An excimer laser gas in a laser tube 2 is excited by a microwave introduced
from awaveguide 1, and electric field concentration occurs in a
slit-shaped gap 3 provided in a plate member 11c, causing plasma
discharge. Then the phase of plasma light is regulated and the light is
resonated, to cause excimer laser light. This construction realizes plasma
excitation entirely uniform along a lengthwise direction of laser light
emission, and enables uniform laser light emission with minimum energy
loss.
