1 James N. Bellinger Robert Handler University of Wisconsin-Madison 11-Monday-2009 Laser fan non-linearity James N. Bellinger 20-March-2009

2 Motivation Dr. Handler discovered some discrepancies in what should have been constants along the laser line: Differences of differences: No matter what the DCOPS rotation, if the angles are small the differences in opposite CCD measurements should have the same differences. The reference lasers don’t agree w/ the rest

3 Setup Laser and DCOPS 110mm apart, adjust table to scan across laser beam fan. Scan horizontal fan, use vertical to calibrate the table motion. ½ turn per step. DCOPS readout via terminal server

4 Laser, DCOPS details Pair of polarizing filters added to reduce signal size

5 Horizontal scan When the table was at the step shown by the red line, the vertical laser was centered in CCD1/3 Laser fan not parallel to table, so tilt is expected. Curl at the ends isn’t CCD4 CCD2

6 Calibration Fit each line (for CCD2 and 4) and average the slopes to calibrate the table (.976mm/1/2 turn)

7 SLM Schematic Laser beam hits a cylindrical lens to produce a fan of light Downstream DCOPS sample very small angles in the beam fan Reference DCOPS samples large angles of the fan First chamber DCOPS samples small fan angles

8 Subtract slope; Overlay Eyeballed shift to be 40 steps Ideal is 38.2 Agreement is very good, down to fine detail, at left and at the center. Central flat region is about 26mm

9 Aperture Flat region is O(26mm) Horizontal laser is shifted 13mm from SLM center: usually closer to CCD4 Distance between CCD apertures (filter gaps) varies from 28 to 35mm Red bar represents ME+1 (28mm) Green bar ME+4 (35mm) or

10 Corrections Corrections vary from 30 to 90 pixels 0.4 to 1.3mm or

11 Not unique to one laser Each laser system has 2 lasers. I rotated the mount to look at the other one of the pair, shown in green in this lower-statistics plot. The orientation differs, but the distortion shapes are the same. (Not remounted in exactly the same position, so  horizontal offsets

12 Plans Test the other laser pair we have Overlay distortion curves to see if same shape Do longitudinal scan to check flatness of smaller angle region (first chamber DCOPS) Do horizontal scan at 2 meters to check flatness of very small angle region Acquire and test Transfer Line laser Check if vendors have better lasers

13 Solutions Short term: Figure out which CCD is closer to the laser fan center and drop the other one from the fit. Medium term: Figure out a correction term and see if it works Long term: Get better lasers

14 BACKUP

15 “Aperture” Aperture per David’s notes is open space in center. I also need the distance from one CCD opening to the other—the apertures into the CCDs Light enters CCD here

16 Horizontal scan

17 Vertical Scan