Measurement of beam waist of the long focal laser system

A new application of Hartmann-Shack sensor is introduced to measure the beam waist from the information of measured intensity and phase profile of wavefront. The result is achieved by Fresnel-Kirchhoff diffraction theory with proper numerical approximate algorithm. In this paper, the algorithm is applying to the circumstance of long distance propagation. For this specialty, a simulation process in the case of a Gaussian distributed beam and a thin lens of focal length 100m is presented. And the results show the possibility of this method and the degree the result is affected because of the inevitable error introduced in the measurement.