NAOJ GW Elog Logbook 3.2
Today I installed an optical lever to sense the motion of the suspended input mirror of the filter cavity. Such lever uses a lens and a pair of PSD respectively placed in the focal plane and in the image plane. In these scheme the PSD in the focal plane is only sensitive to mirror tilts while the one on the image plane can only sense its shift. A picture of the optical lever is shown in the figure attached.
A first injection of white noise has been performend in order to excite mirror resonances. After identifying the degree of freedom (tilt or shift) at which each resonance belongs it could be possible to fine-tune the PSD positions to optimize the signal decoupling.
I measured the beam profile of probe and pump near the crossing point.
Set a vertical blade to the translation stage and move it from PCI software.
Read data on the power meter and fit with erf function.
This table is a summary of the results.
| Probe | Pump | |||||
| z (mm) | y_0 (mm) | halfwidth (um) | y_0 (mm) | halfwidth (um) | ||
| 0 | 37.5 | 178 | 39.75 | 172 | ||
| 20 | 39.7 | 145 | 39.85 | 48 | ||
| 30 | 41 | 126 | 39.92 | 70 | ||
| 50 | 43 | 94 | 40 | 172 | ||
The probe waist is about 94um (radius at 1/e^2) but it is not near the crossing point. At the crossing point the beam size is about 290um (diameter).
The pump waist is about 48um (radius at 1/e^2) and is near the crossing point. At the crossing point the beam size is about 100um (diameter).
The angle between pump and probe is 0.105rad, or 6°.
The PCI manual said beamsizes of 200um and 70um. Which were the values I used until now in my simulations.
I will put those new measured parameters in the simulations.
We tested two properties of the laser will be used in the squeezing light experiment:
1. The correspondence between the current of diode and the output power of Laser
2. The position of the laser beam waist
The reports will be shown in the attachment.
Members: Eleonora, Manuel, Tatsumi, Yuefan
Some preliminary work has been done to prepare the installation of the oprical lever for controlling filter cavity input mirror (already suspended in NM2)
Mirror check
The suspendend mirror has been checked after the earthquakes of the past weekend. No damages have been found.
Coil drivers connection
The four coil drivers to be used to move the mirror have been connected.
PSD electronics
The electronics necessary to power and to read signals from the two PSD need for the optical lever has been assembled and checked. (See picture attached)
PSD calibration
PSD have been calibrated by shining a laser to them and looking at the change in the output voltage when gradually varying their position in x and y direction.
In the plot attached the voltage value has been normalized using the total output value (SUM). The (normalized) calibration value found is about 6.6*10-3 m/V
Laser check
We checked the dimension and the beam power of the laser to be use for the optical lever. Dimensions of the beam (measured with a beam profile after 30 cm) are about 1.1 mm. The recommended dimensions for the PSD are beetween 0.2 and 7 mm.
We also checked the PSD output as a function of the laser power and we observed that the signal saturates for a power higher than 0.15 mW.
The three mirror mounts has been delivered, unboxed and checked.
One mount for Kagra-size mirrors (ø220mm x 150mm)
One mount for Tama-size mirrors (ø100mm x 60mm)
One mount for 2inch samples (and smaller with adaptors that we already have).
All parts go well on the large translation stage and the stage can move without any obstruction.
-----------------------------------------------------------------------------------------------------------------------
The large translation stage, has been disassebled and packed.
Today the company person pick it up to clean it and to grease it.
I simulated the signal of the absorption system, in order to be able to compare the measurement reported in this post .
The reference sample is made of silica and absorbs 116%/cm. Thickness is 3.6mm. Chopper frequency 400Hz.
I attach an animated gif to show three aspects:
1. The colored image represents the temperature distribution inside the bulk reference sample, heated by the horizontal pump beam. The shadow represents the probe beam at an angle of 7° to the pump.
Moving the sample along the z axis (along the pump beam) make the crossing point of pump and probe to scan the depth of the sample, and it is equivalent to move the probe vertically respect to the pump.
2. The interference pattern is the difference between the intensity of the probe passing through the heated sample and the intensity of the probe not passing through the sample. This is because the heating is modulated. The signal is given by the integral of the interference pattern in the area of the photodetector. The area of the photodetector is represented by the black square.
3. The plot is the calculated signal from the lock-in as a function of the sample depth. The 0 is when the pump-probe crossin point is at the surface of the sample.
Members: Takahashi, Tatsumi, Guo, Manuel.
We suspended a temporary mirror in the NM2 vacuum tank.
Set the earthquake stoppers at about 1mm from the mirror.
Set the 4 coil actuators coaxially aligned to the magnets.
Closed the vacuum tank.
I made glueing of four magnets on a LISM mirror.
See attched PDF file.
Page 1: Magnet polarity check
Page 2: Anti-Reflection coating check by green lase pointer
Page 3: Overall view of the glueing JIG
Page 4, 5: Closer view of Magnet clamping parts
See JPEG file:
This is TAMA traditional magnet configuration.
I also follow this.
Members: Tatsumi, Guo, Manuel.
We moved and clean an optical table in the central room of TAMA. The attached image shows from where to where.
I and Torii-san finished writing a manual for the JASMINE scatterometer in the ATC.
It is uploaded on the JGW website and available in Japanese and English.
I study on modulation frequency for SHG cavity.
Because the cavity is very short (30mm or less),
it has FSR of 4 GHz and has a finesse of 75.
These correspond to resonant width of 53 MHz.
By using FINESSE simulator,
I checked the PDH signals for each modulation frequency.
fmod merit demerit
600MHz non-resonant sideband modulation frequency is too high
15MHz TAMA used this freq. The PDH signal get smaller by a factor of 10.
I think that modulation frequency of 15 MHz is acceptable for us.
I made four test samples as shown in bellows.
Before the glueings, mirror surfaces were cleaned up by First Contact
(mainly to remove oils on these).
I will send sample A and C to Hirose-san on 25 December (tomorrow).
Because we found that Sapphire Wire Breakers are broken in the curing process of the glueing,
(see k-log http://klog.icrr.u-tokyo.ac.jp/osl/?r=451)
we inspected the remaining eight Sapphire WBs.
I cannot find any obvious cracks in these.
Due to the sand surfaces of that, I cannot inspect micro-cracks.
[RELATED ENTRY]
http://www2.nao.ac.jp/~gw-elog/osl/?r=45
JGW-T1503409 http://gwdoc.icrr.u-tokyo.ac.jp/cgi-bin/private/DocDB/ShowDocument?docid=3409
Because we found that Sapphire Wire Breakers are broken in the curing process of the glueing,
(see k-log http://klog.icrr.u-tokyo.ac.jp/osl/?r=451)
we inspected the remaining eight Sapphire WBs.
I cannot find any obvious cracks in these.
Due to the sand surfaces of that, I cannot inspect micro-cracks.
A gap between the data of VB measured with our back-scatterometer and the data provided by SurreyNanoSystems made me curious about a possible offset in our data (our data were constantly 10 x higher). So I searched for systematical errors and ended up on the beam-splitter. It seems that by illuminating it with the laser, the PD gets a signal of 0.252nA even when the backscattering is cut of.
My interpretation is that this additional signal is actually scattering from the beam-splitter.
I am now thinking how we can get rid of this influence without violating the SNR too much severely.
Workers: Eleonora and Tatsumi
Today we replaced the double pendulum installed in NM2 vacuum tank with the one used to suspend the TAMA power recycling mirror (placed In RM vacuum chamber)
Power recycling mirror was still suspended and we succeded in moving the suspension with the mirrorr hanged. In the next days we planned to take a spectrum of the mirror motion to check the effectiveness of the stack and suspension system.
We also started preparing an optical lever needed to measure this spectrum.
Workers: Eleonora, Tatsumi, Takahashi
Today we completed the installation of the vibration isolation system needed to suspend the filter cavity input mirror in the NM2 vacuum tank.
Such a system is composed by (from bottom to top):
- A baseplate (see picture 1)
- A three layer stack made of rubber and metal blocks (see picture 2)
- A top-plate
- A double pendulum system
In picture 3 the empty bottom of the vacuum tank is showed while in picture 4 the complete system can be seen.
Some test of vibration isolation are planned for the next days.
Workers: Eleonora and Tatsumi
Today current TAMA SAS system has been safely removed from NM2 vacuum tank. The vibration isolation system to be installed at its place is currently placed in PD vacuum tank ( e-log 201) and can be now moved in NM2 vacuum tank.
I have measured the new VB-S sample and again the original VB-plate in order to compare these two.
Surprisingly, the VB-S sample is more "black" than the original sample although the other way around should have been occured. Also, it seems that the VB-plate-blackness altered when comparing this with a measurement from January...
In all these, I have to add that the data in the measurement from January may be not comparable as the system was still under reconstruction at that time. Also, as it is the first time for me to use Torii-sans setup, I am not sure whether there is still a mistake in the absolute values...
We star by checked the double-pendulum system which were moved form warehouse to TAMA central room.
We found that coil mass and electric cable were missing (fig 1-2).
We opened PD vacuum chamber and we found a completely assembled isolator stack with a double-pendulum system (fig 3).
(It was meant to be used to suspend a signal recycling mirror in TAMA.)
We checked this system too and we found that just the electric connectig cable was missing.
Since this vibration isolation system (both double pendulum and stack isolator) is in a better condition than the one stored in the warehouse,
we planned to use this one for suspending filter cavity input mirror in NM2 vacuum tank.
In order to do that, we checked that system dimensions were compatible with the ones needed for NM2 tank (fig 4-5).
Next week we will remove current TAMA SAS system from NM2 vacuum tank and we will replace it with the vibration isolation system at present placed in PD vacuum chamber.
