High-peak-power 1.7 µm pulse generation by cascaded second- and third-order nonlinearity

We report an efficient and novel method for generating high-peak-power 1.7 µm laser pulses by cascaded optical parametric oscillation (OPO) and stimulated Raman scattering (SRS). The 1064 nm fundamental wave was first converted to 1535 nm by the KTA OPO, and further extended to 1.7 µm by a SRS process. The configuration of OPO + SRS can provide high-intensity pumping light for subsequent Raman conversion, and allows for better wavelength expansibility benefitting from the non-phase-matching requirement of SRS. Two types of Raman conversion using the low-frequency Raman shift in KY(WO 4 ) 2 and high-frequency Raman shift in YVO 4 were further studied. Up to the 8th-order cascaded KY(WO 4 ) 2 Raman laser (KRL) using the high gain 87 cm −1 Raman mode and a YVO 4 Raman laser (YRL) using the 890 cm −1 Raman mode emitting at 1.7 µm were realized, respectively. The output wavelengths at 1556, 1577, 1599, 1622, 1646, 1670, 1695, 1720 nm and the output wavelength at 1778 nm were observed in the KRL and YRL, respectively. The maximum total average output powers of 1.26 W and 1.05 W, minimum pulse widths of 8.4 and 24 ns and maximum pulse peak powers of 33.3 kW and 9.4 kW were obtained respectively from the KRL and YRL, enabling the 1.7 µm laser source to have practical applicability in medical imaging, industrial processing, and mid-infrared laser generation.