NAOJ GW Elog Logbook 3.2
Yaochin and Yuhang
Since we did the optimization of the HWP angle for BAB. By this chance, we did again what Aritomi-san reported in elog1587.
First, we rotated HWP then measured the peak height of the s-pol peak and the p-pol peak.
|
BAB HWP angle |
286.5 |
290 |
294 |
298 |
302 |
306 |
310 |
314 |
|
s-pol (mV) |
4560 |
4400 |
4120 |
3720 |
3240 |
2640 |
1960 |
1440 |
|
p-pol (mV) |
2 |
95 |
372 |
880 |
1400 |
2080 |
2840 |
3480 |
We derived visibility from the peak height difference. We also considered the loss introduced by non-optimal visibility is the square of (1-visibility).
Then we removed BAB and put again CC and pump. We measured only squeezing at the previous HWP angle. (Now I realize that it will be better to measure anti-squeezing) Anyway, the measurement result is attached to the first picture.
Finally, by using the formula of FIS degradation, we plotted the calculated squeezing value and compared it with measurement. The result is attached to the second picture. However, it seems data and calculation don't match very well.
I think it's better to measure visibility directly.
>> We also considered the loss introduced by non-optimal visibility is the square of (1-visibility).
This seems not correct. This is how I calculated additional loss in entry 1587.
1. Measure voltage of LO, BAB (HWP 0deg), DC offset, visibility (HWP 0deg)
2. Rotate HWP and measure maximum and minimum of visibility
3. Solve the following equation in terms of V_BAB
(V_max-V_min)/(V_max+V_min-2*V_DC)/(2*sqrt((V_LO-V_DC)*(V_BAB-V_DC))/(V_LO+V_BAB-2*V_DC)) == visibility (HWP 0deg)
4. Additional loss should be 1-V_BAB/V_BAB (HWP 0deg)
I am sorry that what I wrote is wrong. The additional loss is 1-visibility**2. I think it is very clear for us that the efficiency of homodyne is visibility**2. This is written in Henning's thesis.