Absolute calibration of optical tweezers including aberrations

Dutra, R. S.; Viana, Nathan B.; Neto, Paulo A. Maia; Nussenzveig, H. M.

doi:10.1063/1.3699273

Cited by 27 publications

(24 citation statements)

References 12 publications

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“…The resulting Mie-Debye-spherical aberration (MDSA) theory of optical tweezers [34] thus accounts for the spherical aberration introduced by refraction at the glass slide. Excellent blind agreement with experiments was obtained when additional optical aberrations are also included [35,36]. Figure 3a shows the optical axial force Q z variation with the microsphere position z with respect to the focal point (normalized by the radius r = 1825 nm).…”

Section: Mie-debye Theory Of Optical Tweezerssupporting

confidence: 60%

Optimizing optical tweezing with directional scattering in composite microspheres

et al. 2018

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Trapping of microspheres with a single focused laser beam is usually limited to materials with relative refractive indexes slightly larger than one. We show that directional light scattering can be employed to optically trap high-index materials. For this purpose, we propose a material platform to achieve zero backward scattering (ZBS), also known as the first Kerker condition, in a composite media containing spherical inclusions of silica embedded in a SiC microsphere. By tuning the volume filling fraction of inclusions and the microsphere radius, stable trapping can be achieved, provided that ZBS is combined with the condition for destructive interference between the fields reflected at the external and internal interfaces of the microsphere when located at the focal point. We show that our proposal also holds even in the presence of a significant amount of spherical aberration, which is a common condition in most optical tweezers setups. In this case, achieving ZBS is essential for trapping high-index materials.

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Section: Mie-debye Theory Of Optical Tweezerssupporting

confidence: 60%

Optimizing optical tweezing with directional scattering in composite microspheres

et al. 2018

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“…Points corresponding to a given sample speed appear to be lumped together as expected. We measure α from a linear fit of all points corresponding to a given θ (the transverse stiffness can also be obtained and the results are compatible with theoretical MDSA+ values [29,30]). We intentionally rotate the camera by ∼ 30 o with respect to the axes of the microscope stage so as to have comparable displacements along x and y axes.…”

Section: Methodsmentioning

confidence: 62%

Negative optical torque on a microsphere in optical tweezers

Diniz¹,

Dutra²,

Pires³

et al. 2019

Opt. Express

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We show that the optical force field in optical tweezers with elliptically polarized beams has the opposite handedness for a wide range of particle sizes and for the most common configurations. Our method is based on the direct observation of the particle equilibrium position under the effect of a transverse Stokes drag force, and its rotation around the optical axis by the mechanical effect of the optical torque. We find overall agreement with theory, with no fitting, provided that astigmatism, which is characterized separately, is included in the theoretical description. Our work opens the way for characterization of the trapping parameters, such as the microsphere complex refractive index and the astigmatism of the optical system, from measurements of the microsphere rotation angle.

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“…In order to trap small particles with optical tweezers, one has to consider the optical properties of the material that they are made, since these properties are critical to determine the resulting forces acting on the object. When subjected to a highly focused Gaussian light beam, dielectric particles are known to yield stable trapping in three dimensions, which was theoretically described by R. Gauthier, S. Wallace and A. Ashkin in geometrical optics regime [3,29] (λ << l, where λ is the laser wavelength and l is the particle radius), by J. Gordon in Rayleigh regime [30] (λ >> l), and by P. Maia Neto, H. Nussen- * Corresponding author: warlley.campos@ufv.br zveig and coworkers in Mie regime [31,32] (λ ∼ l). Metallic particles can be trapped under very special conditions.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2018

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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.

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Absolute calibration of optical tweezers including aberrations

Cited by 27 publications

References 12 publications

Optimizing optical tweezing with directional scattering in composite microspheres

Optimizing optical tweezing with directional scattering in composite microspheres

Negative optical torque on a microsphere in optical tweezers

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

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