Continuous-wave cascaded Raman laser at 1.3, 1.5, and 1.7 μm

Semiconductor disk lasers (SDLs) are capable of several Watts of continuous-wave (CW) output power in a single transverse mode, with emission demonstrated from the visible to the mid-infrared. Moreover, their highfinesse extended cavities allow the incorporation of intracavity nonlinear crystals to convert to wavelengths where direct emission of SDLs is non-trivial. SDLs based on InGaAs QWs exhibit highest efficiency and output power (10s of Watts CW), but direct emission of such gain structures is limited to ~920-1180 nm [1]. Considerable effort has been devoted to extending their coverage to longer wavelengths by reducing the bandgap via the incorporation of small amounts of nitrogen (dilute nitrides) [1], or by lattice-matching to InP substrates and subsequently using wafer fusion techniques [2]. For some applications, an attractive alternative to such demanding fabrication is to use the optimised and commercially tested InGaAs-based SDLs with efficient intracavity down-conversion.There are now several demonstrations of high power, tunable, CW Raman lasers intracavity-pumped by SDLs (e.g. [3]). Here we demonstrate emission at even longer wavelengths via cascaded Raman laser oscillation in an InGaAs-based SDL. The Raman gain crystal is KGd(WO 4 ) 2 (KGW), chosen for its large Stokes shift of 901 cm-1 such that, with Raman conversion cascaded to a 3rd Stokes shift, oscillation is achieved simultaneously at ~1.31, ~1.49 and ~1.72 μm collinearly with the 1174 nm SDL beam. To the best of our knowledge, this is the first demonstration of 3rd Stokes Raman oscillation in an SDL, the longest wavelength achieved via Raman conversion of an SDL, and the first SDL system to emit in the 1.7 μm tissue transmission window.