s-pol mismatching solved

Participant: Eleonora and Yuhang

As we said during the last filter cavity meeting, the matching of s-pol inside OPO is becoming worse. Today we checked again and found something different. Especially we checked the shape of the first higher order mode. And another important effect is the higher order mode becomes higher after moving screws for yaw. All of these prove that the higher order mode is because of yaw misalignment.

Then we aligned s-pol and also p-pol. The alignment condition is taken as a photo and attached. The first one is for s-pol and the second one for p-pol.

Locking both p pol PLL and CC PLL

Cables we need

0.5 m LEMO-SMA x 2

2 m SMA-SMA x 2

5 m LEMO-SMA x 2

Please check the cable before you use it !

Test of PLL servo box

Since we found that we cannot lock PLL, I did the test of PLL by sending signal inside and checking output signal.

The PLL servo box contains

Input	local oscillator, beat note
output	fast control, slow control, mux
function	filter, integrator(switchable)

(Before doing test, we succeed in connecting computer and servo. We also succeeded in writing a desirable command to servo.)

 

Input signal:

1.Beat note: (1) 20MHz Sine wave with 100Hz frequency modulation, deviation of 1MHz. (2)20MHz Sine wave with 100Hz frequency modulation, deviation of 1kHz. (see attached figure 1 and 2)

2. Local oscillator: 20MHz from DDS board.

 

The purpose of using these two signals is to check how PLL acts when we have a "beat note" signal deviating from local oscillator. The result is as following:

1. Close the fast control loop. Sending beat note (1) and local oscillator. We check on oscilloscope and found it almost give just an offset of 10V. If we look at the AC of this signal, there is something(20mV) and the frequency is 100Hz. So it is sensing the difference between LO and BEAT.(see attached figure 3 and 4)

2. Open the fast control loop. Others are the same with rsult 1. We found almost nothing. So this means the small AC signal we get is because of the comparison of LO and BEAT.

3. We also tried to reduce the deviation. Close the loop and send beat note (2) and local oscillator. Then we got an AC signal without a clear frequency.

 

Conclusion: The PLL board has a problem. Actually we did the same test when Chienming was here. At that time, the signal we get from output channel is quite large.

Floor repaired in TAMA circuit prefab

Last Monday, the damaged part of the floor of TAMA circuit prefab (a.k.a elecshop) has been repaired.

In order to allow for the floor replacement we moved away everything in the interested area and we took the chance to do some cleaning.

We will put everything back in the next days and possibly tidy up a bit.

PLL lock input signal magnitude measurement

local oscillator amplitude 16dBm(DDS3 CH0)

beat note amplitude (p pol-main laser before amplification) is -7dBm

beat note amplitude (s pol-main laser before amplification) is -10dBm

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.