Participaint: Aritomi, Eleonora, Matteo and Yuhang

First we checked the homodyne dark noise. The purpose is to compare this result with Henning's result. We are using network analyzer, but itself's noise level is not low enough to see the dark noise of homo-dyne. So we decided to use Stanford research SR560 to amplify the homodyne noise. We gave it a factor of 100(40dB). Then we got the result as shown in attached figure 1 and 2. The difference is they have a marker located at 1kHz and 10kHz, others are the same. We can see below 3kHz, the noise should be dominated by electronic noise. And above 3kHz, the noise level should be the noise level of homodyne. In this case, the real noise level of homodyne should be around -122-40 = -162dBV/sqrt(Hz). However, the result from Henning is 

-156dBV/sqrt(Hz). This is not a neligible difference.

We are arriving to the point to operate homo-dyne. We power up homo-dyne with a DC voltage supply at +/- 19V. For checking both the alignment of the beam inside homodyne and also if the homodyne work well, we send an amplitude modulation to the main laser beam. At the beginning, we send a 100mV pk-pk and 1kHz signal into the current control of main laser. However, this modulation seems not stable. Then we decide to modulate the PZT of IRMC, in this case, we moved the locking point of IRMC around the TEM00 peak. Then the modulation became very clear. Here the clear or stable means if the signal we see on the oscilloscope shows clear line or can be triggered.

We also find out that the the even we send the voltage +/- 19V to homodyne. The current going inside seems like zero.

And when we see the 1kHz amplitude modulation signal on the monitor PD with amplitude of several volts. We can only see the same signal on homodyne with amplitude of several millivolts. Seems like we didn't switch on homodyne.

The last figure shows the homodyne on our bench.