Warning: Undefined variable $s in /var/www/public_html/osl/classes/DAO.php on line 959
NAOJ GW Elog Logbook
LOG-IN
Displaying report 1-1 of 1.
R&D (FilterCavity)
Print this report.
EleonoraCapocasa - 11:55, Tuesday 13 March 2018 (694)Get code to link to this report
Monitoring the cavity round trip losses

PARTICIPANTS: Yuhang, Yuefan, Eleonora

In the past days we have monitored the cavity round trip losses. We computed them from the cavity reflectivity with the tecniques described here.

In the actual setup the losses are measured using the IR reflected beam, sensend by a TAMA fotodiode. The reflected beam is filtered whith a bandpass filter in order to get rid of the residual green and it is focused on the photodiode using a 2 inch lens with f = 30 mm. (See first attachment for the setup scheme) 

With this setup we have found that the reflectivity (ratio between reflected power in lock and out of lock) changes from day to day and takes values between 0.88% and 0.82%. It corresponds to a variation in the RTL between 40 ppm and 75 ppm.

The change can be due to the different alignment condition (the beams impinges on different points of the mirror which scatter differently) and/or to some other factor affecting the measurement and not yet understood. 

In the attached plotes there are some measurments from the last days. Unfortunately not all the measurements from which we deduce the RTL variation reported before have been recorded. 

Images attached to this report
694_20180313035122_rtl0803.png 694_20180313035134_rtl0903.png 694_20180313035201_rtl1203.png
Non-image files attached to this report
Comments related to this report
EleonoraCapocasa - 14:13, Tuesday 27 March 2018 (724)

In order to increase the statistic yesterday we repeated the measurement of the round trip losses, with the lock unlock technique.

Since we did it in two different moments of the day  the alignement conditions were likely to be different.

  reflectivity losses
#1 0.87±0.02 50±13
#2 0.80±0.03 81±16

The reflectivity has been computed by taking the mean of the time series between a lock and an unlock period. The error is computed as the progagation of the standard deviation of these two set of data. 

We estimated that 7% of the input light does not couple into the cavity.

EleonoraCapocasa - 16:06, Wednesday 28 March 2018 (728)

New did a new measurement of RTL with lock/unlock. 

Reflectivity 84% +/- 2%  => Losses  63±12 ppm

We considered that 7% of the input light is not coupled into the cavity.

EleonoraCapocasa - 10:48, Thursday 29 March 2018 (729)

Loss measurement 28/03/18

Reflectivity: 89%+/- 2.5%  => Losses: 44 +/- 12 ppm

Mismatching/misalignement  considered in the estimation: 11% (worse than usual)