Construction of multiple-beam optical traps with nanometer-resolution position sensing

• Published in: IEEE journal of selected topics in quantum electronics Vol. 2; no. 4; pp. 1066 - 1076
• Main Authors: Visscher, K., Gross, S.P., Block, S.M.
• Format: Journal Article
• Language: English
• Published: IEEE 01.12.1996
• Subjects: Charge carrier processes; Instruments; Laser beams; Micromotors; Object detection; Optical design; Optical microscopy; Optical polarization; Structural beams; Time sharing computer systems
• ISSN: 1077-260X; 1558-4542
• DOI: 10.1109/2944.577338

We describe the design and construction of two different types of multiple-beam optical tweezers, each equipped with nanometer-resolution position detectors. Multiple optical traps can be created either by splitting a laser beam in two parts, based on its polarization, or time-sharing a single beam among several different locations. The advantages and disadvantages of optical tweezers based on either scheme are discussed, along with details of specific implementations. Various ways to detect microscopic movements of an optically trapped object are presented and compared, including designs that are relatively insensitive to absolute location of a trapped particle within the field of view. Two of many possible applications for such instruments are illustrated: the detection of molecular steps by kinesin motor molecules, and determinations of the stiffness of single microtubules.