Katsuki, Marc

This is a summary of these past days activities.

As reported in entry 2863 we found out that the pump beam was larger than expected (48.5 um instead of 36 um).

In summary we had to act on the two lenses on the pump beam path to recover the good beam size and position following Jammt simulations.

These 2 lenses are now about 1 cm closer to the laser source.

During this realignment we also checked the the probe beam size to have a reference waist position.

We found out that it is not feasible to use the absorption DC photodiode together with the razor blade because there is scattering when we start to cut the beam that creates a spikes in the data and prevent a good fit of the data.

Furthermore, the probe beam is really large on this photodiode and is really astigmatic when setting up the imaging unit translation stage at z_IU = 0 mm (ie farthest from the translation stage).

In the end, we installed a power-meter in between the imaging unit lens and sphere and could get good data.

We also found out that a good step size for the translation stage is 20 um as it allows to get good enough resolution while not taking too long.

The attached figure reports the beam profiles of probe beam in vertical and pump beam in both vertical and horizontal directions.

The z axis is the same as Manuel's measurement (see elog 1089) ie the 0 mm is at 75mm from the breadboard.

We had to tweak a bit the tilt of the lenses to minimize the pump beam astigmatism.

We recovered the expected pump beam waist size and position so we will now switch to absorption measurement.

Note that probe beam power is 2.5 mW and pump beam power was about 150 mW for this measurement.