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Message ID: 7872     Entry time: Wed Jan 2 15:33:23 2013
Author: Jenne 
Type: HowTo 
Category: Locking 
Subject: We should retry in-air locking 

Immediate things to do include finishing installation of new TTs and re-routing of oplev paths in the BS chamber, but after all that, we should retry in-air locking.

The last time we (I) tried in-air locking, MICH wouldn't lock since there was only ~ 6uW of light on AS55 (see elog 7355).  That was before we increased the power into the MC by a factor of 10 (see elog 7410), so we should have tens of microwatts on the PD now.  At that time, we could barely see some PDH signal hidden in the noise of the PD, so with a factor of 10 optical gain, we should be able to lock MICH.

REFL should also have plenty of power - about 1.5 times the power incident on the PRM, so we should be able to lock PRCL. 

Even if we put a flat G&H mirror after the PRM to make a mini-cavity, and we lose power due to poor mode matching, we'll still have plenty of power at the REFL port to lock the mini-cavity.

For reference, I calculate that at full power, POX and POY see ~13uW when the arms are locked.

 

POX/POY power =  [  (P_inc on ITM) + (P_circ in arm)*(T_itm)  ] * (pickoff fraction of ITM ~ 100ppm)

REFL power = (P_inc on PRM) + (P_circ in PRCL)*(T_prm)     =~ 1.5*(P_inc on PRM)

ELOG V3.1.3-