Non-centrosymmetric Y(HCOO)3 � 2 H2O crystal. A new inorganic material for Raman lasers with large frequency shift of three promoting vibration modes of its [O-CH-O]- formate anions: effective high-order Stokes and anti-Stokes generation and cascaded self-frequency [?(3)(SRS) ??(2)(SHG, SFM)] and [?(2)(SHG, SFM) ??(3)(SRS)] conversions

Abstract

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 (gssR ≥ 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)