I checked some optics in the ATC cleanroom to prepare for the construction of the new OPO.

We can use the Faraday isolator Thorlabs IO-5-1064-VLP - aperture 5mm diameter, 9cm length, maximum power 1.7 W, 25 W/cm^2 (blocking), 100 W/cm^2 (transmission).

Using an f = 100 mm lens placed as shown in figure 1, we can maintain the beam waist below 1mm diameter over a distance of [distance] from the 100mm lens, so it is sufficient to use for the FI.

I did a rough estimate (figure 2) and measurement (figure 3) of the beam size to make sure. We can maintain < 1mm beam diameter to about 35cm from where I placed the lens.