Today I increased the laser diode current to 3A.

I also took compared the output power as a function of HWP angle :

I set the HWP to 49 degrees did a large z scan and could see some AC signal.

I checked the viewport center :

Z_center = 73.4 mm (from phase = 0)

Y_center = 120.95 mm (from ac/dc = 0)

X_center ~ 331.75 (one of the extrema was not possible to estimate because I placed a stop in Zaber to avoid burning the holder.

The X_center was estimated from the top X value of 383.9 mm and assuming a similar radius as the Y direction (52.15 mm)

I tuned the DC at this position and got as a preliminary absorption value :

corr = 1;
ac = 8e-4;
dc = 4.08;
Pin = 0.613;
R_surf = 17.033
absorption = ac/(dc*P_in*R_surf)*corr ~416 ppm 18 ppm (Edit : I took wrong power in previous estimation...)

The absorption map is now on-going with a 3 cm radius and 50 um step size.