Xiaofei Diao

Frequency stabilization of an internal mirror He-Ne laser with a high frequency reproducibility.

A method has been developed for the stabilization of an internal mirror He-Ne laser to achieve a high frequency reproducibility that is mainly influenced by the temperature of the stabilized laser. However, it is difficult to achieve a reproducible temperature in a short time under different ambient temperatures. In this paper, the He-Ne laser is stabilized based on the relationship between the laser mode number and the laser cavity temperature where a reproducible temperature can be rapidly achieved under different ambient temperatures, resulting in a high frequency reproducibility. Experiments have demonstrated that the He-Ne laser used can be stabilized in approximately 10 min, typically 6 min; the frequency stability is less than 2×10(-10); the frequency reproducibility is less than 1×10(-9).

Identification and elimination of half-synthetic wavelength error for multi-wavelength long absolute distance measurement

A multi-wavelength absolute distance measurement method based on synchronous occurrence and phase measurement of coarse and refined synthetic wavelength is proposed to remove the effect of vibration on the measurement distance. The phase value of refined synthetic wavelength is monitored to see if half-synthetic wavelength error occurs by judging whether it is near to 2π or 0. If yes, a new suitable refined synthetic wavelength is generated to re-measure the distance with phase near π. A measuring system has been built with a He–Ne laser source and three acousto-optic frequency shifters for implementation of this method. A comparative measurement has been performed using a counting laser interferometer at a distance of 20 m. Actual measurements indicate that half-synthetic wavelength error has been identified and eliminated with uncertainty of smaller than 60 µm under laboratory conditions.

A fast and ultra-precision laser heterodyne interferometry signal processing method based on digital delay line loop

To achieve higher dynamic resolution of laser heterodyne interferometry, a new signal processing method based on digital delay line technology is proposed. To implement ultra-multiple electronic subdivision, the multiple frequency of the reference signal which is generated from an analog phase-lock loop is passed through a multi-tap digital delay line. On every positive edge of the measurement signal, each tap of the delay line is captured and decoded to obtain the exact occurrence time. And according to the reference period, the system can also provide a real time output of the displacement results. Simulations and experiments show that using a laser heterodyne interferometry with its beat frequency of 1MHz, the system can provide a dynamic position resolution of 0.83nm at velocities up to 260mm/s by using a 64 multiple analog phase-lock loop and a 6-tap digital delay line, the update rate of the displacement positions is up to 100KHz.