Intensity Spatial Profile Analysis of a Gaussian Laser Beam at Its Waist Using an Optical Fiber System

In many applications, it is important to know the waist of a laser beam. However, it is impossible to measure it directly because the intensity is high at the waist. We have used an optical fiber-scan system to characterize the Gaussian intensity profile of a focused femtosecond laser beam. The measurement system employs a single-mode optical fiber that is fixed on a motorized three-dimensional translation stage to collect the laser energy and the other end is connected to an optical power meter to measure the intensity profile. Using the measure data and geometry formulas, one can calculate the beam waist and far-field divergence angle of a laser beam. The measured beam waist size is essentially consistent with the result of theoretical fit.