Efficient third-harmonic generation of broadband picosecond radiation by employing spectrally noncritical phase-matching KDP crystal and cascaded LBO crystals

Abstract To improve the nonlinear frequency conversion efficiency of a broadband picosecond fiber laser, the spectrally noncritical phase matching for frequency doubling, dual-crystal cascaded design for frequency tripling is employed. By this method, we obtain 2.39 W of output power at the third-harmonic wavelength, when the spectral full width at half maximum of the fundamental light is 5.5 nm and the input fundamental light power is 8.6 W. The frequency conversion efficiency of IR-UV is 27.8%. To the best of our knowledge, this is the first time of the broadband third harmonic picosecond ultraviolet laser generation by the combination of the spectrally noncritical phase matching for frequency doubling and dual-crystal cascaded design for frequency tripling.