Attached here with are relevant plots.
We repeated Zygo measurements (using the same setup and method as below) for curved mirrors sn07, sn11, sn12, sn18, sn19, sn25, sn26, and sn30.
sn11 and sn25 still show a large spread in angular measurements (see attached.) This is attributed to the low decentering values for these two mirrors (0.072mm and 0.158mm, respectively).
[Camille, Thejas, Stephen]
We modified the Zygo setup for measuring the sagitta of the curved mirrors. A mirror at 45deg was used to reflect the interferometer beam down towards the surface of the table (see picture). A fused silica flat was placed horizontally with the surface of the table and was used as our reference flat. The back surface of the curved mirror and the top surface of the reference flat were cleaned using top gun and/or swabs. Once it was verified that the surfaces were clean, the curved mirror could be easily placed on the surface of the reference flat.
Once the curved mirror was placed on the reference flat, the fringes of the reference flat were nulled using the 45deg mirror. After nulling the flat's fringes, the data was recorded. The curved mirror was then rotated 90deg clockwise. The measurment was repeated with the curved mirror's fiducial located at 12:00, 3:00, 6:00 and 9:00. The 12:00 position was measured twice to ensure repeatability. (A drop of first contact had been placed at the edge of the optic to indicate where the fiducial arrow is. This helped with clocking alignment.)
The already-characterized aLIGO C7 mirror was measured to verify the setup. After verifying agreement with the results in T1500060, this process was repeated with all the remaining curved mirrors.
The data was analyzed using Thejas's python script (separation distance between mirror center and curvature minimum, angular position of curvature minimum.) Those mirrors with a large spread in the measurements will be remeasured.
Curved mirror radius of curvature raw data can be found in the DCC document: T2300050
The input beam falling on the curved optic was characterized. The beam waist and it's position was found by curve fitting gaussian beam propagation formula in near field:
Fitting gives the following values for the initial beam waist (w_0) and waist position (z_0) (see pdf attached below).
Using these fitted parameters in JAMMT (beam propagation software) gives the following results for a 1.25 m focal length optic:
w_0x: 1.429 mm +/- 0.006 mm
z_0x: 0.421 m +/- 0.131 m
Beam waist @ 3.063 +/- 0.005 m
f = 1.25 m optic @ 1.807 m
Thus beam focuses at 1.256 +/- 0.005 m for the p-plane.
w_0y: 1.526 mm +/- 0.023 mm
z_0y: 0.352 m +/- 0.597 m
Beam waist @ 3.064 +/- 0.02 m
f = 1.25 m optic @ 1.807 m
Thus beam focuses at 1.257 +/- 0.02 m for the s-plane.
Hence we can use the distance measured from the optic to the beam profiler as a suitable figure for focal length (hence radius of curvature). Also astigmatism in the input beam is calculated to have negligible influence in causing astigmatism in following the curved optic. Hence, any astigmatism measured at the focus following the curved optic is due to the curved optic (?). Also because the incident beam on the curved optic is at an arbitrary angle of incidence, this introduces further astigmatism in the reflected beam given by equation 12 in this paper: https://opg.optica.org/ao/fulltext.cfm?uri=ao-8-5-975&id=15813
Chub finished the HEPA enclosure extension project.
I handed Camille the C7 mirror for the cross-calibration of the ROC characterization techniques.
Data can be found in DCC document T2300050.
On Friday. Camille and I measured the flatness of the flat mirror. Tilt values (without subtracting tilt) were less than 100 nm and PV across the surface was about 50 nm.
This checks that the flat mirror surface distortions are not contributing to the systematic deviations in our measurement of curvature minimum with varying the fiducial clocking angle. The deviations in the data show a far more disagreement between Y-Tilt of different clocking angles than the X-Tilt.
[Camille, Stephen, Thejas]
Curved mirror sn02 was used to test the method for collecting Zygo measurements on the curved mirrors. The curved mirror was mounted with its back surface against a reference flat. The reference flat was pitched/yawed until its fringes were nulled. Then a measurement of the surface profile of the curved mirror + flat mirror together was taken.
The curved mirror was rotated in 90deg increments and the measurements were repeated. (5 measurements in total were taken, with the curved mirror's fiducial in the 12:00, 3:00, 6:00, 9:00 and 12:00 again positions.) The curvature minumum was seen to clock as expected with the rotation of the mirror.
The attached figures show the surface profile of the central 8.5 mm diameter of the mirror (central with respect to the coating edge). Also attached is a plot of the surface profile across the line drawn in the figure.
22 March 2023
Beam profile measurements were continued for more of the curved mirrors.
Mirror sn07 was repeated to verify that Camille and Thejas get the same focal length measurement (plot attached).
21 March 2023
We made slight adjustments to the beam expander lenses in the ROC setup. The position of the second lens was moved slightly (a few mm) to improve the collimation of the beam. The beam profiler was used to measure the beam size at various distances (measurements attached). This will be used to characterize the beam divergence.
This beam was reflected off the curved mirror and the beam profiler was used to measure the beam size at various positions near the focal point. This process was repeated for various curved mirrors (measurements attached). These values will be used to determine the ROC of each mirror. ROC=2*FL
Thanks Koji, the lenses available in the cabinet in the lab actually sufficed.
I hope you can find useful lenses from the lens kit in the cabinet. If you need more lenses and mounts, talk to our students in WB and the 40m.
Thanks for teh comment Koji. Yes, I did see this effect by comparing the beam sizes with and without the curved mirror. But the observation did not conform with the expectation that the beam should focus at a distance of 1.25 m from the curved mirror (as seen in the software images). So, I plan to use some lenses to increase the beam waist and perform the measurement.
If the mirror has the RoC, it works as a lens. And you should be able to see the effect in the beam profile.
Just what you need to do is to compare the beam profile without the mirror (or with a flat mirror) and then with the curved mirror.
Today, I tried to measure the radius of curvature of the curved mirror using the input beam for the OMC test set-up. It was noticed that the half inch curved optic (ROC=2.5 m), when placed within the Rayleigh range of the beam waist, did not focus the beam. This is probably becasue the beam diameter is small for this optic's radius of curvature to produce any focussing. This can be illustrated even further using the JAMMT software by replacing a concave sperical mirror with a ocnvex lens of focal length of 1.25 m.
Substrate: 1/2 inch optic with f= 0.25 m
Substrate: 1/2 inch optic with f= 1.25 m
The only wasy to resolve this is by incresing the beam diameter to > 2 mm
RoC: 2.65m ! Interesting. I'll wait for the follow-up analysis/measurements. The RoC may be dependent on the area (diameter) for the fitting. You might want to run the fitting of your own. If so, let me know. I have some Matlab code that is compatible with the CSV file exported from MetroPro data.
[Camille, GarriLynn, Stephen, Thejas]
Folllowing the replacement of the spherical transmission / reference mirror with a flat mirror, on Friday we were able to observe fringes that facilitated characterization of the curvature minimum.
By rotating the curved optic by 90 deg we couodn't reproduce consistent data.
This is probably due to insufficient attention given to the orientation/centering of the curved mirror under the clamp.
[GariLynn, Stephen, Thejas]
Yesterday, we placed an iris (borrowed from OMC Lab) infront of the spherical transmission sphere to limit the spot size, on the other end of the cavity, to only the curved optic. This produced a crisp boundary for the interference pattern. We obtained some data at different imaging focal planes. The transmission optic here is a spherical mirror. This was replaced with a plane reference and the curved optic was moved closer to this optic. Intereference fringes were nuled for the plane mirror upon which the curved optic sits. This ensures that the curved mirror is head on to the laser beam. The spherical fringes were obscured by some diffraction artifacts. Today, we will be makign an attempt to eliminate that and try to see fringes from the whole curved optic.
OMC test set-up
Yesterday, laser beam output from the fibre follwoing teh mode-matching lenses was picked off and beam profile was characterized using beam profiler Thorlabs BP209-VIS.
The gaussian fit beam diameter was measured to be about wx = 939 um wy = 996 um at the location of a distance of 0.4 m from the high reflector. The mode content of this beam is about 98% TEM00. We want to use this beam within the Rayleigh range (near field) to measure radium of curvature of the curved optics.
The Rayleigh range is about 0.74 m.
Today, a more rigorous effort was made to re-measure the position of the optics forming the Fizeau cavity and re-position the curved optic to get more contrasting fringes. Distance measurements were made using a Fluke laser displacement sensor. We obtained a contrasting fringe pattern but the phase profile measured was assymmeteric and un-satisfactory. Tomorrow an attempt will be made to place an iris infront of the curved optic to define the edge of the beam and limit it only to the curved optic surface.
Today, Koji and I cleaned up the the lab space and made some space on the optical table for radius of curvature measurement of the A+ OMC curved mirrors.
[Camille, Stephen, Thejas]
Stephen returned the curved mirror #6 to Liyuan for point transmission measurement. We are now using #5 for to setup/align the ZYGO Fizeau interferometer setup to characterize the curvature center of the mirrors. It was setup such that the focal point of the input reference sphere was coincident with the radius of curvature of the test mirror.
The curved mirror was mounted on a flat reference mirror, with the help of the sub-assembly bonding fixture:
The fringe pattern seen was:
Efforts were made today to improve the contrast of the fringe pattern and take some measurements.
On Feb 16, Camille and I attampted at locking the OMC cavity. It was quick to re-align the beam to the cavity (by using only the fine adjustment of the output fibre couple). This was done by looking to minimize the power reflected from the cavity and observing the mode shapes on the CCD. After we achieved locking we placed the lid of the OMC back and turned off the laser.
Chub, JC, and co worked on the HEPA enclosure improvement.
Yesterday, efforts were made to measure ROC of curved mirrors (#6) in the ZYGO lab using a Fizeau Interferometer. Peculiar observation: Stray fringes were seen that dominated the fringes that conformed with the expectation. The origin of these fringes is still not accounted for (see attached screenshot). moreover, once the right fringe pattern is achieved by moving the end mirror of the interferometer using a translation stage, the cavity length is measured using a metre stick. This makes the measurement limited by the accuracy using ruler stick for cavity length measurement, which is not expected to be any better than usign a beam profiler to find the focal point from the curved mirror. Today we will, move ahead to corved mirror surface profile characterization.
Today, before the ZYGO lab was cleaned and prepared for the cureved mirrors' radius of curvature (ROC) characterization, Mirror no. 6 was mounted into one of the half inch mirror holders. The cleanliness of the envoronment and handling was not satisfactory. Tomorrow efforts will be made to start doing the ROC measurements with class B cleanroom garbing.
PZT model: Noliac 2124
Qty: 18 (Sr. No. 30 - 48)
Today, PZT dimensions were measured. Inner radius of the ring and thickness at different points can be used to determine the wedge angle and direction of the PZTs. This is essential for evaluation of appropriate combination of subassembly (curved mirror + PZT + Hole prism) prior to bonding them.
Yesterday we also measured weight and dimensions of breadboard. Error for the following measurements is same as the least count of the instruments used.
450.56 mm x 41.45 mm x 150.39 mm
450.37 mm x 41.25 mm x 150.17mm
450.83 mm x 41.44 mm x 150.15 mm
450.30 mm x 150.42 mm x 41.42 mm
450.06 mm x 150.18 mm x 41.42 mm
450.01 mm x 150.57 mm x 41.43 mm
450.01 mm x 150.06 mm x 41.44 mm
Yesterday we measured wedge angle of the beamsplitter (BS) prisms. I reckon these measurements are not as important as the BSs will be used outside the cavity and the angle of incidence is significant.
Measurement procedure and setup used are the same as that for the prism mirrors wedge angle measurements.
initial division reading: 9.0
finbal division reading: 2.5
Contnuing the efforts to measure and check perpendicularity: tombstone prisms with holes/ hole prisms (HP).
Note: Veritcal crosshair splitting can be seen in the some of the image. This is probably because the horizontal of the Al flat mirror is not parallel to that of the coupling mirror. This was confirmed by touching the so that the setup roll a bit so as to reduce the vertical splitting. In some cases the position of the prism on the flat mirror was changes to reduce this effect, in some other cases this was not very helpful and measurement was done anyway. We expect that teh vertical splitting and horizontal splitting don't couple into each other. We think the clamping mechanism for this kind of measurement can be improved to avoid these artefacts.
Updated ICS (Shipment-12578) and moved those parts to Storage-9482.
Inspection showed the following:
Observations for aLIGO OMC Unit 4 Build
An ICS Record Navigator search of onboard OMC cables reveals the following quantities appear to have been fabricated for aLIGO.
The leftover cables are all of the long variety (D1300372, D1300375), and the received quantities make sense. 3 aLIGO OMC assemblies used quantity 3 of each cable, leaving the remaining cables which had been stored at LHO:
The received cables from LHO may apparently be used interchangably, and the extra slack (~ 5", compared to the D1300371, D1300374 part numbers) should be managable.
Next Steps for aLIGO OMC Unit 4 Build
We will move forward in fabricating Unit 4 with the received cables from LHO, despite their extra length.
To complete the Unit 4 on board cable set (refer to OMC_Lab/203), we will need to crimp pins onto the PZT leads, and we need to find, clean, and bake quantity 1 4 pin mighty mouse connector.
I will ask Chub to see if there are any Class A spares of the PZT termination connector already on hand.
Continuing with the efforts to measure the perpndicularity.
Perpendicularity measurement for Beam Splitters
Following the wedge angle measurements of the prisms, perpendicularoty of their bottom surface with respect to their HR surface was measured usign the autocollimator. More info. about the procedure can be found in the OMC testing document. We want to set the requiremetns for perpendicularity to better than 30 arcsec (or 0.-0083 deg).
Images of the setup
View through teh autocollimator (AC) while hte prism is unclamped:
Two horizontal crosshair lines can be seen, with a common vertical crosshair. These corresspond to the two separate reflections of the AC beam fom the retroflector (RR) surfaces formed by the prism and the flat Al mirror (see image below). When the RR formed is 90 deg the two horizontal lines overlap. The separation between the lines, when calibrated, represents 4 x the deviation of the prism from perpendicularity. Note that, since this prism is unclamped the crosshairs don't indicate a true reading. Note that since the autocollimator images are in far field, the splitting of the horizontal lines shouldn't depend on the pitch angle of the coupling mirror, this can also be checked by the adjusting the pitch screws.
Multiple images below to check reproducibility:
1 div. of the reticle in the above images corresponds to 1 arc min. By measuring the separation of the horizontal shifting gives angle of deviation from perpendicularity.
From the above images it can be inferred that the surfaces form a 90 deg RR.
As it can be seen in the top images there's a splitting of hte horizontal lines indicating deviation from perpendicularity. The direction of the deviation can be inferred by softly tocuhing/pressing on the front orn the back en of the flat Al mirror surface as shown in the images below.
Continuing yesterday's efforts to measure the wedge angle of the back surface of the prisms. We completed measurement for all the 18 prisms.
The images below accompanying the readings represent the S2 crosshair image on top of the reticle, alighned for yaw.
But note that the vertical misalignement with the reticle does not give an accurate measurement for vertical wedge angle. This is because, as it's notecable in the images,
the S1 reflected crosshair's horizontal axis goes out of coincidence from the horizontal axis of the reticle as the stage is rotated. Our thoughts: MAy be the horizontal
plane of the mount is not the same as the horizontal plane of the autocollimator.
Each unit of the readings corresponds to 0.1 deg., the resolution of the rotational stage is 0.2 deg. The requirement is 0.5 deg of wedge angle. And this angle is related to the horizontal wedge angle by:
Initial reading of the screw on the rotation (yaw) stage (ini): 7.6
Final reading of the screw (fin): 0.2
ini: + 5.1
fin: - 8.0
ini: + 1.8
fin: - 5.5
ini: + 5.8
fin: - 8.5
fin: - 4.2
This totals 18 prisms including yesterdays.
We set up the white light autocollimator in the Downs B119 cleanroom. (Nippon Kogaku, from Mike Smith).
After some initial effort to refine the fixturing and alignment, we located the S1 crosshair reflection and aligned to the autocollimator reticle using the pitch and yaw adjustments in the prism mount.
We subsequently used the rotation stage adjustment to locate the S2 crosshair reflection and measure the vertical and horizontal wedges.
Faint horizontal crosshair from the S2 reflection can be seen in the image below.
This is aligned with the reticle using rotation mount on which the prism mount is clamped.
Initial readiing of the rotation mount screw: 9.2
Final reading: 2.2
Here we see that the crosshair from S2 reflected light is offset in the vertical axis by approx. 2 div. From hte image below this should
correspond to 2 arcmin vertical wedge angle.The horizontal wedge angle is yet to be caluclated.
Attachment 1: North Cabinet 2nd from the left
Attachment 2: North Cabinet 3rd from the left
Attachment 3: South Cabinet (right)
The OMC cables #4 arrived on Feb 3rd. (See Attachment)
This shipment included two DCPD cables and two QPD cables. It means that the direct wiring from the PZT to the mighty mouse connectors was not included in the shipment.
HEPA is quite low for a tall person and also the curtain on the back of us is always heavy. It's very tough for anyone to work with. (See Attachment 1)
I did the lab and table organization so that the HEPA expansion work can be resumed.
The 4th OMC is still on the table with the transport fixture (See attachment 3), but it is secured on the table. The risk of damaging the OMC is low now.
Chub can start working on the HEPA. Occasionally Camille and Thejas may work on the optical setup with the OMC. It is fine as long as both happen at the same time.
The attached photo shows the resulting bond spread.
[Camille, Thejas, Koji]
We added a reinforcement bar at the back of the invar block which had the tilt issue.
The reinforcement bar was added to the backside rather than the side or front such that the DCPD housing does not interfere with the reinforcement bar.
Also, small amount of EP30-2 was added to the CM2 wire so that the repeated bend of the PZT wire cause the disconnection at the PZT.
2/1 2:30PM~ Bonding reinforcement (Last EP30-2 gluing)
2/2 1:00PM~ Peripheral attachment / Optical testing setup
Inserted 4-40 and 2-56 helicoils into the DCPD/QPD housings for the 4th OMC. The retainer caps were also fastened to the housings.
The transport fixture was brought to the 40m clean room to use as an assembly reference.
Yesterday, we noticed that we could not close the transport fixture for OMC #4. We could not fully rotate the knobs of the locks. Today, I took the hooks from the functioning locks of the spare transport fixture.
It turned out that the default dimension of the lock seemed too tight. The functioning one has the through holes elongated by a file or something. This modification will be necessary for future transport fixtures.
The AL metal bracket was replaced with a PEEK version.
Attachments 1/2: Before the replacement. The photos show how the cables are arranged.
Attachment 3: How the replacement work is going. The 1/4-20 screws were super tight. Once the connectors were removed, an Allen key was inserted to a hole so that the 1/4-20 on the short sides were removed by closing Allen key arms. For the screws on the longer sides, the same technique can be applied by using three Allen keys. This time none of the screws/cable pegs were wasted. The clothes were used to protect the breadboard from any impact of the action.
Attachments 4/5: Final state.
OMC #1 repair has been 100% done
We still have 4 correct cable pegs and many 1/4-20 BHSCs for OMC #4.
A beam dump was stacked on the base of the previous beam dump. The angle was determined so that the main transmission goes through while the stray OMC reflection is blocked without clipping at the edge.
The resulting alignment of the beam dump is shown in Attachment 1.
The beam dump tended to slip on the base. To prevent that a couple of weights were placed around the bonding area. (Attachment 2)
1. Flipping the OMC
It turned out that the transport fixture for this OMC could not be closed. The locks are too short, and the knobs could not be turned. We temporarily fastened the long 1/4-20 screws to secure the box and flipped it to make the top side face up.
2. Setting up the top-side template
The top side template was attached to the breadboard. We took care that the lock nuts on the positioning screws were not touched. The margins between the template and the glass edges were checked with a caliper. The long sides seemed very much parallel and symmetric, while the short sides were not symmetric. The lock nut on the short side was loosened, and the template was shifted to be symmetric w.r.t. the breadboard.
3. UV epoxy work
The cylindrical glass pieces were wiped, and the bonding surfaces were cleaned so that the visible fringes were <5 fringes. We confirmed the hooking side is properly facing up. The UV epoxy and UV curing were applied without any trouble. (Attachment 1)
4. EP30-2 bonding of the invar mounting blocks
Six invar blocks were bonded. This time the Allen key weights were properly arranged, so they didn't raise the blocks. The bond properly wetted the mating surfaces.
The final step of the bonding is to remove the template.
And replace the locks of the transport fixture.
During the second UV epoxy session, we did not bond the input beam dump. This is because this beam dump was not the one planned from the beginning and if it was bonded in place, it would have created difficulties when removing the template.
First, we aligned a couple of Allen wrenches to define the location of the beam dump. We've checked that the main transmission is not blocked at all while the stray beam from the OMC reflection is properly dumped.
After the confirmation, the UV epoxy + UV alight were applied.
The resulting position of the beam dump is shown in the attachment.
The bottom side template was separated into two pieces and successfully removed from the breadboard. The template was assembled together again and bagged to store it in a cabinet.
We found that the invar block for DCPD(R) was bonded with some air gap (Attachment2 1/2).
The Allen key used as a weight was too small, which caused it to get under one of the screws used as hooks and lift the block.
We've investigated the impact of this tilt.
- Bonding strength: The bonding area is ~60% of the nominal. So this is weak, but we can reinforce the bonding with an aluminum bar.
- Misalignment of the DCPD housing: The tilt will laterally move the position of the DCPD. However, the displacement is small and it can be absorbed by the adjustment range of the DCPD housing.
- Removal: From the experience with the removal of the beam dump glass, this requires a long time of acetone soaking.
- We don't need to remove the invar block.
- Action Item: Reinforcement of the bonding
Qty1 1/2 mounts
Qty2 prism mounts
Qty6 gluing fixures
Qty1 Rotary stage
Qty1 2" AL mirror
Qty1 Base for the AL mirror
=> Handed to Stephen -> Camille on Jan 27, 2023.