GariLynn Billingsley, Travis Sadecki, Betsy Weaver, Calum Torrie, Nicki Washington (and a BIG support crew)
ITMx inspection with green light and portable microscope revealed several scattering sites. The center most sites were located high and right of center. (Camera images will be attached soon.) One of these (the brightest / closest to center) is shown in the attached picture. It measure roughly 0.5 mm across the halo.
There were many scatter sites of the same character all the way out to the edge of the optic. At the edge we attempted to clean one of these sites using the following solvents (IPA, Acetone, red FC and clear FC) without success.
Following this local cleaning and the overall inspection we then cleaned the entire HR face as per normal procedures i.e. with red first contact (FC) spray along with the cone etc ....
Subsequent inspection showed no change to these scatterering sites.
For full chamber report see alog by Betsy.
GariLynn and team.
A few more pix of various "spots" we saw on the HR surface of ITMX today which did not come off with cleaning.
The first shows 2 very visible spots near the center of the optic which are the "halo" shaped nature that Calum/GariLynn show zoomed in above.
The second picture shows a small damage spot on the lower left of center on the HR surface that we believe has been on the optic since processing/coating/fabricating. This is a surface penetrating feature visible with back-illumination, and is the only one observed of it's kind.
The third picture shows a much different "feature" far right of center, that is not anywhere else on the optic, but interesting.
Here's one more picture of us illuminating the section of the ITMX-HR slightly below and right of center where we DIDN'T find much during inspection.
We did see similarly described "donuts" on the BS-HR - see Kates alog and Betsy's attempt at pictures in ~2014:
https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=12876
Need to review to confirm related!
Calum
Now with the BS picture attempts during the time frame of Kate's alog:
https://ligoimages.mit.edu/?r=24661
https://ligoimages.mit.edu/?r=24659
Here are the articles I mentioned in the SYS call this morning. These are not the same, as they describe a short, intense burst of light on a clean surface, rather than the suspected culprit of a CW beam on a bit of dust. Never-the-less, perhaps they will useful or interesting.
Morphology of femtosecond-laser-ablated borosilicate glass surfaces
Adela Ben-Yakar, Robert L. Byer, Anthony Harkin, Jacqueline Ashmore, Howard A. Stone, Mengyan Shen, and Eric Mazur
Citation: Appl. Phys. Lett. 83, 3030 (2003);
doi: 10.1063/1.1619560
View online: http://dx.doi.org/10.1063/1.1619560
View Table of Contents: http://aip.scitation.org/toc/apl/83/15, Published by the American Institute of Physics
Femtosecond laser ablation properties of borosilicate glass
Adela Ben-Yakar, Robert L. Byer
Citation: Journal of Applied Physics 96, 5316 (2004);
doi: 10.1063/1.1787145
View online: http://dx.doi.org/10.1063/1.1787145
View Table of Contents: http://aip.scitation.org/toc/jap/96/9, Published by the American Institute of Physics
I've included a picture of some of the craters from the second paper (fair use)
Facts: Nothing was found where we were looking for the absorber, low and right from center on the HR surface. Aidan's plot showed ~25 mm down and ~25 mm Right. No particulate was seen standing proud of the HR surface. Nothing was found on the AR surface of the adjacent CP. The features found on the ITM HR surface were of uniform size ~0.5 mm, with no more than 50% variation in size. All of the characteristic spots were circular. There were various dark (uncontaminated?) shapes in the center of the circles - keyhole, linear, dot or uniform (filled) Features were found all over the optic including the very edge - Can’t say if there were any off the coating or not. No immediately apparent distribution. tried the following cleaning on a spot at the bottom edge of the optic to the left of the bevel damage. (in order) Acetone - scrub with cotton swab IPA - scrub with alpha swab DI water - scrub with alpha swab Windex - scrub with alpha swab clear first contact paint red first contact paint Within estimated beam waist we found 7 circular features counted 1 spot (very small) penetrating the coating (glowed when illuminated from behind) - believed to be present as polishing defect. Silica wafer, mounted parallel to ITM03, but low of the arm cavity baffle: no similar scatterers - only small particulate. 1” optic mounted perpendicular to ITM03 on the side of the compensation plate suspension structure: no similar scatterers - only small particulate. Speculation: Possible vaporization of particulate depositing on the surface. Possible contamination underneath the HR coating, present all along. Further investigation at: https://dcc.ligo.org/T1700193
Particle counts during the in-chamber work were taken a few times:
2:30pm PT during first contact work with 1 person in the chamber, 2 people just prio
| Count Size | 10am PT entrance to chamber - Jim was starting ISI locking, 1 person in chamber | 2:30pm PT during first contact work with 1 person in the chamber, 2 people just prior |
| 0.3um | 9 | 135 |
| 0.5um | 2 | 82 |
| 1.0um | 2 | 24 |
BSC3 DOOR WAS OFF FROM ~9am to 5pm PT.