Abstract
Nonlinear cascaded femtosecond third harmonic generation was experimentally investigated pumped by 100 fs pulses at optical communication band 1550 nm using a multi-grating 5 mol. % MgO-doped periodically poled lithium niobate crystal. The optimized efficiency of 10.8% was achieved with the simultaneous phase-matching of the second harmonic and sum frequency process. And the third harmonic spectrum reached as broad as 8.7 nm because of the choosing of a small group velocity mismatching between the fundamental and second harmonic pulses. Nonlinear cascaded method will provide a reference for the efficient frequency conversion in the high intensity range.
Highlights
Frequency upconversion is a useful nonlinear process to achieve short wavelength, and third harmonic generation (THG) is one of the most effective upconversion process, which can be used to generate optical emission with shorter wavelength
Collinear THG was achieved by a short-range-ordered two-dimension nonlinear photonic crystal [7]
We demonstrated a collinear cascaded THG of femtosecond pulses with high intensity in a 5 mol. % MgO-doped periodically poled lithium niobate crystal
Summary
Frequency upconversion is a useful nonlinear process to achieve short wavelength, and third harmonic generation (THG) is one of the most effective upconversion process, which can be used to generate optical emission with shorter wavelength. Besides direct THG method, cascaded THG by second harmonic and sum frequency process is a more efficient method. The most efficient conversion of cascaded THG is achieved when the phase-matching conditions for both second harmonic and sum frequency processes are satisfied. For two-dimension nonlinear photonic crystals, they are often utilized to realize the noncollinear THG [4,5,6]. Collinear THG was achieved by a short-range-ordered two-dimension nonlinear photonic crystal [7]. N. Fujioka realized noncollinear cascaded THG of femtosecond. Pulses using two-dimension periodically poled lithium niobate and THG efficiency of 8% with spectral width of 4 nm was obtained [8]. We demonstrated a collinear cascaded THG of femtosecond pulses with high intensity in a 5 mol. The TH spectral width reached as broad as 8.7 nm with a small group velocity mismatch (GVM) between fundamental pulses and SH pulses
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