OPTICAL INVESTIGATION OF ER-CA2AL2SIO7 AND YB-CA2AL2SIO7 FOR LASER APPLICATIONS IN THE NEAR-INFRARED

Single crystals of the aluminosilicate Ca2Al2SiO7 (GAS) activated with Er3+ or Yb3+ were grown by the floating zone method for several dopan t contents. The crystals of good optical duality, were investigated us ing optical spectroscopy with the aim to assess their potential intere st as laser materials in the 1.5 mu m (Er:CAS) and 1 mu m (Yb:CAS) ran ge, respectively. In both cases, absorption, stimulated emission, and gain cross sections were determined. Radiative and experimental lifeti mes were also calculated. In the two compounds, as the two levels invo lved in the transitions are the ground and first excited states, radia tion trapping and energy migration occur. For Er:CAS, emission around 1.55 mu m (in the middle of the eye-safe range) may be obtained for a reasonable value of the population inversion ratio beta (beta = 0.4). The Judd-Ofelt parameters are significantly higher than those of Er:YA G and the nonradiative relaxation of the excited states located above I-4(13/2) is fast (phonon energy cut-off around 1020 cm(-1)) ensuring efficient population of the I-4(13/2) emitting level. For Yb:CAS, the absorption and emission cross sections are higher than for Er:CAS. Pos itive gain cross section is possible for very low beta values, for ins tance beta = 0.04 at 1045 nm. Taking into account the pump saturation intensity and the beta value, it appears that this compound should be one of the best ytterbium activated laser crystal (if one excepts the apatite-type hosts).