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Entry   Lock, cavity length and finesse estimate, posted by Aurélien Martens at Optical room about lasers and optics | detectors and electronics IMG_20210430_173331.jpg
    Reply   Lock, cavity length and finesse estimate, posted by Aurélien Martens at Optical room about lasers and optics | detectors and electronics 
Message ID: 16     Entry time: Tue Sep 7 11:05:47 2021     In reply to: 10
 Author: Aurélien Martens 
 Status: Fixed 
 Type: report 
 Category: lasers and optics | detectors and electronics 
 Location: Optical room 
 Title: Lock, cavity length and finesse estimate 

we observed that the transmitted light coming from the cavity is made of the cavity mode light and the scattered light on the borders of the mirrors.
the scattered light on the borders of the mirrors is triggered by the cavity mode itself when the cavity is locked.
we didn't put an iris to cut this scattered light coming from the cavity.

Question:

could it be possible that the wrong Finesse value could come from the fact that the transmission was measured with the whole light coming from the cavity and not only the cavity mode light?

Aurélien Martens wrote:

Ronic just suceeded in obtaining a reasonably good lock on the cavity. Air flow is switched off.

We stopped all movements (closed loop, click STOP in the PTC interface) and saw immediately a fair but not excellent lock.

We then switched off the smaract motors and the obtained lock was good. Switching on again the smaract means tthat the references are lost.

We futher saw a drift of the locking point, probalby suggetsing that the thermal load in the cavity slightly changed after switching off the motors.

We then added the second 1GHz BW EOM to add sidebands thanks to the MARCONI RF generator. We observed that the FSR is aroung 867.6MHz (in air). We then looked at the points where the transmission signal related to the sideband is halved. We observed that the corresponding frequencies are 867.296 and 867.776MHz. the corresponding FWHM of about 500kHz corresponds approximately to a 2000 finesse.

Picture color code:
TRANS : Green
REFLECT : Yellow
PZT : Blue

 

 

 

 

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