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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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Raman Backscatter as a Remote Laser Power Sensor in High-Energy-Density Plasmas [Stimulated Scattering as a Remote Laser Power Sensor in High-Density and Temperature Plasmas]

Stimulated Raman backscatter is used as a remote sensor to quantify the instantaneous laser power after transfer from outer to inner cones that cross in a National Ignition Facility (NIF) gas-filled hohlraum plasma. By matching stimulated Raman backscatter between a shot reducing outer versus a shot reducing inner power we infer that about half of the incident outer-cone power is transferred to inner cones, for the specific time and wavelength configuration studied. Furthermore, this is the first instantaneous nondisruptive measure of power transfer in an indirect drive NIF experiment using optical measurements.

42 ENGINEERING↗
DOE OSTI2014

Time-dependent wave front propagation simulation of a hard x-ray split-and-delay unit: Towards a measurement of the temporal coherence properties of x-ray free electron lasers

For the European x-ray free electron laser (XFEL) a split-and-delay unit based on geometrical wavefront beam splitting and multilayer mirrors is built which covers the range of photon energies from 5 keV up to 20 keV. Maximum delays between Δτ = ±2.5 ps at hν=20 keV and up to Δτ = ±23 ps at hν = 5 keV will be possible. Time-dependent wave-optics simulations have been performed by means of Synchrotron Radiation Workshop software for XFEL pulses at hν = 5 keV. The XFEL radiation was simulated using results of time-dependent simulations applying the self-amplified spontaneous emission code FAST. Main features of the optical layout, including diffraction on the beam splitter edge and optics imperfections measured with a nanometer optic component measuring machine slope measuring profiler, were taken into account. The impact of these effects on the characterization of the temporal properties of XFEL pulses is analyzed. An approach based on fast Fourier transformation allows for the evaluation of the temporal coherence despite large wavefront distortions caused by the optics imperfections. In this manner, the fringes resulting from time-dependent two-beam interference can be filtered and evaluated yielding a coherence time of τ c = 0.187 fs (HWHM) for real, nonperfect mirrors, while for ideal mirrors a coherence time of τ c = 0.191 fs (HWHM) is expected.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Method for computationally efficient design of dielectric laser accelerator structures

Here, dielectric microstructures have generated much interest in recent years as a means of accelerating charged particles when powered by solid state lasers. The acceleration gradient (or particle energy gain per unit length) is an important figure of merit. To design structures with high acceleration gradients, we explore the adjoint variable method, a highly efficient technique used to compute the sensitivity of an objective with respect to a large number of parameters. With this formalism, the sensitivity of the acceleration gradient of a dielectric structure with respect to its entire spatial permittivity distribution is calculated by the use of only two full-field electromagnetic simulations, the original and ‘adjoint’. The adjoint simulation corresponds physically to the reciprocal situation of a point charge moving through the accelerator gap and radiating. Using this formalism, we perform numerical optimizations aimed at maximizing acceleration gradients, which generate fabricable structures of greatly improved performance in comparison to previously examined geometries.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

Widely tunable 11 GHz femtosecond fiber laser based on a nonmode-locked source [Widely tunable 11 GHz femtosecond fiber laser based on a non-modelocked source]

An 11 GHz fiber laser built on a modulated CW platform is described and characterized. This compact, vibrationinsensitive, fiber based system can be operated at wavelengths compatible with high energy fiber technology, is driven by an RF signal directly, and is tunable over a wide range of drive frequencies. The demonstration system when operated at 1040 nm is capable of 50 ns bursts of 575 micro-pulses produced at a macro-pulse rate of 83 kHz where the macro-pulse and micro-pulse energies are 1.8 μJ and 3.2 nJ respectively. Micro-pulse durations of 850 fs are demonstrated. Finally, we discuss extensions to shorter duration.

42 ENGINEERING↗
DOE OSTI2020

Long-wavelength-infrared laser filamentation in solids in the near-single-cycle regime

We experimentally demonstrate long-wavelength-infrared (LWIR) femtosecond filamentation in solids. Systematic investigations of supercontinuum (SC) generation and self-compression of the LWIR pulses assisted by laser filamentation are performed in bulk KrS-5 and ZnSe, pumped by ∼ <#comment/> 145 f s , 9 µm, 10 µJ pulses from an optical parametric chirped-pulse amplifier operating at 10 kHz of repetition rate. Multi-octave SC spectra are demonstrated in both materials. While forming stable single filament, 1.5 cycle LWIR pulses with 4.5 µJ output pulse energy are produced via soliton-like self-compression in a 5 mm thick KrS-5. The experimental results quantitatively agree well with the numerical simulation based on the unidirectional pulse propagation equation. This work shows the experimental feasibility of high-energy, near-single-cycle LWIR light bullet generation in solids.

Qu, Shizhen↗
DOE OSTI2018

Real-time standoff detection of nitrogen isotopes in ammonia plumes using a swept external cavity quantum cascade laser

A swept-wavelength external cavity quantum cascade laser is used to measure time-resolved 15NH3 and 14NH3 concentrations and isotope ratios in a turbulent plume source located at 10 m standoff distance. Measurements show excellent agreement with expected values of isotope ratios for samples with natural and enriched 15N abundance. Detection sensitivity of 150 ppb*m is demonstrated for a 50 ms measurement interval, improving to 10 ppb*m with 10 s averaging, with isotopic precision as good as 0.8%.

Phillips, Mark C.↗
DOE OSTI2015

High-resolution single-shot spectral monitoring of hard x-ray free-electron laser radiation

We have developed an on-line spectrometer for hard x-ray free-electron laser (XFEL) radiation based on a nanostructured diamond diffraction grating and a bent crystal analyzer. Our method provides high spectral resolution, interferes negligibly with the XFEL beam, and can withstand the intense hard x-ray pulses at high repetition rates of >100 Hz. The spectrometer is capable of providing shot-to-shot spectral information for the normalization of data obtained in scientific experiments and optimization of the accelerator operation parameters. We have demonstrated these capabilities of the setup at the Linac Coherent Light Source, in self-amplified spontaneous emission mode at full energy of >1 mJ with a 120 Hz repetition rate, obtaining a resolving power of Ε/δΕ > 3 × 10 4 . In conclusion, the device was also used to monitor the effects of pulse duration down to 8 fs by analysis of the spectral spike width.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Structure property relationships in gallium oxide thin films grown by pulsed laser deposition [Structure property relationships in Ga 2 O 3 thin films grown by pulsed laser deposition]

Beta-gallium oxide (β-Ga 2 O 3 ) is of increasing interest to the optoelectronic community for transparent conductor and power electronic applications. Considerable variability exists in the literature on the growth and doping of Ga 2 O 3 films, especially as a function of growth approach, temperature, and oxygen partial pressure. Here pulsed laser deposition (PLD) was used to grow high-quality β-Ga 2 O 3 films on (0001) sapphire and (–201) Ga 2 O 3 single crystals and to explore the growth, stability, and dopability of these films as function of temperature and oxygen partial pressure. As a result, there is a strong temperature dependence to the phase formation, morphology, and electronic properties of β-Ga 2 O 3 from 350 to 550 °C.

14 SOLAR ENERGY↗
DOE OSTI2015

Laser Beam Failure Mode Effects and Analysis (FMEA) of the Solid State Heat Capacity Laser (SSHCL)

A laser beam related FMEA of the SSHCL was performed to determine potential personnel and equipment safety issues. As part of the FMEA, a request was made to test a sample of the drywall material used for walls in the room for burn-through. This material was tested with a full power beam for five seconds. The surface paper material burned off and the inner calcium carbonate turned from white to brown. The result of the test is shown in the photo below.

42 ENGINEERING↗
DOE OSTI2017

The Super Gaussian Laser Intensity Profile in HYDRA's 3D Laser Ray Trace Package

In this note, the laser focal plane intensity pro le for a beam modeled using the 3D ray trace package in HYDRA is determined. First, the analytical model is developed followed by a practical numerical model for evaluating the resulting computationally intensive normalization factor for all possible input parameters.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2015

Development of a Laser-Electron-Interaction Region for Compact High Repetition-Rate Mono-Energetic Laser Based Gamma Sources

Inverse-Compton scattering (ICS) is a well-established technique capable of producing monochromatic radiation over a large range of the electromagnetic spectrum. Most recently, ICS has attracted attention, owing to its compactness and possible coupling with novel acceleration methods to yield compact X- and 𝛄-ray sources. Under this award, we carried out a systematic optimization of the ICS and demonstrate via numerical simulation that combining ICS with a conventional superconducting linac could produce Watt-level average-power 𝛄 rays with high spectral brightness. The study is performed with idealized laser and electron-beam distributions and confirmed with the realistic distributions simulated from start-to-end numerical modeling of the electron accelerator. The studies led to the design and engineering design of an ICS interaction point for the FAST facility along with some beam measurement. Due to the cancellation of the program in Year 3 long with delay in the commissioning of the FAST facility, we were not able to demonstrate the generation of 𝛄 rays, we, however, procured some of the hardware, installed some of the required infrastructures and plan to eventually generate 𝛄 ray pending future interest on the topics and availability of funding.

43 PARTICLE ACCELERATORS↗