a high repetition rate , compact , modular gas discharge , ultraviolet laser . the laser is useful as a light source for very rapid inspections of wafers in an integrated circuit fabrication process . it is also useful for reticle writing at very rapid rates . a preferred embodiment operates at pulse repetition rates of 1000 to 4000 hz and is designed for round - the - clock production line operation . this preferred embodiment comprises a pulse control unit which controls the timing of pulses to an accuracy of less than 4 nanoseconds . preferred embodiments of this gas discharge laser can be configured to operate with a krf gas mixture , an arf gas mixture or an f 2 gas mixture , each with an approximate buffer gas , producing 248 nm , 197 nm or 157 nm ultraviolet light pulses .