Abstract
An adjustable optical cage generated by focusing a partially coherent beam with nonconventional correlation function named the Bessel–Gaussian correlated Schell-model (BGCSM) beam is investigated in detail. With the help of the generalized Huygens–Fresnel integral and complex Gaussian function expansion, the analytical formula of the BGCSM beam passing through an apertured ABCD optical system was derived. Our numerical results show that the generated optical cage can be moderately adjusted by the aperture radius, the spatial coherence width, and the parameter β of the BGCSM beam. Furthermore, the effect of these parameters on the effective beam size and the spectral degree of coherence were also analyzed. The optical cage with adjustable size can be applied for particle trapping and material thermal processing.
Highlights
The optical cage, named the optical bottle beam has attracted growing attention
We show that the size and depth of the generated optical cage is adjustable by modulating the source spatial correlation function, the coherence width, and the aperture radius
We found that cage could be controlled by manipulating the initial spatial coherence width δ0, the parameter β, and the optical cage could be controlled by manipulating the initial spatial coherence width δ0, the the aperture radius a
Summary
The optical cage, named the optical bottle beam (i.e., a three-dimensional dark spot surrounded by regions of higher intensity) has attracted growing attention. Beam were introduced in theory [27], and later generated in experiment with the aid of a spatial light modulator or with a hologram and a diffuser [21,39,40] Their correlation functions are expressed in the form of Laguerre–Gaussian and Bessel–Gaussian functions, respectively. BGCSM and LGCSM beams have advantages over a partially coherent beam with a conventional correlation function (i.e., Gaussian Schell-model beam) to reduce turbulence-induced degeneration upon propagation in turbulent atmosphere [41,42], which will be beneficial in free-space optical communications. Chen et al demonstrated both theoretically and experimentally that by focusing an LGCSM beam with a thin lens and tailoring the source correlation function, a controllable partially coherent optical cage can be generated near the focal area [43]. Our results may find uses in optical trapping and material thermal processing
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