Sang Soo Lee

Theoretical calculations of optical force exerted on a dielectric sphere in the evanescent field generated with a totally-reflected focused gaussian beam

Abstract We investigate theoretically the optical force exerted on a dielectric sphere in the evanescent field, by which the small particles can be pushed or pulled on the scale of the optical wavelength. In our approach we derive an expression of the evanescent field formed at the plane interface with a totally-reflected gaussian laser beam, assuming that the sphere does not affect the boundary conditions. We then solve the scattering problem for the evanescent field incident on a sphere to find the analytical formulas of the cartesian components of optical force. Numerical results show that the magnitude of the optical force for a sphere of radius a =0.5 λ is ≈ 10 −6 (dyne) in the evanescent field of a 1 W gaussian laser beam and the z -component of optical force F z changes the sign according to the refractive index n of the sphere.

Thin-Film Transistors with Polycrystalline Silicon Prepared by a New Annealing Method

A new annealing method, nucleation by rapid thermal annealing (RTA) and grain growth in furnace annealing, has been developed to obtain high-quality polycrystalline silicon (poly-Si) and to reduce the long annealing time for solid-phase crystallization (SPC) of amorphorus silicon (a-Si) film without a decrease in grain size. Poly-Si thin-film transistors (TFTs) were fabricated using this method and the electrical properties of poly-Si film were evaluated. We obtained higher field effect mobility (25 cm2/(Vs)) and better uniformity (≤5% in 5-inch wafer) than those obtainable by the conventional furnace annealing.

Optical force on a sphere caused by the evanescent field of a Gaussian beam; effects of multiple scattering

Abstract We examine theoretically the optical force exerted on a dielectric sphere by the evanescent field of a Gaussian beam, where multiple scattering of light between the sphere and the prism substrate is considered. We derive first an expression of the n th order field ( n ≥ 1) that is scattered by the sphere and we then formulate the optical force due to the scattered fields up to n th order. Numerical results show that the effect of multiple scattering up to third order exerted on the optical force is within the extent of ∼ 10% in resonance regions but it is negligible in off-resonance regions.

Optical torque exerted on a sphere in the evanescent field of a circularly-polarized Gaussian laser beam

Abstract We analyze theoretically the optical torque for rotating a sphere in the evanescent field that is formed at the plane interface by total internal reflection of a circularly polarized Gaussian laser beam. For the incidence of a Gaussian beam in the x – z plane we examine analytically and numerically the Cartesian components of the optical torque T x , T y and T z about the center of the sphere, in comparison with plane wave results. We show that T x and T z rely on the transport of angular momentum to the sphere by a circularly polarized light but the existence of T y does not require any circularly-polarized component of the incident light.

Radiation torque exerted on a rotating sphere in a focused Gaussian laser beam : first-order correction in angular velocities

We investigate the radiation torque exerted on a rotating dielectric sphere in a focused Gaussian beam. In the (inertial) laboratory frame we solve the relativistic scattering problem for the Gaussian beam incident on a rotating sphere by including correction terms of up to first-order in angular velocities. We then derive the analytical formulas of the radiation torque within the framework of a scattering theory and discuss the derived results in comparison with our earlier works for a stationary sphere. Numerical results show that the ratio of the first-order correction to the zeroth-order torque is about 0.2×10-2 at the highest rotational frequency.

Improved four-mirror optical system for deep-ultraviolet submicrometer lithography

The design for a rotationally symmetric four-mirror optical system with reduction magnification 5 x for deep UV (λ = 248 nm of a KrF excimer laser) submicrometer lithography is developed. Initially by using the paraxial quantities, numerical solutions are found for the system, which is free from the four off-axial third-order aberrations-coma, astigmatism, field curvature, and distortion. Aspherization is carried out to the spherical mirror surfaces to reduce the axial and residual off-axial higher order aberrations. The numerical aperture of the final system is as large as 0.38, which gives a Rayleigh resolution of 0.4 μm and hence is useful in submicrometer lithographic applications.

Optical pressure exerted on a dielectric film in the evanescent field of a Gaussian beam

We theoretically investigate the optical pressure for a dielectric film located in the evanescent field of a Gaussian beam. In our approach, we derive the electromagnetic fields at the boundaries of the film by solving the boundary-value problem for a system of four stratified media with the incidence of a Gaussian beam. We also formulate analytically the optical pressure exerted on a dielectric film by using the derived electromagnetic fields. Numerical results of the optical pressure by a Gaussian beam-generated evanescent wave are presented in comparison with the plane-wave results.

First-Order Calculations of Radiation Force for Rotating Sphere Illuminated by Circularly Polarized Gaussian Beam

We use the theory of scattering of a focused Hermite-Gaussian-mode beam by a rotating sphere to obtain the analytic formulas of radiation force, which include the correction terms of up to first order in angular velocities of the sphere. We also numerically investigate the effect of the first-order terms exerted on the net radiation force for spherical particles (near structural resonances) positioned on and off the propagation axis of a circularly polarized Gaussian laser beam. Numerical results show that the first-order correction for a rotating sphere levitated in the 1 W argon-ion laser beam is one or two orders of magnitude below the zeroth-order force at the highest rotational frequency of Ω1.5 GHz.

Cassegrainian-inverse Cassegrainian four-aspherical mirror system (magnification = +1) derived from the solution of all zero third-order aberrations and suitable for deep-ultraviolet optical lithography

A four-aspherical mirror system with unit magnification is investigated for use in deep ultraviolet (DUV) optical lithography. It is derived from the solution of all zero third-order aberrations for the four-spherical mirror system with unit magnification. We have first examined the holosymmetric four-spherical mirror system in which all third-order aberrations are zero and all orders of coma and distortion are also zero. However, the system does not have any optical design freedom left for the correction of higher order aberrations, so a new solution of nonholosymmetric system is derived. In this system aspherizations on the spherical surfaces are carried out to reduce the residual aberrations. The aspherization is optimized to give near diffraction-limited performance for DUV wavelengths of 0.193 μm (ArF excimer laser line). The final system we have obtained consists of all aspherized mirrors with a numerical aperture of 0.35. This reflective system is compact in size and expected to be useful in optical lithographic applications.

Four-mirror optical system for UV submicrometer lithography

A design of a four-mirror optical system for submicron lithography using a KrF excimer laser beam (λ = 248 nm) is presented. By thirdorder aberration theory, analytic solutions for a telecentric, flat-field, anastigmatic four-spherical-mirror system (reduction magnification 5 x ) are found. Aspherization is carried out to the spherical mirror surfaces in order to reduce the residual higher order aberrations and vignetting effect. We obtain a reflection system useful in submicron lithographic application.