Sapphire Namiki 1inch x 20mm

Members: Marco Bazzan, Manuel

P=32mW
We aligned the red probe with the surface reference sample.
Then we calibrated the bulk absorption.
Ac= 0.1V; DC=4.75V. T_ref=55%
R=0.1/4.75/0.032/sqrt(0.55)/1.04=0.85 cm/W

at 17:45 - Mounted the Namiki sapphire sample
Imaging unit position corrected for sample thickness by Delta_z = 8.6 mm
Rised the power to 1 W by rotating the IPC HWP
T_sapp=86%

Although noisy, we can observe an absorption profile by scanning the sample along z (see first screenshot). The profile is confirmed by flipping the sample (see second screenshot).

AC max = 250uV
DC=5V
Max absorption level estimate:

250/5/1/sqrt(0.86)/R*3.34 = 212 ppm/cm

PLL fiber coupling

Re-alignment of fiber for PLL and fiber fluctuation

Replace of fiber splitter

We found the fiber for ppol-mainlaser PLL (FC1064-50B-FC) was broken. We replaced it by a new one (PN1064R5F2).

Locking procedure of coherent control

Original position of flipping mirror for Bright Alignment Beam

Attached picture shows micrometer of  flipping mirror for BAB when BAB is aligned to OPO.

Fiber coupling for coherent control PLL

[Aritomi, Yuhang, Matteo]

500MHz oscillator now provides four clock signals

[Matteo, Eleonora]

Last Friday we have modified the 500MHz oscillator (realized by Pierre) to make it provide two more channels (four in total).

We have simply replaced the two channel splitter inside (pic1) with a four channel splitter (pic 2-3) and modified the front pannel accordingly (pic4).

Now we can supply the 500MHz clock signal to all the three DDS boards we have. 

Installation of KAGRA DGS

Last Thursday and Friday Oshino-san and Miyakawa-san have installed a standalone version of the KAGRA digital sytem in TAMA.

The rack with PC, DAC, ADC and AI and AA filters is placed in the South-East corner of the central building, beside the desks. 

Even if some more work is still necessary and the installation will be completed in the next days,  we can already start to build our similink model.

More details on the system will follow. 

One important caveat: every time that we switch off the computer on the rack (Pic1) we should also disconnect the cables on the back (Pic 2) before switching it on again. 

Comment to Additional DDS board assembled (Click here to view original report: 1181)

DDS1
channel	function	frequency	phase
CH0	EOM SHG/IR-MC	15.2MHz	0deg
CH1	SHG + IR-MC demod	15.2MHz	0deg
CH2	EOM OPO	87.6MHz	0deg
CH3	OPO demod	87.6MHz	135deg

DDS2
channel	function	frequency	phase
CH0	EOM FC/GR-MC	78.0MHz	0deg
CH1	FC demod	78.0MHz	~
CH2	GR-MC demod	78.0MHz	60 deg
CH3

Squeezing at lower frequency

Characterization of all the RF amplification channels

As entitled.

CHANNEL NAME	AMPLIFICATION
AOM FC	37.3dB
EOM SHG+MCIR	20.8dB
EOM FC+MCGR.	20.8dB
EOM OPO	20.9dB
DEMOD SHG	13.6dB
DEMOD MCIR	13.5dB
DEMOD FC	13.6dB
DEMOD MCGR	13.7dB
DEMOD OPO	13.7dB
DEMOD CC	14.1dB
PLL OPO lenght	18.8dB
PLL CC	18.7dB

Labels with the amplification values have been applied to all the channels.

Measurement of first squeezing

Laser demo replacement

The new laser Thorlabs S1FC1310PM was delivered today together with the optical fiber.
I replaced the demo laser with the new laser. (the demo laser was the same model).
I switched it on, it works, and the alignment looks fine.

The demo is ready to be shipped back to Thorlabs.

Today PLL parameters

[Matteo, Eleonora, Aritomi]

Memo of parameter for the lock of the PLL (no green injection, only p-pol and BAB).

T_OPO = 7.038kOhm

ppol PLL LO freq = 130MHz

DDS3_ch0 = 65MHz

PLL R = 1
PLL N = 2
Reference freq = 65MHz
Charge pump setting 1 = 1.875mA

OPO locking parameter

[Matteo, Eleonora, Aritomi]

The gain of the SR560 used for the OPO lock was changed from 5 to 20. The lock seems more stable now.

Re-alignment of HeNe probe and calibration

I switched on everything after the last power shut down.

I re-aligned the HeNe probe with the surface reference sample, and made a calibration scan, then, a calibration scan of the bulk reference sample.

The pump power is 30mW, so,
for the bulk:      R = 0.08/4.75/0.03/1.04 = 0.54 cm/W
for the surface: R = 0.52 /4.1 /0.03 / 0.2 = 21.1 W-1

Re-measurement of parametric gain

Additional DDS board assembled

[Matteo, Eleonora]

We have assembled an additional DDS board able to provide four RF signals.

For the assembly, we took as a model one of the two boards already realized at ATC. Pictures of the new board are attached.

The board have been tested and seems to work well.

Now we have three DDS boards providing four channels each. Here the "final" channel assignment we plan to have:

BOARD 1

Preparation for squeezing measurement(stability after removing second FI, align green into OPO)

[Aritomi, Yuhang]

We recovered the BAB alginment into OPO after removing second FI. The stability is also measured in the infrared path. As shown in the attached figure 1, it is quite stable(the fluctuation is only within 1%). From the experience, the stability is related to how well we align SHG. From the spectrum on the oscilloscpe we got after removing the second FI. And compare with the spectrum we got during Chienming is here. It is obvious that the alignment is worse than that time. So this stable infrared light is reasonable.

We also measured the green production efficiency, now it is 163/540.8=30%. This is lower than the effciency 35% when we have a better matching/alighnment. But still higher than the situation before Chienming came, at that time efficiency is only 20%. Although the efficiency is worse, but we have maximam 50mW going to OPO. While the threshold is 80mW for OPO. So we can use this power to observe a desirable level of squeezing. We can also increase the injection power to SHG if we want higher green power. So it should be fine with this alignment condition.

However, we found the parametric (de)amplification process has some abnormal behavior. If you check this video in the attached link, you can see the scanning peak has a roughly 50% of fluctuation(sorry I didn't take quite long time and this fluctuation doesn't have a clear frequency).  And seems there are two peaks they are competing with each other. Sometimes, the pump goes into one. Sometimes the other. Actually after we realize this problem, we start to check the fluctuation of infrared and green. They are as good as before. We also checked if we have mode hop. Even it is clear form the SHG scanning that we don't have this problem. After trying to change the temperature, we didn't find mode hop around our present situation. I also asked Chienming, he confirmed we didn't have this kind of fluctuation. But we didn't check the phase shifter, temperature control or some vibration. 

https://drive.google.com/open?id=1826D5cbTQ0ybPrw5KCKM0WpFTSIdkpUQ

Figure1: The statics of infrared beam(BAB) power.

Figure2: THe statics of green beam(before green EOM) power.

Figure3: SHG injection beam power.