User:Pranav Rathi/Notebook/OT/2010/08/02/x & y Signal Drift Issue

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The goal has been achieved today. The drift problem is solved by imaging the beam waist (1.26mm; exists inside the AOM) with 1:1 telescope on the QPD. I am very positive that this works, but I am still verifying that it is not happening due to small beam waist at the QPD. I will right the full detail later ; how we achieved it. Investigate the x & Y signal drift: What is causing it; AOM or the laser (most probable it’s the AOM), magnitude of the effect, and possible solution.

Setup & procedure

The setup is fairly simple; laser --> AOM --> two mirrors (down and upstream) --> telescope (1:1)--> QPD.


under work


  1. Measure the beam waist (2 x W=1.5) at the eyepiece lens of the telescope.
  2. Setup the (1:1) telescope: In this case two planoconvex lenses (f=38.1mm of both) are used.
  3. Measure the beam waist again (2 x W =1.5) at QPD, to make sure that the ratio is 1:1.
  4. Straighten the beam after the telescope, using two aperture techniques [[1]].
  5. Setup the QPD on the xyz translation stage.