Modeling the effects of high-energy-laser beam quality using scalar Schell-model sources

Abstract

At the system level, poor beam quality often leads to significant performance degradations. For instance, if a high-energy laser (HEL) source has poor beam quality, then the effectiveness of a beam-control system becomes compromised. This outcome is the result of non-common path phase errors in the HEL beam that are not sensed by the beam-control system. Therefore, phase-compensation performance becomes degraded, because if the phase errors that degrade performance cannot be sensed, then their effects cannot be corrected. To help quantity these system-level performance degradations, we need a reliable and accurate way to model the effects of poor beam quality. As such, this paper develops a statistical approach using scalar Schell-model sources. Applying the work of Santarsiero et al. [J. Opt. Soc. Am. A 16, 106 (1999)], we show that we can quantify the effects of poor beam quality statistically in terms of the M2 parameter. Then, we develop Monte Carlo wave-optics simulations which specify the field correlation coefficient in terms of M2 for modeling HEL phase errors. The results show that we obtain convergence to the desired M2 parameter thus properly modeling the phase errors. In addition, we investigate the statistics of the M2 parameter. We find, quite interestingly, that the instantaneous M2 is very nearly lognormal. This information will be useful in HEL beam-control system design.