1. I clean up the IRMC, fortunatly, the dirty is outside so we can clean it.

2. For the RF signal, I used the TAMA PD which was used for FC reflection.

3. Since we found that we cannot see the modulation produced by OPO EOM, we decided to test this EOM. This EOM is from TAMA(length = 5.5cm, Diameter = 3mm, power density = 4W/mm2, resonant frequency = 40MHz). Since I have already had a good alignment for IRMC, I didn't want to destory it. I just want to add lenses and then put EOM. Besides, I have a lot of space to put lenses and make the beam smaller than 500um of radius with a range larger than 5.5cm. So I don't want to care a lot about mode matching. Note here, the mode matching affected by additional lenses and EOM. Besides, we can compare the 15MHz sideband's power to know how different interference affect the sideband power. Because we know the power of 15MHz sideband before puting the additional lenses as a reference. The set-up of this test is attached as Fig.1. (Note here the beam power is 10mW, even for the concentrated beam, power density is 1.8W/mm2)

For the test of EOM of collimated beam inside, the 15 MHz sideband power is around -26dBm. The 40MHz is around -49dBm. (see attached Fig.2)

For the test of EOM of concentrated beam inside, the 15MHz sideband power is around -32dBm. The 40MHz is around -56dBm. (see attached Fig.3)

Here the 15 and 40MHz sideband disappeared after I blocked the beam.

From these two results, we found although the 40MHz sideband power decreases, it seems come from the worse interference(worse interference verfied by 15MHz reference). (See attached Fig.4 for bad interference)

So the conclusion is: The TAMA EOM works well and the collimation of beam doesn't matter.

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15MHz sideband comes from the TAMA EOM, which is just after the main laser and before the first BS on the bench.