Diamond Raman laser with continuously tunable output from 3.38 to 3.80 μm

We report a pulsed mid-infrared diamond Raman laser with output tuned from 3.38 to 3.80 μm through varying the optical parametric oscillator (OPO) pump wavelength. To our knowledge this is the longest reported wavelength from a solid-state Raman laser. We generated up to 80 μJ with good beam quality and 22% quantum conversion efficiency. Whilst the conversion process itself is efficient, approximately 40% of the generated Stokes light is lost to multiphonon absorption. By introducing a secondary pump beam at the anti-Stokes wavelength to initiate a seed at the Stokes wavelength through Raman resonant four-wave mixing, the laser threshold was reduced by approximately half, and the maximum output increased by 44% to 115 μJ.