[Goptical] focal spot size

[Gregory Vieux]

Hi,

I am wondering if there is a way, using spot analysis, to get the focal 
spot size as defined for a Gaussian beam.
My system is defined by a point source at infinity, a 3 mm radius 
aperture and a f=250 mm plano-convex lens. When using get_max_radius() 
or get_rms_radius() I obtain results of the order of 3 um, which is not 
possible considering Gaussian optics.
Moreover, when reducing the aperture size, the focal spot size is 
decreasing when it should be increasing.
I am wondering if the problem is coming from defining the source as a 
point source.

Any advice is welcome.

Thanks,

Gregory Vieux