SYSTEM FOR CONTROLLING THE AMOUNT OF SUBSTITUTING LASER GAS.

摘要

A laser gas in a discharge tube (51) is substituted by an exhaust pump (7) maintaining a predetermined substitution quantity for a predetermined period of time immediately after the excitation. In the subsequent period of operation, the laser gas is substituted at a rate smaller than the predtermined rate of substitution. The small rate of substitution may be smaller than one-tenth the predetermined rate of substitution required for a predetermined period of time immediately after the excitation and the laser gas is consumed in small amounts.