Device for amplifying a laser beam

A device for amplifying a multi-wavelength laser beam, comprising:

• a solid active laser medium comprising a disc comprising:
• a front face receiving a beam to be amplified each time the beam passes through the active laser medium;
• and
• a reflecting rear face, said front face being inclined with respect to the rear face at a non-zero inclination, said front face and the rear face being inscribed in a right prism with a triangular or trapezoidal base, the rear face being cooled, a beam received on said front face during a first pass being called an incident beam, a beam reflected by the rear face and refracted by said front face during the first pass being called the first useful beam, and a beam reflected by the rear face and refracted by said front face during a second pass being called the second useful beam;
• and
• an optical return unit arranged along the path of the first useful beam, comprising first and second mirrors oriented so that the path of the first useful beam between said active laser medium and the first mirror is symmetrical, with respect to a plane of symmetry, to the path of the first useful beam between the second mirror and said active laser medium, the plane of symmetry being a plane perpendicular to a plane containing the base of said active laser medium and to a plane containing said rear face, the optical return unit returning the first useful beam to said front face for a second pass through said active laser medium so that the sub-beams of each wavelength, forming the second useful beam, are parallel to each other at the end of the second pass.