Solid state laser apparatus

A solid state laser apparatus comprising:

• a plurality of cold heads;
• a cooling apparatus coupled with the plurality of cold heads and configured to cool the plurality of cold heads;
• a plurality of laser media arranged in contact with each of the plurality of cold heads and configured to amplify a first laser beam and reflect the first laser beam;
• and
• a seed light source configured to irradiate a first laser medium of the plurality of laser media with the first laser beam,
• wherein:
• the plurality of cold heads are configured to cool the plurality of laser media;
• each of the plurality of laser media has a first surface in direct contact with a corresponding cold head of the plurality of cold heads and a second surface opposite to the first surface;
• the solid state laser apparatus is configured such that the first laser beam is:
• (i) incident on the first laser medium through the first surface of the first laser medium;
• (ii) reflected by the second surface of the first laser medium;
• and (iii) irradiated from the first surface of the first laser medium;
• and
• the solid state laser apparatus is configured such that the first laser beam is amplified by traveling through an inside of the first laser medium,
• wherein the plurality of cold heads include:
• a first set of cold heads including two or more cold heads;
• and
• a second set of cold heads including two or more cold heads,
• wherein the plurality of laser media include:
• a first laser media group including a laser medium arranged to the first set of cold heads;
• and
• a second laser media group including a laser medium arranged to the second set of cold heads, and
• wherein:
• the first laser media group includes the first laser medium,
• the seed light source is further configured to irradiate a second laser medium included in the second laser media group with a second laser beam;
• one laser medium, which is included in the first laser media group and arranged directly on one cold head of the first set of cold heads, is configured to reflect the first laser beam incident to the first laser medium to another laser medium, which is included in the first laser media group and arranged directly on another cold head of the first set of cold heads different from the one cold head of the first set of cold heads;
• and
• one laser medium, which is included in the second laser media group and arranged directly on one cold head of the second set of cold heads, is configured to reflect the second laser beam incident to the second laser medium to another laser medium, which is included in the second laser media group and arranged directly on another cold head of the second set of cold heads different from the one cold head of the second set of cold heads.