Thousands of traps in counter-propagating Bessel beams

The uniques preoperties of the Bessel beam can be also efficiently used in counter-propagating and interfering Bessel beams. Since the single real beam Bessel beam has negligible intensity gradients along the propagatin axis it can not be used to trap an objects. But two interfering and counter-propagatin Bessel beams create a standing wave. On the contrast to the Gaussian beam where each trap has different properties than its neighboring trap (see figure), the standing Bessel beam creates an array of very similar optical traps. Moreover the traps are narrow lateraly and also axially and an array of them long millimetres can be obtained. Therefore thousands of optical trapps in 3D can be generated and thousands of objects can be trapped there.

 An example of an intensity profile of a standing wave created by two counter-propagating Gaussian beams.



An example of an intensity profile of a standing wave created by two counter-propagating Bessel beams.
The neighboring trapps are very simillar to each other.

Again the standing Bessel beam can be created either by retro-reflection of single incident Bessel beam on the mirror or using two counter-propagating beams.

Therefore two counter-propagating Bessel beams creates two times longer array of optical traps and so also more objects can be trapped in this array.

Experimentally we used two identical counter-propagating Bessel beams at the wavelength of 532 nm with carefully designed paths so that each Bessel beam existed over a distance 1 mm and its diameter of the high intensity core was only 2 micrm.

Using this setup we suceeded in confinement about thousands of polystyrene beads of radius 175 nn in 1 mm long array.

More you can find in our related publications

T. Cizmar, M. Siler, P. Zemanek: "An optical nanotrap array movable over a milimetre range",
       Appl. Phys. B 84, 197-203, 2006,   ABSTRACT   DOWNLOAD

T. Cizmar, V. Garces-Chavez, K. Dholakia, P. Zemanek: "Optical conveyor belt for delivery of submicron objects",
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T. Cizmar, V. Garces-Chavez, K. Dholakia, P. Zemanek: "Optical conveyor belt for delivery of sub-micron objects",
       Proceedings of SPIE 6180, 618027:1-7, 2006, Photonics, Devices and Systems III, Praha(CZ), 8-11 June 2005,   ABSTRACT

T. Cizmar, V. Garces-Chavez, K. Dholakia, and P. Zemanek: "Optical conveyor belt based on Bessel beams",
       Proceedings of SPIE 5930, 0X1-0X7, 2005,   ABSTRACT   DOWNLOAD

T. Cizmar, V. Garces-Chavez, K. Dholakia, P. Zemanek: "Optical trapping in counter-propagating Bessel beams",
       Proceedings of SPIE 5514, 643-651, 2004,   ABSTRACT   DOWNLOAD

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