Measurement of the Optical Force and Trapping Range of a Single-beam Gradient Optical Trap for Micron-sized Latex Spheres

Abstract

A single-beam gradient optical trap was constructed using a 20 mW 632·8 nm He–Ne laser coupled to an optical microscope. Latex spheres were trapped in water at the focal point of a tightly-focused laser beam, which was generated using a 100 × objective. The efficiency of the trap was evaluated by determining the maximum speeds at which the trapped particles could be manipulated. Typical maximum speeds of tens of microns per second were recorded, at the maximum trapping power of 6·7 mW. The effective transverse trapping range for 1–7 μm diameter latex spheres was measured to be 1–3 μm, and the maximum transverse optical force on 1–12 μm diameter latex spheres varied in the range 0·4–4·5 pN.