Yuhang and Michael,

We would like to characterise frequency independent squeezing at the best performance we can manage before replacing the OPO. One task is to optimise the alignment of the local oscillator to the alignment mode cleaner, and same for squeezing (i.e. bright alignment beam). Here we checked the alignment of the LO to AMC. We found that the mode matching was still quite good, but there was some undesirable polarization that was leaking. So we added a half wave plate in the LO path just before the homodyne beam splitter. We adjusted the HWP polarization rotation, as well as the tilt and transverse displacement, to remove the unwanted transmission peaks. Then we aligned the LO to reduce higher order modes. The result is shown in figures 1 (TEM00) and 2 (others).

Also we noticed it was quite hot in the clean room. Checking the air conditioning gave a temperature of 25.9 C and humidity 32.8%. Given that it was cold leading up to this measurement we increased the cooling to the cleanroom air conditioner. Some alignment may be affected.

Marc, Matteo

We removed the AZTEC sample and installed the 2 razor blades on the translation stage.

We tuned the input polarization of the pump beam to s polarization (ie hwp angle of 45 deg)

With the translation stage set at z = 20 mm, we measured the distance between the edge of the injection breadboard and the blades to be 92 mm (horizontal one) and 97 mm (vertical one).

We measured the beam parameters as presented in fig 1 (again the z = 0 mm position is the same as in Manuel PhD) and got w0 = 36.24 um at z = 59.24 mm ie 2 mm further away than previous calibration.

By measuring the distance between the last lens of the inejction breadboard and the blades we tried to improve the vertical incidence angle at better than -0.248 deg.

Using the other blade we confirmed that the horizontal angle of incidence is about 2.7 deg.

For previous surface calibration we used z = 35 mm and z_IU = 68 mm. We did few scans at z = 35 mm and 37 mm but found out that the best calibration was obtained at z = 35 mm.

We measured R_surface = 16.12 /W and R_bulk = 0.6718 cm/W (where z_IU = 67.34 mm).

We reinstalled the AZTEC sample (orientation should be the same as previous measurements) and using the drop in the DC power we measured X_center = 327.293 mm and Y_center = 122.55 mm.

We reinstalled the black cover, all the required beam dumps and increased the laser power to about 7 W.

We started long z scans to find the 2 surfaces of the sample.

At first we found out some strange drop of the dc signal with z about 80 mm. It was because the translation stage was hitting the imaging unit black cover.

After moving it a bit further away we recovered the expected situation and started several measurements in the XY plane with 1 mm step size.

Pictures in the gluing today.

Today Takahashi-san glued the two magnets of end mirror. We will glue the magnet of input mirror and release the input/end mirrors next Monday. 

This entry reports the birefringence measurements of annealed AZTEC sample.

Note that here I normalized the s and p polarization power by their sum (see fig 1) so to be independent on the power fluctuations.

This does not affect the results much as we were considering the ratio of these power in any case.

Marc, Yuhang

We installed the GPS cable on the top of all the cables going around the central building up to the new dgs rack.

During this operation, we found the lightning arrester (HP 58505A). It is now installed above the bottom end of the stairs. We still need to connect it to the ground.

We also found out that the gps receiver had the led 'Alarm' on. But because we now have the lightning arrester we are confident that we could connect the gps cable directly to the irig-b card.

We turned on the 2 pc and during the boot we could saw the hardware that we previously installed. The os 'CentOS' is already installed but we don't know the pcs password so we could not investigate more.

We connected the tcp-ip switch to the switch used by the standalone pc with a 10 m long ethernet cable and connected the 2 pcs to this switch.

While turning off the front end pc (offline) it updated some drivers.

Marc, Yuhang

Today we installed all the required pcs and switches for the new DGS in the rack close to the input chamber.

From top to bottom there is :

• dolphin switch
• front end pc for central building
• myrinet switch
• tcp-ip switch
• data concentrator pc
• gps receiver
• camera server
• smart ups

We put label on each component but did not connected anything yet.

The key of the data concentrator pc is on the blue plastic container on the right side of the rack

I installed 2 adcs cards in cpu 1 slots 1 and 2 (respective S/N are 210128-11 and 210128-26) and 2 dac cards in cpu 2 slots 5 and 6 (respective S/N are 200813-74 and 200813-40).

It means that one cpu is responsible for adc while another one for dac however Aso-san told us that the manufacturer confirmed that every PCI-e slot should be able to communicate with all cpus so we will have to investigate a bit the BIOS.

The dolphin card is installed on the cpu 2 slot 8.

We are also supposed to install the myrinet connection but it seems we don't have more card with SFP connector so I'm guessing we will connect through ethernet to the myrinet switch.

With the 2 adc and 2 dac cards we have 128 channels available.

Marc, Michael

We installed the myricom and irig-b cards inside the data concentrator pc at respectively the cpu slot 7 (PCIe 3.0 * 8) and cpu slot5 (PCI-e 3.0 *8).

We had to change the mounting bracket of the irig-b card to fit in the back io of the pc.

The cpu slot 3 was already occupied with the hard disk controller (we had 32 TB available and extra few slots if necessary).

Note that to install (or remove) the myricom card it is required to first remove the SFP connectors.

We plan to connect the irig-b card to the gps receiver because we could not find the 'lightning stopper' box that is supposed to be at the end of the gps cable.

We also tidy up the rack we plan to use (closest to input chamber).

There are 2 smart ups at the bottom of the rack that were not connected. It could be useful in case of power shortage but we have to test them beforehand as they were made in 2005.

The allocation of the computers is the following:

CSP-38XQDR4: FE computer for Center Area

CSP-30EGSR4: FE computer for End Stations

CSP-32XES: DAQ computer (to run DataConcentrator, FrameBuilder and NDS servers. Also, the IRIG-B card should be installed into this computer.)

813M-3, SN BT0-2947105-001: Probably a server for GigE camera

It was found that the BAB OPO transmission passes through a mirror and a lens close by their edge. So I moved position of mirrors and lens to center them better. After this work, the mode matching from OPO to AMC didn't change.

[Takahashi, Aritomi, Marc, Yuhang]

As reported in elog2881, we suspect the Input H4, End H1,H3 magnets may fall down. To check this, we opened the input and end chambers and found that the Input H4, End H1,H3 magnets fell down as expected. Since the adhesive for glueing is empty, Takahashi-san ordered the new adhesive. Takahashi-san also ordered the jigs to glue more than one magnets at the same time. Takahashi-san will start the glue on next next Monday (April 4th).

I optimized mode matching from BAB to OPO yesterday, as reported in elog2896. In this elog, I suspected that the BAB OPO transmission may dependend on the alignment condition of BAB to OPO. To check this BAB OPO transmission, we can utilize AMC, which is a reference we have for both LO and squeezing (BAB OPO transmission represents squeezing since they are both resonant inside OPO).

The setting for BAB resonant inside OPO is: OPO temperature 7.164, p-pol PLL frequency 300MHz (60MHz is sent to ADF4002 from the second channel CH1 of AD9959). The lock of OPO was not just flicking a switch as usual, which has already been reported to Pierre and we are waiting for his help. Now the lock of OPO is done by firstly manually moving high voltage driver offset to make OPO on resonance. Secondly, put servo operation mode to 'MAN & LOCK'. Finally, flipping SIGN switch to trigger servo lock. Make sure the loop sign is 'INV' but not 'NON INV'.

After optimizing just alignment of BAB OPO transmission to AMC, I got a mode matching of 98.5%. The check of AMC transmission PD signal while PZT scanned is shown in figure 1, 2, 3, and 4. The 98.5% matching is calculated from these figures.

We should note that the higher order mode position is very different from a characterization done last time in elog1867. Also, at that moment, the BAB OPO tranmission matching to AMC is about 99.6%.

This new entry puts result of a better BAB matching to OPO.

The mis-matching is (42.8+6.4*3)/(42.8+6.4*3+1880) = 3.2%

The first two figures are the zoom in for higher orders modes taken from OPO transmission PD when OPO is scanned with PZT.

The third one is the whole signal from OPO transmission PD.

The new OPO construction work has finished. Before replacing the old OPO, we need to characterize the old OPO. However, it was found that the p-pol and BAB matching to OPO was not great (p-pol and BAB). In the case of BAB, it matches OPO's TEM00 by about 87%. So there is a worry that the OPO BAB transmission may contain some higher-order modes, which will be different from the mode shape of squeezed vacuum. If so, the BAB homodyne alignment doesn't permit an equivalent homodyne alignment for squeezing.

According to the Airy function and the higher-order mode spacing on FSR, when a cavity is locked on TEM00, we find that the OPO cavity can suppress TEM01/10 and TEM02/20 by ~1700 in terms of power. Therefore, this 13% higher-order mode will transmit OPO as only 0.006% when OPO is locked on TEM00—in this sense, improving BAB matching to OPO maybe not be very useful.

However, a better mode matching can make more power get transmitted from a cavity. In addition, some higher-order modes may be reduced if alignment can be improved. Especially in the current OPO design, the third higher order is very close to TEM00, which can be reduced if alignment becomes better. Therefore, the improvement of BAB alignment to OPO should be beneficial.

Before this work, the BAB passed through two lenses close to their edges, as shown in the attached figure 1 and 2. This was done on purpose because a 2-inch BS was used. At the moment of exacting BAB (more than three years ago), we had no proper 1-inch BS. So we need to replace 2-inch BS with a 1-inch one. Before this replacement, I checked the power transmitance of the 2-inch BS, as shown in the attached figure 3 (incidence) and 4 (transmission). We can see that 2.2% power is transmitted. In our storage, we have BSX11, which is a 1-inch BS and can transmit 2.4% s-polarized beam. So we can use BSX11 to replace the old BS.

For the moment, a clear edge mirror mount is used for 1-inch BS. Attached figure 5 shows the moment of 1-inch BS installation on mount, which shows also that an arrow on the side of BS barrel directs to the back side of mirror mount. This arrow points to the mirror AR side as per Thorlabs. However, this mirror mount introduces scattered light since some light hits on the 'non-clear' edge of this mirror mount. As shown in the attached figure 6, 7, and 8, we have beam hitting on mirror mount in 6 and 7. Figure 8 shows the scattered light after hitting on a mirror mount. Although expensive, we can solve this problem by using BS mount from FMD.

After this replacement, the CC and BAB alignment to OPO was recovered. At the same time, BAB was made sure to go through optics center as shown in figure 9 and 10. The CC is affected because it passes through this replaced BS. The previous 2-inch BS is thicker than the one-inch BS. So CC needs to be aligned back as well.

While waiting for measurement, I started to analyze data and found out that our measurements are clipped.

Indeed I forgot to change the Y center position of the sample while, to switch from absorption to birefringence, we add 2 steering mirrors that shift quite a lot the beam.

I checked the sample surfaces by looking at the position that minized both the s and p polarization power.

I measured Y_center = 160.37 mm and restarted measurements.

Figures 1 to 5 report the absorption measurements of the annealed AZTEC sample.

fig1 and 2 are respectively xz and yz measurements

fig 3, 4 and 5 are xy measurements at respectively z = 48 mm, z = 58.68 mm (center of sample) and z = 69.36 mm.

Few things to notice :

• Mean absorption is about 90 ppm/cm which is more than previously measured. I had a look at previous measurements and found that there was mistakes. The corrected results are in figure 6 to 8 which also show similar levels of absorption.
• The absorption along z is far less homogeneous than before. It might be a clue for contamination during the annealing and that the annealing duration was too short
• The xy measurements at z = 48 and 69 mm are far more homogeneous than at z = 58 mm. It could indicates that with longer annealing duration we could reach really homogeneous absorption.
• Comparing the xy measurements at the z center position (fig 4 and 6) we can recognize similar patterns. Because the markers on the sample barrel were cleaned before annealing (to avoid contamination), we could estimate that there is some rotation discrepancy between the 2

More analysis are also on-going

I went back to check around 17h.

The led for the phase-lock was on so it seems that we are able to well receive the GPS signal.

However the 1 pps signal did not changed..

I removed the blades and reinstalled the mirror on the translation stage.

I decrease the input power to about 240 uW so that the maximum voltage given by the PSD is about 0.8V (lock-in maximum being 1V).

I tuned the hwp and qwp together to get a linearized polarization.

For that, I roughly went to the s polarization input and then adjusted by hand the qwp angle and by 0.1 deg the hwp angle so to minimize the p polarization readout.

I could finally reach s polarization = 0.7808 V and p polarization = 187.5 uV that corresponds to an ellipticity of sqrt(1 - (s pol / p pol)^2) = 7N

The s polarization corresponds to hwp angle of 45 deg and p polarization to 90 deg (note that the round values come from some reset of the hwp angle readout that is solved by disconnecting/reconnecting the cable).

I started measurements in that condition.

They last about 1h30 hour with 0.5 mm step size and should be finished tomorrow.