Xiaoping Chen

Double-swing method used for polishing off-axis aspherical mirrors

Based on the characteristics of off-axis aspherical surface, a new method used for polishing off-axis aspherical mirrors-Double-Swing Method (DSM) is proposed in this paper, and the polishing mechanism of DSM is introduced. The mathematical model of the DSM with steady movement state is established. The movement of this mathematical model is simulated in a programming language; the comparison of simulation effects under different parameters is made. In order to achieve optimal parameters, a high order off-axis rectangle aspherical mirror has been polished by DSM. The final result of profile measurements of 12nm, RMS is achieved. The result indicates that the method is of practice and has even higher working efficiency and precision.

Study on the calculation and application for asphericity of rectangle off-axis aspherics

Asphericity which affects the manufacturing process and the grinding quantity is an important parameter of optical aspherics. In this paper, the approximation, the least square fitting, wavefront aberration, sag methods are given for the calculation of optical asphericity. The effects of different definitions of optical asphericity are analysed to optimize the process of manufacture. A sag method is presented to solve the best-fit sphere and asphericity for an off-aixs aspheric mirror with a rectangle aperture of 180mm×145mm, and polishing quantity and distribution plots are given. The optical manufacturing and testing technology for different choices of best-fit spheres and asphericity are described and analyzed. Therefore, proper definition of optical asphericity which is useful to manufacturing is very important for optical fabrication and test.

Supplemental optical specifications for imaging systems: parameters of phase gradient

Specifications of phase error, peak to valley (PV), and root mean square (rms) are not able to represent the properties of a wavefront reasonably because of their irresponsibility for spatial frequencies. Power spectral density is a parameter that is especially effective to indicate the frequency regime. However, it seems not convenient for opticians to implement. Parameters of phase gradient, PV gradient, and rms gradient are most correlated with a point-spread function of an imaging system, and they can provide clear instruction of manufacture. The algorithms of gradient parameters have been modified in order to represent the image quality better. In order to demonstrate the analyses, an experimental spherical mirror has been worked out. It is clear that imaging performances can be maintained while manufacture difficulties are decreased when a reasonable trade-off between specifications of phase error and phase gradient is made.

Alignment of off-axis asphere and compensator with four poles

Aspheres are utilized widely thanks to the development of optical design, manufacture and testing. Compensators are usually necessary when aspheres are under test. The alignment of aspheres and their compensators is a risk because its tough to check whether the compensators work in right way. A new method of alignment with four poles is put forward in this paper. Optical interval error can be tight while it is quite important due to direct influence on central curvature, conic constant and high order coefficients of aspherical surface. A modified on-axis Foucault apparatus is set up since it makes the optical axis visible and helps to control the error of off-axis amount. Some small holes are drilled in the metallic cell of the compensator so that the ends of poles can be stably relied on in order to increase operational repeatability. The method has been carried out practically and it matches the measurement result given by a set of theodolites.

Study on the influence and disposal method of the micro-cracks of optical components

Micro-crack is one of the most effective factor to the intensity and service life of optical components. Owing to the micro-crack on surface, actual strength of optical components is reduced severely, even less than ten-percent of its theoretical strength. According to fracture mechanics, the mechanisms of the formation and propagation of micro-crack and the growth theory of sub-critical micro-crack are discussed in the paper firstly. Based on practice, an on-line test method disposing etching holes-the molecule-infiltrating method and the principles of acid-etching method disposing micro-crack are described. Followed by the demolishing mechanism of abrasives and a more reasonable removal redundancy of fine-grinding and polishing during ,optical production is given by using abrasives in different-size orderly.