How light absorption modifies the radiative force on a microparticle in optical tweezers

Abstract

Reflection and refraction of light can be used to trap small dielectric particles in the geometrical optics regime. Absorption of light is usually neglected in theoretical calculations, but it is known that it occurs in the optical trapping of semi-transparent particles. Here, we propose a generalization of Ashkin's model for the radiative force exerted on a spherical bead, including the contribution due to attenuation/absorption of light in the bulk of the particle. We discuss in detail the balance between refraction, reflection, and absorption for different optical parameters and particle sizes. Our findings contribute to the understanding of optical trapping of light-absorbing particles and may be used to predict whenever absorption is important in real experiments.

Germanium microparticles as optically induced oscillators in optical tweezers

“…2(a)], indicating that it is also subject to oscillations along the direction of the laser propagation, a behavior predicted in Ref. [29].…”

Use of Organic Semiconductors as Handles for Optical Tweezers Experiments: Trapping and Manipulating Polyaniline (PANI) Microparticles

“…The dashed red line shown is the theoretical result predicted by a geometrical optics (GO) model previously developed in our group . Such model is based on the Ashkin’s original model for the radiative force on spherical particles, generalized to include the light absorption by the particles via the absorption coefficient of the material . In the present case, the version of the model that neglects spherical aberration provided a better agreement with our experimental data, and all GO calculations presented in this manuscript were thus done under this situation.…”

Optical Trapping and Manipulation of Superparamagnetic Beads Using Annular-Shaped Beams

“…Nevertheless, most approaches use Gaussian beam optical tweezers to manipulate the magnetic beads, which can result in non-negligible heating of these beads (and consequently, of the surrounding medium) due to laser absorption, resulting in an unstable optical trap depending on the laser power and/or bead size [14]. Differently, our approach strongly reduces the laser absorption by cutting off the middle of the original Gaussian beam, which is the beam portion that mostly contributes to the radiation pressure and radiometric forces on the particles, i.e., the forces that disturb the stable trapping of such particles [22,23]. The present work focuses on the characterization of the optical trapping of superparamagnetic beads with the annular beam tweezers.…”