Theoretical determination of the radiation force for a spherical particle illuminated by a focused laser beam
نویسندگان
چکیده
Trapping forces on dielectric spheres in single beam laser tweezers are computed. A focused beam description based on an exact solution of Maxwell’s equations is compared to the 5th order Gaussian beam approximation due to Barton and Alexander. Forces on water droplets suspended in air and on polystyrene spheres suspended in water, exerted by beams focused to varying degree, are calculated. It is demonstrated that the 5th order approximation is accurate for almost paraxial beams (numerical aperture NA <~ 0.25), as compared to the exact treatment. However, for strongly focused beams the 5th order approximation breaks down. Thus it is established that an accurate beam description is vital for modeling optical traps, since, in order to hold a particle effectively in a single beam trap, a strongly focused beam is required.
منابع مشابه
Calculation of the radiation trapping force for laser tweezers by use of generalized Lorenz-Mie theory. II. On-axis trapping force.
The efficiency of trapping an on-axis spherical particle by use of laser tweezers for a particle size from the Rayleigh limit to the ray optics limit is calculated from generalized Lorenz-Mie light-scattering theory and the localized version of a Gaussian beam that has been truncated and focused by a high-numerical-aperture lens and that possesses spherical aberration as a result of its transmi...
متن کاملCalculation of radiation force and torque exerted on a uniaxial anisotropic sphere by an incident Gaussian beam with arbitrary propagation and polarization directions
On the basis of spherical vector wave functions and coordinate rotation theory, the expansion of the fields of an incident Gaussian beam with arbitrary propagation and polarization directions in terms of spherical vector wave functions is investigated, and beam shape coefficients are derived. Using the results of electromagnetic scattering by a uniaxial anisotropic sphere, the analytical expres...
متن کاملCalculation of the radiation trapping force for laser tweezers by use of generalized Lorenz-Mie theory. I. Localized model description of an on-axis tightly focused laser beam with spherical aberration.
Calculation of the radiation trapping force in laser tweezers by use of generalized Lorenz-Mie theory requires knowledge of the shape coefficients of the incident laser beam. The localized version of these coefficients has been developed and justified only for a moderately focused Gaussian beam polarized in the x direction and traveling in the positive z direction. Here the localized model is e...
متن کاملElectromagnetic field calculations for a sphere illuminated by a higher-order Gaussian beam. II. Far-field scattering.
A previously developed theoretical procedure for determination of electromagnetic fields associated with the interaction of a higher-order Gaussian beam with a homogeneous spherical particle is used to investigate the effects of incident beam type on far-field scattering. Far-field scattering patterns are calculated for (0,0), (0,1), and (1,1) mode Hermite-Gaussian beams and for the helix dough...
متن کاملTemperature Distribution of Particles in a Laser Beam
This article studies the particle temperature distribution depending on the laser radiation power and the particle’s trajectory and velocity. The uneven heating of particles moving in the laser radiation field is identified. The regimes of laser heating without melting, with partial melting, and with complete particle melting are considered.
متن کامل