We succeeded in getting the reflected green beam from both ITMY and ETMY.
After we did several things on the end table, we eventually could observe these reflections.
Now the spot size of the reflection from ITMY is still big ( more than 1 cm ), so tomorrow modematching to the 40m cavity is going to be improved by putting mode matching telescopes on right positions.
An important thing we found is that, the beam height of optics which directly guides the beam to the cavity should be 4.5 inch on the end table.
(what we did)
* Aidan, Kevin and Kiwamu set the beam to be linearly polarized by rotating a QWP in front of the Innolight. This was done by monitoring the power of the transmitted light from the polarizer attached on the input of the Faraday of 1064 nm. Note that the angle for QWP is 326.4 deg.
* We put some beam damps against the rejected beam from the Faraday
* To get a good isolation with the Faraday we at first rotated the polarization of the incident beam so to have a minimum transmission. And then we rotated the output polarizer until the transmission reaches a minimum. Eventually we got the transmission of less than 1mW, so now the Faraday should be working regardless of the polarization angle of the incident beam. As we predicted, the output polaerizer seems to be rotated 45 deg from that of the input.
* Rana, Koji and Kiwamu aligned the PPKTP crystal to maximize the power of 532 nm. Now the incident power of 1064 nm is adjusted to 250mW and the output power for 532 nm is 0.77mW. Actually we can increase the laser power by rotating a HWP in front of the Faraday.
* We injected the green beam to the chamber and aligned the beam axis to the ETMY without the modematching lenses, while exciting the horizontal motion of the ETM with f=1Hz from awg. This excitation was very helpful because we could figure out which spot was the reflection from the ETM.
* Once we made the reflected beam going close to the path of the incident beam, we then put the modematching lenses and aligned the steering mirrors and lenses. At this time we could see the reflected beam was successfully kicked away by the Faraday of 532 nm.
* Koji went to ITMY chamber with a walkie-talkie and looked at the spot position. Then he told Rana and Kiwamu to go a right direction with the steering mirrors. At last we could see a green beam from ITM illuminating the ETM cage.
* We excited the ITMY with f=2Hz vertically and aligned the ITM from medm. Also we recovered a video monitor which was abandoned around ETMY chamber so that we could see the spot on the ETM via the monitor. Seeing that monitor we aligned the ITM and we obtained the reclection from the ITM at the end table.
* We also tried to match the mode by moving a lens with f=400mm, but we couldn't obtain a good spot size.