Narrowband coherent Rayleigh-Brillouin scattering from gases confined by a high-intensity optical lattice

Abstract

Molecular nitrogen at 0.8 atm and 300/500 K and methane at 0.8 atm and 300 K were subjected to optical lattices formed by narrowband, 532 nm, laser pulses with intensities on the optical axis near, but below, the gas ionization limit. A third pulse was introduced to experimentally probe the response, as a function of the lattice velocity, of the gas to the deep monochromatic potential wells formed by the lasers. Coherent Rayleigh-Brillouin scattering (CRBS) line shapes were recorded and compared to numerically predicted magnitudes of the density perturbations induced in the gas. Both experimental results and those from direct simulation Monte-Carlo simulations show deviation from previously published low intensity CRBS line shape models. The deviation indicates a similar trend, as a function of lattice velocity, as that relating to previously published energy and momentum transfer calculations for high intensity lattices. Furthermore, the deviation indicates a maximum intensity at which current CRBS theory is valid.

Numerical Analysis of Ion-Funnel Transmission Efficiency in an API-MS System with a Continuum/Microscopic Approach

“…The axially symmetric parallel capability of SMILE was used. In the past, SMILE has been extensively used to solve the Boltzmann equation, with and without the force term, and validated in a number of multidimensional problems [34][35][36]. The majorant frequency scheme [37] was used to calculate intermolecular interactions.…”

Optical lattice gas heating simulation under application of intrapulse frequency chirping

“…demonstrated high fidelity in modeling the impact of non-resonant laser interference patterns on gases [5,20,[24][25][26]. Modified to include the non-resonant, optical lattice gas interaction described above, the code approximates the force on a particle by a temporally and spatially varying acceleration, which was considered constant over the duration of a simulation time step.…”

“…It should be noted that a similar chirped laser system has been successfully used in the chirped lattice gas acceleration studies of Maher-McWilliams et al [30]. These laser parameters were chosen to be in a regime below the optical breakdown threshold [17,31,32], and excepting gas-dependent pulse duration and the temporal flattop profile of the pulse, correspond to similar experimental conditions to those found in [5,20,26,33]. While the laser upon which these simulations are based specifies chirp excursions in excess of 10 GHz/µs, the maximum chirp rates and frequency shift limits for single-mode behavior are largely dictated by the design and cavity size of the master microchip and amplifier lasers.…”

Neutral gas heating via non-resonant optical lattices

“…The optical lattice heating technique was first treated theoretically 16 and subsequently studied using detailed gas kinetic simulations. [17][18][19] Precursory experiments have explored the effect of light scattering by neutral gases perturbed by optical lattices at lower optical intensities 20,21 and those near breakdown; 22 however, this study offers experimental proof-of-principle for the non-resonant deposition of energy from a pulsed optical lattice to neutral gases. From this proof, future experimentation may be conducted for the optimization of the technique and its eventual use in other research applications.…”

“…The numerical study utilized the direct simulation Monte Carlo (DSMC) code SMILE which has been previously applied and experimentally validated for optical lattice-gas interactions. [20][21][22] Applying a relatively high intensity pulsed optical lattice to a continuum gas relies on the use of the induced dipole force as a mechanism for depositing energy directly into the translational mode of the gas along the laser axis, which in turn is redistributed through collisions. 4,5 For a pair of idealized anti-parallel, coherent, collimated laser pulses, tuned to a frequency lower than the particle's resonant frequency, the force acting on a particle within the potential region, along the laser axis is given by…”