I used a 200um-diam pinhole to set the position of the crosspoint between the pump and the HeNe probe ().
First I checked the position of the pump waist, by looking for the position of the maximum transmitted power through the pinhole. I found 185mW/206mW at 11.9cm +/- 0.5cm (14cm from the board) which is consistent with the previous measurement with the beam profiler and fit.
Then, using a crosshair, with the help of Matteo, I aligned the HeNe laser to be at 0.1rad (5.7deg) with the pump beam and passing through the crosspoint at 14cm from the board.
I mounted the pinhole to the 2inches mount using the 1inch-to-2inch adaptor. I centered the pinhole at the crosspoint and checked the absolute position in microsteps (1mm = 8063steps):
@1-axis 2641973
@2-axis 279284
@3-axis 981325
Then I made a fine adjustment of the probe position to maximize the transmission through the pinhole.
I measured the beam profile of the HeNe laser without focusing lenses and with a f=150mm lens. See plot. The waist of the probe should be at the cross point (14cm from the board). There are two ways to move the probe waist: or move the lens, or change the lens focal length.
I calculated with Jammt the best position and focal length in order to have a probe waist of 180um at the cross point. So I replaced the lens with a f=300mm lens and measured again the profile. Then I plot the pump and probe profiles together. The waists positions are aligned well, within 1cm to the crosspoint. Next step is to align the imaging unit and maximize the absorption signal of a reference sample adjusting the pump position.
I had to adjust a bit the position of some parts of the translation stage, sothe new pin-hole position at the cross point is
@01-axis: 2646049 2646049
@02-axis: 279284 279284