Yuhang and Michael

We attempted to measure the OPO ringdown using the new RF switch described in 2865, 2866. 

Figure 1 shows the result of the ringdown for the transmission (red) and reflection (blue). The behaviour is a bit strange, so we haven't analysed in detail yet. The reflection ringdown is too fast, while the transmission ringdown starts off too fast and then becomes too slow. As a reminder, we are expecting about 3-4 µs ringdown from calculation. The RF switch is controlled by a 5V 1Hz square wave (i.e. digital logic on/off). Figure 2 shows the result of switching off the switch control manually. The electrical contact bounces and causes the switch to rapidly turn on and off. Normally this result doesn't seem very useful, but even here we can see the reflection ringdown being too fast and the transmission ring down being too slow.

Current mode matching status is:
34 mV TEM00
8.6 mV HOM
5.1 mV HOM
3.9 mV noise floor

We also attempted to measure the optomechanical transfer function of the cavity. We used Mokulab's Frequency Response Analyzer, taking Mokulab IN1/IN2, with:
Mokulab IN1: Taken from T connected to Source A of SR560. This is the input of the servo before noise injection.
Noise injection: Injected at Source B of SR560, which applies a low pass filter to A - B.
Mokulab IN2: Taken from T connected to 50 Ohm out of SR560 (before PZT high voltage driver). This is the output of servo going to the plant. Thus, IN1/IN2 should be the TF of the plant.
The result is shown in Figure 3. However, it is not very meaningful. The error signal is probably too high versus the noise injection for frequency response analysis.