Daniel, Alexa, Sheila
We have tried to measure the green modulation depth of the X arm by moving the modulation frequency (24.410610MHz) so that the sidebands are antiresonant in the cavity, and then locking the cavity on the carrier (+polarity on servo board) then the sidebands. We used H1:ALS-C_COMM_A_LF_OUTPUT to measure the transmitted power.
| carrier | sideband | |
| no attenuator | 491.3 | 184 |
| 6dB | 620.34 | 81.67 |
| 12dB | 664 | hard to measure |
I have changed the offset to -66 counts, so that with no light on the PD we get zero counts (-0.26 counts) (someone had changed this from the -61 I originally set to -100 sometime last week, I am not sure why). With the single shot beam we get 46.06 counts.
Below are plots ot the transmitted powers (normalized) when locked on the carrier and sideband, and the second plot is their ratio. I used the ratio to do a simple fit for the modulation depth that we started with, and got 0.80 Now the modulation frequency is restored to the nominal 24.407079MHz and the 12dB attenuator is in place so our modulation depth should be 0.2.
Also, the ratio of the transmitted power on resonance/ single shot beam should be:
1/(1-sqrt(R1*R2))^2=22.6 for a perfectly mode matched carrier with R1=0.63, R2=0.99, taking into account the 0.2 modulation depth we would expect 22.17. Since we curently measure a ratio of 14.4 between the single shot and locked trans power, which is 65% of what we would expect. This means we have about 45% of our power in higher order modes.
Daneil's alog about the RF powers is 9484
