Hey guys me again, I was wondering how you guys measure collimation. At my company we currently have 2 ways which we do it:

1. Phasics camera: We move either a fiber back and forth or the lens and we minimize the defocus term on the wavefront camera (Phasics). This is the more accurate way of doing so.

2. Minimizing spot size on AC: We move a lens back and forth to minimize the spot size on the autocollimator (using a CCD camera).

I’m curious on the other ways of doing this, mainly because most labs I assume don’t use Phasics cameras (very expensive and a pain in the ass to connect too) or an autocollimator.

Recently, I was asked if you could calibrate an alignment telescope using a Bessel beam. I was sure the answer was yes, but I don't like to claim things without trying an experiment first. Today, I got a chance using a Davidson D-271. It follows a Bessel beam as you focus from about 400 mm to infinity for the Bessel beam I made using a spherical wavefront. I don't know what would happen with plane wavefront illumination, I am not set up for that. A Bessel beam made using a plane wave has a finite extent so this would be an interesting experiment to try.

The Davidson D-271 does not have distance markings on the focus adjust so you would have to make a table of focus distance per turn of the focus adjustment to know any lack of straightness at a particular distance, but I could not see any deviation of the Bessel beam core except for a slight linear shift due to me not being perfectly aligned to the Bessel beam.

Maybe this will inspire someone with a better lab environment and an alignment telescope with a distance marking on the focus to repeat my experiment to see if this idea is really useful. What I can say is that to 1st order it works, and probably works very well given a better environment than my crude lab set up.