Enatioselective Rotation of Chiral Particles by Azimuthally Polarized Beams

Abstract

Light beam carries linear momentum, when it is scatted or absorbed by a particle, the transfer of momentum can cause the motion of the particle. Thus, the light beam can be used to manipulate particles, known as optical manipulation. [1] Due to its unique advantages of noncontact and noninvasive operation capability, optical manipulation has been widely used in modern scientific research, especially in biology, physical chemistry, and medicine. [2][3][4] One special but important class of optical manipulation is to rotate trapped particles. [5] This light-induced rotation can be achieved from the shape asymmetry of the particle [6,7] or the transfer of optical angular momentum from light to the particle. [8,9] Generally, photons may have two different types of angular momentum: optical spin angular momentum (SAM) and optical orbital angular momentum (OAM). The former is related to the state of polarization of light, which can cause the rotation of a particle around its own axis, whereas the latter is associated with the helical wavefront of light, which will result in the orbital rotation of particle around the optical axis. [10] The advent of new optical principles and methods has fostered the development of optical manipulation techniques. Various extraordinary optical manipulations, such as optical pulling, [11][12][13] transverse spin, [14][15][16] and left-handed optical torque, [17][18][19] etc. have been discovered and investigated. Among which, optical manipulation of chiral particles has received much attention, due to its potential applications in optical chiral separation and identification. [12,18,[20][21][22] The concept of chirality, introduced by Lord Kelvin to designate the non-superimposable property of an object with its mirror image, pervades in nature from subatomic to galactic scales. [23] Chiral particles which with the same chemical composition but opposite chirality, called enantiomers, can have completely different chemical properties and biological functions. [24] For example, one enantiomer forms a powerful medicament, while the other has no therapeutic effect or even may cause serious side effects. [25] Thus, the separation and identification of chiral substances consist of a very active, interdisciplinary, and meaningful research topic. [26][27][28][29] Traditional probes of chirality, such as circular dichroism and rotatory power, [30,31] typically provide an average chiral response of substances, failing in detecting the properties of single particles. In recent years, the study of chirality-dependent optical forces has attracted tremendous attention not only for the optical separation of enantiomers but also for the further chiral identification of single particles. [32][33][34][35][36][37][38][39][40][41][42] Proposed methods include using lateral optical forces to deflect paired enantiomers in opposite directions, [32][33][34][35] enantioselective transporting of particles by optical pulling forces and optical conveyor belt, [12,[36][37][38] as well as the enantioselective trappi...

The Combination of the Azimuthally and Radially Polarized Beams: Helicity and Momentum Densities, Generation, and Optimal Chiral Light

“…Accordingly, the next step would be to calculate the photoinduced forces on a chiral dipolar particle illuminated by an ARPB with an emphasis on the OC configuration, similarly to what was done in ref. [77] for a tightly focused APB. To aid future research experiments, we have also provided the schematics for an optical setup that generates an ARPB and provided a polarization rotator that changes the handedness of an OC‐ARPB.…”

Polarization‐Dependent Optical Forces Arising from Fano Interference

“…These unique characteristics of the Fano-resonance-induced forces would provide additional degrees of freedom for optical manipulation. [33][34][35][36][37] For example, achieving controllable optical forces to actuate optomechanical devices is essential for levito-dynamics systems. [38,39] Generally, the gradient force acts as the actuation force and, hence, the force, and therefore the devices, can be controlled by changing the light wavelength.…”

Double and Square Bessel–Gaussian Beams

“…New varieties of the BG beams considered in this work will be useful for probing the atmosphere, in wireless communications, microparticle manipulation, and in quantum informatics for generating entangled pairs of photons. In micromechanics, these laser beams can be used for controlling the movements of microparticles along circular trajectories [ 31 , 32 , 33 ]. For instance, the one-dark-spot distribution of the square BG beams (from Figure 2 ) can be adopted for trapping a non-spherical metallic microscopic object and for rotating it around its center of mass, whereas the two-ring distributions of the double BG beams (from Figure 3 ) can be used for guiding metallic particles along circular paths since such particles, in contrast to dielectric ones, tend toward dark regions instead of bright regions.…”

“…New varieties of the BG beams considered in this work will be useful for probing the atmosphere, in wireless communications, microparticle manipulation, and in quantum informatics for generating entangled pairs of photons. In micromechanics, these laser beams can be used for controlling the movements of microparticles along circular trajectories [31][32][33].…”