Matrix Material

Solid matrix materials can be broadly divided into two categories: crystalline and glass. The body must have good optical, mechanical, and thermal properties to actually withstand the harsh operating conditions of the laser.

Ideal parameters include hardness, chemical inertness, no internal strain and refractive index variation, resistance to radiation-induced color centers, and ease of fabrication. Several interactions between the matrix and the added ions limit the number of material combinations that can be utilized. These limiting factors include size differences, valence, spectral persistence, and more. Ideally, the size and valence state of the additional ion should match the size and valence state of the host ion it replaces.

The following key criteria must be considered when selecting a suitable crystal for the laser ion matrix:

• The crystal must have good optical properties, and changes in the refractive index can cause light to travel unevenly within the crystal, resulting in poor beam quality.
• Crystals must have mechanical and thermal properties that allow high average power to operate, and the most important parameters are thermal conductivity, hardness, and crack strength.
• The lattice site of the crystal must be able to receive doped ions, and its local crystal field must be symmetrical and have the intensity necessary to elicit the desired spectral properties. In general, ions located within the crystal matrix should have a long radiation lifetime, with a cross-section close to 10-20 cm2.
• It must be possible to grow doped crystals proportionally while maintaining high optical quality and high yields.