I did some check based on fiber equations that you can find on Thorlabs or Newport.

The fiber to the SHG is PM980 (polarization maintaining 980nm in-fiber wavelength) with a mode field diameter 6.6 um. This gives f/D = pi*MFD/(4 lambda) = 4.8. Thorlabs FC/ACP connector fiber collimators are sold with f = 2.0, 4.6, 7.5, 11.0, 15.3, 18.4mm focal lengths, giving input beam diameters D = 0.41, 0.94, 1.53, 2.26, 3.14, 3.8 mm. The clear apertures are 2.0, 4.9, 4.5, 4.4, 5.0, 5.5 mm. In retrospect, maybe I should have picked the f = 4.6mm. But it's maybe not super important. exp(-2*(r/w0)^2) = 0.00051 (510 ppm diffraction loss) for the current coupler. r > 2.7 w0 gives < 1 ppm diffraction loss.