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Efficient high-order stimulated Raman scattering was excited under picosecond pumping in the visible and near-IR in four crystals of the α-alum family - novel isotropic χ(3)-active crystalline materials. All observed Stokes and anti-Stokes lasing components were identified and attributed to the promoting ≈1000 cm-1 vibration modes of these crystals. Their one-micron steady-state first Stokes Raman gain coefficients were estimated as well.

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Efficient multi‐phonon steady‐state stimulated Raman scattering (SRS) was excited in the novel χ(3)‐active crystal of orthorhombic yttrium formate dihydrate, Y(HCOO)3 · 2 H2O, at room temperature under picosecond laser pumping in the visible and near‐IR regions. Besides high‐order Stokes and anti‐Stokes generation in this non‐centrosymmetric crystal, several cascaded second (χ(2))‐ and third (χ(3))‐order nonlinear interactions were observed under 1 μm pumping. Among them are self‐frequency χ(2) → χ(3) conversion effects by simultaneous second harmonic generation (SHG) and SRS, as well as χ(3) → χ(2) lasing action by successive SRS + SHG and SRS + SFM (sum‐frequency mixing). All the recorded Raman‐induced lasing wavelengths were identified and attributed to the SRS‐promoting optical vibration modes wSRS1 ≈ 1395 cm–1, wSRS2 ≈ 1377 cm–1 and wSRS3 ≈ 2895 cm–1 of the [O–HC–O]– ionic groups of the crystal. The measured large Raman frequency shifts and estimated moderately high steady‐state Raman gain coefficient for the first Stokes generation (g St 1‐1ssR ≥ 7.5 cm GW–1) in the visible of the first SRS‐promoting mode, as well as the fact that it is easy to grow large crystals of Y(HCOO)3 · 2 H2O make this material attractive for a number of new applications in modern quantum electronics and nonlinear optics. Y(HCOO)3 · 2 H2O offers the largest Raman frequency shifts among all known SRS‐active inorganic crystals. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)