Alexis Labruyère

Polychromatic filament in quadratic media: spatial and spectral shaping of light in crystals

We demonstrate that monochromatic infrared laser pulses can generate polychromatic light in noncentrosymmetric crystals simultaneously covering the ultraviolet, visible, and infrared domains. The spatial shape of the beam and its energy can influence this multicolor frequency conversion, unveiling complex and interesting dynamics. We performed our experiments in a bulk crystal of periodically poled lithium niobate, working close to the optimal condition for second-harmonic generation. We used an input laser beam wide enough that, at very low intensities, the diffraction leaves its diameter unchanged along the propagation in the crystal. At high intensities instead, as we show in this work, such a spatially wide laser beam can be reshaped into a beam of much smaller diameter and guiding multispectral components. We also show how this outcome may permit exploitation of other parameters, like the crystal temperature, for tuning the spectrum of the generated multicolor light.

Control of near-infrared supercontinuum bandwidth by adjusting pump pulse duration

We experimentally and numerically investigated the impact of input pump pulse duration on the near-infrared bandwidth of supercontinuum generation in a photonic crystal fiber. We continuously stretched the temporal duration of the input pump laser (centered at 1030 nm) pulses from 500 fs up to 10 ps, while keeping fixed the pump peak power. We observed that the long-wavelength edge of the supercontinuum spectrum is increased by 200 nm as the pump pulse duration grows from 500 fs to 10 ps. We provide a quantitative fit of the experimental results by means of numerical simulations. Moreover, we have explained the observed spectral broadening enhancement induced by pump pulse energy by developing an approximate yet fully analytical model for soliton energy exchange through a series of collisions in the presence of stimulated Raman scattering.

Efficiency of dispersive wave generation in dual concentric core microstructured fiber

We describe the generation of powerful dispersive waves that are observed when pumping a dual concentric core microstructured fiber by means of a sub-nanosecond laser emitting at the wavelength of~1064 nm. The presence of three zeros in the dispersion curve, their spectral separation from the pump wavelength, and the complex dynamics of solitons originated by the pump pulse break-up, all contribute to boost the amplitude of the dispersive wave on the long-wavelength side of the pump. The measured conversion efficiency towards the dispersive wave at 1548 nm is as high as 50%. Our experimental analysis of the output spectra is completed by the acquisition of the time delays of the different spectral components. Numerical simulations and an analytical perturbative analysis identify the central wavelength of the red-shifted pump solitons and the dispersion profile of the fiber as the key parameters for determining the efficiency of the dispersive wave generation process.

Dispersive Wave Emission in Dual Concentric Core Fiber: The Role of Soliton–Soliton Collisions

Soliton-soliton collisions have a crucial role in enhancing the spectrum of dispersive waves in optical fibers and collisions among in-phase solitons lead to a dramatic enhancement of the dispersive wave power, as well as to its significant spectral reshaping. We obtained a simple analytical model to estimate the spectral position, width, and amplitude of the dispersive waves induced by a collision of two in-phase solitons. We tested our theory in the case of a dual concentric core microstructured fiber.

Spectro-temporal shaping of supercontinuum for subnanosecond time-coded M-CARS spectroscopy

A supercontinuum laser source was designed for multiplex-coherent anti-Stokes Raman scattering spectroscopy. This source was based on the use of a germanium-doped standard optical fiber with a zero dispersion wavelength at 1600 nm and pumped at 1064 nm. We analyzed the nonlinear spectro-temporal interrelations of a subnanosecond pulse propagating in a normal dispersion regime in the presence of a multiple Raman cascading process and strong conversion. The multiple Raman orders permitted the generation of a high-power flat spectrum with a specific nonlinear dynamics that can open the way to subnanosecond time-coded multiplex CARS systems.

Self-increased acceptance bandwidth of second harmonic generation for high-energy light sources

We report a series of experimental results showing that the acceptance bandwidth of second harmonic generation in quadratic crystals may substantially broaden when using pumps at high intensities. We highlight the co-existence of second harmonic generation and strong unconventional spatial beam reshaping. Our experimental results are in good agreement with our numerical simulations.

Soliton-Soliton Collision Enhanced Dispersive Wave Emission in Microstructured Fiber

We developed an analytical approach to estimate the influence of soliton-soliton collision on the growth rate of dispersive waves in optical fibers. Our theoretical model shows an excellent agreement with numerical results.