LIGO- G R 40m weekly meeting, Jan 05, Explore demodulation phase for DDM on 40m RSE prototype Osamu Miyakawa, Caltech LIGO-G R

40m weekly meeting, Jan 05, Setup ITMy ITMx BS PRM SRM Laser SP33 SP DDM Carrier 33MHz 166MHz  Signal for l + is extracted from Symmetric Port (SP).  SP33 is a 33MHz single demodulation PD used for lock acquisition.  Then it switches to SP DDM (double demodulation).  We assume that l s and l - are locked.

LIGO- G R 40m weekly meeting, Jan 05, Abs Design Lock point SP33 Lock point 0.56 degree +166resonance +33 resonance +33 off-resonance

LIGO- G R 40m weekly meeting, Jan 05, Original design (no offset) Abs Design Lock point SP33 Lock point 0.56degree +166resonance +33resonance +33 : off-resonant -33 : off-resonant +166: resonant -166 : anti-resonant l + and l s plot separated Difficult

LIGO- G R 40m weekly meeting, Jan 05, l degree, l s degree Abs Design Lock point SP33 Lock point 0.56degree +166resonance +33resonance +33 : resonant -33 : resonant +166: resonant -166 : anti-resonant l + and l s plot overlapping DC line changed Easy (if l + is moved, servo try to move l s.)

LIGO- G R 40m weekly meeting, Jan 05, l degree Abs Design Lock point SP33 Lock point 0.56degree +166resonance +33resonance +33 : resonant -33 : resonant +166: off-resonant -166 : anti-resonant l + and l s plot overlapping DC line changed Difficult

LIGO- G R 40m weekly meeting, Jan 05, l s degree, Abs Design Lock point SP33 Lock point 0.56degree +166resonance +33resonance +33 : off-resonant -33 : off-resonant +166: resonant -166 : anti-resonant l + and l s plot separated Same DC line Difficult

LIGO- G R 40m weekly meeting, Jan 05, Exploring phase  Lock l + to SP33.  Adjust gain during SP33, SP133 and SP199.  Find maximum l + signal on SP133 and SP199.  Move to DC=0 line.  Add calculated phase on SP133 and SP199.  Add offset on SP33 until SP DDM has no offset.  Switch SP33 to DDM.

LIGO- G R 40m weekly meeting, Jan 05, m vs. Ad-LIGO 40m Ad-LIGO x6 x2

LIGO- G R 40m weekly meeting, Jan 05, Summary  Off-resonance of 33MHz makes good signal separation between l + and l s.  We can find a way to optimize demodulation phase for DDM at SP, which has good signal separation and no offset.  Ad-LIGO using 9-180MHz sidebands has less signal separation between l + and l s, but better signal separation for l - and l s