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Broadband coherent Rayleigh-Brillouin scattering (CRBS) was used to measure translational gas temperatures for nitrogen at the ambient pressure of 0.8 atm using a purpose-built Fabry-Perot etalon spectrometer. Temperatures derived from the CRBS spectral analysis were compared with experimentally-measured temperatures, and were found to be, on average, within 2% of the experimentally-measured value. Axial flow velocities from a double jet at a pressure ratio of 0.38 were also measured by looking at the Doppler shift of the CRBS line shape. With recent developments in chirped laser technology and the capacity of CRBS to simultaneously provide thermodynamic and bulk flow information, the CRBS line shape acquisition and analysis technique presented here may allow for future time-resolved, characterization of aerospace flows. [ABSTRACT FROM AUTHOR]

With a focus on optical lattice gas heating, direct simulation Monte Carlo was used to investigate the interaction between molecular nitrogen, argon and methane, initially at 300 K and 0.8 atm, with pulsed, chirped optical lattices. Created from two 700 mJ, 532 nm, flattop laser pulses, the optical lattice parameters simulated are based on published optical lattice-based experiments, to ensure that pulse energies and durations do not exceed published optical breakdown (ionization) thresholds. Resultant translational gas temperatures, as well as induced bulk velocities, were used quantify energy and momentum deposition. To maximize available gas temperature changes achieved using the technique, laser pulses were linearly chirped to produce lattice velocities able to more effectively facilitate energy deposition throughout the pulse duration. From the initial conditions, the maximum, end pulse axial translational temperature obtained in nitrogen was approximately 755 K, at a lattice velocity of 400 m/s linearly chirped at 25 Gm/s² over the 40 ns pulse duration. To date, this stands as the single largest, numerically-predicted temperature change from optical lattice gas heating under the numerical integration of real world energy and laser-based limitations. [ABSTRACT FROM AUTHOR]

With a focus on optical lattice gas heating, direct simulation Monte Carlo was used to investigate the interaction between molecular nitrogen, initially at 300 K and 0.8 atm, and ten successive, pulsed optical lattices in the presence of two multipass cavity concepts. Created from two 5 ns, 130 mJ, 532 nm laser pulses, the optical lattice parameters simulated were chosen based on published optical lattice-based experiments. Similarly, the cavity concepts used were simulated with optical energy losses comparable to that observed experimentally. Translational gas temperatures were sampled on every cavity round trip and found to facilitate several hundred Kelvin increases in some cases. Importantly, these simulation results suggest that while optical energy losses significantly limit attainable gas temperatures in the context of multipass optical cavities, net momentum deposition into the gas profoundly impacts the energy deposition potential and gas temperature changes achievable through optical lattice gas heating. [ABSTRACT FROM AUTHOR]

The DSMC method was used to investigate the interaction between a test gas and ten successive, pulsed, optical lattices. The one-dimensional lattices were formed by two 100 ps, 393 mJ, 532 nm, simulated laser pulses and assumed to be far from resonance. The maximum centerline temperature was simulated as a function of the intervening time between pulses. An optimum intervening time was found and related to the mean collision time and available energy modes. Subsequent pulses can act to cool the gas for intervening times near zero. For long intervening times, thermal diffusion carries energy away from the centerline, reducing the maximum temperature. At one atmosphere the optimal intervening time was found to be 0.7, 1.0 and 0.25 ns for argon, nitrogen, and methane respectively. The highest temperature simulated for nitrogen was 2480 K after 50 pulses with an optimal intervening time. The combination of small intervening time and high intensity requires the use of an optical cavity for successive laser pulses as commercially available high repetition rate lasers have neither the repetition rate nor the energy per pulse. [ABSTRACT FROM AUTHOR]