Mapping out tractor beams: Topological angular momentum and reduced axial flux; gradient versus non-conservative forces

Gabriel C. Spalding (Lead / Corresponding author), Patrick M. Dahl, Christine E. Démoré, Zhengi Yang, Peter Glynne-Jones, Andreas Melzer, Sandy Cochran, Michael P. MacDonald

    Research output: Chapter in Book/Report/Conference proceedingConference contribution

    Abstract

    We experimentally demonstrate continuous attraction of macroscopic targets (> 1 cm) towards the source, against a net momentum flux in the system. Use of a simple setup provides an easily understood illustration of the negative radiation pressure concept for tractor beam, and how these are distinct from the gradient force acting in conventional optical tweezers. Here, we map out regimes over which negative radiation forces dominate, and (favorably) compare the thresholds observed to those that emerge from simulations. Theoretical explorations of tractor beam action commonly invoke higher-order Bessel beams, and here we make clear that the reason for this is because of the reduction in axial momentum associated with such hollow-core beams, which allows effects associated with off-axis “skew” momentum to become dominant. Ultimately, there is interest in exploring the language used for describing such effects: radiation pressure versus gradient force (which we suggest might be better described in terms of non-conservative versus conservative forces), and “orbital” angular momentum (which we suggest might be more appropriately termed “topological” angular momentum).
    Original languageEnglish
    Title of host publicationOptical Trapping and Optical Micromanipulation X
    EditorsKishan Dholakia, Gabriel C. Spalding
    Place of PublicationBellingham
    PublisherSPIE-International Society for Optical Engineering
    ISBN (Print)9780819496607
    DOIs
    Publication statusPublished - 2013
    EventSPIE Optics+Photonics 2013: Optical Trapping and Optical Micromanipulation X - San Diego Convention Center, San Diego, United States
    Duration: 25 Aug 201329 Aug 2013
    http://spie.org/x103812.xml

    Publication series

    NameProceedings of SPIE
    PublisherSPIE
    Volume8810

    Conference

    ConferenceSPIE Optics+Photonics 2013: Optical Trapping and Optical Micromanipulation X
    CountryUnited States
    CitySan Diego
    Period25/08/1329/08/13
    Internet address

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    Cite this

    Spalding, G. C., Dahl, P. M., Démoré, C. E., Yang, Z., Glynne-Jones, P., Melzer, A., Cochran, S., & MacDonald, M. P. (2013). Mapping out tractor beams: Topological angular momentum and reduced axial flux; gradient versus non-conservative forces. In K. Dholakia, & G. C. Spalding (Eds.), Optical Trapping and Optical Micromanipulation X [881004] (Proceedings of SPIE; Vol. 8810). SPIE-International Society for Optical Engineering. https://doi.org/10.1117/12.2027136