First Contact Kit by Calum
Class A Kapton sheets
The OMC mode matching sled was fixed on the nominal part of the table. Then the OMC was located at the nominal position marked by three poles.
The input periscope was adjusted to have the input beam roughtly centered on the OMC QPDs. This made the beam from FM2 aligned to the missing CM1, and the beam just went through the hole of the mounting prism. Very promising!
I wanted to use the new (modified) mirror gluing fixture to hold a curved mirror on the mounting prism. It turned out that the fixture was neither cleaned nor assembled. I will ask Downs Team to help me to get the cleaned and assembled fixtures.
Meanwhile, I just reused the original gluing fixture upside down in order to proceed cavity alignment and locking. (Attachment 1)
In fact, once the mirror is placed on the mounting prism, the cavity started to flash without further alignment. I thank for the very precise (repeatable) alignment of the OMC optics and PD/QPDs.
The next steps are initial cavity locking, more alignment, and mode matching.
The OMC cavity was locked. The alignment was precisely adjusted. The mode matching was optimized by the lens positions. The reflection during the lock is ~0.01 compared to the full reflection on non-resonance, meaning the mode matching is ~99%. The error signal was maximized (i.e. demod pahse was adjusted) by sweeping the modulation frequency. Note that the EOM is broad band. The modulation freq chosen today was 34.6MHz.
- The error signal has not been preamplified at all yet. Because of this, the reflection is very much sensitive to the input offset.
- The OMC needs wind shield to prevent from the noise caused by air turbulance.
- The laser PZT was actuated via the Thorlabs HV amp. Otherwise, the thermal path needs to be configured.
- One of the CCD monitor is dead. Needs more replacement.
- All the electronics should be moved to the rack. This required long BNC and SMA cables.
- The optical table needs cleaning.
- DC output of the trans RF PD was connected to the BNC patch panel. => Now CH4 of the scope is monitoring this signal
- The RF sweep signal from the network analyzer is connected to the power combiner for the EOM drive via the SMA patch panel.
- The trans RF PD was aligned first to the leakage beam. It turned out that this signal is too weak. Then the PD was aligned to one of the main OMC transmission. For this purpose, the OMC DCPD (T) was removed from the OMC breadboard.
- It seems that there is a significant amount of RF AM from the EOM. I suspect it is associated with the residual S-pol and birefringence of the steering mirrors (45deg HR). But the HWP at the output of the Faraday is fixed on the Faraday body with a screw and cumbersome for fine adjustment. A PBS and an HWP are added right before the EOM. This made the fiber coupler slightly misaligned. I suppose this new setup still has S&P on the fiber too. Thus, readjustment of the fiber rotations at the input is necessary.
- Input power to the fiber should be determined before the EOM. Otherwise, touching the HWP before the EOM causes too much power change at the optics of the OMC side.
- Precise adjustment of the RFAM is still necessary.
- The OMC curved mirror should be held by the new fixture.
- Check the beam spots
- Measure cavity parameters. (transmission/FSR/HOM/etc)
==> Then the curved mirror and the PZT will be glued on the prism
Last week, I further worked on the RF system to install 20dB coupler on the agilent unit and setup the R channel. This allowed me to make the FSR/TMS measurement of the OMC.
And today several optical improvement has been done.
- The input/output fiber couplers were adjusted to have the maximum transmission through the PBS right before the OMC.
- The HWP on the output side of the faraday was adjusted to have ~40mW input to the OMC.
Then, the OMC curved mirror is now held by the new in-situ gluing fixture instead of the conventional fixture attached upside down.
The OMC was ocked again and the input alignment was adjutsed. The fixture is blocking the QPD path, so it's not possible to confirm the proper alignment of the cavity (w.r.t. the QPD paths).
The precise positions of the spots could not be confirmed as the battery of the IR viewer was empty. Quick check of the spots by the card tells that the spot on the CM2 (PD side) is slightly too close to FM2 (output coupler). I wonder if this could be solved by rotating the curved mirror.
Otherwise everything look good. Let's try to glue the curved mirror tomorrow.
Note: Spot on CM2 is too close to the edge of the hole on the mounting prism. The meausrementof CM1 is telling that the curverture center is located 2.7mm upper side of the center of the mirror if the HR side arrow is up (and it is the case). If we move the arrow to the QPD path side (90deg CW viewed from the face side), this corresponds to ~1.1mrad CCW tilt in Yaw (viewed from the top of the prism). According to the matrix calculation (T1500060) this will induce ~1.5mm shift of the beam. This should be tried before gluing.
- Replaced the PZT with the one used from the beginning. This must be PZT #21. After the replacement, the spot positions look very good. I even went up. So I decided this is the configuration to proceed to the gluing. The CM1 mirror has the HR arrow at the top.
- The input beam was realigned w.r.t. the OMC.
- Tried to use the IR viewer with the new rechargable battery brought from the 40m. But the view still didn't work. The possibility is a) the viewer is broken b) the battery is empty.
- Tried to use the stainless clean regulartor for the UHP N2. The outlet has a short tube with a different diameter. The O.D. of the old tube is 6.3mm, while the new one is 9.5mm. If I insert the thinner tube in the new tube, it approximately fits. But I don't believe this is the way...
- Forgot to close the cylinder valve...
v HEPA prefilter (20"x20"x1" MERV 7)
- Replace the filter for the air conditioning
v Texwipe TX715 SWAB http://www.texwipe.com/store/p-817-tx715.aspx
v Gloves ~3 bags
VWR GLOVE ACCTCH NR-LTX SZ7.0 PK25 79999-304 x3
VWR GLOVE ACCTCH NR-LTX SZ7.5 PK25 79999-306 x1
v Vectra IPA soaked cloths
v Sticky mats
ORDERED AUG 9, 2017
The OMC #002 was packed for the transportation to Downs.
===> And transported to Downs 227 on Jul 6th.
Attachment 1: The PD was removed from the transmission side of the OMC #002 (former LHO OMC - the one blasted by the optical pulse in Aug 2016).
It was confirmed that the PD has the scribing mark saying "A".
Attachment 2: This diode had no glass cap on it. The photodiode sensitive element is still intact. For ease of handling, it should be kept in a cage. There are four cages in the OMC lab, but they are ocuppied with the High QE PDs and others. So, the cage for this PD was offered by Rich from his office, meaning the cage was not clean.
Attachment 3: The sensor side is capped by a plate. This cap can be removed by unscrewing the two cap screws in the photo.
Attachment 4: The PD legs are shorted. (Just to match the style with the LLO one).
Attachment 5: Wrapped with AL foil and double bagged. (Repeat: It is not anything clean.)
Attachment 6: The bag was left on Rich's desk.
Norna Robertson, Stephen Appert || 29 Nov 2017, 2 pm to 4 pm || 227 Downs, CIT
We made some preparations for modal testing, but did not have enough time to make measurements. Below is an after-the-fact log, including some observations and photos of the current state of the OMC bench.
I’ve borrowed the black and decker toaster oven to dry some sonicated parts. It is temporarly located in the QIL lab.
Attached is a block diagram of the test setup used in the 40m lab to measure the modulation index of the IO modulator
The impedances of the new LLO EOM were measured with the beat note setup at the 40m PSL (as described in the previous ELOG entry.
At the target frequencies (9.1MHz, 24.1MHz, 45.5MHz, 118.3MHz), the modulation responses were (0.09, 2.9e-3, 0.053, 0.021) rad/V.
This corresponds to the requirement for the driving power as follows.
0. If you have an RF signal whose waveform is , the amplitude is constant and 1.
1. If the waveform , the amplitude has the DC value of 1 and AM with the amplitude of 0.1 (i.e. swing is from 0.9 to 1.1). Therefore the RMS RIN of this signal is 0.1/1/Sqrt(2).
2. The above waveform can be expanded by the exponentials.
Therefore the sideband carrier ratio R is 0.025/0.5 = 0.05. This corresponds to 20 log10(0.05) = -26dBc
In total, we get the relationship of dBc and RIN as , or R = RIN/sqrt(2)
OMC #002 Optical tests
(Cabling / Wiring)
(Packing / Shipping)
OMC(002) repair completed
When the cable harness of OMC(004) is going to be assembled, the cable harness of OMC(002) will be replaced with the PEEK one. Otherwise, the work has been done.
Note that there are no DCPDs installed to the unit. (Each site has two in the OMC and two more as the spares)
More photos: https://photos.app.goo.gl/XdU1NPcmaXhATMXw6
Preparation for the PZT subassembly bonding (Section 6.2 and 7.3 of T1500060 (aLIGO OMC optical testing procedure)
- Gluing fixture (Qty 4)
- Silica sphere powder
- Electric scale
- Toaster oven for epoxy mixture qualification
- M prisms
- C prisms
- Noliac PZTs
- Cleaning tools (forceps, tweezers)
- Bonding kits (copper wires, steering sticks)
- Thorlabs BA-2 bases Qty2
- Razor blades
Preparation for the PZT subassembly bonding (Section 6.2 and 7.3 of T1500060 (aLIGO OMC optical testing procedure)
- Gluing FIxture (Qty4)
- Silica Sphere Powder
- Electric scale
- Toaster Oven for epoxy mixture qualification
- M prisms
- C prisms
- Noliac PZTs
- Cleaning tools (forceps, tweezers)
- Bonding kits (copper wires, steering sticks)
- Thorlabs BA-2 bases Qty2
- Razor Blades
Also brought to the 40m on 10 April, in preparation for PZT subassembly bonding:
- new EP30-2 epoxy (purchased Jan 2019, expiring Jul 2019 - as documented on documents attached to glue, also documented at C1900052.
- EP30-2 tool kit (maintained by Calum, consisting of mixing nozzles, various spatulas, etc)
Already at the 40m for use within PZT subassembly bonding:
- "dirty" ABO A with temperature controller (for controlled ramping of curing bake)
- clean work areas on laminar flow benches
- Class B tools, packaging supplies, IPA "red wipes", etc.
Upon reviewing EP30-2 procedure T1300322 (current revision v6) and OMC assembly procedure E1300201 (current revision v1) it appears that we have gathered everything required.
The baking of the PZT subassemblies was more complicated than we initially thought.
The four PZT subassemblies were placed in the air bake oven A. We meant to bake the assemblies with the ramp time of 2.5h, a plateau of 2h at 94degC, and slow ramp down.
The oven controller was started and the temperature has been monitored. The ramping up was ~20% faster than expected (0.57degC/min instead of 0.47degC/min), but at least it was linear and steady.
Once the temperature reached the set temperature (around t=120min), the temperature started oscillating between 74 and 94degC. Stephen's interpretation was that the PID loop of the controller was not on and the controller falled into the dead-bang mode (=sort of bang-bang control).
As the assembly was already exposed to T>70F for more than 2.5hours, it was expected the epoxy cure was done. Our concern was mainly the fast temperature change and associated stress due to thermal expansion, which may cause delamination of the joint. To increase the heat capacity of the load, we decided to introduce more components (suspension balance weights). We also decided to cover the oven with an insulator so that the conductive heat loss was reduced.
However, the controller thought it was already the end of the baking process and turned to stand-by mode (i.e. turned off everything). This started to cause rapid temp drop. So I (Koji) decided to give a manual heat control for mind cooling. When the controller is turned off and on, it gives some heat for ramping up. So the number of heat pulses and the intervals were manually controlled to give the temp drop of ~0.5degC/min. Around t=325, the temperature decay was already slower than 0.5degC/min without heat pulse, so I decided to leave the lab.
We will check the condition of the sub-assemblies tomorrow (Fri) afternoon.
(Friday afternoon) We retrieved the PZT sub-assemblies to the clean room.
We started removing the ASSYs from the fixtures. We noticed that some part of the glass and PZT are ripped off from the ASSY and stuck with the fixture. For three ASSYs (except for #9), the effect is minimal. However, ASSY #9 has two large removals on the front surface, and one of the bottom corners got chipped. This #9 is still usable, I believe, but let's avoid to use this unit for the OMC. Individual inspection of the ASSYs is posted in the following entries.
This kind of fracture events was not visible for the past 6 PZT sub-ASSYs. This may indicate a few possibilities:
- More rigorous quality control of EP30-2 was carried out for the PZT ASSY bonding. (The procedure was defined after the past OMC production.) The procedure leads to the strength of the epoxy enhanced.
- During the strong and fast thermal cycling, the glass was exposed to stress, and this might make the glass more prone to fracture.
For the production of the A+ units, we think we can avoid the issues by modifying the fixtures. Also, reliable temperature control/monitor technology should be employed. These improvements should be confirmed with the bonding of spare PZTs and blank 1/2" mirrors before gluing any precious components.
Probably the best glued unit among the four.
Attachment #1: Mounting Block SN001
Attachment #2: PZT-Mounting Block bonding looks completely wet. Excellent.
Attachment #3: The other side of the PZT-Mounting Block bonding. Also looks excellent.
Attachment #4: Overall look.
Attachment #5: The mirror-PZT bonding also look excellent. The mounting block surface has many EP30-2 residue. But they were shaved off later. The center area of the aperture is clear.
Attachment #6: A small fracture of the mirror barrel is visible (at 7 o'clock).
Attachment #1: Mounting Block SN007
Attachment #2: Overall look.
Attachment #3: Some fracture on the barrel visible.
Attachment #4: It is visible that a part of the PZT removed. Otherwise, PZT-Mounting Block bonding looks pretty good.
Attachment #5: The other side of the PZT bonding. Looks fine.
Attachment #6: Fractured PZT visible on the fixture parts.
Attachment #7: Fractured glass parts also visible on the fixture parts.
Attachment #8: MIrror bonding looks fine except for the glass chip.
The most fractured unit among four.
Attachment #1: Mounting Block SN017
Attachment #2: Two large removals well visbile. The bottom right corener was chipped.
Attachment #3: Another view of the chipping.
Attachment #4: PZT-mounting block bonding look very good.
Attachment #5: Another view of the PZT-mounting block bonding. Looks very good too.
Attachment #6: Fractures bonded on the fixture.
Attachment #7: Front view. The mirror-PZT bonding look just fine.
Attachment #1: Mounting Block SN021
Attachment #2: PZT-Mounting Block bonding looks just excellent.
Attachment #3: The other side of the PZT-Mounting Block bonding is also excellent.
Attachment #4: The mirror-PZT bonding also look excellent. Some barrel fracture is visible at the lower left of the mirror.
We are going to use A5 and A14 for FM1 and FM2. (The role of these two can be swapped)
The reason for the selection is the better perpendicularity among the available prisms.
A11 has the best perpendicularity among them. However, the T didn't match with the others. The pair of A5 and A14 has a good matching with small compromise of the perpend.
The attachment is the excerpt from T1500060.
Apr 16, 2019
Borrowed two laser goggles from the 40m. (Returned Apr 29, 2019)
Borrowed small isopropanol glass bottole from CTN.
Apr 19, 2019
Borrowed from the 40m:
- Universal camera mount
- 50mm CCD lens
- zoom CCD lens (Returned Apr 29, 2019)
- Olympus SP-570UZ (Returned Apr 29, 2019)
- Special Olympus USB Cable (Returned Apr 29, 2019)
[Stephen, Philip, Koji, Joe]
Breadboard D1200105 SN06 was selected as described in eLOG 338. This log describes unwrapping and preparation of the breadboard.
Relevant procedure section: E1300201 section 6.1.5
Breadboard was unwrapped. No issues observed during unwrapping.
Visual inspection showed no issues observed in breadboard - no large scratches, no cracks, no chipping, polished area (1 cm margin) looks good.
Initially the breadboard has a large amount of dust and fiber from the paper wrapping. Images were gathered using a green flashlight at grazing incidence (technique typical of optic inspection).
PROCEDURE IMPROVEMENT: Flashlight inspection and Top Gun use should be described (materials, steps) in E1300201.
Top gun was used (with medium flow rate) to remove large particulate. Breadboard was placed on Ameristat sheet during this operation.
Next, a clean surface within the cleanroom was protected with Vectra Alpha 10 wipes. The breadboard, with reduced particulate after Top Gun, was then placed inside the cleanroom on top of these wipes. Wiping with IPA Pre-wetted Vectra Alpha 10 wipes proceeded until the particulate levels were acceptable.
Joe and Koji then proceeded with placing the breadboard into the transport fixture.
[koji,philip, joe, liyuan, steven]
*still need to add photos to post*
PZT 11 was removed and inspected for so dust/dirt on the bottom of the prism. We saw a spot. We tried to remove this with acetone, but it stayed there. (Attachment 2, see the little white spec near the edge of the bottom surface of the prism)
current micrometer positions:
Swapped PZT for PZT 22, cleaned the bottom and put it into position of CM1. We saw a low number of newton rings, so this is good.
We got a rough initial alignment by walking the beam with the periscope and PZT 22 mirrors. Once we saw a faint amount of transmission, we set up the wincam at the output. The reflected light from the cavity could also be seen to be flashing as the laser frequency was being modulated.
Once it was roughly aligned, using the persicope we walked the beam until we got good 00 flashes. We checked the positions of the spots on the mirror with the beam card. This looked a lot better in the verticle direction (very near the centre) on both curved mirrors. We locked the cavity and contiued to align it better. This was done with the periscope until the DC error signal was about 0.6V. We switched to the fibre coupler after this.
Once we were satisfied that he cavity was near where it would be really well aligned, we took some images of the spot positions. Using these we can work out which way to move the curved mirrors. Koji worked this out and drew some diagrams, we should attach them to this post. [Diagram: See Attachment 1 of ELOG OMC 350]
We made the corrections to the cavity mirrors
The scatter from CM1 looked very small, it was hard to see with a viewer or CCD. We had to turn up the laser power by a factor of 3 to begin to see it, indicating that this is a good mirror.
Once this was done, the spot positions looked uch nearer the centre of each mirror. They look pitched 1mm too high, which might be because of the bottom surfaces of the prisms having a piece of dust on them? For now though it was good enough to try take the detuned locking FSR measurement and RFAM measurement.
To see the higher order mode spacing, we misaligned them incoming beam in pitch and yaw so that the TM10 and TM01 modes were excited. The cavity transmission beam was aligned onto the photodiode such that we could make a transfer function measurement (i.e. shift the beam along the photodiode so that only half of the beam was on it, this maximises the amount of photocurrent).
attachment 1 shows the fitting of the detuned locking method for measuring FSR and cavity length/
I saved this data on my laptop. When I next edit this post (hopefully I will before monday, although I might be too tired from being a tourist in california...) I want to upload plots of the higher order mode spacing.
in units 20um per div on the micrometer [n.b. we reailised that its 10um per div on the micrometer]
CM1 inner screw pos: 11.5
cm1 outer screw pos: 33.5
cm2 inner screw pos: 11
cm2 outer screw pos: 13
the cavity is currently 3mm too long, move each mirror closer by 0.75mm
CM1 inner screw pos: 11.5+37.5 = 49
cm1 outer screw pos: 33.5+37.5= 71
cm2 inner screw pos: 11+37.5 = 48.5
cm2 outer screw pos: 13+37.5 = 50.5
The screws on the micrometers were adjusted to these values.
cleaned cm1 (PZT 11). There was a mark near the edge which we were not able to remove with acetone. On the breadboard there were 3 spots which we could not remove with acetone. Once we wiped the mirror and breadboard we put the mirror back.
FM2 (A5). The prism looked quite bad when inspected under the green torch, with lots of lines going breadthways. We thought about replacing this with A1, however this has had the most exposure to the environment according to koji. This has a bit of negative pitch, so would bring down the beam slightly. We decided to continue to use A5 as it had worked fairly well before. The breadboard was cleaned, we could see a few spots on it, they were cleaned using acetone.
FM1 (A14). Near the edge of the bottom surface of the prism we could see some shiny marks, which may have been first contact. We attempted to scrape them off we tweezers. The breadboard looked like it had a few marks on it. These were hard to remove with the acetone, it kept leaving residue marks. We used isopropanol to clean this now, which worked much better. The sharp edges of the breadboard can cause the lens tissue to tear a bit, so it took a few rounds of cleaning before it looked good to put a prism on. The mirror was put back onto the breadboard.
The cavity was aligned, then we realised that 1 turn is 500um, so its still too long (1.75mm long). The FSR was 264.433Mhz, which is
CM2 still showed quite a bit more scattering than CM1, so we want to move this beam.
want to increase by 1.7/4 = 0.425, so
we tried to align the cavity, however the periscope screws ran out of range, so we changed the mircometers on CM2. We tried this for quite some time, but had problems with the beam reflected from the cavity clipping the steering mirror on the breadboard (to close to the outer edge of the mirror). This was fixed by changing the angle of the two curved mirrors. (We should include a diagram to explain this).
The cavity was locke, the FSR was measured using the detuned locking method, and we found that the FSR = 264.805 MHz, which corresponds to a cavity length of 1.1321m
we took some photos, the spot is quite far to the edge of the mirrors (3 to 4mm), but its near the centre vertically. photos are
123-7699 = CM2
123-7697 = CM1
That is an expanding fire pillow, also known as firebrick. It is used to create a fire block where holes in fire-rated walls are made and prevents lab fires from spreading rapidly to adjacent labs. I had to pull cable from B254 to our labs on either side during a rather narrow window of time. Some of the cable holes are partially blocked, making it difficult to reach the cable to them. The cable is then just guided to the hole from a distance. With no help, it's not possible to see this material getting shoved out of the hole. I can assure you that I took great pains not to allow the CYMAC coax to fall into any equipment, or drag against any other cables.
The 40m Bake Lab's Dirty ABO's OMEGA PID controller was borrowed for another oven in the Bake Lab, so I have had to play with the tuning and parameters to recover a suitable bake profile. This bake is pictured below (please excuse the default excel formatting).
I have increased the ramp time, temperature offset, and thermal mass within the oven; after retuning and applying the parameters indicated, the rate of heating/cooling never exceeds .5°C/min.
The ABO is controlled by a different temperature readout from the data logger used to collect data; the ABO readout is a small bead in contact with the shelf, while the data logger is a lug sandwiched between two stainless steel masses upon the shelf. I take the data logger profile to be more physically similar to the heating experienced by an optic in a gluing fixture, so I feel happy about the results of the above bake.
I plan to add the data source file to this post at my earliest convenience.
The 40m Bake Lab's Dirty ABO's OMEGA PID controller was borrowed for another oven in the Bake Lab (sound familiar? OMC elog 377), so I have had to play with the tuning and parameters to recover. This bake seemed to inadequately match the intended temperature profile for some reason (intended profile is shown by plotting prior qualifying bake for comparison).
The parameters utilized here are exactly matching the prior qualifying bake, except that the autotuning may have settled on different parameters.
Options to proceed, as I see them, are as follows:
Follow up on OMC elog 379
I was able to obtain the following (dark blue) bake profile, which I believe is adequate for our needs.
The primary change was a remounting of the thermocouple to sandwich it between two stainless steel masses. The thermocouple bead previously was 1) in air and 2) close to the oven skin.
OMC PZT Assy Production Cure Bake (ref. OMC elog 381) for PZT Assy #9 and #10 started 27 September 2019 and completed 28 September 2019. Captured in the below figure (purple trace). Raw data has been posted as an attachment as well.
We have monitored the temperature in two ways:
1) Datalogger thermocouple data (purple trace).
2) Checking in on temperature of datalogger thermocouple (lavender circles) and drive thermocouple (lavender diamonds), only during initial ramp up.
Comments on bake:
This post captures the curing timeline followed by OMC PZT Assys #9 and #10.
Source file posted in case any updates or edits need to be made.
[Koji, Jordan, Stephen]
The beam dumps, bonded on Fri 06 Dec 2019, were placed in the newly tuned and configured small dirty ABO at the Bake Lab on Fri 13 Dec 2019.
Images are shared and references are linked below
Bonding log entry - https://nodus.ligo.caltech.edu:8081/OMC_Lab/386
Bake ticket - https://services.ligo-wa.caltech.edu/clean_and_bake/request/992/
OMC Beam Dump - https://dcc.ligo.org/LIGO-D1201285
The beamdumps were taken out from the oven and packed in bags.
The bottom of the V are completely "wet" for 17 BDs among 20 (Attachment 1/2).
3 BDs showed insufficient glue or delamination although there is no sign of lack of rigidity. They were separated from the others in the pack.
Item lending as per Ian's request: Particle Counter from OMC Lab to QIL
The particle counter came back to the OMC lab on Aug 10, 2020
Check-in to the OMC lab to see the status. Nothing seemed changed. No bug. The HEPA is running normal. The particle level was 0.
Went into the HEPA enclosure and put a cover on the OMC. Because of the gluing template, the lid could not be close completely (that's expected and fine).
The IPA vector cloth bag was not dry yet but seemed expired (some smell). There is no stock left -> 5 bags to be ordered.
are there any measurements of the BRDF of these things? I'm curious how much light is backscattered into the incoming beam and how much goes out into the world.
Maybe we can take some camera images of the cleaned ones or send 1-2 samples to Josh. No urgency, just curiosity.
I saw that ANU and also some labs in India use this kind of blue/green glass for beam dumps. I don't know much about it, but I am curious about its micro-roughness and how it compares to our usual black glass. For the BRDF, I think the roughnesss matters more for the blackness than the absorption.
According to the past backscatter test of the OMC (and the black glass beamdump: not V type but triangular type on a hexagonal-mount), the upper limit of the back reflection was 0.13ppm. https://nodus.ligo.caltech.edu:8081/OMC_Lab/209
I don't have a BRDF measurement. We can send a few black glass pieces to Josh.
The output of Mephisto 800NE (former TNI laser) was measured.
The output power was measured with Thorlabs sensors (S401C and S144C). The reference output record on the chassis says the output was 837mW at 2.1A injection.
They all showed some discrepancy. Thus we say that the max output of this laser is 1.03W at 2.1A injection based on the largest number I saw.
To spare some room on the optical table, I wanted to mount the two TFT monitor units on the HEPA enclosure frame.
I found some Bosch Rexroth parts (# 3842539840) in the lab, so the bracket was taken for the mount. This swivel head works very well. It's rigid and still the angle is adjustable.
BTW, this TFT display (Triplett HDCM2) is also very nice. It has HDMI/VGA/Video/BNC inputs (wow perfect) and the LCD is Full-HD LED TFT.
The only issue is that one unit (I have two) shows the image horizontally flipped. I believe that I used the unit with out this problem before, I'm asking the company how to fix this.
The image flipping of the display unit was fixed. The vendor told me how to fix it.
- Open the chassis by the four screws at the side.
- Look at the pass-through PCB board between the mother and display boards.
- Disconnect the flat flex cables from the pass-through PCB (both sides) and reconnect them (i.e. reseat the cables)
That's it and it actually fixed the image flipping issue.
See this entry: https://nodus.ligo.caltech.edu:8081/40m/15642
Thorlabs' powermeter controler + S401C head was lent from OMC Lab.
FEMTO DLPCA200 low noise preamp (brand new)
Keithley Source Meter 2450 (brand new) => Returned 11/23/2020
were brought to the OMC lab for temporary use.
Item loan: SRS LCR meter SRS720 borrowed from Downs. The unit is at the 40m right now for testing with an excelitas PD. Once it is done, the setup will be moved to the OMC lab for testing the high QE PDs