User:Steven J. Koch/Notebook/Kochlab/2009/07/10/More calibration again

Steve Koch 01:40, 11 July 2009 (EDT): OK, the viscous drag test even made a bit of sense. So, as an experiment, I'm doing this:

• beam expander 120
• refocused z-telescope substantially to bring the bead into focus
• it was focusing below the field of view...does this indicate better trapping? not really sure, but it pushed me over the edge to give it a try
• moved detector in about 3/4 of an inch (this maybe was dumb, but oh well)
• lowered beam power to 100.1 mW
• power spectrum (fitting the whole thing, not ignoring the big fucking 120 Hz spike)
  • 188 Hz, 192 Hz, 182 Hz. Choosing 188
    • pN/nm/Watt = 0.11

(NOTE: I think at high power PS is shitty because there aren't enough magnitude to the X Brownian fluctuations (compared to noise)

• beam expander 100 (data file 29)
  • NOTE: NEW BEAD! I lost the bead because I didn't turn power up when trying to z-focus. So, the method is: turn up power, refocus z-telescope; turn back down power (sort of tedious)
  • PS
    • 246, 237, 247. Choosing 245 hz
    • pN/nm/Watt = 0.14

• beam expander 90
  • Did not refocus z-telescope, because it didn't look different to me
  • NOTE: All of these for the last few hours, my method is to focus 2 microns up from touching coverglass.
  • PS
    • 240, 231 (variance 109)

• beam expander 80
  • PS
    • 253 (variance 108), 238 (110)
  • LOWERING POWER to 39.95 mW
  • PS
    • 146 (323), 141 (338) (reduced scan rate to 5000 from 10000 before next one) 147 (333) (Choosing 145)
    • 0.22 pN/nm/Watt
  • LOWERED POWER TO 14.08 mW (data file 33)
    • 45.8 (906 mV^2), 45.5 (958 mV^2)
    • 0.19 pN/nm/Watt

• beam expander 70
  • PS
    • 156 (309 mV^2), 155 (271 mV^2), 154 (292 mV^2), choosing 155
    • 0.23 pN/nm/Watt (slightly more than beam ex 80)

• beam expander 60
  • PS
    • 162 (296 mV^2), 162 (300 mV^2), 161 (291 mV^2) choosing 162
    • 0.24 pN/nm/Watt (slightly more than 70)

• beam ex 50
  • PS
    • 168 (313 mV^2), 166 (321), 162 (302) choosing 165

• beam ex 40
  • (NOTE: I can tell over the long term that the bead focus is changing a bit compared with last time I decided not to refocus)
  • PS
    • 164 (316), 170 (323), 168 (330)

• beam ex 30
  • • LOST BEAD

• beam ex 40 NEW BEAD (data file 38)
  • PS
    • 174 (315), 165 (345), 170 (this isn't all that different than the other bead above)
  • refocusing (at higher power then back to lower)
    • FUCK lost the bead due to hitting surface. found another bead. refocused compared with above (darker, looks better)
  • PS
    • 181 (276), 183 (262), 178 (258)
    • 0.27 pN/nm/Watt.

• beam ex 60 same bead
  • PS
    • 165 (260) , 165 (254)

[[Image:090710 powerspectrum graph.bmp|right|thumb|These are the power spectrum data taken at 39.95 mW. Notice the trend is opposite the viscous drag trend. I looked at it and figured that 60 is a good choice. What would be really good is to be able to measure the z-stiffness, but that's tough to do. It appears when looking that the bead jiggles much more at lower settings (40 versus 60 say)...but since x stiffness appears not to be less, it may indicate a much lower z-stiffness (which would be consistent with smaller beam diameter, of course, and also explain the easy loss of the bead at lower settings (e.g. 30). OK, I feel like the power spectrum is working, and some things about the numbers make a little sense. But I'm surprised at how little the trap stiffness changes with beam expander setting. Am I turning the wrong knob? Well in any case, I think I'll leave it at the magic number of 60 that Andy chose. One thing that is evident is that I am getting very used to these tweezers. I am confused about the (supposed) low stiffness number (maybe the objective just sucks a lot more?????!!!! yes this may be quite true in terms of IR transmission, since we had a special one on our Nikon). But I think we can definitely go with it. Noise is going to be an issue.

Key to getting the Power Spectrum to be reasonable: Low enough power so that Brownian fluctuations are a big deal on the detector.

OK, I really want to look at the 0.5 micron beads, but that will take way too long. So, calling it quits until probably Tuesday, given kinesin stuff we need to do in between.