SHAPE MEASUREMENT OF ROUGH STEP LIKE SURFACE USING A LASER DIODE -THE METHOD WITH THREE-WAVELENGTH PHASE SHIFTING

摘要

The authors propose a new method which can measure a shape of rough step like surface by means of a speckle interferometry with a wavelength-changeable laser. A speckle phase available in the interferometry is usually affected not only by an optical path difference but also by a random component associated with surface roughness. The phase shifting method using two different wavelengths ( λ_1,_2λ)is, therefore, limited to a single phase map about the optical path difference, because of the random component which remains without cancel .The single phase map is available only for the calculation of the shape of a continuous surface. In the proposed method, the authors use three different wavelengths (λ_1,λ_2,λ_3) to obtain a double phase map, which is capable of a discontinuous surface shape calculation by means of a fringe-counting two-wavelength method. The validity of the method is experimentally demonstrated and discussion is extended to an accuracy of the measurement and an extent of the measurement range.