Spectroscopic investigation of the near infrared laser materials: Chromium doped forsterite and calcium, chromium doped yttrium aluminum garnet

The purpose of this study was to determine the nature of the optical center in the recently developed near infrared laser materials Cr:Mg{dollar}sb2{dollar}SiO{dollar}sb4{dollar} (forsterite) and Ca,Cr:{dollar}rm Ysb3Alsb5Osb{lcub}12{rcub}{dollar} (YAG). Special techniques such as fluorescence line narrowing and piezospectroscopy have been employed along with more conventional spectroscopic techniques including absorption, excitation, and emission measurements to identify the position of electronic energy levels.; A discussion of the theoretical concepts necessary to interpret the measurements is presented. The theories discussed are concerned with the behavior of a transition metal ion occupying various crystalline sites. Using these models and the measured optical properties, the near infrared centers are assigned in terms of Cr oxidation number and the symmetry of the Cr site in the crystals.; Using fluorescence line narrowing and high resolution absorption measurements, the ground state energy levels of the lasing center in Cr:forsterite have been determined. The ground state was found to be a triplet with energy level positions of 0, 2.05 and 2.35 cm{dollar}sp{lcub}-1{rcub}.{dollar} Additional measurements in the presence of an applied magnetic field have allowed the identification of two magnetically inequivalent sites. The field dependence of the ground state energy levels has been modeled using results of electron paramagnetic resonance measurements. These results have been interpreted in terms of Cr{dollar}sp{lcub}4+{rcub}{dollar} ions occupying a tetrahedral site, most likely a vacancy in the pure crystal.; The optical measurements of Ca,Cr:YAG have enabled the identification of several electronic levels associated with the near infrared active center. The electronic levels responsible for the near infrared emission have been measured to be a doublet at energies 7815 and 7843 cm{dollar}sp{lcub}-1{rcub}{dollar}. The piezospectroscopic measurements have enabled these levels to be identified as components of the {dollar}sp3{lcub}rm T{rcub}sb2{dollar} electronic level. The identification of other components of the same electronic level have also been made as a result of the stress measurements. The observed optical properties are interpreted in terms of a Cr{dollar}sp{lcub}4+{rcub}{dollar} ion occupying a site possessing S{dollar}sb4{dollar} symmetry which is consistent with the tetrahedral site in YAG.