Hello,

I want to design a Gaussian beam (laser, coherent source) with a divergence angle of 0.3 mrad, i.e. 0.3 mm (FWHM) at the 1 meter point.

w0(1/e^2) = 0.8493218 x FWHM

When using the above formula, the beam size (1/e^2) at the 1M point was calculated to be approximately 0.510mm.
Using this value and the wavelength of 13.5nm, the Gaussian source's beam size and position were calculated and entered.

However, when I place the detector at the 1M point, change the Detector viewer's Data from incoherent irradiance to coherent irradiance, and use the FWHM macro, it appears to have 0.22mm.

I used the FWHM macro below.

ZPL Operand: Extract FWHM from non-sequential detector | Zemax Community

which part of my method is wrong?

If possible, can you share the files you designed?