Participant: Eleonora, Marco and Yuhang.

1. Open the loop if you want to change the object you want to lock. Because we have only one board for locking up to now.

2. Reconnect the photodiode, PZT(in the back of red laser head) and pietie(int the back of white laser box and the middle one) from the previous one to the one you will control.

3. Check the photodiode output, and try to adjust steering mirrors to see if you can improve the fiber coupling or not. Sometimes if someone touch the collimator or mirror, the coupling will be changed.

4. Then connect this beatnote between these two lasers to spectrum analyzer. Remember to choose range from 0Hz to 1.3GHz. And change the temperature from the laser box. You will see from the spectrum analyzer the beatnote moves with your changing. Move it close to 20MHz, the frequency we want to use for demodulation. Note here that sometimes if the spectrum analyzer doesn't work, press the preset button. 

5. Then look at it more closely and check the level of the peak you want to lock, it should be larger than -16dB. If not, you can check again the fiber coupling. Usually try to change the polarization.

6. Move the peak as close as 20MHz. Here is a splitter(10:90), 10 percent is used to monitor while 90 percent is used to lock the PLL. Then firstly put on the fast control and then slow.

7. If you want to measure the phase noise, check firstly the level of this signal. Change the demodulation phase to make it close to zero, means fluctuating around several hundred microV to 1mV.

8. Change the demodualtion frequency and use oscilloscope to see this frequency component to get the calibration factor.

9. Use DC couple and put the close to zero signal to the network analyzer. Then you will get noise spectrum.