After some failed attempts to install a noise eater:
- 1 EOM (an amplitude modulator) was thermally unstable above 3mW, even though it was well within the rated max optical intensity (turns out, crystal was LiNbO3, ie not doped with Mg which seems to improve thermal stability).
- Another EOM had RF issues (a phase modulator used as an amplitude modulator with appropriate input/output polarization optics).
- Another (IR) EOM (also a PM used as AM with in/output polarization optics) rejected too much green to be useful.
- One AOM also had RF issues (and was for a wavelength of 1064 nm anyway).
we have now installed a 532 nm 200 MHz AOM from MIT.
Beam profile after this AOM looks fine (attached) with ~45 mW input power. The green pump fiber had to be realigned and again has 83+/-2% coupling efficiency to the patch panel on ISCT6 (so this fiber is fine).
However the power to SQZT6 has dropped recently and is still low, but is clearly not due to any failure of the fibre between the Green input coupler on ISCT6 and the patch-panel on ISCT6. Nutsinee will add a post with more information on this.
The frequency synthesizer doesn't have enough power to get enough diffraction power, so I added a ZHL-1A Mini-Circuits amplifier. The settings on the ifr are 200MHz/0dBm for the carrier with an external AM modulation at 50% bias. Since the CM board for the OPO isn't used at the moment, we connected the first input the to DC monitor of the OPO REFL diode, the second input is connected to a DAC channel (OPO_EXC) with a 100Hz low pass. The later provides a DC bias to set the requested power level. The fast output is then connected to the modulation input of the frequency synthesizer with a 450Ohm series resistor (which forms a 1:10 divider together with the 50Ohm input). The bandwidth of the AM modulation input of the ifr is about 30kHz. However, we measured a significant phase lag which will limit the ugf to less than 20kHz.