Wave-optics investigation of turbulence thermal blooming interaction: II. Using time-dependent simulations

Abstract

Part II of this two-part paper uses wave-optics simulations to look at the Monte Carlo averages associated with turbulence and time-dependent thermal blooming (TDTB). The goal is to investigate turbulence thermal blooming interaction (TTBI). At wavelengths near 1 μm, TTBI increases the amount of constructive and destructive interference (i.e., scintillation) that results from high-power laser beam propagation through distributed-volume atmospheric aberrations. As a result, we use the spherical-wave Rytov number, the number of wind-clearing periods, and the distortion number to gauge the strength of the simulated turbulence and TDTB. These parameters simply greatly given propagation paths with constant atmospheric conditions. In addition, we use the log-amplitude variance and the branch-point density to quantify the effects of TTBI. These metrics result from a point-source beacon being backpropagated from the target plane to the source plane through the simulated turbulence and TDTB. Overall, the results show that the log-amplitude variance and branch-point density increase significantly due to TTBI. This outcome poses a major problem for beam-control systems that perform phase compensation. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Wave-optics investigation of branch-point density

“…53 This toolbox uses the split-step beam propagation method (BPM) to simulate the propagation of monochromatic and polychromatic light through the atmosphere. [15][16][17][18][19][20][21][22] In practice, the split-step BPM divides the atmosphere into independent volumes, such that a phase screen represents the atmospheric aberrations present in a volume. Angular-spectrum propagation to each phase screen (from the source plane to the pupil plane) then represents the propagation of light through the atmosphere.…”

“…), which typically require the use of high-fidelity and wave-optics simulations. [15][16][17][18][19][20][21][22] For example, Voitsekhovich et al 23 were the first to perform a wave-optics investigation of branch-point density (i.e., the number of branch points within the pupil-phase function). They did so as a function of propagation distance with the effect of a finite inner scale but for a fixed grid sampling.…”

Branch-point detection using a Shack-Hartmann wavefront sensor

“…3,4 The work of Fried and Vaughn first investigated the problem of branch-point formation caused by propagation through distributed-volume turbulence. 5 After which, researchers began investigating 1) the impact that branch-point formation has on laser-propagation systems [6][7][8][9][10][11][12][13][14] and 2) the physical insight that can be gleaned about the atmospheric turbulence environment through which the beam propagated. 3,4,[15][16][17][18][19][20][21][22][23][24][25][26] These motivations make it advantageous to develop approaches which easily and robustly identify branch points from optical-turbulence measurements.…”

Comparison of branch-point detection approaches using a Shack–Hartmann wavefront sensor

“…Furthermore, these branch points form in pairs of opposite helicity with an associated branch cut connecting them 3 , 4 . The work of Fried and Vaughn first investigated the problem of branch-point formation caused by propagation through distributed-volume turbulence, 5 after which researchers began investigating (1) the impact that branch-point formation has on laser-propagation systems 6 – 14 and (2) the physical insight that can be gleaned about the atmospheric turbulence environment through which the beam propagated 3 , 4 , 15 – 26 These motivations make it advantageous to develop approaches that easily and robustly identify branch points from optical-turbulence measurements.…”