Papers by Keyword: Focal Length

Abstract: Laser technologies are considered to be unconventional technologies. Laser cutting is one of the most popular industrial operations that use a laser beam. Fibre lasers are most commonly used for cutting metallic materials. The aim of this paper is to experimentally demonstrate a procedure for determining the focal length of a laser beam from the output of the cutting head of a JK400FL fibre laser. Along with other factors, the correct position of the focal point of a laser beam cutting materials, plays a vital role in the quality of the cut and also in determining the cutting speed. It is possible to use a higher cutting speed of the laser machine, without compromising the quality of the cut.

Abstract: This paper presents the fabrication of a micro-lens array surface with a single-mask process and two etching steps with KOH water solution. Numerical analysis of optics was used to determine the optimal design parameters such as curvature sagitta and radius. The dimension of each lens is 20μm x 20μm. We used anisotropic etching of <100> silicon through a circular and squar mask to produce a pyramidal pit formed by four (111) planes. The oxide mask is stripped and the immersion of the sample in the etchant solution favors the etching of (411) plane transforming the pit into a smooth hemispherical cavity. An intermediate stage exists when a wider 19.47⁰ <411> - face pyramid replaces the initial 54.74⁰ inverted pyramid. The dependence of surface roughness on concentration and temperature of KOH is investigated in the range of 25%-40% and 60°C-80°C, respectively, and compared between them. The surface profiles and roughness was characterized by AFM. The etching depth and radius of micro-lens array was obtained from the SEM images and AFM data. Also, the array of concave depressions was directly used as a mould for replication of KER-2500 transparent polymeric silicon from Shin-Etsu with a refractive index n=1.41. The perfectly matched array of micro-lenses can be detached from substrate and used as a local solar concentrator. Optical properties such as the focal length of the plano-convex micro-lens array, obtained by replication, are measured and analyzed.

Abstract: The focal length of the lens in the spatial filter should simultaneously satisfy the requirement of vacuum and the minimum spherical aberration. In order to filter the high frequency components, the divergence angle of the filter must be less than a certain value according to the system requirement. So the aperture of the filter hole used in the high power laser system is about 20 times of the diffraction limitation. At the same time, the scope of the location of the filter hole in the optical axis is reasonable as long as the location within the focal depth. In addition, the model was built by means of the optical design software to simulate validation. The simulation results show that the designed spatial filter according to the method presented in the paper can effectively filter out the high frequency components and stray light in the system.

Abstract: Focal length of lens is an important parameter to determine the relationship between objective and image. It must be measured accurately. The traditional method of using optical bench to measure the focal length of lens has big man-made errors. So we used linear array CCD camera instead of eyes as the receiver to measure the focal length of lens in this paper. Based on the theory of point spread function, it firstly determined the evaluation function of focal plane. With the threshold method, it determined the location coordinate of sharp signal. Then it proved the feasibility of this scheme through experiment. Finally we compared the experimental data obtained with this method with the experimental data obtained with traditional method, which showed that it was more accurate to measure the focal length of lens with this method.

Abstract: In micro lens, the adaptive lenses are potential breakout in the future. The adaptive liquid lenses had been reported in several literatures. However, it’s regret for existing adaptive liquid lenses who can’t realize zoom synchronously keeping the image surface stable. For solving the problem a pair of all-silicone lenses called lens group was put forward. The lens group was firstly fabricated and assembled. The lens group was researched from theoretical calculation to find the synchronous relation between the front lens and the back lens. At last the lens group was seriously tested including its total focal lengths and image surface drifts. The theoretical researches and the testing result testified the all-silicone lens group was possible to facilitate the adaptive lens into applications.

Abstract: The focal length, zoom, irradiating power and cylinder speed of laser head influence the exposure quality directly in computer-to-plate (CTP) process. This paper determined the most optimal parameters which used screen thermal sensitive device PT-R4100 by changing the focal length, zoom, irradiating power and cylinder speed of laser head. The most optimal parameters of focal length, zoom, irradiating power and cylinder speed in CTP process were 1500puls, 6700puls, 90%, 600r/min respectively。Compared with computer-to-film (CTF), we found that the image quality of CTP process was better. The average density, register accuracy and ink trapping of CTP process were higher than that of CTF. Ink formation was also better.

Abstract: The exposure quality was influenced by focal length, zoom, irradiating power and cylinder speed of laser head in computer-to-plate (CTP) process. This paper determined the most optimal parameters which used screen thermal sensitive device PT-R4100 by changing the focal length, zoom, irradiating power and cylinder speed of laser head. Adjusted the setting parameters in order to divide the CTP plate into 13 test strips and each strip was divided into 13 small test pieces. This method could determine the most clear image teat strip by observing and measuring color and density of the test strips or test pieces, and then calculated the most optimal parameters. The results showed that this method could determine the parameters quickly and accurately. The most optimal parameters of focal length, zoom, irradiating power and cylinder speed in CTP process were 1500 puls, 6700 puls, 90%, 600r/min respectively。

Abstract: In this work, we propose integral photography using bi-convex variable focusing lens arrays (hereafter will be abbreviated as bi-convex VFLA-IP) to obtain wider viewing angle and faster response time and the enhanced depth without decreasing resolution of integrated image. We designed a bi-convex lens structure to apply to 3-dimensional moving pictures. We fabricated twodimensional bi-convex liquid crystal lens arrays using lithography. The response time and the focal lengths of the lens array are measured. Applied voltage to the cell alters the effective refractive index of the liquid crystal layer and results in a change of the focal length. From the results of measuring electro-optic properties of the fabricated cell, we discovered that synchronized elemental image array for real or virtual mode can be integrated in front of or behind the lens array without decreasing resolution by adjusting the focal length.