Trapping and delivery  in co-propagating Bessel beams 

Set-up and trapping

The set-up is shown in the figure below. We used laser Verdi with 5.5W of output power emitted at the wavelength 532 nm. We used polarizing beam splitters (PBS1, PBS2) to split and merge the beams, mirrors M to direct the beam to proper direction and lenses L to form the beam shapes. Polarizer is rotated 45 deg to the orthogonal polarizations of both beams to get interference of beams. Lenses L3 and L4 decrease the size of both Bessel beams so that they overlaped in the cuvette C.

The radii of the high intensity Bessel beam cores were 0.4 and 1.5 micrm. Unfortunately the quality of the axicons was not good enought for such small dimensions and so we observed aberrated beam profiles (see Figs. 6 and 7 in the NJP paper below). This was the principle reason why we have not reached optical trapping without the help of counter-flowing water in the cuvette. This flow compensated the radiation pressure of both beams. The distance between neighboring intensity maxima were zT=7.7 micrm and it corresponded to the distance between trapped objects. The sizes of confined objects are shown in the figure belowe together with the fluid velocity estimated from the motion of free objects in the fluid.

Many objects delivery - optical conveyor belt in co-propagating beams

Movement of the mirror M1 caused axial movement of the intensity maxima and so also the optical traps with confined objects. A different example of the optical conveyor belt is obtained. However in this case, there is much bigger distance between the optical traps and so between the trapped objects, too. Therefore, the beam has enough space to reconstruct behind the object even before it reached the neighboring object.

MOVIE

More details can be found in the papers:

T. Cizmar, V. Kollarova, Z. Bouchal, P. Zemanek: "Sub-micron particle organization by self-imaging of non-diffracting beams",
       New Journal of Physics 8, 43:1-23, 2006,  LINK TO JOURNAL  ABSTRACT   DOWNLOAD   MULTIMEDIA

T. Cizmar, V. Kollarova, M. Siler, P. Jakl, Z. Bouchal, V. Garces-Chavez, K. Dholakia, P. Zemanek: "Non-diffracting beam synthesis used for optical trapping and delivery of sub-micron objects",
       Proceedings of SPIE 6195, 619507:1-7, 2006, Nanophotonics, Strasbourg(FR), 3-5 Apr 2006,   ABSTRACT       DOWNLOAD

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Last modification: 29 Jul 2007