I made a scan of the calibration sample with the 1310nm. Attached first screenshot. AC=0.115V; DC=2.14; phase=-85; power=34mW -> R=7.9W^-1.

Then I set the power at 10W and made a scan of the crystalline coating in the center, with and without loop. The loop doesn't make a lot of difference.

the peak signal is 380microV, with DC=1.65, the calibrated value is 2.9ppm. A lot more than expected.

Then I made a map of radius 4mm around the center, resolution 100micron. There are a few peaks where the signal saturated the lockin scale, but most of the map is uniform at around 3.4ppm.