How Does CCD Offset Affect Laser Beam Exit Angle?

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    Laser Stability
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Discussion Overview

The discussion revolves around the relationship between the offset of a laser beam from the focal point of a CCD camera and the angle at which the beam exits the laser. The context includes experimental measurements of laser pointing stability using a focusing lens and a CCD.

Discussion Character

  • Experimental/applied
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant notes that if both the laser source and the CCD are in focus, there should be no offset, suggesting an ideal condition for measurement.
  • Another participant describes their setup, indicating a distance of 2 meters from the light source to the CCD, with a lens positioned 10 cm before the camera, and mentions observing instability in the laser beam's position in the focal plane.
  • A participant proposes that if the camera's focus is set to infinity, the vertical position of the laser should not affect the measurements, and introduces a relationship involving the sine of the angle and the focal length to describe displacement.
  • A link to external information about beam pointing fluctuations is provided, which may offer additional context or insights into the topic.

Areas of Agreement / Disagreement

Participants express differing views on the impact of the laser's vertical position on the measurements, with some suggesting it does not matter under certain conditions, while others focus on the observed instability in the laser's pointing. The discussion remains unresolved regarding the exact relationship between offset and exit angle.

Contextual Notes

Participants have not fully clarified the assumptions regarding the ideal conditions of the camera and lens setup, nor have they resolved the mathematical relationship between angle and offset in detail.

_Matt87_
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hi,
I'm measuring my laser pointing stability with a focusing lens and a CCD.
Could you guys tell me what would the relationship be between the offset from focal point in CCD and the angle with which the beam exits the laser?

CCD is in focus.
 

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That depends on your setup. If the laser source is in the focus (as well as the CCD), there is no offset at all - that is the idea of the focus,
 
light source is about 2 meters from the ccd with a lens 10cm before the camera (100 mm f).
software fits a gaussian to an image of the beam and tells me the central coordinates. Now I see that the laser is unstable in a way that the centrum of the Gaussian moves up and down in the focal plane, meaning that the beam hits the lens sometimes higher/lower than the middle. I'm trying to relate the angle from the source to that offset (see the attachment) in μradians.
 
Okay, so focus of the camera is basically set to infinity. Then the vertical position of the laser does not matter (in an ideal camera) and you can consider rays going through the center of the lens. The displacement is just sin(angle)*focal length.
 

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