Accuracy of laser beam parameters and beam propagation from real-time Hartmann-Shack experiments

Abstract

Experiments in laser physics often require more comprehensive information about a beam than can be extracted from single spatial profile measurements alone. In particular, the determination of irradiance and phase distribution at locations were measurement is difficult as well as the accurate measurement of important 2^nd order moment based beam parameters, as e.g. M², divergence or Strehl-ratio, are quite often essential for a wide class of laser applications. Here we compare Hartmann-Shack results of numerical beam propagation and parameter estimation to camera based profile measurements and the standard ISO 11146 procedure, respectively. He-Ne fundamental mode beams (with and without aberration) were investigated. For spatially coherent, high to moderate quality beams (M²<2) the numerically propagated and measured beam profiles are in good agreement and 2^nd order moment beam parameters differ by less than 5% for the standard method and Hartmann-Shack. Partial coherent beams on the other hand require information beyond Hartmann-Shack. Drawbacks and opportunities of the Hartmann-Shack technique for means of laser beam parameters are discussed.