20100408 Seed Laser Tuning & Locking

Today the seed laser would not lock to the external reference. The output power was checked and was ~450mW which was lower than expected (~500mW). Takano San tuned up the cavity by cleaning the mirrors and adjusting their alignment. He adjusted the SESAM and M3. See Seed Tuning for details on specific mirrors. The output power was increased to 520mW, but the laser still would not lock. Using the spectrum analyser, it was found that the reference signal was close to 359MHz as opposed to the laser (and ATF) frequency of 357MHz. 2MHz is far outside the laser's tuning range and so despite a higher output power, it couldn't lock.

After further investigation, the signal generator that synthesises the 357MHz frequency locally was found to not be operating properly. Changing the synthesis mode to "Auto" solved this.

The laser now locks stably.