Automatic Wavelength Control for Interferometric Ruling Machine

Presented in this paper is an automatic wavelength control used in the interferometric ruling machine for standard line scale. The machine has a fringe counting interferometer to control the positions to be ruled using the wavelength of Kr86 0.565μm line. The machine also has a Fizeau interferometer to control the wavelength used in the position-controlling interferometer in order to obtain an integral counting number of fringes for the scale line intervals of 1mm and to remove the errors caused by variation of the refractive index of surrounding air and thermal expansion of scale blanks. The Fizeau interferometer is set in a closed vessel and the interference fringes of five visible lines of Hg198 lamp are detected by photoeletric elements. The conditions are calculated for obtaining the maximum fringe signals from the Fizeau interferometer. The optimum values for the reflactance of the mirrors and the distance between them are found to be 50-60% and 67-80mm respectively. The air pressure in the vessel is controlled by the on-off system operated by the fringe signals of the Fizeau interferometer. The accuracy of the wavelength controlled by this method is found to be ±2×10-7. This accuracy can be kept even in long run test.