Abstract
Optical tweezers find applications in various fields, ranging from biology to physics. One of the fundamental steps necessary to perform quantitative measurements using trapped particles is the calibration of the tweezer's spring constant. This can be done through power spectral density analysis, from forward scattering detection of the particle's position. In this work we propose and experimentally test simplifications to such measurement procedure, aimed at reducing post-processing of recorded data and dealing with acquisition devices that have frequency-dependent electronic noise. In the same line of simplifying the tweezer setup we also present a knife-edge detection scheme that can substitute standard position sensitive detectors.
Highlights
Optical tweezers were conceived as tools capable of harvesting radiation pressure to hold and manipulate tiny objects [1, 2]
We have derived mathematical expressions for the position of a trapped particle measured by forward scattering detection
The first of these approximations imply that the PSD calculated from the division of X(t) by S(t) at each sample is almost identical to that obtained directly from X(t)
Summary
Optical tweezers were conceived as tools capable of harvesting radiation pressure to hold and manipulate tiny objects [1, 2]. The beam deviation is proportional to the radial particle position, which can be obtained by dividing X and Y by S, aside from a constant Once this operation is performed for each signal sample, it can be used to calculate the power spectral density and find the desired spring constants after fitting the data to a Lorentzian function and using the proportionality relation between the trap stiffness and the Lorentzian’s corner frequency [28]. Still motivated by the interest in reducing the cost and complexity of an optical tweezer setup [30, 31], we propose a knife-edge method that aims to substitute a position sensitive detector by regular power-sensing silicon detectors These detectors present the advantage of having an increased bandwidth which can be explored in statistical mechanics experiments involving trapped particles [32]. We close with a brief discussion and the conclusions of this work
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