Abstract

For the development of diode pumped ultra short pulsed lasers, materials with broad absorption and emission bands are investigated. The crystals with disordered structure determined by the multiple occupancy of specific crystallographic cationic sites with ions of different species or with different valence states could be a solution. Among these materials, the rare earths (RE³⁺) doped calcium niobium gallium garnets (CNGG) or calcium lithium niobium gallium garnets (CLNGG) gained interest in the last years. These crystals have the advantage of iridium free technologies. X ray or Raman data show that the congruent composition of CNGG is different from the stoichiometric one, with excess of Nb⁵⁺ and with Ga³⁺ cationic vacancies that could be deleterious for high power regime of the lasers [1,2]. It was also found that by Li⁺ addition these vacancies could be eliminated and a new crystal is formed CNLGG - Ca₃Li_0.275Nb_1.775Ga_2.95O₁₂. RE³⁺ ions substitute the Ca²⁺ ions in dodecahedral sites and the charge compensation is accomplished by an excess of Nb⁵⁺ ions in octahedral sites in CNGG and by a proper proportion of Nb⁵⁺ and Li⁺ ions in the octahedral sites in CLNGG; Ga³⁺ vacancies could also contribute. The low temperature spectra of Nd³⁺ revealed at least five nonequivalent centers [2,3] and are slightly different in the two crystals. Spectroscopic characteristics of various RE³⁺ ions in these crystals have been reported [4]. Recent work revealed the possibility of subpicosecond pulse emission in Nd: CLNGG [5], suggesting the possibility of utilization of Yb³⁺ in these crystals for short-pulse generation. Spectroscopic data are reported only for Yb: CNGG [6], only three centers were considered. CW Yb³⁺ laser emission was also reported [7].

© 2009 IEEE