Low Noisy Dual Wavelength Digital Holography and Application in the Ultra-precision Machining Surface Measurement
PAN Weiqing;GONG Guofang;FAN Yufeng;Department of Physics,Zhejiang Science and Technology University;Department of Mechanical Engineering, Zhejiang University;Institute of Micro-optics Manufacturing Technology,Zhejiang Science and Technology University;
Through the subtraction of two digital holographic wrapped phases for different wavelengths, it yields a beat phase image corresponding to an equivalent wavelength to remove the phase wrapping. By comparing the beat phase image with any recoding wavelength, the position and multiple of the single wavelength phase jump are confirmed. Hence, the wrapped phase in single wavelength phase is wrapped and the phase noise is kept fixed. Simulation and experimental results demonstrate the measure error induced by the phase noise can be reduced to 2∧/λm. An optical microstructure element surface is measured by the proposed digital holography with dual wavelength of 650 nm and 632.8 nm. The measured optical element is produced with Fast Tool Servo(FTS). The unwrapped phase image of machining mark on the surface of microstructure element is acquired clearly. The equivalent wavelength is 0.024 mm. Then, the three dimensional data of the microstructure profile respectively in high frequency and low frequency regions are obtained by frequency filtering. The roughnesses corresponding to different frequency region are 33.2 nm, 19.3 nm and 23.4 nm respectively. The affecting factors for different machining mark are analyzed. The cutting parameters of the FTS are also deduced.