Writing in Optics Letters, Ming-Hsiung Wu and collaborators have now implemented a new method based on an off-axis monolithic KTP crystal Raman oscillator, in which waves resonate with zigzag paths via total internal reflections between the crystal surfaces. When pumped with a Q-switched Nd:YAG laser at 1064 nm, the KTP crystal oscillator generates a cascade of Raman Stokes waves with an ultrabroad bandwidth across the near-infrared up to 1800 nm, which is simultaneously down-converted into the visible from 540 nm to 750 nm through second-harmonic generation (SHG) and sum-frequency generation (SFG). Wu et al. further demonstrated two efficient schemes to couple out this supercontinuum light trapped in the monolithic KTP oscillator, using either a linear array fiber bundle or a wedge-polished glass rod to frustrate the total internal reflections. This novel Raman SC comb light source is compact and simple, and therefore could find many applications in spectroscopy and microscopy.
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