Inhomogeneous line shape broadening of glass laser and improvement of the line shape by crystallization

Glass lasers are one type of solid state laser that uses glass as gain medium where active ions (Nd3+, Er3+ Ho3+, Tm3+ etc.) are doped. Materials for laser operation must possess sharp fluorescent lines, strong absorption bands, and reasonably high quantum efficiency for the fluorescent transition of interest. These characteristics are generally shown by solids (crystals or glass) which incorporate in small amount of elements in which optical transitions can occur between states of inner, incomplete electron shells. Thus the transition metals, the rare earth (lanthanide) series, and the actinide series are of interest in this connection. For this paper Nd:glass is of interest that shows inhomogeneous broadening. For inhomogeneous broadening central frequency is shifted due to local variation of electric field and thus gain reduces as gain is inversely to line width. But in case of homogeneous broadening each atom response in an identical fashion causes line broadening. However, this broadening is much less than inhomogeneous broadening and affect gain profile less severely. On the other hand, if the glass structure can be crystallize by external parameter like temperature, pressure etc. than local field variation will be compensated and we might reach to homogeneous broadening.