Type-T thermocouples: check this company Physitemp.
Can be used to measure the sample temperature in the optical tweezer experiment.
Can be used to measure the sample temperature in the optical tweezer experiment.
Type-T thermocouples: check this company Physitemp.
Can be used to measure the sample temperature in the optical tweezer experiment.
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"Calibration of optical tweezers with positional detection in the back focal plane", REVIEW OF SCIENTIFIC INSTRUMENTS 77, 103101 (2006)
"Calibration of Optical Tweezers for In Vivo Force Measurements: How do Different Approaches Compare?", Biophysical Journal 107, 1474–1484 (2014) This active power-spectrum method has several advantages, particularly relative to the assumptions required for the passive power spectrum: 1), it is able to determine trap stiffness k and converting factor b simultaneously, 2), it does not require prior knowledge of viscosity of the medium, the size of the bead, or the height of the trapped object above the surface; and 3), it is less sensitive to temperature changes. It is insensitive to system noise, its result inherently includes the output of the passive power-spectrum method, and it allows simultaneous measurement of b and k. “Calibration of light forces in optical tweezers,” Appl. Opt. 34(6), 977–982 (1995) This equation can be found at this book:
J. Happel and H. Brenner, Low Reynolds Number Hydrodynamics, 2nd ed. Nordhoff, Groningen, 1973 “Construction and calibration of an optical trap on a fluorescence optical microscope,” Nat. Protoc. 2, 3226–3238 (2007).
In this protocol, we aim to provide a clear exposition of the methodology of assembling and operating a single-beam gradient force trap (optical tweezers) on an inverted fluorescence microscope. A step-by-step guide is given for alignment and operation, with discussion of common pitfalls. “Rapid, accurate particle tracking by calculation of radial symmetry centers” Nat. Methods 9, 724–726 (2012).
Another good paper: “Methods of digital video microscopy for colloidal studies,” J. Colloid Interface Sci. 179, 298–310 (1996). "Comparative study of methods to calibrate the stiffness of a single-beam gradient-force optical tweezers over various laser trapping powers", J. Biomed. Opt. 19, 115001 (2014).
Output voltage of the QPD was calibrated against displacement using the PZT as follows: The position of a trapped bead in the field of view was initially taken as the reference point to center the QPD. Subsequently, in the absence of the optical trap, a bead was attached to the cover slip and brought to the exact transverse position of the trapped bead using the PZT. Check this paper:
"Optical tweezers with millikelvin precision of temperature-controlled objectives and base-pair resolution" Optics Express, 17, 17190-17199 (2009) Summary and comparison on different calibration method for Optical force:
"Comparative study of methods to calibrate the stiffness of a single-beam gradient-force optical tweezers over various laser trapping powers", J. Biomed. Opt. 19, 115001 (2014). If X is the time series of the x voltage from a QPD, sampling_f is the sampling frequency in experiment. Then do the following calculation:
fNyq = sampling_f / 2; #calculate the Nyquist frequency delta_t = 1 / sampling_f; #time interval time = np.arange(0, np.size(X))*delta_t ; T = np.max(time); f = ([1 : length(X)] / T #do FFT to X and multiple by the time interval FT = delta_t*fft(X); P = FT * np.conj(FT) / T; # power spectrum ind = find(f <= fNyq); # only to the Nyquist f f = f(ind); P = P(ind); |