Since the laser, which is currently used for the JASMINE scatterometer, features a far too high spreading of its width, I installed a lens to refocus the beam toward the sample.
This focussing had to be measured and compared with the theoretical development of the width (the beam should be Gaussian).

The result is satisfying as the theoretical curves mach the measured values within averaged errors of less than 5%.
It should be noted that the beam has two different width distrubutions, perpendicular to each other, which I denominate X and Y.

In the attached figure the development along a lenght-axis (the way of the laser) is shown with indicated positions of the laser, a mirror (this is the point zero, for practical reasons), and the used lens (f=200mm).
On the left side of the lens, the measured values of the laser widths as the laser produces them are shown (dots). They were fitted with the respective Gaussian beam development w(z) (lines).
On the right side of the lens, the measured values of the focussed laser widths are shown (again in dots), together with the theoretical development (lines), calculated out of the parameters as given by the fits of the left-side beams.

For the scatterometer itself, the sample is located approximately 27 - 28 cm away from the lens. The width should, thus, be in the range of 0.13 - 0.17 mm.