ISSN 1060-992X, Optical Memory and Neural Networks (Information Optics), 2007, Vol. 16, No. 2, pp. 91–98. © Allerton Press, Inc., 2007. 91 Micromanipulation in Higher-Order Bessel Beams 1 R. V. Skidanov, V. V. Kotlyar, S. N. Khonina, A. V. Volkov, and V. A. Soifer Image Processing Systems Institute, Russian Academy of Sciences, Samara State Aerospace University, ul. Molodogvardeiskaya 151, Samara, 443001 Russia Abstract—We discuss experiments on micromanipulation in the higher-order Bessel beams generated by diffractive optical elements (DOEs). Comparison is made of the rotation efficiency in the Bessel beams of the fifth and tenth order. We show that a two-fold increase in the Bessel beam number results in about a two-fold increase of the linear velocity of the microparticle circular movement, despite the fact that the laser beam intensity shows over a three-fold decrease. DOI: 10.3103/S1060992X07020051 1. INTRODUCTION Among the micromanipulation problems, that of transferring the angular momentum deserves special notice. There are two major approaches to making microobjects rotate in the light fields: First, using a spin angular momentum associated with circularly polarized fields. In this case, only bire- fringent microparticles, e.g. made of Iceland spar, can be set in motion [1–4]); Second, using an orbital angular momentum resulting from a spiral character of phase, like the higher- order Laguerre-Gaussian and Bessel beams. The orbital angular momentum is being transferred due to par- tial absorption of light by the microparticle [5]. The Bessel beams (BB) can propagate through a limited distance on the optical axis without diffraction [1]. They can (a) form a light pipe or light cavity on the optical axis [2], (b) be self-reproduced after prop- agating for some distance after an obstacle found on the optical axis [3–5], (c) carry an orbital angular momentum [6, 7]; (d) have a longitudinal periodicity [8], and (e) rotate about the optical axis while propa- gated [9, 10]. These properties make possible their use for microobject rotation, with the microobjects located at different distances on the optical axis. The BBs can be generated with an axicon [11], an amplitude digital hologram [2], or a phase diffractive optical element (DOE) [12]. The BBs came into use for micromanipulation several years ago. In [13–16] the BB was reported to be used as a new type of optical microparticle trap, making it possible to simultaneously trap and manipulate a chain of microparticles. Optical manipulation of quartz pellets 1–5 μm in diameter was reported in [14]. An inversion optical trap was presented in [13], in which the laser BB was directed upwards, oppositely to the gravitation force. In this case, being pushed upwards by the light beam, the microparticles are arranged into a vertical chain. The authors succeeded in assembling a vertical chain composed of 16 quartz pellets 5 μm in diameter. A successful displacement of the chain as a whole and even its inclination by 5 degrees was also reported. A simultaneous optical trapping of microparticles in a pair of cells put in a row on the BB axis at a 3 mm distance was also reported in [15]. In the first cell, a hollow dielectric pellet of diameter 5 μm was trapped in the minimal intensity zone found between the center and the first bright ring of the zero-order BB. In the second cell, three quartz pellets of diameter 5 μm were trapped in arrow on the beam’s optical axis. The transfer of the orbital angular momentum from the first-order BB to a low-index microparticle was demonstrated in [16]. The microparticle was trapped in a dark annular region, rotating about the beam axis with a period of 8 s. In [6] a third-order BB was generated using a neodymium laser of wavelength 1064 nm and power 1 W in combination with an axicon and a digital phase diffraction grating with the first order diffraction efficiency of about 80%. Using the beam, four quartz beads of diameter 1 μm were trapped in the inner bright ring of diameter 2.9 μm and rotated with a period of 16 seconds. In this paper, we discuss results of the experiment on trapping and rotating 5 polystyrene beads of diam- eter 5 μm in BBs of the fifth and tenth order that were generated when a phase DOE was illuminated by light of a solid-state laser of wavelength 532 nm and power 500 mW. Comparison of the rotation efficiency in the light Bessel beams of the fifth and tenth order is made. It is demonstrated that a twofold increase in 1 The text was submitted by the authors in English.