More details of locking

In the first picture, I showed the component on the optical bench now, and the red line represents the infrared and green line for green. As it shows in the picture, the transmit beam of the cavity divided by the BS mirror, the reflection part goes into the PD and the transmission part goes into the CCD, so I can see the shape of the beam through the screen connect to it.

And the second picture shows the loop I used to lock the cavity,the red line stands for the beam, I only list the optical component which connected to this loop. The black lines and the orange lines show the wire, but the wires in orange only used for the first step.

As I mentioned in my last report, the Function Generator on the left provides a 15.2MHz sin wave, which is sent to EOM to do the modulation, and also there is the other line come out from this, goes into the 'LO'(Local Oscillate) port of the demodulation board.

Then from the output of PD also goes to two different ways, one goes to the 'RF'( radio frequency) port of the demodulation board and the other goes to the channel 1 of the oscilloscope which shows in yellow on the screen of it.

The signal of 'RF' and 'LO' mixed together in the demodulation board and the output of it will go through the low pass filter of the board and then connected to the channel 2 of the oscilloscope, it shows the error signal and it is blue.

At the first beginning, I used the Function Generator on the right to send a triangle wave to the PZT driver to scan it and find the mode matching. Then when I got the error signal(the output of the demodulation board), firstly, this signal was sent to Stanford who acts as a low pass filter and then the output of Stanford goes to the PZT driver also.Now the loop has been closed.

And then I stopped scanning the cavity(plug out the orange lines), but just change the voltage of the PZT driver by myself. Until from the CCD screen, I am around the maximum of the TEM00 modes. Then I checked, the cavity is locked and the green beam is very powerful.

That's how I did until now, but actually the lock can not keep for very long, only last about 20-30 mins. So since I cannot switch off the loop(there is no switch I can use), I just need to plug out one off the wire and change the voltage of the PZT driver near the resonance and recover the loop. Try to do it this way and find out if I can get better result or not.