Patent ID: 7292343

Claim:
A wavemeter for a gas discharge DUV laser, for measuring bandwidth on a pulse to pulse basis, comprising: a focusing lens having a focal length; an optical interferometer creating an interference fringe pattern; an optical detector positioned at the focal length from the focusing lens; a bandwidth calculator calculating bandwidth from the position of interference fringes in the interference fringe pattern incident on the optical detector, defining a D ID and a D OD , the respective distances between a pair of first fringe borders and between a pair of second fringe borders in the interference fringe pattern on an axis of the interference pattern, and according to the formula Δλ=λ 0 [D OD 2 −D ID 2 ]/[8f 2 −D 0 2 ], where λ 0 is an assumed wavelength and D 0 =(D OD −D ID )/2, and f is the focal length.