New calibration method for position detector for simultaneous measurements of force constants and local viscosity in optical tweezers

• Published in: Optics communications Vol. 230; no. 4; pp. 357 - 368
• Main Authors: Buosciolo, A., Pesce, G., Sasso, A.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-02-2004; Elsevier Science
• Subjects: Exact sciences and technology; Fundamental areas of phenomenology (including applications); General equipment and techniques; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Local viscosity; Mechanical effects of light on atoms, molecules, electrons, and ions; Optical tweezers; Optics; Physics; Position detector; Quantum description of interaction of light and matter; related experiments; Quantum optics; Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing; 41.20Bt; 07.60.P; Position detector; Optical tweezers; Local viscosity; 42.62−b; 42.50V; 42.50C; Optical trapping; Force measurement; Light matter interaction; Position sensor; Force constants; Experimental device; Viscosimetry; Calibration; Experimental study; Photodiodes
• ISSN: 0030-4018; 1873-0310
• DOI: 10.1016/j.optcom.2003.11.062

We present a new method to calibrate a quadrant photodiode used as position detector to monitor latex beads trapped in optical tweezers. The method combines the dragging Stoke’s force with the thermal noise analysis (power spectral density (PSD)) of the Brownian motion of the trapped bead. Position detector calibrations used in other similar methods normally utilise a bead attached to the coverslip: the voltage-position calibration factor is found by translating the bead across the waist of a laser beam. The so determined calibration factor is then assumed to be the same when beads are investigated in the optical trap. This procedure presents some drawbacks since attached beads can be affected by proximity effects due to the coverslip glass surface which alter the position sensor response itself. On the contrary, our method is able to provide, simultaneously, the calibration factor, the trap stiffness, and the local viscosity of the medium making use of a single trapped bead.