NAOJ GW Elog Logbook 3.2
We can send infrared light from input-coupler side. After that, we take reflection and transmission power. By doing ring-down measurement, we can extrapolate well information of P0, P1, r1, t1.
P0 is power coupled to OPO cavity, P1 is power not-coupled to OPO cavity, r1 is amplitude reflectivity of input coupler, t1 is amplitude transmissivity of input copuler.
I did a calculation with the ideal parameters of OPO, which tells us decay time of ~4us.
To measure this decay, we should be able to lock OPO and switch off incident laser faster than ~100ns. To do this we need to use signal generator to send a square wave to an AOM which is before OPO. According to the spec of MT110-A1.5-1064, the rise time can be smaller than 100ns if the beam size is smaller than 0.6mm (diameter). We will design a small enough beam to make this rise time small enough to measure ring-down.
The expected ring-down for reflection and transmission is attached as figure 1.
Since OPO is finally closed, the next step is to characterize the intra-cavity losses. This is important for us because we are suspecting some of the optical losses are from OPO (current estimated loss budget for FDS). So this is an important step to understand the loss budget in the frequency dependent squeezing experiment.
I modified a bit the code to see the difference of measurement for different OPO intra-cavity losses.
Now, the laser is injected from the crystal side of OPO. I did a simulation of this case as Fig. 1. In this case, we will miss the information of OPO reflection. The blue and orange curves overlap for reflection.
If laser is injected from in-coupling mirror, as shown in Fig.2, we find that although decay time is not enough to indicate optical losses. We can extract losses from reflection signal.
So we will rotate OPO next week and inject laser from the in-coupling mirror side.