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Study on Alignment Method of a Laser Synthetic Wavelength Nanomeasurement Interferometer

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Tutor: ChenBenYong YanLiPing
School: Zhejiang University of Technology
Course: Measuring Technology and Instruments
Keywords: Laser interferometer,Synthetic wavelength,corner cube,four-quadrant detector(QD)
CLC: TH744.3
Type: Master's thesis
Year:  2011
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Abstract:
In recent years, with the rapid development of micro-electronics, ultra-precision machining and other high and new technologies, nano-displacement measurement techniques and instruments are required have the performance of measuring long-range displacement with nanometer accuracy. In order to guarantee the high precision of the nanodisplacement measurement instruments and to reduce or eliminate the unnecessary error, it is necessary to monitor alignment of the instrument during the whole measurement process in synchronous. Based on¡°The development of a laser synthetic wavelength nanodisplacement measurement interferometer¡±(NSFC, No.50827501). The alignment method of the laser synthetic wavelength nanodisplacement measurement interferometer is studied and a method for the alignment of the laser synthetic wavelength nanodisplacement measurement interferometer is proposed by using a four-quadrant detector.The alignment method of the laser synthetic wavelength nanodisplacement measurement interferometer is described in this paper, the optical properties of corner cube which is used as a measuring mirror and a reference mirror are analyzed when the deflection or the lateral movement occurs in theory and a mathematical model is built correspondingly. The principle of four-quadrant detector and the signal processing method are described, a hardware system for the signal processing method is designed in detail and realized, including an I/V switching circuit, a signal pre-processing circuit, an addition circuit, a subtraction circuit, a division circuit and a power circuit. Based on Visual Basic language, the corresponding measurement software for the signal processing method is designed.In this research work, experiments are done as below:(1) Experiment on the influence of the lateral movement of corner cube on the measurement accuracy of the laser synthetic wavelength interferometer: Firstly, simulation based on actual parameters are done and the results show that under the condition of interference, when the corner cube only has a translation in the x direction, the influence on interference caused by lateral movement is much smaller than that on intensity of laser amplitude, and there is no influence on the order change of interference fringes. When it moves in both direction of x and z, interference fringes will change and the change of interference fringes is caused by the change of optical pathlength in the direction of z while its lateral movement in the x direction has no influence on the order change of interference fringes. Secondly, the corresponding testing experiments were carried out and the experiment results show that the trends of the measured interference fringes changing are identical with the results of simulation which proves that the influence of the small lateral movement of corner cube on the length measurement accuracy of a laser synthetic wavelength interferometer is little and can be ignored.(2) Alignment measuring experiment of the reference corner cube: The experiment is done with step increment 10 mm in the range of 300 mm, the standard deviations are reduced from 7.038 mV to 1.6 mV in the direction of x and from 30.118 mV to 1.119 mV in the direction of z.(3) Alignment measuring experiment of the measurement corner cube: The experiment is done with step increment 10 mm in the range of 200 mm, the standard deviations are reduced from 3.2049 mV to 1.202 mV in the direction of x and from 2.831231 mV to 0.673 mV in the direction of y. The experimental results show that the alignment method can achieve the goal on the alignment of a laser synthetic wavelength nanodisplacement measurement interferometer and has high reliability and practicability.
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