Multimode anharmonic third-order harmonic generation in a photonic-crystal fiber

Abstract

While the third harmonic of a monochromatic pump field with a frequency omega0 is generated exactly at the frequency 3omega0, frequency tripling of broadband ultrashort pump pulses in extended nonlinear media tends to generate isolated spectral peaks substantially shifted from 3omega0. We demonstrate this phenomenon by studying nonlinear spectral transformations of femtosecond Cr:forsterite laser pulses in multimode photonic-crystal fibers. Third-harmonic generation is shown to map adjacent guided modes of the third harmonic onto a manifold of spectral peaks within a 150-THz range around 3omega0. The spectral shifts and the widths of these peaks are controlled by the phase and group-velocity mismatch between the pump field and third-harmonic modes, as well as the length of nonlinear-optical interaction and broadening of the pump spectrum, allowing the spectral content of the third-harmonic signal to be engineered by tailoring the fiber dispersion.

Axial spectral scans of polarization dependent third harmonic generation in a multimode photonic crystal fiber

“…Previously [15] a multipeak anharmonic THG was reported using the same sample concluding that the XPM induced phase shift and subsequent peak narrowing might be responsible for the multipeak nature of the TH spectra. This approach also predicts the TH spectral width to evolve as z −1 with the propagation coordinate z.…”

Simultaneous generation of second and third harmonics by red-shifted solitons in photonic crystal fibre

“…Because of the intrapulse Raman scattering (IRS), the solitons formed by the short pulses in the anomalous dispersion region undergo a soliton self-frequency shift (SSFS). The red-shifted solitons can serve as the pumps for SHG and THG [4][5][6]. In this Letter, for the first time, the second and third harmonics are simultaneously generated from the red-shifted solitons.…”

Static third-harmonic lines in widely variable fiber continuum generation

“…Experimentally, the static view was supported by the prediction of signal wavelengths and modes from fiber structure [1,12]. However, this is ambiguous because similar simulations have made such prediction from the dynamic view [3,10,13]. The insensitivity of signal wavelength to the pump could be the definitive evidence [12], except for the claims that the dynamic view could lead to the same conclusion [3,13].…”

“…However, this is ambiguous because similar simulations have made such prediction from the dynamic view [3,10,13]. The insensitivity of signal wavelength to the pump could be the definitive evidence [12], except for the claims that the dynamic view could lead to the same conclusion [3,13]. These factors may have contributed to the lower popularity of the static view.…”

“…The dynamic view of this convergence would require a delicate combination of the pump wavelength and coupling power (Kerr effect) to target the 302.6 nm [3,9,10,13], which is in contradiction with the observed wavelength stability against the coupling power. In contrast, the static view of this phenomenon simply attributes the emergence of the 302.6-nm ( ω h ) THG lines to the presence of their fundamentals 302.6 × 3 nm ( ω h /3) in the continuum, regardless of the pump wavelength and coupling power.…”