Abstract
When ultrafast noncritical cascaded second-harmonic generation of energetic femtosecond pulses occur in a bulk lithium niobate crystal optical Cherenkov waves are formed in the near- to mid-IR. Numerical simulations show that the few-cycle solitons radiate Cherenkov (dispersive) waves in the λ = 2.2 - 4.5 μm range when pumping at λ₁ = 1.2 - 1.8 μm. The exact phase-matching point depends on the soliton wavelength, and we show that a simple longpass filter can separate the Cherenkov waves from the solitons. The Cherenkov waves are born few-cycle with an excellent Gaussian pulse shape, and the conversion efficiency is up to 25%. Thus, optical Cherenkov waves formed with cascaded nonlinearities could become an efficient source of energetic near- to mid-IR few-cycle pulses.
Highlights
Nonlinear optics dawned when second-harmonic generation (SHG) was demonstrated 50 years ago [1]
When ultrafast noncritical cascaded second-harmonic generation of energetic femtosecond pulses occur in a bulk lithium niobate crystal optical Cherenkov waves are formed in the near- to mid-IR
Numerical simulations show that the few-cycle solitons radiate Cherenkov waves in the λ = 2.2 − 4.5 μm range when pumping at λ1 = 1.2 − 1.8 μm
Summary
Nonlinear optics dawned when second-harmonic generation (SHG) was demonstrated 50 years ago [1]. Since nIcasc ∝ −de2ff/Δk the phase-mismatch Δk = k2 − 2k1 controls both the magnitude and sign of the cascaded nonlinearity [2] This has been used to study, e.g., spatial, temporal and spatiotemporal solitons [4,5,6], high-energy pulse compression [7,8,9,10], supercontinuum generation [11], and all-optical signal processing [12]. We investigated high-energy pulse compression through few-cycle solitons generated in cascaded SHG, and showed that the soliton can couple to dispersive waves [13, 14]. We showed experimentally that noncritical cascaded SHG in lithium niobate (LN) can support nearIR few-cycle solitons [10], and the predicted phase-matching to mid-IR Cherenkov waves [14] was confirmed numerically. The conversion efficiency is 125%, depending on how far the Cherenkov wavelength is from the soliton wavelength, implying that this scheme could be used as an efficient source of energetic few-cycle mid-IR pulses
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