Attached are some comparison images of ETMy before and after it was cleaned just before Christmas. I have also attached a pitcure or ETMx before it was cleaned, although it is taken at a much longer exposure and is not as well focused making direct comparision of images difficult. The three very bright spots which were previously visable on the ETM are no longer visible, these would have been the three macroscopic pieces of first contact which were removed from the mirror.
Imaging method:
The camera position is identical in the before and after images. For all pictures, an image is taken with the test mass is illuminated with IR locked in the arm. The trans mon is misaligned so there is minimal green light present. A background image is taken with no IR (ITM misaligned), and this is subtracted from the original image to produce the final image. The analogue gain is set to 100, a 12 bit image is taken, and each image is made of 100 averages. The exposure of the ETMx images is 10000micoseconds, and ETMx is taken at 500000 microseconds.
BRDF calculation:
Done using the same method as alog15633, with calibration factor 1.6x10-10 (µs)(W)/count (same as before). The incident power is calculated by averaging ASC-TR_A_SUM_OUTPUT and ASC-TR_B_SUM_OUTPUT as outlined by Dan in alog 15431.
| OPTIC | Date taken | Incident power (W) | Power scattered onto photodoide (W) | BRDF |
| ETMy | 10 December 2014 | 18W | 8.4e-7 | 0.023 |
| ETMy | 5 January 2015 | 21W | 1.16e-7 | 0.004 |
| ETMx | 11 December 2014 | 45W | 8e-8 | 0.001 |
ETMy shows a factor of ~6 improvement since being cleaned, but it still doesn't look as good as ETMx. I will see if I can focus the camera better on ETMx to get a nicer comparison.
