Narrow band excimer laser and wavelength detecting apparatus

A narrow band excimer laser comprising:

• a laser chamber adapted to be filled with a laser gas;
• a front mirror disposed in front of the laser chamber for reflecting one part of a laser beam outputted from the laser chamber and transmitting another part of the laser beam;
• a beam expander disposed behind the laser chamber for expanding the laser beam outputted from the laser chamber in a predetermined direction;
• a grating disposed behind the beam expander and having a plurality of grooves formed in a direction substantially perpendicular to a direction of beam expansion by the beam expander for selectively reflecting a laser beam having a desired wavelength among those of the laser beam expanded by the beam expander;
• and
• a window disposed on the laser chamber constructed and arranged such that the window makes Brewster's angle with respect to an optical axis of laser beam in a plane defined by the direction of beam expansion by the beam expander and the optical axis of the laser beam for converting the laser beam output from the laser chamber into a linear polarized light wave which is substantially parallel with the direction of beam expansion by the beam expander.

A narrow band excimer laser comprising:

• a laser chamber adapted to be filled with a laser gas;
• a front mirror disposed in front of the laser chamber for reflecting one part of a laser beam outputted from the laser chamber and transmitting another part of the laser beam;
• a beam expander comprising at least one prism disposed behind the laser chamber for expanding the laser beam outputted from the laser chamber in predetermined direction;
• a grating disposed behind the beam expander and having a plurality of grooves formed in a direction substantially perpendicular to a direction of beam expansion by the beam expander for selectively reflecting a laser beam having a desired wavelength among those of the laser beam expanded by the base expander, and
• a polarizing film provided on at least one face of at lest one prism constituting the beam expander for converting the laser beam outputted from the laser chamber into a linear polarized light wave which is substantially parallel with the direction of beam expansion by the beam expander.

A wavelength detecting apparatus used for a narrow band excimer laser which outputs a narrow band laser beam comprising:

• a reference light source for outputting a reference light having a known wavelength;
• means for splitting a laser beam of unknown wavelength outputted from a narrow band excimer laser into parts;
• a light mixing means for mixing one part of a laser beam outputted from a narrow band excimer laser and the reference light outputted from the reference light source;
• etalon means for receiving a mixed light mixed by the light mixing means;
• light condensing means for condensing light transmitting through the etalon means;
• light detecting means for detecting hot.sub.b a first interference fringe based on the laser beam of unknown wavelength outputted from the narrow band excimer laser and a second interference fringe based on the reference light outputted from the reference light source with the first and second interference fringes being formed by the light condensed by the light condensing means,
• said light detecting means being constructed and arranged to detect the absolute wavelength of the laser beam outputted from the narrow band excimer laser on the basis of the detected first interference fringe of the unknown wavelength laser beam and the second interference fringe of the known wavelength reference light source, thereby alleviating precise control of pressure and ambient temperature resulting in high accuracy of said detecting means.

A wavelength detecting apparatus used for a narrow band excimer laser which outputs a narrow band laser beam comprising:

• a reference light source for outputting a reference light having a known wavelength;
• means for splitting a laser beam outputted from a narrow band excimer laser into parts;
• light mixing means for mixing one part of the laser beam outputted from the narrow band excimer laser and the reference light outputted from the reference light source;
• etalon means for receiving the light mixed by the light mixing means;
• light condensing means for condensing light transmitting through the etalon means;
• light detecting means for detecting at different times respectively a first interference fringe based on the laser beam outputted from the narrow band excimer laser and a second interference fringe based on the reference light outputted from the reference light source, the first and second interference fringes being formed by the light condensed by the light condensing means;
• means for establishing a detection period of the first interference fringe which is longer than a detection period of the second interference fringe, and
• said detection period establishing means being constructed and arranged to detect the absolute wavelength of the laser beam outputted from the narrow band excimer laser on the basis of the detected first and second interference fringes.