This weekend I continued work on ISCT6. The path as it is now is shown in the first attachment. Compare with the layout (second attachment), I've had to swich some things as mentioned in my previous alog. It's not quite done yet.

AOMs and EOM

First I aligned the beam through the two 80 MHz AOMs, driving them with signal generators and borrowing the RF amplifiers on the top of the table. I found that when the power in the first order beam is maximised there is also some power in a second order beam, not sure if that's normal. In the third attachment (photo) the brightest spot is the first order beam, the 0th order beam is to the right of it.

The drive power to both AOMs is 26.4 dBm, I measured the diffraction efficiency to be 73% for both AOM1 and AOM2.

I haven't hooked up the EOM - I don't need to drive it to align the path. But the transmission through it was ~100%

Mode Matching

I tried to place the modulators on either side of a 100um waist. The 4th attachment shows my a la mode mode matching solution. The lenses are f1=100mm, f2=100mm, and f3=50mm. Final attachment is the a la mode code.

For mode matching into the fiber, I did my calculations based on Sheila's measurements of a beam coming out of a similar collimator. She measured a waist of ~30um ~0.13m in front of the collimator. Since I'm using a new colimator (still a Thorlabs PAF2-5A) I might want to remeasure this, or try to adjust the collimator to get a close approximation of this. With the lenses I have now, and a bit of fiddling with alignment and lens positions, I only got 1% of the light through the fiber so far. But I had some trouble using the rotational adjustors to the collimator. The fiber I used I stole from the bottom of the squeezer grey cupboard. There are still 3 other spares there.

Still to do

• Get more light into the fiber
• Install photodiode
• Install flipper mirror