Both cylindrical lenses are placed at the focal distance from the laser head and neck, that is, X=F, ω0' reaches the maximum ω 0' = λ/(π ω 0) * f, so that θ0' reaches the minimum value, and the laser beam is collimated into parallel light and the spot is shaped into a circle.

These are the original words in the "Optical Experiment Guide"

Although it was a long time ago, by the way, is LZ a student of HKUST?