Mid-infrared diamond Raman laser with tuneable output

We present an OPO pumped mid IR diamond Raman laser with tuneable output from 3.49 μm to 3.78 μm, which to our knowledge is the longest wavelength produced in a solid state Raman laser. Up to 59 μJ is generated with a conversion efficiency of 10%. We also determine the Raman gain coefficient of diamond at 1.864 μm through measurement of the amplification of a seed signal. With pump and probe polarisations aligned with the <110< crystal axes a value of 4.8 cm/GW is measured, which corresponds to 6.4 cm/GW for polarisation aligned with the <111< crystal axes. Achievable conversion efficiencies were limited by multi-phonon absorption at the Stokes wavelength. Numerical modelling shows that increasing the output coupling factor of the cavity reduces the impact of multi-phonon absorption and leads to higher conversion efficiencies. By reducing the output coupler reflectivity from 55% to 5% and eliminating Fresnel reflections from cavity components, 30% conversion efficiency (44% quantum conversion efficiency) is predicted.