Abstract

The use of focused Gaussian laser modes to trap and manipulate micron-sized particles, pioneered by A. Ashkin over a decade ago, ¹ is a powerful non-invasive technique. More complex beams, such as Laguerre-Gaussian (LG) beams, can also be used to trap microscopic particles.² We have extended the concept of optical trapping and manipulation with LG beams by overlapping two LG modes of opposite phase helicity (one with a positive azimuthal index l and one with a negative l) to create an interference pattern consisting of a set of bright spots. This pattern remains intact as it propagates in the z-direction, due to the matched beam parameters of the overlapping beams unlike patterns produced using phase or intensity masks. A simulation of such a pattern is shown in Fig. 1, where two modes of the same radial index (p = 0) but opposite azimuthal indices (l₁, = 2 and =−2) have been interfered. In this work the pattern was produced by splitting a holographically produced LG beam into two separate beams in a Mach-Zehnder interferometer with a dove prism in one arm to reverse the helicity of one beam. The two beams could then be recombined to form the spot pattern.

© 2002 Optical Society of America