User:Anthony Salvagno/Notebook/Research/2010/05/19/Next thing to do for the Tweezers

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After yesterday's experiments Koch offered some very good follow ups:

  • power spectrum with beam expander
  • power spectrum at different distances from glass
    • I personally think that we were working too near the glass so this looks like a promising place to start.

Notes for today

We started by messing around with the beam expander trying to figure out exactly how that worked. We managed to adjust the beam expander to a size that was manageable so that we could expand it in the upcoming experiments. I will take notes on here today.

Note Section

  • Pranav is practicing with the condenser alignment
  • We are first going to do some power spectrum data (which can be seen below) with the cooler off and getting data at various heights.
  • We adjusted the beam expander
    • Pranav noticed that the beam was way overfilling the back aperture and we adjusted it so it is about the size of the aperture (it may be a little smaller right now, and I know that isn't optimal but whatever).
  • After adjustment we got much better sum signals
  • moving the focus into the water (in the up direction on the microscope) gave us much better stiffness
    • see results below
  • We were able to get really high forces at 1W (based on estimation from the formula)
  • We then redid the experiment from yesterday (power measurement at QPD position)
  • Finally we tried to take sum signal measurements with a trapped bead
    • the sum signal didn't change enough to take any decent data
    • but it did increase ever so slightly
    • plus the jumpiness of the sum signal made it difficult to truly ascertain what the sum signal was
    • so it did increase but I have no real way to measure and determine how much


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We performed the same experiment from yesterday where we measured the power at the QPD position. We did this because we changed the beam expander. We got much better powers than yesterday which correlates to a much better stiffness as we were getting in the data above. Very promising stuff. The new data is the much larger scale seen below. <html><img src="" /></html>

For Tomorrow

  • power spectrum with big beads
  • try some ghetto unzipping
    • maybe some real unzipping