Laser apparatus and extreme ultraviolet light generation system

A laser apparatus used together with an external device, the laser apparatus comprising:

• a master oscillator configured to output a first pulse laser beam;
• at least one amplifier disposed on an optical path of the first pulse laser beam output from the master oscillator;
• a sensor disposed on an optical path of a second pulse laser beam output from the at least one amplifier;
• and
• a laser controller configured to control operation of the laser apparatus based on a burst signal sent out from the external device and a signal obtained from the sensor,
• the laser controller
• causing the laser apparatus to perform burst oscillation based on the burst signal,
• controlling a beam parameter of at least one of the first pulse laser beam and the second pulse laser beam based on a signal obtained from the sensor in a burst duration in which the burst oscillation is performed, and
• detecting self-oscillation light from the amplifier based on a signal obtained from the sensor in a burst stop duration in which the burst oscillation is stopped, wherein
• the sensor is a beam profiler including a thermal infrared detection element,
• the beam parameter is an optical axis, and
• the laser controller determines that self-oscillation is occurring when a light amount detected by the beam profiler in the burst stop duration is equal to or larger than a light amount threshold set in advance and beam area of a light amount equal to or larger than the light amount threshold is equal to or larger than a beam area threshold set in advance.