Difference between revisions of "User:Pranav Rathi/Notebook/OT/2010/03/23"

From OpenWetWare
< User:Pranav Rathi‎ | Notebook‎ | OT‎ | 2010‎ | 03
(Beam Collimation)
Line 1: Line 1:
==OT alignment==
==OT alignment==
Line 22: Line 21:
[[Category:Optical Tweezer]]
[[Category:Optical tweezers Notes Archive]]

Latest revision as of 12:58, 15 November 2012

OT alignment

  • Collimating the beam

Beam Collimation

Method:I used our regular CCD camera with 3+2 O.D. filters + 25mm lance at .10W. First I diverted the beam at 90 degrees with two mirrors after the telescope, and then I placed the camera on the rail in near far-field. I captured the image and move the camera about 60cms (far field) and captured the image again. I compared the spot size in the two images with the help of image-j. In far-field beam looks smaller so I made its size equal (increase) to near-field, through the center dial of the telescope. I came back in near field and check the size again, this time it was bigger, so made it equal (decrease) to far-field by using the eye-piece of the telescope. I followed the process iteratively until the beam sizes match in far and near-field. The results are presented below. Measurement of size; Once the beam is collimated I used the camera in the background with an aperture infront. I adjusted the aperture such its center coincides with the beam axis. In this scenario; when the aperture is closed its overlap the beam periphery from all sides as seen through the camera. Once the aperture inner-circle touches the beam periphery, I stop and measured the circle size, our spot size at .10 W. This is not a very accurate way to measure the spot size, because CCD was somewhat saturating at this power, so spot size might be less. I verified this by projecting the beam at a surface though an aperture and observe it through a cell-phone camera; I closed the aperture until it hits the beam periphery. It came-out to be little less 5mm. I still need a better idea on this one.


Beam in near-field at .10W; 6mm diameter
Beam in far-field at .10W; 6mm diameter
Comparison between near & far-field at .10W; 6mm diameter

The two spot sizes are compared, the far field looks little smaller but they agree pretty well in the course of few pixels. Next Task is to align the periscope on thursday.