Light amplifier and laser processing device

A light amplifier, comprising:

• a light amplifying fiber that amplifies seed light by exciting light;
• a seed light source that pulses the seed light a plurality of times during an emission period;
• an excitation light source that generates the exciting light of a power at a first level, during a non-emission period which is immediately before the emission period, and generates the exciting light of a power at a second level, which is greater than a power of the first level during the emission period;
• a detector that detects a power of an output light pulse that is output from the light amplifying fiber;
• and
• a controller that controls the power at the first and second levels of the exciting light of the non-emission period, based on a value of the detected power from the detector, to cause a power of first output light pulses, which are generated during the emission period, to be the same as a power of final output light pulses, wherein
• a length of the emission and non-emission periods respectively correspond to a length of pulse and non-pulse outputs of the seed light source.