Radiation force and torque on an absorptive electromagnetic conductor sphere by an arbitrary-shaped optical polarized beam

In recent years, electric-magneto metamaterial [1], [2], [3], [4], [5] has played an increasingly critical role in multitudinous fields, such as metasurface [6], [7], camouflage technique [8], [9], thermophotovoltaic [10], [11] and wireless communication [12], [13]. As a kind of distinctive electric-magneto metamaterial, perfect electromagnetic conductor (PEMC) [14] has become a hot spot in current research because of the “optical rotation” effect [15], [16], which is extensively used in ice crystal scattering [17], physical chemistry [18], rain attenuation measurement [17], [19], and medicine [20], [21]. In addition, it also takes effect in field pattern purifiers for aperture antennas, polarization transformers, and radar reflectors [14].

The PEMC combines the characteristics of both perfect electrical conductor (PEC) [22], [23] and perfect magnetic conductor (PMC) [24], [25], thus it has promising application prospects in the electromagnetic screen. An admittance parameter M dominates the characteristic of PEMC, which degenerates into PEC or PMC when M→∞ and M=0 [26], respectively. For its unique feature, there has been numerous research on PEMC since it was put forward. A study first puts forward the PEMC resonator [27]. With the deepening development of the PEMC resonator, a series of related achievements were produced [28], [29]. Besides, the polarizabilities for a PEMC sphere in chiral metamaterial are discussed in research [30]. So far, the FDTD [31], [32], small perturbation method [33], extended boundary condition method [34], and surface integral equation approach [35] have been applied to explore the characteristic of PEMC. In previous years, the PEMC went from theory to reality that practical realization of perfect electromagnetic conductor (PEMC) boundaries has been attained using ferrites, magnet-less non-reciprocal metamaterials (MNMs), and graphene [36]. It further promotes the application of PEMC.

Although a comprehensive study has been carried out on PEMC, the interaction between a PEMC and an electromagnetic field is always a noteworthy part. A study analyses the scattering characteristic generated by the interaction between a PEMC half-screen and an electromagnetic wave [37]. Another research discusses the scattering effect when an electromagnetic wave illuminates a PEMC cylinder set in the vacuum [38], [39], lossy medium [40], and non-magnetized isotropic plasma medium [41]. The interaction between a PEMC cylinder coated with various materials and an electromagnetic wave is investigated, and a series of achievements have been attained [42], [43], [44], [45], [46]. Later, the scattering of a PEMC elliptic cylinder by a plane wave is studied [47]. After that, plane wave scattering by a PEMC sphere also arouses others’ interest. Many achievements on this issue have been continuously developed [48], [49], [50], [51]. In subsequent research, the optical radiation force (ORF) and optical spin torque (OST) exerted on a PEMC particle by a plane wave are also paid attention to [52], [53], [54]. Because the losses of the PEMC can be introduced, which has been proposed by I. V. Lindell and A. H. Sihvola [55] earlier, the ORF and OST exerted on an absorptive electromagnetic conductor (AEMC) sphere by a circular polarization plane wave are studied [56].

Because of the distinct property of structured beams, they are always widely used in experiment and application fields. As a common incident beam, the Gaussian beam has been used in various research due to its extensive prospect. Correspondingly, the Bessel beam is considered an excellent incident for its characteristics in optical tweezers, such as higher energy concentration, limited-diffraction [57], and self-reconstruction [58]. Moreover, the Airy beam [59] also is a specially structured beam used in particle manipulation for its self-accelerating [60], [61] except for the above properties. Therefore, the exploration of the interaction between structured beams and a PEMC is of great significance. In recent years, the electromagnetic radiation force on a PEMC sphere by a vortex electromagnetic wave is studied [62]. And then, a study discussed the scattering that a Laguerre–Gaussian beam exerts on a PEMC cylinder coated with chiral material [63]. Even though, the interaction between the structured beams and a PEMC is still to be excavated. For this purpose, we discussed and analyzed the scattering from arbitrary-shaped optical polarized beams to a PEMC sphere [64] for the first time. Along with the thorough research, we took the Bessel beam incident on a PEMC sphere as an example and researched that radiation force and torque caused by the interaction between arbitrary-shaped optical polarized beams and a PEMC sphere [65]. However, the differences that various structured beams act on a PEMC sphere are still worth studying to further explore the ORF and OST exerted by arbitrary-shaped optical polarized beams. Besides, how the AEMC sphere with losses Mi is affected by structured beams is still a blank field at present. Consequently, this manuscript is dedicated to solving these problems and takes the Airy beam as an example because of the characteristic that energy concentration, limited-diffraction, self-reconstruction, and self-accelerating.

Our work is carried out according to the following layout. The theoretical background is presented in the second section, and the analytical expressions of the ORF and OST are derived based on the generalized Lorenz–Mie theory (GLMT). Both the ORF and OST are divided into three components, which are co-polarized, cross-polarized, and interference components. In the third section, the numerical results of ORF and OST that an Airy beam interacts with an AEMC sphere are provided as an example to discuss the interaction between an AEMC sphere and an arbitrary-shaped optical polarized beam at first. And then, the innovation different from the previous achievements is given. The comparison that the Airy beam interacts with a dielectric sphere and an AEMC sphere is given. Moreover, the difference that an Airy beam and a Bessel beam illuminating an AEMC sphere is presented. As significant parameters affecting ORF and OST, not only the influence of particle size parameter ka and admittance parameter M of the AEMC sphere on the ORF and OST but also the polarization states of the incident beam are emphasized. As the most noteworthy part in the field of particle manipulation, the optical pulling force on an AEMC sphere by Airy beams is focused on for discussion. In the last section, the whole work is summarized.

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