Using the razor blades, I checked the IR beam propagation.

Note that this measurement can not be done with I_laser = 7A as this requires to have the HWP that controls the beam power in a position where the beam is highly deforms..

This HWP should be replaced.

I found a waist size of 36 um that overlapped with the probe beam measurement of last July (this probe beam seems quite stable since Manuel measurements).

Using the last periscope mirror and the last lens on the pump beam path, I tuned the propagation direction to have about 2.72 deg incidence in the horizontal plane and about 0 deg in the vertical plane.

I installed the surface reference sample and after tuning both the translation stage and imagning unit z position I measured R = 14.01 /W with z = 33.7 mm and z_iu = 69.5mm.

I installed the 0.5 inch mirror with the curved side (HR coated) facing the laser sources.

I has 6.5mm thickness and I assumed it has a refractive index of 1.53 to tune the imaging unit position.

However, because this mirror is coated for 1550nm, I could see a lot of spurious beam due to the etalon effect (see fig 1)

I tried to tune the mirror position to maximize the DC and pump laser transmitted (ie I tried to center the beams on the mirror surface).

But even with 0.1 mm step, the spurious beams were present so I decided to not use too large power to not burn the 0.5inch to 1 inch plastic adapter.

I increased the power from 28mW up to 1W and I report the last 2 absorption measurements in figure 2.

It seems the coating absorption of the HR side is about 20 ppm (see the peak at about z=33mm).

If my assumption on the substrate refractive index is wrong, I expect the absorption to be even larger.