| Dual-frequency laser interferometers working at the wavelength of 633nm have been widely used in various metrological applications. However, due to the phase ambiguity, the range of step height measurement is normally limited to be no more than half-wavelength (316.5nm). To meet the requirement of measuring larger step heights, we propose to build a dual-frequency laser interferometer based on a commercial 543nm He-Ne laser. Thus two-wavelength interferometry can be realized by combining the 543nm (green) dual-frequency laser interferometer with the 633nm (red) dual-frequency laser interferometer. By this means the range of step height measurement is extended to be 1.9μm, half of the synthesis wavelength of 543nm and 633nm. Consequently, the measurement of step heights or the like in a micron level becomes feasible, e.g., the step height of micro-electronic mask, the tilt or vibration of hard-drive disks, etc..We built a green Zeeman He-Ne laser and investigated the tuning characteristics of Zeeman beat frequency and the intensity difference between Zeeman-split modes. We then stabilized the 543nm Zeeman laser by means of beat frequency locking method and intensity difference locking method separately. The achieved long-term optical frequency stability is±3×1 0?8 and±3×1 0?7, respectively. Then we constructed a dual-frequency green laser interferometer based on the frequency stabilized 543nm Zeeman He-Ne laser. The interferometer has been tested in stationary stability measurements and dynamic displacement measurements in comparison with a commercial 633nm dual-frequency laser interferometer. Test results show that the 543nm dual-frequency laser interferometer has equivalent static drifts and accuracy in displacement measurements as the commercial dual-frequency red laser interferometer. The realization of dual-frequency green laser interferometer has paved the way for the construction of the dual-color-dual-frequency interferometers. |
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