| The absolute distance measurement by multiple-wavelengths has much more advantages over the traditional heterodyne interferometry at least in two aspects: needlessness of guidelines and directly phase detecting while measuring. It could not only largely meet the demand of metrological needs but also be used almost everywhere in real life. Thus, it enjoys a good academic value and application. In recent years, research works mainly focus on the selection of synthetic wavelengths, high precision measurement of phase, the correction of external disturbances, and commercialization of the interferometry. Therefore, in this thesis, theoretical and experimental studies on the several techniques in interferometry are presented. The main work included as follows:1. Based on the classical theory of excess fraction method and multiple wavelength interference, the transition fitting condition and the accuracy refining theory are conducted. By analysis of the oscillating properties of various light sources, we come up with a blue print of interferometer by using the 633nm band He-Ne laser, constructing synthetic wavelengths with 2 lines and 3 frequencies. The demands of the light sources in interferometry are analyzed.2. According to the demands of light sources in interferometry, considering of the difficulty of the single 629nm oscillation in common He-Ne laser as well, we analyze the hardship of line selection particularly in two nearby transition lines with gains of sharp contrast. Shortcomings of usual line selection methods are discussed as well. Based on the F-P etalon's transmittance theory, a new method to select the nearby lines by using an internal F-P etalon in He-Ne laser is presented. By this method, the general line selection condition is conducted, which must be in accordance with the length and refractivity of etalon. At last, by using the Gaussian beam transmission theory, we simulate the transmitting properties of light in laser cavity.3. By using the line selection method mentioned before, a single line 629nm He-Ne laser with an internal F-P etalon is designed. The laser can emit 629nm and 633nm line respectively when the angle of etalon is adjusted. Experiments are done such as, detecting the output power of laser while the current is changing, modes scanning by an external F-P interferometry. Furthermore, by scanning the laser cavity, we measure the modes of light in laser, which prove our conclusion of modes distribution as well. A frequency stabilization method by small mechanical dither is applied to stabilize the 629nm He-Ne laser. Experiments results of frequency stabilization by that method are also provided.4. The stability and mode properties of beat frequency in the double-mode He-Ne laser are discussed. Considering of the mode pulling effect, we conduct the relationship between the stability of the single mode and the beat frequency theoretically. By using PID control method, we stabilize the double-mode He-Ne laser with equal light intensity. Experiments are done to compare with a standarded iodine-stabilized laser to testify our conclusion.5. Experiments of absolute distance measurement by using 629nm and 633nm wavelength, consisting of a synthetic wavelength of 117μm, both in dynamic and static situations are presented. The errors caused by the synthetic wavelength, the refractive turbulence and the electronic turbulence are discussed in detail.
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