Marc, Matteo

Today we first removed the PBS (it was taking too much place and prevented the installation of QWP and HWP).

We tweaked the last lens on the injection (L2) and recovered proper signals using the surface reference sample.

We placed the pinhole and tune its position at the waist (z=41mm) and plus/minus one Rayleigh range (ie Z = 36 and 46 mm). We checked that at these position all the pump power was properly transmitted (ie P_t = P_in = 28.8 mW)

We installed back the PBS and started to try to align it.

It was not possible to recover more than 22 mW. We checked that it was not due to misalignment by moving the pinhole that also gave 22 mW of transmitted power at maximum.

We simulated the effect of the PBS on waist size and position using Jammt : It moves the waist by ~ 10 cm. But this can be recovered by moving L2 by ~1 cm towards the imaging unit.

We did this change and could recover more than 27 mW at the extremum positions of the pinhole.

We then placed the razor blade (that cuts the beam in vertical) so that it is at the center of the pinhole holder.

We wanted to use the Translation_Stage_v3.vi to automatize the measurement but no values except the position changed...

By using the ..._v2.vi we got the beam waist = 33.39 um at z = 40.76 mm (see figure 1).

We reinstalled the surface reference sample and moved the translation stage to 40.8+1.5 = 42.3 mm (to compensate for the 3 mm thickness of this sample) and by tuning the horizontal and vertical screws of L2 we recovered the expected AC value (ie >0.4V).

We reinstalled the QWP and HWP, beam dump in reflection of the PBS and a small one instead of the steering mirror that catches the pump beam reflection from the sample (not enough space with the current holder) as in figure 2.

We did a Z scan of this sample and found R = 18.57 /W.

Either the alignment was the best since few months, either there are some polarizations effects that prevented to reach this value before I guess.

Finally, we started to reinstall the imaging unit part as in figure 3.

The steering mirror that was removed is now placed in front of the high-power power meter to allow for quick switch between absorption and birefringence measurement.

A 2" lens and the PBS inside the black tubing were also installed.

We still have to install ND filters and the 2 photodiodes on the readout path as well as proper walls.

Also, the motorized HWP is not yet connected to PC.