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

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

• File:090710 Preliminary stiffness.xlsx excel notes

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 /

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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.