This morning we blocked the reference beam of the PCs on B4 and B1p and stopped the scanner to investigate the frequency content of the beam coming from the interferometer. Several sets of raw ADC data were taken, each set contains 100 acquisitions of 2^15 samples with a sampling frequency of 500 MHz. Data has been acquired with two modulation indices for the 6 MHz with a difference of 9 dB.
Additionally, raw data after the demodulation has been stored. Therefore, the demodulation frequencies were adjusted, the frequencies are now:
- beat of carrier with 6 MHz (in general not stored)
- beat of carrier with 56 MHz (only used for PDH images)
- beat of 6 MHz sidebands (not visible in the noise, in general not stored)
- beat of 56 MHz sidebands (in general not stored)
- the ususal PC channels (beat with reference): 6 MHz upper and lower, 56 MHz upper and lower, 8 MHz upper and lower, carrier
Note: the beat of the carrier with the 6 MHz was already available but demodulated at 6.2701 MHz instead of 6.2708 MHz. However, the signal was neither stored nor used.
Analysis of the acquired data will follow.