Abstract
Using the theory of electromagnetic scattering of a uniaxial anisotropic sphere, we derive the analytical expressions of the radiation forces exerted on a uniaxial anisotropic sphere by an off-axis incident Gaussian beam. The beam's propagation direction is parallel to the primary optical axis of the anisotropic sphere. The effects of the permittivity tensor elements ε(t) and ε(z) on the axial radiation forces are numerically analyzed in detail. The two transverse components of radiation forces exerted on a uniaxial anisotropic sphere, which is distinct from that exerted on an isotropic sphere due to the two eigen waves in the uniaxial anisotropic sphere, are numerically studied as well. The characteristics of the axial and transverse radiation forces are discussed for different radii of the sphere, beam waist width, and distances from the sphere center to the beam center of an off-axis Gaussian beam. The theoretical predictions of radiation forces exerted on a uniaxial anisotropic sphere are hoped to provide effective ways to achieve the improvement of optical tweezers as well as the capture, suspension, and high-precision delivery of anisotropic particles.
Highlights
Since radiation force was first applied for the optical acceleration and trapping of a particle in 1970, as first reported by Ashkin [1], optical tweezers have attracted considerable attention due to advantages such as the capability to hold and manipulate particles, such as biological cell, with micrometer and sub-micrometer dimensions non-intrusively
Based on the GLMT [9] and scattering coefficients of a uniaxial anisotropic sphere scattered by an off-axis Gaussian beam [24, 25], we have studied the axial and transverse radiation forces exerted on a uniaxial anisotropic sphere
The analytical expressions of radiation forces exerted on a uniaxial anisotropic sphere by an off-axis Gaussian beam are derived
Summary
Since radiation force was first applied for the optical acceleration and trapping of a particle in 1970, as first reported by Ashkin [1], optical tweezers have attracted considerable attention due to advantages such as the capability to hold and manipulate particles, such as biological cell, with micrometer and sub-micrometer dimensions non-intrusively. Ashkin produced remarkable studies on these [2, 3] On basis of his works, many other researchers investigated the radiation forces exerted on spherical particles of various sizes using different methods. For a particle much larger than the incident wavelength ( d / λ > 10 ), many scholars employed the ray optics theory (ROT) as it is most applicable to radiation force calculations. It is critical and interesting to exploit the radiation forces exerted on a uniaxial anisotropic spherical particle by an off-axis incident Gaussian beam. Based on the GLMT [9] and scattering coefficients of a uniaxial anisotropic sphere scattered by an off-axis Gaussian beam [24, 25], we have studied the axial and transverse radiation forces exerted on a uniaxial anisotropic sphere. Time dependence of the form exp(−iωt) is assumed and suppressed, where ω is the circular frequency
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