The ultimate goal of the study is to provide an imaging tool to detect the earliest signs of glaucoma before clinically
visible damage occurs to the retinal nerve fiber layer (RNFL). Studies have shown that the optical reflectance of the
damaged RNFL at short wavelength (<560nm) is reduced much more than that at long wavelength, which provides
spectral contrasts for imaging the earliest damage to the RNFL. To image the spectral contrasts we built a dual-band
spectral-domain optical coherence tomography (SD-OCT) with centered wavelength of 415nm (VIS) and 808nm (NIR),
respectively. The light at the two bands was provided by the fundamental and frequency-doubled outputs of a broadband
Ti: Sapphire laser. The depth resolutions of the VIS and NIR OCT systems are 12.2μm and 4.7μm in the air. The system
was applied to imaging the rat retina in vivo. Significantly different appearances between the OCT cross sectional
images at the two bands are observed. The experimental results showed that the dual-band OCT system is feasible for
imaging the spectral contrasts of the RNFL.
The lithography ion-exchange method of producing the gradient index micro-cylinder lens with gradual focus is
presented. The lens is developed for the coupled shaping of the pump beam of side-pumped disk fiber laser, its main
purpose is to make the LD beam which coupled into the ring disk container and the radial of the ring disk container have
a certain angle, and ensure that all the pump beams couple into the interior of the ring disk container through the thin slit
of the side. The micro-cylinder lens with different shapes can be obtained by the special designs of ion-exchange
windows. The focused spot of the parallel beam passed through the lens is a special curve with required setting.
Consequently, the lens also adapt to other applies with gradual focus. The experimental results coincide with the design.
The method of producing the orthogonal micro-cylinder lens arrays on the two surfaces of the glass substrate with ion-exchange is
presented. The former and latter arrays are used for beam shaping of the fast-axis and slow-axis of LD respectively. In this paper, the
ray transfer matrices of the optical system have been obtained, the numerical calculation results coincide with the experimental results.
This numerical calculation results have a good role in guiding the design of micro-cylinder lens arrays and the optimization of
Topography of a granite surface has an effect on the vertical positioning of a wafer table in a lithographic tool, when the wafer table moves on the granite. The inaccurate measurement of the topography results in a bad leveling and focusing performance. In this paper, a method to measure the topography of a granite surface with high accuracy is presented. In this method, a double frequency laser interferometer is used to measure the tilts of the wafer table in the X and Y direction. From the tilts information, the height of every point on the surface can be obtained by a special algorithm. Then, according to the height information, a high order polynomial is fitted to express the topography of the granite surface with high accuracy. Experiment results shows that the measurement reproducibility of the method is better than 10 nm.
An effective and simple method to determine the energy range of FOCAL is described in this paper. Relationship between the chop line width and defocus is analyzed. Simulated curves of the chop line width versus defocus are obtained by PROLITH. By choosing the curves which satisfy certain conditions, the energy range of FOCAL is determined off line. Independent of the lithographic tool, the method is time-saving and effective. The influences of some process factors, e.g. resist thickness, PEB temperature, PEB time and development time, on the energy range of FOCAL are analyzed.
As feature size decreases, especially with the use of resolution enhancement technique such as off axis illumination and phase shifting mask, fast and accurate in-situ measurement of coma has become very important in improving the performance of modern lithographic tools. The measurement of coma can be achieved by the transmission image sensor, which is an aerial image measurement device. The coma can be determined by measuring the positions of the aerial image at multiple illumination settings. In the present paper, we improve the measurement accuracy of the above technique with an alternating phase shifting mask. Using the scalar diffraction theory, we analyze the effect of coma on the aerial image. To analyze the effect of the alternating phase shifting mask, we compare the pupil filling of the mark used in the above technique with that of the phase-shifted mark used in the new technique. We calculate the coma-induced image displacements of the marks at multiple partial coherence and NA settings, using the PROLITH simulation program. The simulation results show that the accuracy of coma measurement can increase approximately 20 percent using the alternating phase shifting mask.