Investigation of the pulse evolution dynamics in cascaded nanosecond diamond Raman lasers.

Raman lasers based on diamond crystals, known for their high Raman gain and high power-handling capabilities, have garnered significant attention in recent years for their potential in high-power multi-wavelength laser applications. While extensive research has been conducted on gain competition among multiple wavelengths in the Raman cascade process, the impact of this competition on the pulse waveforms of different Stokes orders has received limited focus. In this work, we investigate how gain competition influences the pulse waveforms during cascaded conversion in a Raman oscillator. This study introduces what we believe to be a novel approach to generating short-pulse outputs in Raman lasers. Experimental results reveal that when the fourth-order Stokes pulse begins to oscillate, the third-order Stokes pulse exhibits pulse narrowing. Furthermore, both second-order and third-order Stokes pulses show "step-like" features in their waveforms due to losses from higher-order Stokes generation-a phenomenon corroborated by theoretical simulations. Using a 532 nm laser as the pump source to excite diamond, we successfully achieve second-order, third-order, and fourth-order Stokes cascaded Raman laser outputs at 620 nm, 676 nm, and 743 nm, respectively. The measured energy output reaches 632.4 μJ, with an optical-to-optical conversion efficiency of 36.38%.