[Clement, Marc]
Yesterday, Shalika and Clement found a spare laser controller nearby TAMA input laser bench that seemed to work properly.
We tried to use it but the current range is between 1.4A to 2.6A.
Clement made power vs current graph that will be uploaded soon.
While the laser manual specifies a waist 5cm after the laser head aperture, it seems to be more around 15cm.
We started to install a power controller (rotating HWP + tilted beam sampler) but somehow the reflected power is almost independent of HWP angle.
We replaced the beam sampler by a TFP polarizing beam splitter and got similar result...
We added a QWP after the HWP and got same result.
Note that we're using (for the first time) a high power power meter head found in PCI (S145).
Why should the power change when you rotate HWP? The polarization from laser is perfectly linear. So, all you do when you rotate hwp is rotate polarization. The power can be rather controlled with a rotating polarizer.
by rotating the polarization before a pbs or a tilted beam sampler we should be able to tune the reflected (or transmitted) power.
However the typical change we saw (0.3%) is far lower than expected.