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

TLDR

Optical traps can be generated by beam splitting or time‑sharing, each with distinct advantages and disadvantages that are discussed in detail. The study presents the design and construction of two types of multiple‑beam optical tweezers with nanometer‑resolution position detection. The authors detail the construction of the tweezers and compare several position‑sensing methods that are robust to the particle’s absolute location. The instruments are demonstrated by detecting kinesin motor steps and measuring single microtubule stiffness.

Abstract

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.