User:Steven J. Koch/Notebook/Kochlab/2009/07/10/trap calibration things

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Steve Koch 22:52, 10 July 2009 (EDT): Andy fixed the trap (in one hour!) and we did some more tests. I will try to fill in details later.

  • Looking at old calibration data:
    • xstiffness_pN per nm per mV = 1.30707 (assuming mV is for sum signal)
  • Quick conversion
    • Trap stiffness: 0.9440 pN / nm / W
    • Detector sensitivity s 7.17 mV / nm
    • Laser power from Sum (mW/mV) = 0.1177 (=1/8.5)


Here's what Andy and I found (all for apparently 1 micron beads, laser power at 350 mW) (no sum correction on QPD): (Beam expander is 1 tick below 70 or 69, although I think maybe there's only 8 ticks between numbers?)

  • Andy Maloney 00:16, 11 July 2009 (EDT): The ticks are actually 1 mm each and the major divisions are 1 cm. Well, they are supposed to be. I just looked at my graphic and saw that it is messed up so that there are 9 division between major marks. Sorry. I'll fix this.
    • Steve Koch 03:52, 11 July 2009 (EDT): I thought so! Not worth fixing, though, since from my experience today, I don't think we'll do anything with more precision than 60, 65, 70, etc.
  • Escape force (data file 26)
    • Bead escaped somewhere between 1000 and 2000 microns per second.
      • 0.6 MHz / loop. Loop time about 425 microseconds. 1.4 microns / MHz
    • Detector signal was 672 mV
    • See excel sheet, this speed corresponds to a force about about 19 pN for a 1 micron diameter sphere far away from surface.
    • It took a piezo control voltage of about 330 mV to get from center to peak of DOG. This is one micron (3.0 microns / volt).
    • So, stiffness is approximately 19 pN / micron = 0.019 pN / nm.
    • Laser power is 350 mW
    • So stifness is approximately 0.05 pN / nm / W (for 1 micron bead)
    • This does not compare well with above numbers (20x stiffer for smaller bead).
      • But escape velocity is a poor way to characterize it, and not using a good controlled velocity either (irregular loop time) (velocity clamp would be better)


Raw notes from Evernote

To get from peak to peak on the DOG is about 330 mV sinewave amplitude (660 mV total?) minimum is -7.65, maximum is 10

200 mV sine wave applied to piezo (600 nM amplitude) gives us a 200 mV amplitude detector X signal. (peak of DOG is about 500 mV)

Tentative calibration is 200 mV / 600 nM = 1/3 mV / nm or 0.333 mV / nm.

.03 MHz / loop (42 nm/ loop); loop time is 400 microseconds so, about 100 nm / millisecond or 100 microns / second

Data file 21 shows about an integer displacement of 400 units for 100 microns / second

Using oscilloscope, the jump is 88 mV on the detector (for 1 pN).

Above, had 1/3 mV / nm,

1 pN / 88 mV * 1/3 mV/nm = 1 pN /


0.6 MHz / loop cycle; bead escaped at voltage of about 672 mV. data file 26. average loop time is 8500 ticks on 20MHz clock so 425 microsecond loop time.

=0.6MHz*1.4microns/MHz/0.425 milliseconds = 2 microns/milliseconds. = 2000 microns/second.

Laser power is 350 mW from controller.

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