Optical trapping with a perfect vortex beam
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Vortex beams with different topological charge usually have different profiles and radii of peak intensity. This introduces a degree of complexity the fair study of the nature of optical OAM (orbital angular momentum). To avoid this, we introduced a new approach by creating a perfect vortex beam using an annular illuminating beam with a fixed intensity profile on an SLM that imposes a chosen topological charge. The radial intensity profile of such an experimentally created perfect vortex beam is independent to any given integer value of its topological charge. The well-defined OAM density in such a perfect vortex beam is probed by trapping microscope particles. The rotation rate of a trapped necklace of particles is measured for both integer and non-integer topological charge. Experimental results agree with the theoretical prediction. With the flexibility of our approach, local OAM density can be corrected in situ to overcome the problem of trapping the particle in the intensity hotspots. The correction of local OAM density in the perfect vortex beam therefore enables a single trapped particle to move along the vortex ring at a constant angular velocity that is independent of the azimuthal position. Due to its particular nature, the perfect vortex beam may be applied to other studies in optical trapping of particles, atoms or quantum gases.
Chen , M , Mazilu , M , Arita , Y , Wright , E M & Dholakia , K 2014 , Optical trapping with a perfect vortex beam . in K Dholakia & GC Spalding (eds) , Optical Trapping and Optical Micromanipulation XI . Proceedings of SPIE , vol. 9164 , SPIE , Bellingham , Conference on Optical Trapping and Optical Micromanipulation XI , Canada , 17/08/14 . https://doi.org/10.1117/12.2064080conference
Optical Trapping and Optical Micromanipulation XI
Copyright 2015 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited. Chen, M., Mazilu, M., Arita, Y., Wright, E. M., & Dholakia, K. (2014). Optical trapping with a perfect vortex beam. In Dholakia, K., & Spalding, G. C. (Eds.), Optical Trapping and Optical Micromanipulation XI. (Proceedings of SPIE). http://dx.doi.org/10.1117/12.2064080
DescriptionThe authors would like to thank the UK Engineering and Physical Sciences Research Council (EPSRC) for funding.
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