Hsun-Chung, Chien-Ming, Michael

The infrared probe and green pump are both mode matched into the OPO cavity. The green steering mirror closest to the OPO was replaced with a PZT phase shifter at 45 degree incidence, like the one in TAMA.

The PDH locking setup was constructed. Originally we were going to use 40 MHz modulation onto the IR probe beam to lock the OPO, but since the IR probe is injected into the high reflectivity M2 mirror, the amount of IR coupling is quite low and the PDH signal is small. Instead we clone the 40 MHz sidebands onto the green beam using the SHG (or rather, SFG - sum frequency generation) and can get good sideband amplitude. 

To lock the cavity we planned to use the grey Mokulab from TAMA FC. The Mokulab output was sent to a really old 33 dB RF power amplifier (it has an analogue dial), which works. However, the grey mokulab input ports are not working properly. This was tested by sending a function generator input into the IN ports and checking oscilloscope and spectrum analyzer functions.

So, we need either a working Mokulab unit or PDH locking hardware (currently we do not have sufficient equipment for 40 MHz RF amplification). A long time ago we were using a Red Mokulab in ATC (I think this was purchased using my old JSPS funding or Matteo Kiban A) which seems to have moved on to another experiment right now.

Hsun-Chung and Chien-Ming left today since their flight tomorrow is very early. Since everything is aligned and mode matched, once we get the PDH locking equipment I should be able to do the OPO nonlinear gain test (IR probe amplification and deamplification from a slowly phase modulated green pump injection, at different levels of green power) by myself and infer the threshold power, which is an important number for the squeezer performance.