Laser beam amplifier and laser apparatus using the same

A laser beam amplifier for amplifying an incident laser beam to output the amplified laser beam, the laser beam amplifier comprising:

• a container configured to accommodate a laser medium;
• an optical system configured to form an optical path between a first point and a second point which are conjugate to each other so as to focus a transfer image of the laser beam incident upon said first point onto a third point in the optical path between said first point and said second point at least once, and then, focus the transfer image onto said second point;
• and
• a pair of electrodes arranged in said container and configured to perform discharge in the laser medium to form an amplification region between said first point and said second point, wherein
• said optical system includes at least one concave mirror having a reflection surface facing the amplification region.