Hello everyone. I am currently working with an input collimated gaussian laser beam of 0.8mm width, which propagates through several lenses and focuses at a distance of 30mm from the last surface of the lens. My objective is to measure the spot size and rayleigh length of my Gaussian beam at an off-axis position. I attempted to use POP (Physical Optics Propagation) for this purpose, but unfortunately, the results did not align as expected.

Could anyone offer assistance in identifying the underlying issue?

Thank you in advance.