Abstract
We report a compact source of high power, tunable, ultrafast yellow radiation using fourth-harmonic generation of a mid-IR laser in two-stage frequency-doubling processes. Using ${\rm{C}}{{\rm{r}}^{2 +}}{:}{\rm{ZnS}}$ laser at 2360 nm frequency-doubled in a multi-grating MgO:PPLN crystal, we have generated near-IR radiation tunable across 1137–1200 nm with average output power as high as 2.4 W and pulse width of ${\sim}60\;{\rm{fs}}$. Subsequently, the near-IR radiation is frequency-doubled using a bismuth triborate (BIBO) crystal to produce coherent yellow radiation tunable across 570–596 nm with a maximum average power of ${\sim}1\;{\rm{W}}$. The source has a maximum mid-IR to yellow (near-IR to yellow) single-pass conversion efficiency as high as ${\sim}29.4\%$ (${\sim}47\%$). Without any pulse compression, the yellow source has output pulses at a repetition rate of 80 MHz with a pulse width of ${\sim}130\;{\rm{fs}}$ in Gaussian-shaped and a spectral width of ${\sim}4\;{\rm{nm}}$ corresponding to a time-bandwidth product of 0.45. The generated output beam has a Gaussian transverse beam profile with measured ${M^2}$ values of $M_x^2 \sim 1.07$ and $M_y^2 \sim 1.01$.
© 2020 Optical Society of America
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