Jae Heung Jo

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.

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.

Moiré patterns of two different elongated circular gratings for the fine visual measurement of linear displacements

An elongated circular grating having the shape of an athletic track was proposed to determine both the moving displacement and its direction within an accuracy of ten times that of conventional circular gratings. The properties of moire´ fringes from two complementary elongated circular gratings were investigated for fine visual measurement of linear displacements. Moire patterns formed by superposition of two different elongated circular gratings were demonstrated to ´ provide a simple fringe-counting method for determining both the relative linear displacement and its direction within the accuracy of 1r10 pitch of the grating. The measurement of the refractive indices of C H and CCl and the thermal 61 2 4 expansion coefficient of aluminium, using elongated circular gratings, are presented. q 1998 Elsevier Science B.V. All rights reserved.

Determination of the absolute order of shadow moiré fringes by using two differently colored light sources

We present a simple method of determining the absolute order of shadow moiré fringes by using two differently colored light sources. This technique is based on the periodic color structures generated by superimposing two moiré patterns with different colors.

OPTICALLY INDUCED ROTATION OF COMBINED MIE PARTICLES WITHIN AN EVANESCENT FIELD OF A GAUSSIAN BEAM

We demonstrate a windmill type rotation of combined Mie particles caused by optical forces of the evanescent field generated at the surface of a Gadolinium Gallium Garnet prism where a linearly polarized Nd:YAG laser beam (of wavelength 532 nm and power 100 mW) is totally reflected. The combined particles such as doublets (or triplets) consisting of polystyrene latex (or yeast) spheres with diameters of 3–5 µm are reported to rotate with angular velocities of 1 rpm in water when the particles are slightly displaced from the center of the Gaussian evanescent spot. The particle rotation in the inhomogeneous evanescent fields can be useful for a potential application to micromotors or microaccelerometers.

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.

Colored Shadow Moiré Topography Using Colored Light Sources: Red, Green, and Blue

We present a simple method of determining the absolute order of fringes and the depression or elevation of the surface using colored moire patterns (red, green, and blue). This technique is based on the various color patterns generated by the superposition of the three differently colored moire fringes.

Label-free detection of hepatitis B virus using solution immersed silicon sensors

Highly sensitive solution immersed silicon (SIS) biosensors were developed for detection of hepatitis B virus (HBV) infection in the early stage. The ultrasensitivity for overlayer thickness at the nonreflecting condition for the p-polarized wave is the basis of SIS sensing technology. The change in thickness due to biomolecular interactions and change in refractive index of the surrounding buffer medium were assessed simultaneously using two separate ellipsometric parameters (Ψ and Δ), respectively, from a single sensing spot. A direct antigen-antibody affinity assay was used to detect and quantify hepatitis B surface antigen (HBsAg), which is the early stage biomarker for HBV infection. The detection limit of 10 pg/ml was achieved for HBsAg in the human blood serum, which is comparable with the results of enzyme-linked immunosorbent assay and other hybrid assays. The SIS sensors response time was less than 10 min. The SIS sensors exhibit excellent stability and high signal-to-noise ratio, and are cost-effective, which makes them a suitable candidate for point-of-care applications.

Optical design and illumination simulation of Fresnel lenses for marine signal lanterns

Providing marine signal lanterns, Fresnel lens has been adopted to transfer the beam from the lanterns up to 10 nautical miles (18.53 km). The Fresnel lens with diameters of 250 mm was designed by a ray tracing program and optimized by adjusting the groove parameters of the lens. Each optical sag element which is a part of a lens was independently designed by using the analytical method. The angular luminous intensity distributions (ALID) of this lens were calculated by the illumination analysis program considering the ALID of a light bulb. The ALID of a C-8 type bulb (24 W) was measured with a goniophotometer and its luminous flux was measured by an integrating sphere to be 397 lm. At the best alignment of the bulb, the maximum luminous intensity of the lantern was more than 1000 cd for the 250 mm lens. The ALID was investigated as a function of distance from the lens focus to determine the tolerance margin of the alignment. Horizontal deviations of the light bulb from the focus along the optical axis widened the angular FWHM of the vertical ALID. However, vertical deviations caused shifts of the vertical ALID without spreading the angular FWHM. The designed 250 mm aspherical lens of marine signal lantern was made by the injection molding with single peace acryl. We measured the luminous intensity distribution of acryl lens and found that the MLI of the lens was 827 cd. And the full width at half maximum of the diverging angle of the diverging beam was 3.5 deg. Although the measured MLI was 83% of the calculated result, it would be increased with surface polishing of prototype molding pattern.

New synthetic evaluation of color display using polychromatic MTF

A new synthetic evaluation method for the color display is studied. A testing system to measure the luminance, chromaticity, contrast ratio, uniformity, viewing angle as well as the PMTF (polychromatic modulation transfer function) is presented. The PMTF is calculated from the values of the monochromatic MTFs weighted by the CIE photopic luminous efficiency function of the human visual system. A high-precision XYZ translation stage to move the testing system and a two-axis goniometer to tip and turn the display under test to the desired viewing angle are used.