New method to characterize Gaussian beams

In this work we propose a method to characterize a laser beam based on the Gaussian beam propagation through a lens with a simple experimental setup that can accurately measure the magnitude and location of the beam waist. The experimental setup involves a lens and a chopper located on a mechanical mount separated by a distance equal to the focal length of the lens. To characterize the laser the setup is moved away parallel to the axis of the beam beginning at a distance shorter than the focal length. A photodetector behind the chopper measure the periodic transmitted intensity and an electrical circuit generates a square wave whose pulse width is proportional to the beam width at the location of the chopper. The position of the chopper where the beam width is minimum allow us to calculate the location of the waist, we just need to make a final measurement of the beam width without the lens to find the magnitude of the waist. All the measurements are fast and only few are needed to determine accurately the position and magnitude of the beam waist.