[Matteo, Simon]

Today we switched on the 1064nm pump laser for the first time after four months. We had some problem identifying the correct COM port (COM11) but solved that the laser could be successfully switched on and controlled from the PCI computer. One thing to be noticed is that the power cord of the pump laser seems to have connection instabilities, please remember to be careful and never touch the plug in into the power supply.

After the successful result on the pump laser we switched on the probe laser (633nm). No problems on that. We had to install a variable OD filter in front of the probe laser not to saturate the photodiode on the imaging unit. We aligned the probe on the imaging unit without any reference sample to have about 4V of DC output as read by the lock in. We then installed the surface reference sample and performed some z scan. NOTE: the written part present on the sample is facing the imaging unit. At this stage we aligned again the probe beam into the imaging unit photodiode maximizing the DC to compensate for the misalignment introduced by the reference sample, we then aligned the pump beam to maximize the AC signal at the crossing point.

MEMO: to align the probe on the IU photodiode we used the IU lens translation stage; to align the IR beam we used the translation stage on the last lens before the sample area.

Attached (1) the screenshot of the absorption measurement for surface reference sample (try one).

After speaking with Manuel, he told us that the written part of the surface reference sample should be facing the pump side and not the IU side. We flipped the surface reference sample and optimized again the alignment and performed again the z scan. Result is in attached figure (2).

In the end we substituted the surface reference sample with the bulk reference sample and measured the z scan. Result is in the attached figure (3).

From measurements shown in (2) and (3) we can obtain the calibration of the system.

R_surf = AC_surfref/(DC_surfref*P_in*abs_surfref) = 16 [1/W]
where AC_surfref = 0.42V, DC_surfref = 3.85V, P_in = 0.031W and abs_surfref = 0.22

R_bulk = AC_bulkref/(DC_bulkref*sqrt(T_bulkref)*P_in*abs_bulkref) = 0.604 [cm/W]
where AC_bulkref = 0.067V, DC_bulkref = 4.64V, T_bulkref = 0.55, P_in = 0.031W and abs_bulkref = 1.04/cm

The two calibration values are compatible with old calibrations.