Generation of multiple focal spot and focal hole segments using phase modulated cylindrically polarized annular multi-Gaussian beam
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We investigated the focusing properties of a cylindrically polarized annular multi Gaussian beam tightly focused with a high NA lens and a complex phase filter. It is observed that a properly designed complex phase filter can generate multiple focal spot and focal hole segments along optical axis its useful for the manipulation of multiple optical traps of low and high refractive index particles.
KeywordsVector diffraction theory Cylindrical vector beam Multiple optical trapping
Recently, there is an increasing interest in the spatially inhomogeneous polarization, mostly driven by the advances made in micro-fabrication techniques and theoretical modeling techniques that were not available homogeneous polarization. One example of such spatially inhomogeneous polarization that has attracted much of the interest is the so-called cylindrical vector (CV) beams. Cylindrical vector beams are solutions of Maxwell equations that obey cylindrical symmetry both in amplitude and polarization. Cylindrical vector beams can be divided into radially polarization, azimuthal polarization and generalized cylindrical polarization, according to the actual polarization pattern. One can use two cascaded half-wave plates to conveniently convert a radially polarization or azimuthal polarization into a generalized cylindrical vector beam, or vice versa (Zhan and Leger 2002; Friedman et al. 2002). Growing interest in the generation of three-dimensional (3D) optical beams that are dark regions in space surrounded by light are driven by wide ranging applications including dark optical traps for atoms (Zhan and Leger 2002; Friedman et al. 2002), manipulation, guiding and binding of microparticles and biological cells (Cizmar et al. 2010), erase beams for super-resolution fluorescence microscopy (Watanabe et al. 2003), etc. Over the past years, a variety of techniques have been proposed for generating such optical bottle beams for applications in optical tweezers and atom traps (Garcia-Sucerquia et al. 2004; Chen and Zhan 2006; Bokor and Davidson 2006; Ahluwalia et al. 2006; Arlt and Padgett 2000; Ahluwalia et al. 2004; Yelin et al. 2004; Pu et al. 2005). However, stable trapping of a single particle is expected if we can make the bottles small enough and comparable to the particle size. Such “microbottles” were established recently with the volume speckle field (Isenhower et al. 2009). Recently particle trapping experiment is successfully done by Ashkin et al. (1986), particles manipulations have drawn great interests. For example, owning to the abilities to manipulate and isolate microscopic objects in a precise and nondestructive manner, optical tweezers are widely used in micromachines and microscopy (Unger and Marston 1988; Crocker and Grier 1994; Wright et al. 1990; Tadir et al. 1989). In order to improve the speed of particle trapping, the optical tweezers with multitraps are ideal (Huang et al. 2011; Guo et al. 2011). In 2002, two dimensional arrays of focal spots are formed by multi beam systems (Eriksen et al. 2002). However, it is just for two dimensional particles trapping. In 2005, Casaburi et al. (2005) achieve multi-3D-optical trapping by utilizing two- and three-beam interference, which, in order to ensure destructive interference at the focus, require extremely high interferometric precision among the three beams. Recently several methods to generate the multiple optical trapping have been suggested (Prabakaran et al. 2014a, b; Zhao et al. 2005; Cao et al. 2013; Jian-Nong et al. 2011; Charles et al. 2014). In this paper, we wish to analyze the focusing property of the phase modulated cylindrically polarized annular multi Gaussian beam (CVAMB) tightly focused with high NA lens.
2 Principle of the optical focusing system
Basing on the above equations, focusing properties of cylindrically polarized annular multi Gaussian beam (CPAMGB) with complex phase plate can be investigated theoretically.
3 Results and discussion
In conclusion, a novel method for demonstrated the effect of phase modulation on the intensity distribution on tight focusing of cylindrically polarized annular multi Gaussian beam in the focal region of high NA lens using Vector diffraction theory. We presented possible design of complex phase filter to achieve multiple focal spot and focal hole segments which finds wide applications in optical tweezers, micromanipulation of high and low refractive index particles, microscopy, and optical storage.
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