Stabilization of synthetic wavelength using offset-frequency locking for the measurement accuracy improvement of the laser synthetic wavelength interferometer

Abstract

In the laser synthetic wavelength interferometer (LSWI), enhancing the stability of the synthetic wavelength is very important for the improvement of displacement measurement accuracy. A synthetic wavelength stabilization scheme using offset-frequency locking for LSWI is proposed. By locking an external cavity diode laser to the +3rd sideband of an I2 frequency-stabilized He–Ne laser modulated with an electro-optic modulator, a stabilized large synthetic wavelength with frequency difference of 815 MHz can be obtained for LSWI. The optical configuration and principle of offset-frequency locking is described in detail. The experiments of frequency stability and displacement measurement were carried out to demonstrate the feasibility and effectiveness of the proposed scheme. Frequency stability experimental results show that the relative stability of the frequency difference between the two lasers is about 1.84 × 10 − 11 at 1 s averaging time. Nanometer and micrometer displacement measurement results show that subnanometer accuracy can be realized. These results indicate that the proposed scheme is able to evidently improve the displacement measurement accuracy of LSWI.