The direction of the probe changes inside the sample according to the Snell's law. As I calculated in this post

I included this effect in the optical part of my simulations. I show the simulation of the scan of the silica bulk reference sample, with and without the refraction effect.

The sample thickness is 3.6mm. With the refraction effect, the simulation is more similar to the measurement. Apart from the unknown scale factor.

I attach the slides that I presented at the last meeting on May 18 (slides from 1 to 6)

and the slides about the progress I did in these these days (slides from 7 to 11).

Slides 8 and 9 have two animations which don't move in the pdf.

I attach also the GIFs.

X axis unit of the histograms in the GIFs is ppm/cm

I couldn't upload the pdf file at once, so I had to split it in two.

We got the SiC samples back from KEK last week. Unfortunately, I discovered some dark spots on the polished surface on at least 3 of 7 samples. 

The pictures below show these spots on a NFC (first picture) and Covalent (second one) sample.

I made a calculation that might explain why I couldn't see any absorption signal.

The cross point between pump and probe changes position when there is a thick sapphire sample.

Details are in the attached slide.

This might also explain why in my simulations the simulated scan shows a thicker sample than the measured scan. I will include this effect in the simulations and check the result.

I attach a report about the measurements I did this week

I set the parameters thresholds on the controller (CLD1015) as specified in the butterfly package specs (FPL1053P):

LD max current: 450mA

TEC max current: 500mA

There are two possible operation modes: "Constant Current mode" and "Constant Power mode"

- The "Constant Current" mode keeps the LD current constant (and is used for fast laser modulation)

- The "Constant Power" mode uses the current of a PD placed inside the butterfly package to monitor the output power. 

I set the operation mode on "Costant Current" and make measurements of the optical power using a powermeter. I attach the pdf of the  measurements.

I couldn't use the "Constant power" mode because as soon as I switch on the laser, the  LD current reaches immediately the maximum (450mA as set before), even if I set the minimum PD current. It looks the controller is not able to measure the PD current, I attach a picture of this situation (pic1).

I also noticed that the PAF-X-11-C is bent (pic2) like Pisa's tower, I disassembled the clamp plate (pic3) and removed the "Bulkhead", which is the bent part, I think it is a fabrication defect.

Because Manuel claimed that the optical chopper has some problems,

I checked the chopper before sending it back.

[ CONCLUSION ]

The chopper has no problems and works well.

I mounted the butterfly package FPL1053P on the controller following the instructions step by step:

 - Check the 14 pins orientation.

 - Remove the laser mount and install it according to the type of pinout (Pinout standard: "Pump"). Actually it was already in the right orientation.

 - Open the ZIF ("Zero Insertion Force") socket clamps. Picture.

 - Apply the thermal conductive pad to improve thermal contact between laser and heat sink. Picture.

 - Fix the laser diode to the laser mount using the attached 4 screws and close the clamps. Picture.

In order to ensure the best thermal contact between the bottom plate of the laser diode (hot side of peltier) and the surface of the laser mount, the instructions recommend to use thermal compound.

Do we have it?

To mount the fiber I used the PAF-X-11-C but I need something like this HCA3-SM1, do we have it?

I'm doing the ignition test of the 1310nm laser.

I have to install the "Butterfly package" FPL1053P inside the laser diode controller CLD1015.

First of all, according to the instructions, a good grounding is needed because electrostatic shocks are very dangerous for the laser.

On the rear panel of the controller there is a 4mm-diameter hole for the ground jack, but the cable is not included. So I made it.

Since the optical table has plastic wheels, it might be a bad ground. So I think the best way is to connect it to the network ground.

I isolated the brown and blue wires of a power cable, selected the ground wire and soldered it to a banana connector.

I proofed and confirmed the adjustment of the new PD in the scatterometer.

Hence, the exchange of the PD is now officially finished.

Members: Tatsumi, Manuel, Fabian

We cleaned up a bit in Tama central room: floor, garbage and a lot of dust (as usual, the picture can give an idea).

We moved the black rack and a small optical table downstairs. Removed the covering frame and  put it below the vacuum pipe in the west arm.

Now  there are two cleaned (shining) small optical tables: one is for Fabian's experiment, and one will be used to make ignition test of the new 1310nm laser for GaAs absorption measurements.

I finished the English version of the manual for the back-scatterometer.

It can be downloaded from the JGW document server (I and Torii-san are the authors).

Members: Tatsumi, Manuel

Measured the bulk reference sample: Pump_power=30mW, Chopper=430Hz; AC=74mV; DC=3.94V; Abs=1.16/cm; --> calibration factor R=0.55W^-1. fig.

Measured the surface reference sample:  Pump_power=30mW, Chopper=430Hz; AC=380mV; DC=4.75V; Abs=0.22; --> calibration factor R=12W^-1. fig.

Both values of R are consistent with the calibrations we made last year (considering a repeatability of 5-10%).

=================================================================================================================

Measured the shinkousha little sample (1.5"diameter) with pump maximum power 9W.

Scan along z axis: fig. Today's measurement looks noisier because I didn't apply the filter

Resolved map: fig. It show the same unhomogeneus pattern al last time we measured it.

=================================================================================================================

Measured the 2 sapphire tama-sized samples Hirose-san sent us few months ago:

the translation stage is too weak to bear 100mmx60mm samples, so we tried to put a height tunable jack on the table and the new mirror mount over it. Unfortunately, because of the translation stage position, there was not room enough to to reach the center of the sample. So we  changed the jack with some heavy blocks and a V-shape. Then we could reach the center of the sample. We measured the probe AC noise and we found that with the probe passing through the sample, the noise (~50microV) is double respect to the noise without the sample (25microV). This means that a large part of the noise is due to the sample vibrations. So we put a rubber sheet below the block. But the noise doesn't change considerably. fig.

So we have ~50microV of noise level, which correspond in ppm/cm for sapphire at 9W pump power to ~50e-6V*3.34/6.5/9W/0.55W-1 = ~6ppm/cm

The specs say 5ppm/cm for silica at 1W, which for sapphire (3.34 correction factor) and 9W, correspond to about 2ppm/cm. So we have a noise level higher than what the specs say.

To measure the signal I take the mean of the AC signal (lock-in time constant 1s) over 100s

The point positions are  shown in the picture. As best as I could do with this setup, the positioning has a 3mm error.

The measured absorption value is always below the noise.

On friday afternoon Flaminio and me noticed that the chopper frequency is quite unstable, about 5Hz of standard deviation. The old one was not that unstable. We should check it.

Two days later, I found that the wheel was stopped.

Therefore, I and Manuel replace the new motor with chopper also.

I made a simulation of the temperature distribution on a GaAs sample of 0.4mm in thinckness and 5% of absorption.

First with the absorption distributed on all the substrate (bulk) and then only on the coating (surface).

Plot the map of the temperature, as a function of the depth and of the radius, for both cases (bulk and surface).

Used the temperature distribution in the optical simulation with a 1310nm wavelength probe.

Simulated a scan along the sample for both cases and found the same value of the AC/DC PD signal. 

I and Akutsu-san went to Hashimoto today and insected the final results on the Doughnut Baffle production.
So far, it seems that the results are OK and within the constraints of bKAGRA. However, due to the baking procedure, scratches appeared on at least on side of each baffle. Yet, they will probably have no big impact on the scattering, according to the simulations.

The results plus some pictures taken at the facility, are summarized in a JGW document.

Because the mechanical chopper on absorption measurement bench was broken,

we bought new one (Stanford research instruments SR540).

Today I repalce the controller (motor driver with local oscillator) of the chopper.

Old chopping motor and wheel are unchanged, since we want to keep the setup

as much as possible.

After the replacement, I checked all of cable connections.

And then, I found that many cables are unplugged.

Tomorrow I will check the absorption measurement system by using reference samples.