[Disha, Johannes]
Today we aligned the incident beams to the cavities and locked both lasers for the first time. As a reminder, this is the procedure we're following:
- Estimate BB lens positions
- Align beams into cavities
- Lock lasers
- With lasers locked, tune the placement of the BB lenses on the transmission side for parallel, level beams with 5" separation and 4" beam height above the optical table to hit the viewports (BB is in nominal suspended position for this, but propped up on posts, with springs not attached)
- Turn the BB around
- Rinse & repeat to tweak the input lens placement as well
- Turn breadboard again
- Optimize input mode-matching
- Close cavity cans
- Suspend breadboard
- BB balancing
For now the input mode-matching is not yet optimized, just placed approximately following some initial calculations. Reflected light drop was of order 60-70% and the lasers locked just fine with plenty of light being transmitted (easily visible on card = good for aligning lenses). Work to be continued tomorrow.
Some good news: In air the beat frequency between the locked lasers was 446 MHz, which is on the lower end of expected natural resonance differences. With the old cavities, the cryogenic beat frequency was within 10% of that at room temperature with no thermal control. The FSR of the new cavities is 4 GHz, so it looks we're quite lucky: we're in the top 25 percent of favorable beat frequencies, well within the bandwidth of our photodetectors, and can see the signal on AG4395's. Hopefully this is true at cryo as well.
|