OMC (002) after repair
History:Mirror replacement after the damage at H1. Measurement date 2019/1/10

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:

1. reposition the oven's driving thermocouple closer to the load and attempt to qualify the oven again overnight
2. retune the controller and attempt to qualify the oven again overnight
3. proceed with current bake profile, except monitor the soak temperature via data logger thermocouple and intervene if temperature is too high by manually changing the setpoint.

Connector unmounting

- (Attachment 1) The connector nut rings were removed using an angled needle nose plier. The connector shell has a tight dimension relative to the hole on the bracket. But of course, they could be extracted.

- The 4 screws mounting the bracket to the invar blocks were successfully removed. No extra damage to the bonding.

- (Attachment 2) The plan was to remove the cable pegs by unfastening the button head 1/4-20 screws from the bracket and then just replace the bracket with the new one. However, these screws were really tight. The two were successfully removed without cutting the PEEK cable ties. Two cable ties were necessary to be cut to detach the bracket+pegs from the fragile OMC. Then one screw was removed. However, the final one could not be unfastened. This is not a problem as we are not going to recycle the metal cable bracket... as long as we have spare parts for the new bracket.

- (Attachment 3) Right now, the new bracket is waiting for the helicoils to be inserted. So the OMC lid was closed with the cables piled up. Just be careful when the lid is open.

Checking the spare parts

- Conclusion for OMC#2: need PEEK cable ties
- for more OMCs: need more BHCS / PEEK cable ties / Helicoils

• Helicoils: 1/4-20 0.375 helicoils / Qty 4 / Class A (Attachment 1)
  • looks like there are many more as the transport fixture bags (Attachment 2). Stephen noted that they are meant to be CLASS B
     
• Cable pegs: D1300057 / Qty 24 + 3 recycled from OMC#2 / Class A (Attachment 3)
  • Requirement: 3+3+4 = 10 for the 4th OMC / 3x4 =12 for the cable bracket replacement -> we have enough
     
• PEEK Cable Ties: Stephen reported they were deformed by baking heat... did not check how they are in the bags.
   
• Button Head Cap Screws 1/4-20 length ? none found in the bags.
  • Qty 4 spare (forgot to take a picture) + 3 recycled. So we have sufficient for OMC#2

[Camille, Koji]

- Removed the first contact we left on Monday.

- Measured transmission (Set1) Very high loss! Total optical loss of 18.5%! Observation with the IR viewer indicated that CM1 has bright scattering. We suspencted a remnant of FC.

- Applied the second FC on the four cavity mirrors. This made the CM1 sport darker.

- Measured the transmission (Set1~Set3). We had consistent loss of 4.2~5.0%. We concluded that this is the limitation of this OMC even with the cleaning.

Antonio borrowed: Rich's PD cutter (returned), Ohir power meter(returned), Thorlabs power meter head, Chopper

[Camille Koji]

We started buikding the OMC #4.

• Removed OMC #1 from the optical setup and placed it at a safe side on the optical table/
• Fixed OMC #4 in the optical setup
• Cleaned the OMC cavity mirrors
• Placed the OMC cavity mirrors
  • FM1: A1
  • FM2: A3
  • CM1: PZT #11
  • CM2: PZT #12
• Aligned the beam to the cavity
• Locked the cavity on TEM00
• Finely aligned the beam to the cavity

The four cavity mirrors in OMC #1 were each scrubbed using acetone and a cotton swab.
Then, the four mirrors were painted with First Contact (picture attached). The First Contact was allowed to dry for 20 minutes, then removed while using the top gun.

The 3IFO EOM test performed at the 40m. Result: 40m ELOG 13819

[Rich Koji]

3IFO EOM (before any modification) was tested to measure the impedance of each port.

The impedance plot and the impedance data (triplets of freq, reZ, imZ) were attached to this entry.

3IFO EOM dark microscope images courtesy by GariLynn and Rich

Attachment1/2: Hole #1
Attachment3/4: Hole #2
Attachment5: Hole #2

Jan 15, 2015 3rd OMC completed

The face caps of the DCPD/QPD cables were installed (Helicoils inserted)
PD7&10 swapped with PD11(for DCPD T) and PD12(DCPD R).
Firct Contact coating removed

Note on the 3rd OMC

Before the 3rdOMC is actually used,

- First Contact should be applied again for preventing contamination during the installation

- DCPD glass windows should be removed

Regarding: D1200971

- 4 CLASS A wire clamp obtained from the OMC spare
- 4 more DIRTY wire clamp obtained from WB experiments (they no longer use these)

Once the later ones are C&Bed, we have enough.

I helped to complete the 5th OMC Transport Fixture. It was built at the 40m clean room and brought to the OMC lab. The fixture hardware (~screws) were also brought there.

The transport fixture was brought to the 40m clean room to use as an assembly reference.

[Rich Koji]

The 9MHz port was tuned and the impedance was measured.

[Stephen, Koji]

The perpendicularity of some of the A and M prisms were tested.

Results

- The measurement results are listed as Attachment 1 and 2 together with the comparisons to the measurement in 2013 and the spec provided from the vendor.
- Here, the positive number means that the front side of the prism has larger angle than 90deg for the air side. (i.e. positive number = facing up)
- The RoC of the curved mirrors is 2.5m. Therefore, roughly speaking, 83arcsec corresponds to ~1mm beam spot shift. The requirement is 30 arcsec.
- The A prisms tend to have positive and small angle deviations while the M prisms to have negative and large (~50arcsec) angle deviations.
- The consistency: The measurements in 2013 and 2019 have some descrepancy but not too big. This variation tells us the reliability of the measurements, say +/-30arcsec.

Setup

- The photos of the setup is shown as Attachments 3/4/5. Basically this follows the procedure described in Sec 2.2.2 of T1500060.
- The autocollimator (AC) is held with the V holders + posts.
- The periscope post for the turning Al mirror was brought from Downs by Stephen.
- The turning mirror is a 2" Al mirror. The alignment of the turning mirror was initially aligned using the retroreflection to the AC. Then the pitching of the holder was rotated by 22.5deg so that the AC beam goes down to the prism.
- The prism is held on a Al mirror using the post taken from a prism mount.
- If the maximum illumination (8V) is used, the greenish light becomes visible and the alignment becomes easier.
- There are two reflections 1) The beam which hits the prism first, and then the bottom mirror second, 2) The beam which hits the bottom mirror first and then the prism second. Each beam gains 2 theta compared to the perfect retroreflection case. Therefore the two beams have 4 theta of their relative angle difference. The AC is calibrated to detect 2 theta and tells you theta (1div = 1 arcmin = 60 arcsec). So just read the angle defferencein the AC and divide the number by 2 (not 4).

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.

On breadboarfd cabling for 3IFO OMC

D1300371 - S1301806
D1300372 - S1301808
D1300374 - S1301813
D1300375 - S1301815

Yesterday we also measured weight and dimensions of breadboard. Error for the following measurements is same as the least count of the instruments used. 

26

6149 g 

450.56 mm x 41.45 mm x 150.39 mm 

23

6127 g

450.37 mm x 41.25 mm x 150.17mm

25

6155 g

450.83 mm x 41.44 mm x 150.15 mm

24

6158 g

450.30 mm x 150.42 mm x 41.42 mm

20

6147 g

450.06 mm x 150.18 mm x 41.42 mm

22:

6149 g

450.01 mm x 150.57 mm x 41.43 mm

21:

6143 g 

450.01 mm x 150.06 mm x 41.44 mm

A+ OMC Build efforts ongoing or completed this week:

•  PZT lead onboard strain relief (D2000172)
  • Brief discussion in A+ SUS call - PEEK material callout is to be updated in v2, Don is handling this.
  • v1 drawings posted and UK team out for production, with Angus already communicating PEEK grade requirement to vendor during procurement process.
  • DCN is WIP per Russell.
• Rework of Helicoil holes
  • D1201278 and D1300498 were already Class A, but we recognized that the hole callouts were not consistent with current LIGO notation, and we decided to make sure that these holes were in a good state.
  • Don and I chased the holes with taps (gloves on, but in a dirty area)
  • Don created a C&B Ticket request/1835
• PZT characterization (ref. T1500060-v2 - PZT Testing Section 2.3.2)
  • DC Response measurement - see OMC_Lab/542 for initial findings.
    • 11 units appear to be good, 2 units appear to be damaged, 5 units need to be recharacterized (after soldering rework).
    • Quantitative results WIP.
  • Lab move to Downs 320 - this work needs to be logged.
    • DC Response setup updated, beam focusing was changed.
    • Oplev setup for Length to Angle measurement constructed for the first time.
• Component matching for Curved Mirror Subassembly
  • Continued work on algorithm-based matching code
  • Discussion with Gari and Calum - we will move toward manual matching to expedite

We have the following plans for the week ahead:

• Complete PZT DC Response data analysis.
• Finish solder rework of PZT leads.
• Start PZT Length to Angle measurement.
• Manually match Curved Mirror Subassembly components, enough to bond first 4 assemblies.
  • (this will be pending full characterization of PZTs)
• Make sure clean and bake ticket gets processed for reworked parts mentioned above.

We have the following near future plans:

• Start PZT reliability testing (burn-in test) (ref. T1500060-v2 - PZT Testing Section 2.3.4),
  • Focused on units that will be used to bond first 4
• Bond first batch of Curved Mirror Subassemblies.
  • Make sure we have enough EP30-2 for subsequent batches (some used by HoQi effort)..
• Resume transport fixture build effort at 40m Bake Lab.
• Conduct walkthrough of OMC lab with build in mind.
• Follow updates of top level assy D2000172, and send finalized assy for 3D printing of mockup unit.

A+ OMC Build efforts ongoing or completed in the last two weeks:

•  PZT lead onboard strain relief (D2000172)
  • Some more discussion in A+ SUS calls - PEEK material callout is to be updated in v2, Don is handling this.
  • Looking forward to timeline update in coming week
• Rework of Helicoil holes
  • Don's C&B Ticket is being processed by Maty, will go for bake next week - request/1835
• PZT characterization (ref. T1500060-v2 - PZT Testing Section 2.3.2)
  • DC Response measurement - no new data collection.
    • 5 articles need to be recharacterized (after soldering rework).
    • Code for quantitative results is 90% complete, still debugging (WIP).
  • Lab move to Downs 320 - updated setup logged in OMC_Lab/545.
    • DC Response setup has not been rebuilt yet, but will need to be for more testing after solder repairs and/or reliability testing.
    • Oplev setup for Length to Angle measurement is operational.
  • Length to Angle measurement - lots of setup, refinement, and growing pains toward data collection.
    • 11 PZTs measured, just like DC Response (5 articles requiring solder rework)
• Component matching for Curved Mirror Subassembly
  • Matching calculations first draft (implemented manually) was supplied by Thejas.
  • EP30-2 batch (2x 50mL syringes) arrived, plenty for all curved mirror subassembly bonding and first OMC unit bonding, at least.

We have the following plans for the week ahead:

• Complete PZT DC Response and Length to Angle data analysis. (WIP)
  • We have been making manual comparisons / data quality checks throughout data collection.
  • Comparisons with past results from aLIGO build have suggested that our results are reasonable.
• Finish solder rework of PZT leads. (had been planned, solder hasn't arrived yet)
• Set up shadow sensor in new lab for future DC Response measurements.
• Set up PZT reliability testing (burn-in test). (ref. T1500060-v2 - PZT Testing Section 2.3.4)
• Resume transport fixture build effort at 40m Bake Lab.
  • Summer student Maria will be heavily involved.
• Insert helicoils in Class A plasma-sprayed DCPD housings

We have the following near future plans:

• Bond first batch of Curved Mirror Subassemblies.
• Conduct walkthrough of OMC lab with build in mind.
  • Transport Class A components that are ready for build to OMC cleanroom.
• Follow updates of top level assy D2000172, and send finalized assy for 3D printing of mockup unit.
  • Make sure that strain relief components are all on order and we know the timeline.

[Stephen, Thejas]

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. 

[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. 

[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.

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

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

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.

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.

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 Koji, the lenses available in the cabinet in the lab actually sufficed. 

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:

P-plane

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.

S-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

Restimation of the parameters

Camille and I went back to the lab to re-measure the beam profile follwoing the beam expanding lenses. I was observed after turning on the laser that the beam spot on  the turning mirror had displaced off to the mirror edge. We had to re-align the beam.

We have the following parameters from the fitting now, see attached.

w_0x: 1.44 mm +/- 0.0016 mm 
z_0x: 0.575 m +/- 0.046 m
w_0y: 1.50 mm +/- 0.0014 mm
z_0y: 0.004 m +/- 0.029 m

For the p - plane:

Beam waist occurs at 1.249 m +/- 0.002 m from the curved optic of f = 1.25 m 

For the s plane:

Beam waist occurs at 1.269 m +/- 0.001 m from the curved optic of f = 1.25 m 

And the angle of incidence on th ecurved optic was astimated to be 2.66 deg. This imparts a very negligible astigmatism in the reflected beam. But after collecting more data points of the beam profile we see that there is significant astigmatism in the input beam which translates to a decent amount of astigmatism in the reflected beam. 

w_0x: 1.429 mm +/- 0.006 mm
z_0x: 0.421 m +/- 0.131 m

w_0y: 1.526 mm +/- 0.023 mm
z_0y: 0.352 m +/- 0.597 m

[Thejas, Camille, Stephen] 

Here are some notes on how I plan to approach matching of the PZTs, mounting prisms and curved optics. 

Step 1: Match the prisms and the PZTs such that resulitng 18 combiations will have minimum vertical wedging.

- I will be usign scipy.optimize.minimize to implement this.

Step 2: Arrange the curved mirror wedge angles ascending order. This prioritizes matching of low wedge angled mirorrs first. The high wedge angled ones have a much larger range of vertical component of wedge angle due to freedom of rotation of the mirrors. Attention should also be given to error in the wedge angle due to phase spread of the various clocking data. The more the wedge angle, the more it is sensitive to this error.

- This will be implemented using standard loops. 

Oplev setup was built: arm length about 2 m 

As the PZT 44 was actuated with a drive voltage 0-150 V signal was observed on the Spectrum Analyser.

The signal on the top and bottom are X and Y signals from the QPD. This will analyzed and other PZTs will undergo similar measurement. 

[Camille, Stephen, Thejas]

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. 

PZT dimension analyzed and characterized. The blue dot in the images represents the position of the cathode. The length of the arrows indicates the amount of wedging. 

[Camille, Stephen, Thejas]

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 

Prism 1: 

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. 

Clamped: 

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. 

Prism 2

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. 

Prism 4

Prism 5

Prism 6

Prism 7

Prism 9

Prism 10

Prism 11

Prism 12

Prism 13

Prism 14

[Camille, Stephen, Thejas]

Continuing with the efforts to measure the perpndicularity.

Prism 15

Prism 16

Prism 17

Prism 22

Prism 24

Prism 26

Perpendicularity measurement for Beam Splitters

BS 25

BS 29

BS 28

BS 36

BS 33

BS 34

BS 35

BS 37

BS 38

BS 39

Herewith attached are the results of curved mirror radius of curvature characterization. 

Koji's mirror measurement result attached herewith for comparison. 

[Camille, Stephen, Thejas]

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.

BS25

initial division reading: 9.0 

finbal division reading: 2.5 

BS28

ini: 9.0 

fin: 2.0 

BS29

ini: 9.0 

fin: 1.9 

BS33

ini: 9.0 

fin: 2.0 

BS34

ini: 9.0 

fin: 1.7

BS35

ini: 9.0 

fin: 2.0

BS36

ini: 9.0

fin: 2.3

BS37

ini: 9.0 

fin: 2.3

BS38

ini: 9.0

fin: 2.2

BS39

ini: 9.0

fin: 2.4

[Camille, Stephen, Thejas]

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.

[Camille, Thejas, Stephen]

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.

[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. 

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.

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. 

[Camille, Stephen, Thejas]

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. 

HP40

HP41

HP42

HP43

HP44

HP45

HP46

HP47

HP48

HP49

HP50

HP51

HP 52

HP 53

HP 54

HP 55

HP 56

HP 57

[Camille, Thejas, Stephen]

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.

[Camille, Thejas, Stephen]

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: 

Prism 02

Initial reading of the screw on the rotation (yaw) stage (ini): 7.6 

Final reading of the screw (fin): 0.2

Prism 04

ini: + 5.1

fin: - 8.0

Prism 05

ini: + 1.8

fin: - 5.5

Prism 06

ini: + 5.8

fin: - 8.5

Prism 07

ini: 8.2

fin: 1.0 

Prism 09

ini: +1.0

fin: - 4.2

Prism 10

ini: +9.1

final: +2.2

Prism 11

ini: 9.1

fin: 2.0 

Prism 12

ini: 9.0

fin: 2.2

Prism 13

ini: 9.0 

fin: 2.2

Prism 14

ini: 9.0 

fin: 2.1

Prism 15

ini: 9.0

fin: 2.0 

Prism 16

ini: 9.0 

fin: 2.2

Prism 17

ini: 9.0

fin: 2.0

Prism 22

ini: 9.0 

fin: 2.1

Prism 24

ini: 9.1

fin: 2.1

Prism 26

ini: 9.0 

fin: 2.3

This totals 18 prisms including yesterdays.