Spodumene, α-LiAlSi2O6 – A new natural SRS-active crystal with three χ(3)-promoting vibrational modes

α-LiAlSi ₂O ₆, known as mineral spodumene, is introduced as a novel SRS-active crystal with monoclinic symmetry C2/c. Under picosecond laser excitation Raman-induced steady-state χ ⁽³⁾-nonlinear generation in the visible and near-IR is observed in the crystals. All recorded Stokes and anti-Stokes high-order lasing components are identified and correspond to three SRS-promoting phonon modes with ω _SRS1 ≈ 709 cm ⁻¹, ω _SRS2 ≈ 357 cm ⁻¹ and ω _SRS3 ≈ 1074 cm ⁻¹. On the basis of the results of a spontaneous Raman scattering study they were assigned to vibrations of the tetrahedral [SiO ₄] groups of the silicate chains and lattice modes of Li-O or Al-O of the crystal structure. A brief review in tabular form of so far known SRS-active natural crystals (minerals) is given as well.