the resonant ions and the collisional background.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

NASA NTRS1995

(abstract) Mars Global Surveyor: A Global Mapping Mission

The Mars Global Surveyor Mission will launch a single spacecraft to Mars in November 1996. After arrival at the planet in September 1997 aerobraking will be used to lower the spacecraft into a low, sun-synchronous, polar-mapping orbit over several months. Early in 1998 mapping observations will begin and continue for a Mars year (687 days). Following completion of this first Mars year of mapping the spacecraft will continue to act as a relay orbiter for an additional three Earth years. The five instruments carried involve magnetometry, surface and atmosphere imaging, atmospheric sounding, laser altimetry, gravity and thermal emission spectroscopy. In addition, the spacecraft carries a Mars relay receiver/transmitter which will operate over the entire five year orbital mission ending in January of 2003. The Mars Global Surveyor mission is intended to accomplish a portion of the scientific objectives of the Mars Observer mission which was lost in 1993 three days before entering Mars orbit. The instrumentation to be used for the magnetometers, cameras, laser altimeter, emission spectrometer and radio science are very nearly the same as those carried by Mars Observer. The spacecraft design will be new but will use spare equipment from Mars Observer and has a mass about two and one-half time smaller. All experiments will be controlled remotely from their investigators home installation. The long planned period of observation supports the mission's global and seasonal objectives.

Mars Global Surveyor Mars Observer mapping spectro↗

DOE OSTI2023

Ultrafast x-ray detection of low-spin iron in molten silicate under deep planetary interior conditions

The spin state of Fe can alter the key physical properties of silicate melts, affecting the early differentiation and the dynamic stability of the melts in the deep rocky planets. The low-spin state of Fe can increase the affinity of Fe for the melt over the solid phases and the electrical conductivity of melt at high pressures. However, the spin state of Fe has never been measured in dense silicate melts due to experimental challenges. We report detection of dominantly low-spin Fe in dynamically compressed olivine melt at 150 to 256 gigapascals and 3000 to 6000 kelvin using laser-driven shock wave compression combined with femtosecond x-ray diffraction and x-ray emission spectroscopy using an x-ray free electron laser. The observation of dominantly low-spin Fe supports gravitationally stable melt in the deep mantle and generation of a dynamo from the silicate melt portion of rocky planets.

58 GEOSCIENCES↗

NASA NTRS2009

Tuning a Tetrahertz Wire Laser

Tunable terahertz lasers are desirable in applications in sensing and spectroscopy because many biochemical species have strong spectral fingerprints at terahertz frequencies. Conventionally, the frequency of a laser is tuned in a similar manner to a stringed musical instrument, in which pitch is varied by changing the length of the string (the longitudinal component of the wave vector) and/ or its tension (the refractive index). However, such methods are difficult to implement in terahertz semiconductor lasers because of their poor outcoupling efficiencies. Here, we demonstrate a novel tuning mechanism based on a unique 'wire laser' device for which the transverse dimension w is much much less than lambda. Placing a movable object close to the wire laser manipulates a large fraction of the waveguided mode propagating outside the cavity, thereby tuning its resonant frequency. Continuous single-mode redshift and blueshift tuning is demonstrated for the same device by using either a dielectric or metallic movable object. In combination, this enables a frequency tuning of approximately equal to 137 GHz (3.6%) from a single laser device at approximately equal to 3.8 THz.

Qin, Qi↗

NASA NTRS1994

Differential absorption lidar measurements of atmospheric water vapor using a pseudonoise code modulated AlGaAs laser

Lidar measurements using pseudonoise code modulated AlGaAs lasers are reported. Horizontal path lidar measurements were made at night to terrestrial targets at ranges of 5 and 13 km with 35 mW of average power and integration times of one second. Cloud and aerosol lidar measurements were made to thin cirrus clouds at 13 km altitude with Rayleigh (molecular) backscatter evident up to 9 km. Average transmitter power was 35 mW and measurement integration time was 20 minutes. An AlGaAs laser was used to characterize spectral properties of water vapor absorption lines at 811.617, 816.024, and 815.769 nm in a multipass absorption cell using derivative spectroscopy techniques. Frequency locking of an AlGaAs laser to a water vapor absorption line was achieved with a laser center frequency stability measured to better than one-fifth of the water vapor Doppler linewidth over several minutes. Differential absorption lidar measurements of atmospheric water vapor were made in both integrated path and range-resolved modes using an externally modulated AlGaAs laser. Mean water vapor number density was estimated from both integrated path and range-resolved DIAL measurements and agreed with measured humidity values to within 6.5 percent and 20 percent, respectively. Error sources were identified and their effects on estimates of water vapor number density calculated.

Rall, Jonathan A. R.↗

DOE OSTI2023

Aggregation‐Induced Stimulated Emission of 100% Dye Microspheres

Dyes with aggregation-induced emission (AIE) properties have gained interest due to their bright luminescence in solid-state aggregates. While fluorescence from AIE dyes is widely exploited, relatively little is known about aggregation-induced stimulated emission. Here, stimulated emission of tetraphenylethene (TPE)-based organoboron AIE dyes, TPEQBN, in thin films and in microcavity lasers is investigated. Using femtosecond pump–probe spectroscopy, gain coefficients up to 230 cm -1 at 500 nm are measured. Using rate equations, concentration- and pump-dependent gain dynamics as well as laser build-up dynamics are analyzed. During laser oscillation, radiative stimulated emission allows high instantaneous quantum yield greater than 90% to be achieved. Solid-state microspheres made of 100% AIE dyes are fabricated via microfluidic emulsion and solvent evaporation method. Coupled with high gain and high refractive index of 1.76, microspheres as small as 2 µm in diameter show lasing by nanosecond pumping with a threshold of ≈10 pJ µm –2 . Polymer coated, but not bare, microspheres are internalized by live cells and generate narrowband cavity-mode emission from within the cytoplasm. This work shows the potential of AIE dyes as laser materials.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Non-intrusive measurement of magnetic field strengths in a low-pressure argon plasma using quantum beat spectroscopy

Abstract Accurate measurement of magnetic field strengths is critical in many plasma environments, ranging from astrophysical systems to fusion energy research. In this work, a non-perturbative laser-based optical diagnostic known as quantum beat spectroscopy is demonstrated to be good alternative for measuring the magnetic field strength in low-pressure laboratory plasmas. The technique is investigated using both ns and fs pulsed lasers in an argon plasma. Preliminary results for a helium plasma are also given. Zeeman-split J = 1 electron states with transitions from metastable states were identified and tested for neutral argon ( 2 P 1 / 2 o ) 4 p 2 [ 1 / 2 ] and neutral helium 1 s 3 p 1 P 1 o . Magnetic fields are measured with sub-Gauss precision at near single laser pulse acquisition rates.

Gilbert, Tyler J. (ORCID:0000000160400119)↗