This program is used to calculate the waist of a Gaussian laser beam behind the lens.

We can get all the information of a Gaussian beam with a certain frequency, if we know its waist radius and waist position. The beam paramters changes after each lens. This program can greatly simplify the calculation of the waist parameter after some lens. It will be very useful when we need to set a beam waist with a certain radius at a certain position. Such as coupling a laser mode to a cacity/fiber mode, or realizing a certain waist radius at the sample position.