Enhanced, fast-running scaling law model of thermal blooming and turbulence effects on high energy laser propagation

Noah R. Van Zandt,Steven T. Fiorino,Kevin J. Keefer

doi:10.1364/oe.21.014789

Abstract

A new scaling law model is presented to rapidly simulate thermal blooming and turbulence effects on high energy laser propagation, producing results approaching the quality normally only available using wave-optics code, but at much faster speed. The model convolves irradiance patterns originating from two distinct scaling law models, one with a proficiency in thermal blooming effects and the other in turbulence. To underscore the power of the new model, results are verified for typical, realistic scenarios by direct comparison with wave optics simulation.

Highlights

The Directed Energy (DE) community has come to rely on fast-running scaling law codes to efficiently model high energy laser (HEL) propagation and beam control performance and to provide a first-order, broad-ranging assessment of a laser system and its concept of employment [1,2,3,4]
Simple thermal blooming metrics such as distortion number and critical power have not shown direct correlation with wave optics irradiance patterns [5,6]. For these reasons and to enhance their utility, we explored the possibility of convolving the far-field irradiance patterns from optimized scaling-law models—each delivering outcomes comparable to wave optics simulation in certain regimes—retaining the advantage of speed while providing higher quality laser performance simulation
We have noted HELEEOS – Adaptive Optical Compensation of Thermal Blooming (AOTB) was relatively more pessimistic for S2S PIB calculations. Though this partly may be due to the HELEEOS – AOTB convolution step’s inherent inability to fully treat the concurrent interaction of turbulence-induced beam spread and heating effects giving rise to thermal blooming, we attribute this to the underlying AOTB scaling law, which tends to become more conservative as thermal blooming increases [13]

Summary

Introduction

The Directed Energy (DE) community has come to rely on fast-running scaling law codes to efficiently model high energy laser (HEL) propagation and beam control performance and to provide a first-order, broad-ranging assessment of a laser system and its concept of employment [1,2,3,4]. Simple thermal blooming metrics such as distortion number and critical power have not shown direct correlation with wave optics irradiance patterns [5,6]. For these reasons and to enhance their utility, we explored the possibility of convolving the far-field irradiance patterns from optimized scaling-law models—each delivering outcomes comparable to wave optics simulation in certain regimes—retaining the advantage of speed while providing higher quality laser performance simulation. In this paper we describe our new, fast-calculating HEL scaling law model and its ability to capture the shape and displacement of a thermally-bloomed far-field irradiance pattern in the presence of turbulence. We applied the model to multiple scenarios, simulating both horizontal and oblique realistic engagement geometries

Approach: update existing end-to-end scaling law simulation using convolution

Verification using multiple laser engagement scenarios

Findings

Conclusion