The goal of this study was to characterize optical turbulence in the near-coastal environment. Measurements to obtain the refractive index structure parameter and other meteorological data were taken over the course of a month along the shore of Monterey Bay. The results were compared to a new version of the Navy Vertical Surface Layer Model (NAVSLaM), a model of turbulence originally developed for maritime environments but now extended to terrestrial environments. The new version has not been previously validated by comparisons to experiments, particularly in a complex environment such as near the coastline. Our experimental results showed generally good agreement between measured and modeled levels of turbulence. Specifically, the differences between experimental and modeled values of the refractive index structure parameter were less than an order of magnitude in most conditions and followed the same diurnal trend. There were some greater differences during near-neutral conditions, but this is a known limitation of the model. Overall, this extended model appears to do a good job of predicting turbulence in this environment for the observed time period.

Free electron lasers (FELs) are favored in many research applications due to their ability to operate primarily in the fundamental (Gaussian) mode. In oscillator FELs, the appropriate basis set for decomposition is uniquely determined by the cavity parameters. Since FEL amplifiers generate and amplify the optical field over the length of the undulator influenced only by the electron beam, the appropriate basis set is not uniquely determined. A methodology is presented to decompose the optical fields with a Hermite-Gaussian basis set chosen such that the number of higher-order modes is minimized. The methodology is used to study amplifier FEL optical beams for comparison with experiment. DOI: http://dx.doi.org/10.1103/PhysRevSTAB.13.030702 This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.