Displacement measurement with λ/8 resolution based on the bifurcatesubcavity modulation effect in a dual frequency laser

摘要

A novel method for displacement measuring is proposed based on the bifurcate subcavity modulation effect in a dualfrequency laser. Owing to the intracavity wave plate, the laser operates on two orthogonally polarized modes. If aportion of laser, channeled into a subcavity by the wave plated, is reinjected back to the resonator, the mode intensitiesare modulated with a period of a half of wavelength, respectively. And the two modulations behave a 90° phasedifference, which could subdivide a period into four regions: horizontal polarization, two polarizations, verticalpolarization, and no light. In this paper, this subcavity modulation effect is demonstrated experimentally andtheoretically. Furthermore, a displacement measurement of the subcavity mirror is developed with resolution up to X18,viz. about 79nm at laser wavelength of 632.8nm. The direction discrimination of measuring could also be realizedutilizing the sequence of four different subdivision zones. The measuring range, mainly limited by both the splittingfrequency difference and the bifurcate subcavity length, could reach tens of millimeters. Measurement results arepresented and the corresponding error analyses are discussed. This system has great potential in applying tometrological fields for its simplicity, compactness and high quality performance.