daniel.sigg@LIGO.ORG - posted 21:37, Wednesday 03 July 2013 (6987)
VCO work
(Stefan Daniel)
We moved the additional frequency difference divider to the common VCO. This required an increase of the PLL gain from 5 to 20. The unity gain was measured to be around 40 kHz. This also means that the gain for the common mode feedback increased by 10. We adjusted by lowering the gain of the SR560 from 10 to 1.
We took the opportunity to set all VCOs to a nominal frequency. The nominal frequency of the PSL/IMC VCO and the fiber AOM driver is 79'200'000 Hz. All ALS VCOs (EX/EY, COMM, DIFF) are set to a nominal frequency of 78'920'000 Hz.
| Location | Frequency (Hz) | Comment |
|---|---|---|
| Fiber | –79'200'000 x 4 | downshift |
| PSL | –79'200'000 x 4 | downshift, laser relative to ref. cav. |
| EX laser | –78'920'000 + fiber | relative downshift |
| EY laser | +78'920'000 + fiber | relative upshift |
| COMM VCO | +78'920'000 | |
| DIFF VCO | +78'920'000 | |
| Beat EX/laser | –78'920'000 | fiber - PSL + EX laser |
| Beat EY/laser | +78'920'000 | fiber - PSL + EY laser |
| Beat EY/EX | +157'840'000 | EY laser - EX laser |
| EX invariant | 0 | fiber - PSL + EX laser + COMM VCO |
| EY invariant | 0 | fiber - PSL + EY laser - COMM VCO |
| DIFF invariant | 0 | EY laser - EX laser - DIFF VCO |
The lasers in the end stations can be locked up or down by changing the sign of the phase frequency discriminator.