Optical forces and torques in nonuniform beams of light

David B. Ruffner, David G. Grier

    Research output: Contribution to journalArticlepeer-review


    The spin angular momentum in an elliptically polarized beam of light plays several noteworthy roles in optical traps. It contributes to the linear momentum density in a nonuniform beam, and thus to the radiation pressure exerted on illuminated objects. It can be converted into orbital angular momentum, and thus can exert torques even on optically isotropic objects. Its curl, moreover, contributes to both forces and torques without spin-to-orbit conversion. We demonstrate these effects experimentally by tracking colloidal spheres diffusing in elliptically polarized optical tweezers. Clusters of spheres circulate deterministically about the beam's axis. A single sphere, by contrast, undergoes stochastic Brownian vortex circulation that maps out the optical force field.

    Original languageEnglish (US)
    Article number173602
    JournalPhysical Review Letters
    Issue number17
    StatePublished - Apr 24 2012

    ASJC Scopus subject areas

    • General Physics and Astronomy


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