I list the plan for measuring the effect of RIN to Frequency noise.
1) Measure the TF between FASTMON / RCTRANSPD. FASTMON [V]will be converted to frequency [Hz]. RCTRANSPD will be converted to power of the laser [W]. This will be useful once we know the coupling coefficient and want to project the noise in the noise budget.
1.1) TF between FASTOUT and FAST MON will be measured. We observe the signal from FASTMON, but the signal from FASTOUT will drive the laser, so they will not be exactly the same because of other electronic components along the paths, for example, low pass filter at 10Hz for FASTOUT. We already know that the calibration at FAST modulation at the laser input is 3.09 [MHz/V].
2) Amplitude modulate the laser power by modulating the polarization of the laser via EAOM. The beam is sent to a PBS which allows only one polarization out. Thus the amplitude of the transmitted beam through the PBS will be modulated. I choose to modulate at 10 Hz, because the frequency is not too high so the effect is small, and the frequency is not too low that it might be masked by seismic noise.The modulating voltage is 2Vpkpk, I want the Vmod to be large enough, so that I can see the signal, but not too large because we want the system to have linear response.
3) Measure the PSD of FASTOUT, RCTRANSPD, make sure that the peak at 10 Hz is visible.
The input power is 1mW, I will increase more power later. I want to see if the signal is measurable at this power level. If so, the higher power should increase the signal by the same factor.
To sum up, I'll repeat the measurement with
1) changing the laser power
2) changing the modulation depth
3) changing the modulating frequency
and see if the effect behaves like what we expect. It should be smaller as the laser power or modulation depth decrease, or at higher frequency.