Four-wavelength switching interference measurement system for surface topography

Phase-shifting interferometry is an important measurement method for surface topography, but the depth measuring range is limited by the wavelength.A four-wavelength interference measurement system for surface topography was proposed.Through rotating the filters, 4 light sources with different wavelengths were switched out from LED light, and the single wavelength interference was conducted in turn. A data processing method for multiple wavelength interference images was put forward, which used the algorithm of elliptic fitting and the combination of varied scales to achieve wide-range highprecision surface topography measurement on the condition of calculating the phase point-by-point and frame-by-frame. Experimental results show that under the measurement depth expanded to nearly 41 times, the relative measurement error of surface roughness of square wave specimen with multiple grooves is only 4.09%,compared to the data calibrated by China Institute of Metrology. Therefore, the system can realize high-precision measurement for surface topography in a certain range.