NAOJ GW Elog Logbook 3.2
[Aritomi, Eleonora P.]
We checked error signal of OPO reflection with new PD. Attached picture shows error signal of OPO reflection. The amplitude is 112 mVpp as expected.
As you can see from second attached picture, error signal of OPO reflection (and its control loop) is not stable mainly because CC PLL lock is not stable.
CC PLL lock should be checked.
Also we need to optimize the control filter.
1/ Every LEMO connector was tested successfully on the 7 SERVOFILTER modules
2/ The current consumption was tested successfully on the 7 SERVOFILTER modules:
* +12V: 130mA
* -12V: 85 mA
3/ The 5V supply was tested successfully on the 7 SERVOFILTER modules
4/ A closed loop test was performed successfully in injecting a perturbation on the RAMP IN input (square signal, 200 Hz, 1 Vpp, 5.1V offset).
The SERVO OUT output is connected to the input of a RC filter (R= 150 Ohm, C= 1 microFarad).
The output of this RC filter is connected to the ERROR IN input.
Thus, a pole is created (fc = 3.8 kHz - 42.7 Ohm/ 1 microFarad)
Tests performed successfully:
- SCAN MODE: the SERVO OUT was observed on the 7 modules to check that the triangular signal is correct
- Manual and Auto locking modes
- 1/f and 1/f3 filtering modes
- differentiator filtering (ON/OFF)
- ENABLE IN function
Remark: in Auto mode locking, the THRESHOLD is tuned in order to have -2.2V a voltage level on the THRESHOLD OUT output.
A voltage level Vth is injected on the TRANSMIS. IN input.
Vth < 2.2V => unlocked
Vth > 2.3V => locked
The ENABLE OU and LOCKED MON out outputs were checked:
LOCKED => 5V level
UNLOCKED => 0V level
Conclusion:
After transportation, the integrity of the 7 SERVOFILTER modules was checked successfully.
See attached pictures files of the 7 SERVOFILTER modules.
[Matteo, Eleonora C.]
In order to have a larger error signal for the CC in reflection from OPO we have modified the15 MHz resonant TAMA PD (S/N00Z405) to increase the gain of the RF channel.
We have modifiided the RF amplication stage as follow (pic 1 and 2):
R1 = 1K (before it was disconnected)
R2 = 9.1K (before it was shortcutted)
The gain has changed from 1 to 10.
The TF of the PD measured before and after modification are shown in pic 3.
The TF was measured by injecting the signal directly on PD pin (A), so they don't match those reported in (http://tamago.mtk.nao.ac.jp/tama/ifo/general_lib/circuits/011217_PD/011217_PD_fit.pdf) but they are just a relative measurements.
[Aritomi, Eleonora P.]
P pol PLL frequency where parametric amplification is miximized is 207 MHz with 49mW green.
We measured parametric gain.
Amplification: 2.92V, De-amplification: 120mV, without green: 312mV
The parametric gain is 2.92/0.312 = 9.4. It was 21.6 before.
We changed OPO temperature around 7.178kOhm, but it doesn't change so much.
Tomorrow we'll investigate this problem.
[Aritomi, Eleonora P.]
Today we recovered visibility and shot noise.
For the alignment of LO in AMC, peak is 8.08V and mismatch is 28mV+3.6mV, which means mode matching is 99.6%.
We maximized BAB transmission from OPO by changing p pol PLL frequency. It was 291MHz without green.
For alignment of BAB in AMC, peak is 568mV and mismatch is 18.4mV, which means mode matching is 96.9%.
Then we measured visibility. Max is 7.76V and min is 2.4V, which means visibility is 0.528. Power of LO is 1.2mW and BAB is 0.107 mW. So theoretical visibility is 0.548. Mode matching estimated from visibility is 0.528.0.548=96.4%.
After alignment of homodyne, we got shot noise above 1kHz.
Tomorrow we'll recover squeezing and check shot noise level with CC.
[Eleonora P., Eleonora C.]
We wanted to investigate the system performances after reducing CC power of a factor 10.
We locked the PLLs, the OPO and checked the CC error signal in reflection from it.
We could see a demodulated signal (at 14 Mhz) when the green phase was scanned (10 Hz 1.5 Vpp as last time) but the amplitude is quite small: ~10 mV. (see pic1)
The power of the CC beam (with OPO locked) just before the homodyne BS is 11.5 uW.
Then we wanted to proced with the shot nosie and squeezing measurement but we found out that the visibility (of LO and BAB) was very low. So we confirmed that the aligment of the two beams into the AMC was poor but we managed to recovered it with some difficulties. (We followed the usual procedure: first we align LO with the two steering mirrors before AMC then we align BAB with the steering mirrors on the squeezing path after PBS.)
Current status:
- BAB flipping mirorr is on (BAB injected)
- Homodyne flip mirror is OFF to check alignement to AMC
- BAB and LO are aligned into AMC but visibility has to be re-measured
NOTE: We discovered that the fibered PD used for CC PLL monitor has a broken part (see pic2). This part is used to connect the PD the power supply insead of using battery. Since we don't have any spare we replaced it with a battery. Before leaving, we took the battery off to avoid consuming it. Remember to put battery in the PD if you want to check the CC beat note.
I just measured there are 3uW of p-pol is going also into homodyne.
[Eleonora P. Eleonora C.]
=SHG=
IR input = 0.6 W GREEN output = 0.2 W Efficiency ~30%. (as last time, entry #1180)
SHG coupling 80%
It seems that the highest HOM is 2nd order and cannot be easily removed improving alignment (has matching changed?)
Note that sometimes HV driver for SHG gets stuck and need to be switched on and off.
=GRMC=
Max power transmitted when MZ is on the bright fringe = 80 mW
GRMC coupling 90%
A reference value for GRMC transmission: 49 mW corresponds to 1.78 V on the signal from PD in trasmission (TRA GRMC)
[Aritomi, 2*Eleonora]
We have realigned the CC and ML pick-off into the fibers:
ML: 1.4 mW → 0.19 mW, coupling: 0.19*2/1.4 = 27%
[Aritomi, Eleonora P., Eleonora C.]
Yesterday we have realigned both the BAB and the CC beam. After the difficuties found last week we decided to put a beamspliter in transmission from OPO and check the beam both with camera and PD.
The aligment was quite easy to achieve but even in a good condition we could see some residual scatteerd light coming from OPO in the camera.
We had a coupling of about 85% for BAB (pic 1) and 95% for CC (pic2).
The BAB is now injected using a magnetic flipping mirror (http://www.1md.co.jp/fbp1000s_E.php). (pic 3) We checked the reproducipility of the aligment after taking off and putting back the flip mirror. It is quite good (but not as good as reported in the datasheet (http://www.1md.co.jp/fbp1000s_E.php)): anyway a clear FSR with highTEM00 can be seen and the optimal condition is easy to recover.
Finally we had re-aligned the CC and Main laser pick-off into the fiber.
NOTE: Please when putting on and off the mirror follow the procedure in pic 4.
[Aritomi, 2*Eleonora, Matteo]
This is work on 8th last week.
First we replaced a flipping mirror for BAB. Then we changed the position of OD1 from f=125mm lens to before the flipping mirror as shown in attached pictures to reduce only CC power.
CC power before OPO with OD1 is 11.6mW and 121mW without OD1.
Then we tried to align BAB, but it was difficult. We also found that CC was misaligned a lot, too. P pol was fine. We checked the beam shape of transmission from OPO with a camera as shown in last attached picture. Apart from usual beam spot on the right of the camera, there was scattering light from OPO on the left.
We'll align BAB and CC this week with camera and PD.
with the parameters reported in elog entry 1239 we did the scan and the map of the black sapphire sample from Shinkosha.
Since the absorption is about 80%, there is a heavy depletion, so the scan is not symmetric.
The calibrated map looks different from the screenshots. It is because the screenshot shows the AC signal only, while the calibrated map is proportional to AC/DC, where DC is not constant because the probe is absorbed not uniformly.
[Matteo, 2*Eleonora]
We tried to check the effect of CC loop on the squeezing.
While bringing up the whole bench we had some trouble acquiring and keeping the lock of the CC PLL.
By modulating the green phase (10 Hz, 1.5 Vpp) we obtained a nice error signal for CC in reflection from OPO. Since the amplitude of such signal is maximum when the parametric gain is maximum we used it to find the optimal freqency offset for the p-pol PLL lock. It is 170 MHz and the correspondent CC error signal amplitude is ~ 65mV pp.
We centered the error signal around zero adding an offset and stopped the green phase modulation. See pic1.
We closed the loop (acting on the green phase shifter) using two stanford SR560 in series with the following parameters:
| cut off | gain | order | |
| 1- SR560 | 5 Hz | 200 | 1 |
| 2- SR560 | 30 Hz | 100 | 1 |
With only one SR560 we were not able to make it work.
We checked the CC error signal from the homodye: it shows a strange, not sinusoidal shape (even after checking and optimizing alignment). See pic2. We tried to close the loop on the LO phase shifter with one SR560 but we didn't succeed.
We measured squeezing at zero span at 200 kHz with the CC loop on the green phase closed and scanning the LO phase. Even if we saw the usual McDonald shape modualtion in the shot noise, its value was much higher than the shot noise level reference without squeezing. This is probably due to the CC beam reaching the homodyne. We will investigate the possibility to reduce its power.
Scanned the surf ref sample with the HeNe probe - Fig 1
R=AC/DC/P/Abs= 0.54/4.7/0.034/0.2 = 16.9W-1
Scanned the surf ref sample with the 1310nm probe - Fig 2
R=AC/DC/P/Abs= 0.086/1.98/0.034/0.2 = 6.4W-1
When changing the samples we wanted to have about the same DC signal on the PD so we changed the current of the 1310nm laser source.
1310nm parameters:
laser source current 0.7A -> PD DC: 2V (ref sample)
laser source current 1.97A -> PD DC: 2V (cryst coating sample)
Scanned the crystalline coating sample with the 1310nm probe - Fig 3
Abs = AC/DC/P/R = 0.0018/1.9/10/6.4 = 14.8ppm
Map 4mm diameter - Fig 4
Calibrated Map and histogram - Fig 5
Incident power 36mW
Transmitted power 6mW
x=305.432
y=118.823
zmax=65.55
x=305.432
y=111.823
zmax=65.55
x=310.432
y=118.823
zmax=65.55
MAP
range x: 310.432 - 298.432
range y: 109.823 -124.823
More precise measurement of the reflection/absorption characteristics of the sample. Chopper OFF (cw beam)
Sample position X = 304.432 Y = 117.323 Z = 65.55
Incident: 80+-1 mW
Transmitted: 7.45 +/- 0.05 mW
Refl: 6.3+/-0.3
The incident power on the sample was always P = 10 W.
[Marco Bazzan, Manuel Marchiò, Matteo Leonardi]
This is an update of the measurement campaign on Shinkosha sample S#4 where several time consuming maps were recorded.
Calibration as in entry 1221
We started a XZ map but it looked a little blurred (Figure 1), so we decided to launch a new one with a smaller step along X (Figure2). In that case the detail is better. We then tried a XY map with a small step, resulting in a series of striations with a period of about 50 microns (Figure3).
A final XY map was taken on a larger area (Figure 4).
The incident power on the sample was always P = 10 W.