camilla.compton@LIGO.ORG - posted 12:21, Monday 10 October 2022 - last comment - 10:45, Tuesday 11 October 2022(65277)
CO2 Power Required, currently get 9% laser power to vacuum with central mask
After finding our CO2 lasers are starting to degrade (alog 64739) and will need fixing or replacing, the question has come up (FRS 25384):
Do we really need 50W lasers? Answer: Yes.
Caveat: If we reduced on table losses, i.e. only 25% power to FLIR / Power meter, we could have a 25W CO2 laser getting 3W or ~13.5% though the central mask into vacuum. I found a design expecting we would need ~6W T060083 4.1.3.1, whats the up to date numbers?
There is currently 9% of power from the laser getting into vacuum with central mask.
This is using Ryan S.'s alog 62848 CO2X rotation stage calibrations with 34.9W out of the laser:
| Heating Type | Max power into Vacuum (W) | Percent of 34.9W out of Laser (%) |
|---|---|---|
| No mask | 12.10 | 35% |
| Annular | 5.88 | 17% |
| Central | 3.27 | 9% |
It's not very unexpected as the CO2 beam has gone though 3 polarization dumps, 99% BS for the ISS, 99(?)% for QPDs, 50% to power meter and FLIR, see layout on T1200007. This would leave 49% if no polarization was dumped and there was no other on-table losses (which it appears there are 27369). Then the masks transmit 30% for central and 50% for annulus.
The CO2 power meter has a "Watts at CP" gain of 2.3215 at ITMX and 2.304 for ITMY, I assume to account for the 50/50 FLIR and Power meter split. Have we checked this since 2016 alog27369?
Currently when locking we use send in 2.6W on CO2X with annulus mask (requested 2W as RS is calibrated for central mask), we expect to need more CO2 when increasing powers.
Redid this measurement for CO2Y with 32W out of the laser (head incorrectly reads 48W alog65264), we get similar results: