WAVELENGTH DETECTING APPARATUS

摘要

A wavelength detecting apparatus which assures that the wavelength of a laser light (1) or the like can be detected with a high accuracy is disclosed. With the wavelength detecting apparatus of the present invention, the temperature of a vapor obtained from a specific element such as a mercury or the like containing plural isotope is elevated in excess of a predetermined temperature so that an oscillation line of the specific element is divided into plural oscillation lines. One of the divided oscillation lines is used as a reference light (Lb) so as to practically detect the wavelength of a light (La) to be detected. In addition, a specific isotope contained in the specific element such as a mercury or the like is selected from plural isotopes contained therein so as to practically detect the light (La) to be detected under a condition that an oscillation line derived from the vapor of the specific isotope is used as a reference light (Lb). Since each of the divided oscillation lines or an oscillation line derived from the specific isotope has a narrow wavelength width, the position of an interference fringe (8a) appearing on the detecting surface of an optical detector (8) can be detected at a high accuracy when the oscillation line is irradiated toward the detecting surface of the optical detector (8). Additionally, the wavelength of the light (La) to be detected can practically be detected at a high accuracy based on a difference between the position where the interference fringe (8a) is detected and the position where an interference fringe (8b) appearing on the detecting surface of the optical detector (8) is detected when the light (La) -to be detected is irradiated toward the detecting surface of the optical detector (8) as well as a known wavelength of the oscillation line. When the wavelength detecting apparatus of the present invention is used to detect the wavelength of an excimer laser light oscillated by a narrow-band oscillating excimer laser light unit, oscillation of the excimer laser light can be stabilized within the narrow-band oscillatory range by properly controlling the wavelength of the excimer laser light based on the detected wavelength. Further, with the wavelength detecting apparatus of the present invention, the detected wavelength can be unchangeably maintained at a high accuracy while assuming a preset wavelength.