Kiwamu, Elli

Yesterday after removing the lexan viewport covers from all of the ITM cameras, we focused the ITMX_green and ITMY_green cameras and looked at the images of the ALS beams on the ITMS when ALS is locked.  We noticed that the picture on ITMY is a fairly  diffuse beam with few point scatterers, while the image on ITMX is mostly point scatterers. 

We wondered if these images showed a real difference in the ITMs or whether there was a difference in the cameras, for example maybe there is a smudge on the IMTY_Green camera lens which makes the beam look more diffuse than the ITMX_Green beam.  So today we refocused the ITMy_Spool and ITMx_Spool cameras, which are usually focused in IR but which have no color filters on them, to green.  This way we have a second pair of cameras looking at the ITMs.  The saw the same difference in pattern (ITMy diffuse beam, ITMx many point scatterers)  with the ITMX_Spool and ITMY_Spool cameras.  This might mean there are more point scatterers around the center of ITMX than around ITMy.

We tried looking at the pixel sum of these cameras to compare the relative brightness of the scattered light.  Comparing images taken with the same settings, the pixel sum is higher on ITMX_Green than for ITMY_Green (eg 1,550,000 counts on ITMY_Green vs 960,000 counts on ITMX_Green when counts on ALS-C_TRY_A_LF are 1050 and on ALS-C_TRX_A_LF 1370, with camera settings exposure=100000microsecods, analog gain=100, image type = mono12.).  The IMTY_Spool camera pixel sum = 845,000 and ITMX_Spool =186,500.  THis is a factor of 4 difference between the intensity on the ITM spool cameras, which we can't explain.  We expected them to be roughly the same!