Optical levitation

Optical levitation is a method developed by Arthur Ashkin whereby a material is levitated against the downward force of gravity by counter forces stemming from photon momentum transfer. Typically photon radiation pressure of a focused laser beam of enough intensity counters the downward force of gravity while also preventing lateral (side to side) and vertical instabilities to allow for a stable optical trap capable of holding small particles in suspension.

A force diagram showing how axial and lateral stabilization occurs in an optical trap.
An example of spherical aberration creating low pockets of energy near the focus where the particles can be trapped.

Micrometer sized (from several to 50 micrometers in diameter) transparent dielectric spheres such as fused silica spheres, oil or water droplets, are used in this type of experiment. The laser radiation can be fixed in wavelength such as that of an argon ion laser or that of a tunable dye laser. Laser power required is of the order of 1 Watt focused to a spot size of several tens of micrometers. Phenomena related to morphology-dependent resonances in a spherical optical cavity have been studied by several research groups.

For a shiny object, such as a metallic micro-sphere, stable optical levitation has not been achieved. Optical levitation of a macroscopic object is also theoretically possible,[1] and can be enhanced with nano-structuring.[2]

Materials that have been successfully levitated include Black liquor, aluminum oxide, tungsten, and nickel.[3]

See also

References
  1. Guccione, G.; M. Hosseini; S. Adlong; M. T. Johnsson; J. Hope; B. C. Buchler; P. K. Lam (July 2013). "Scattering-Free Optical Levitation of a Cavity Mirror". Physical Review Letters. 111 (18): 183001. arXiv:1307.1175. doi:10.1103/PhysRevLett.111.183001. PMID 24237512.
  2. Ilic, Ognjen; Atwater, Harry, A. (April 2019). "Self-stabilizing photonic levitation and propulsion of nanostructured macroscopic objects". Nature Photonics. 13 (4): 289–295. doi:10.1038/s41566-019-0373-y. ISSN 1749-4893.
  3. Smalley, D. E.; Nygaard, E.; Squire, K.; Van Wagoner, J.; Rasmussen, J.; Gneiting, S.; Qaderi, K.; Goodsell, J.; Rogers, W.; Lindsey, M.; Costner, K. (January 2018). "A photophoretic-trap volumetric display". Nature. 553 (7689): 486–490. doi:10.1038/nature25176. ISSN 0028-0836.
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