Zhai Zhongsheng

A measurement system for surface topography based on three-wavelength interferometry

Optical microscopic interferometry is an important measurement method for surface topography. There is usually contradiction between enlargement of measuring interval and improvement of measuring precision. In this paper, a three- wavelength interference measurement system for surface topography based on wavelength switch and phase shift scanning is proposed. A data processing method for three- wavelength interference images is proposed, which use the phase extraction and recognition algorithm based on elliptic fitting and combined size scales of phase difference. The method can effectively improve the overall precision of surface topography measurement and expand measuring interval to nearly 27 times that of single wavelength 640 nm. Experimental results have shown that the relative measurement error of surface roughness of square wave specimen with multiple grooves is only 4.1% compared to the calibrated data which is produced by China National Institute of Metrology. Therefore, the three-wavelength interferometry method can realize high precision measurement for surface topography in a certain measuring interval.

Defects detection of composite material using laser shearography

Laser shearography is applied to the defects detection of the airplane composite materials with interfacial viscose brushing off and delaminating damage. The form and the theory of laser shearography system are analyzed in this paper. Results show that the damage can be exactly quickly located ignoring the global displacement with the Wollaston prism.

A microscope with large depth of the field realized through an axicon

It has been an active research topic to extend the depth-of-field of optical imaging systems. The axicon that can image a point into a line segment along the optical axis, it can be used to extend the depth of field of a microscope. A large depth of field microscope, realized by the axicon and digital imaging processing technology, is presented in this paper. The parameters of the expected microscope system are given with ZEMAX. The depth of field is analyzed based on the condition of focal segment. Imaging experiments show that the axicon can extend the depth of field.

Analysis the image transfer characteristics of integral photography

Integral photography (IP) technology provides a method for recording and display of 3D animated images at real-time. In order to analysis the 3D image transfer capability of integral photography (IP), the relationship between the longitudinal resolution of an image and the optical parameters of the system was derived. According to the imaging method of the system, the modulation transfer function (MTF) of capture and display micro-lens array, which includes the effect of the defocusing were deduced, and the Overall MTF of IP systems at different object distance in the direction of depth were obtained. Based on above work, the image transfer characteristics of the systems focusing on different plane position were analyzed, The result show that , if the focus is at the central plane of the object , the response is high for the reconstructed image of the object that only exists in an narrow depth direction; by focusing on the position at infinity, we can obtain a nearly flat images response over a wide rang of depth.

A two-dimensional table with long travel and micropositioning

High-precision, long travel two-dimensional tables are widely used in ultra-precision machining, multi-dimensional measuring machine, surface grinder and advanced manufacturing fields. A two-dimensional table with long travel and micro-nano positioning is presented in this paper. The table is controlled by the combination of a computer and a FPGA (Field Programmable Gate Array) device. The moving units are consisted of AC servo motors and piezoelectric ceramics (PZT), which are used to achieve macro and micro-positioning respectively. The positioning accuracy is controlled by diffracting gratings and four-quadrant photoelectric receiver (QPD). Experimental results show that the positioning error of this table is 0.2µm, and the working range is 100×100mm2.