A YAG ceramic bonded body in which a YAG ceramic and a YAG ceramic or optical glass are bonded, wherein the YAG ceramic bonded body comprises glass as a bonding layer, and has a rate of change of transmittance that is within 7%. An object of this invention is to provide a bonded body in which a YAG ceramic and a YAG ceramic are bonded, or a bonded body in which a YAG ceramic and optical glass are bonded, and which is capable of suppressing the reflection of light at the bonded interface, as well as the production method thereof.

In one embodiment a laser amplifier includes a light pump source that can generate light at a first wavelength or range of wavelengths. The laser amplifier further includes an optically pumped laser amplifier having a gain medium that amplifies light at a second wavelength or range of wavelengths in response to receiving generated light from the light pump source. A housing is used to at least partially surround the gain medium and hold a coolant fluid able to absorb the second wavelength or range of wavelengths.