| 摘要 |
PURPOSE:To obtain a stable oscillation output from an excimer laser device by a method wherein optical distances are determined between mirrors and the values thus determined are employed to control the inclination of a Fabry- Perot etalon so that the mirrors will let through an excimer laser always at its central frequency. CONSTITUTION:A measuring beam from a light source 13 after passing through the periphery of a Fabry-Perot etalon 4 generates, owing to an imaging optical system, isogradient interference fringes on a focal plane. Such isogradient interference fringes change in diameter according to a change in the optical distance between the mirrors of the Fabry-Perot etalon 4. A measuring means using said measuring beam measures, through determining changes in diameter of the isogradient interference fringes, the optical distance between the two mirrors of the Fabry-Perot etalon 4. The value thus obtained is employed to adjust the inclination of the Fabry-Perot etalon 4 so that it will let through only a desired laser oscillation wavelength. This design oscillates a stable excimer laser with its central wavelength constant and its narrowed wave width free of fluctuations. |
