Room-temperature vibronic pulsed laser action in trivalent chromium-activated forsterite (Cr3+:Mg2SiO4) is reported for the first time. The free-running laser emission is centered at 1235 nm of the broad 4T2→4A2 fluorescence band, and has a bandwidth of ∼22 nm.
We have systematically studied the behaviour of the absorption bands due to the O - H bond-stretching vibration and its polarization characteristics in with the use of well characterized crystals. It has been found that the O - H bond-stretching vibrational frequencies, , have a strong correlation with Nb concentration in the crystals as in the case of MgO-doped . The values of shift to the higher-frequency region when the Sc concentration in the crystal exceeds about 2.5 mol%. The magnitude of the frequency shift is smaller and the polarization dependence of the absorption bands due to is weaker in -doped than in MgO-doped . These features are attributed to the difference of the charge between and . We have also proposed an ideal defect structure model for -doped , which is based on the Li-site vacancy model as an intrinsic defect structure model. The observed behaviour of is consistently explained by the proposed defect structure model. This supports the justification of the extrinsic defect structure model based on the Li-site vacancy model for -doped as well as for MgO-doped .
The noncritical phase-matching temperature, Tpm, of Sc2O3-doped LiNbO3 was measured as a function of Sc2O3 concentration (0.0, 0.5, 1.0, and 1.5 mol % Sc2O3). Increasing the Sc2O3 concentration increased the phase-matching temperature, but to a lesser extent than reported in MgO:LiNbO3. The maximum phase-matching temperature was 46.5 °C in the 1.0 mol % Sc2O3:LiNbO3 crystal with an estimated temperature bandwidth of 1° cm. Photorefractive damage, determined by distortion in the transmitted beam, decreased with increasing Sc concentration, reaching a damage level comparable to that observed in 5.0 mol % MgO:LiNbO3 crystal in the 1.5 mol % Sc2O3:LiNbO3 crystal.
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