User:Pranav Rathi/Notebook/OT/2010/10/04/Investigation for elliptical beam (crystalaser)

Today I investigated the possibility of beam (crystalaser) to be elliptical, and I did it because the outer periphery of the trap in the video looks horizontally elliptical (major axis to be horizontal in CCD frame).

• In the process first I explored; how the beam orientation changes from laser to CCD? At the laser output beam front/ phase front have some spatial profile in transverse plan (circular or elliptical). If the profile is circular than the spot size (beam diameter) is same horizontally and vertically. If it’s elliptical (major axis might have any orientation, for simplification I consider it to be horizontal or vertical) than the spot size along the major axis should be greater or in other words the measurement of the spot size should be different horizontally and vertically. This is what I have investigated; if they are significantly different at two different locations, than it will be proved that our beam is elliptical.
• The orientation of the beam front interchanges as it’s reflected by the mirrors. The result of the interchange can be seen in the picture. Horizontal axis at the laser becomes vertical at the camera and vice versa. This means if the beam looks vertically elliptical at the CCD than its horizontally elliptical at the laser. The reason we still see the beam horizontally elliptical in the video is the orientation of the camera. The camera is installed (on its side) such that the horizontal axis of CCD (corresponding horizontal axis in frame) is vertical and vice versa. So the beam is actually vertically elliptic at the CCD and horizontally elliptic at the laser.

Result

• I measured the beam diameter vertically and horizontally at two different locations. First 64 inches away from the laser: Horizontal diameter= 21.39-20.35=1.04*2=2.08mm
• Vertical diameter=14.15-13.15=1*2=2mm; difference=2.08-2.00=.08mm (3.84% of 2.08)

At 128 inches  : Horizontal ( after periscope mirrors horizontal becomes vertical) diameter=12.15-9.45=2.7*2=5.4mm

• Vertical (after periscope mirrors vertical becomes horizontal) diameter=10.16-7.62=2.54*2=5.08mm; difference=5.4-5.08=.32mm (5.9% of 5.4)
• So at different locations the beam diameter is average 5% more horizontally. At the objective the beam is 5.9% more elongated of perfectly circular. So do we see an elliptical trap due to this elongation??????
  • Steve Koch 22:17, 4 October 2010 (EDT): This seems like it could be the case. I don't think the beam was promised to have the exact same waist x & y anyway, right? Do you think it's good to go?
  • pranav rathi Yes that’s true, even it is seen that in solid state lasers beam is mostly elliptical. In our case it is not that bad, so I think we are good to go.