Íñigo J. Sola

Spatiotemporal amplitude-and-phase reconstruction by Fourier-transform of interference spectra of high-complex-beams

We propose what we believe to be a novel method to reconstruct the spatiotemporal amplitude and phase of the electric field of ultrashort laser pulses using spatially resolved spectral interferometry. This method is based on a fiber-optic coupler interferometer that has certain advantages in comparison with standard interferometer systems, such as being alignment-free and selection of the reference beam at a single point. Our technique, which we refer to as the SpatioTemporal Amplitude-and-phase Reconstruction by Fourier-transform of Interference Spectra of High-complex-beams, offers compactness and simplicity. We report its application to the experimental characterization of chirped pulses and to spatiotemporal reconstructions of a convergent beam as well as plane-plane and spherical-plane waves interferences, which we check with our simulations.

Nonlinear response of a unidirectional erbium-doped fiber ring laser to a sinusoidally modulated pump power

The response of a unidirectional erbium-doped fiber ring laser, excited by a sinusoidally modulated pump power, is analyzed both experimentally and theoretically. Experimentally, several resonance peaks are observed, as well as different frequency ranges showing bistable behaviour. Appearance of all resonance peaks obtained can be explained taking into account simple relations between the pump modulation frequency and the system natural frequency. Theoretically, it is shown how a model which combines the theory of erbium-doped fibers and the semiclassical laser treatment can account for all phenomena observed, with good agreement. In particular, it is demonstrated that a correct description of the bistable regions requires taking into account powers and population distributions along the laser active medium.

Above-millijoule super-continuum generation using polarisation dependent filamentation in atoms and molecules

We demonstrate for the first time that input polarisation control inducing one single filamentation is a very robust technique to accurately control the filamentation dynamics enhancing throughput energy of the supercontinuum generation up to 1.2 millijoule. Reaching the above-millijoule regime opens the way to post-compression of multi-terawatt laser pulses.

Self-compression controlled by the chirp of the input pulse

Self-compressed (SC) pulses have been achieved through the filamentation process in air without any additional dispersion compensation, using the input pulse chirp as the control parameter. For any studied input pulse energy (3-5 mJ), we have found two opposite sign input group-delay dispersion values for which SC pulses can be achieved systematically. In addition, we have observed that the energy coupled into the inner core of the filament is always of the order of 20% of the total input pulse energy, which opens the way to a scalable technique to obtain intense short pulses directly from the filamentation process.

Spatio-temporal characterization of ultrashort pulses diffracted by circularly symmetric hard-edge apertures: theory and experiment

We carry out a complete spatio-temporal characterization of the electric field of an ultrashort laser pulse after passing through a diffractive optical element composed of several binary amplitude concentric rings. Analytical expressions for the total diffraction field in the time and spectral domain are provided, using the Rayleigh-Sommerfeld formulation of the diffraction. These expressions are experimentally validated. The spatio-temporal amplitude and phase structure of the pulse are measured at different planes beyond the diffractive optical element using spatially-resolved spectral interferometry assisted by an optical fiber coupler (STARFISH). Our results allow corroborating theoretical predictions on the presence of multiple pulses or complex spectral distributions due to the diffraction-induced effects by the hard-edge ring apertures.

Erbium doped fibre characterisation by laser transient behaviour analysis

A procedure to extract spectroscopic information from erbium doped fibres (EDF), based on transient laser behaviour analysis, is presented. It achieves a complete characterisation of EDF on wavelengths corresponding to pump and laser emission, obtaining respective absorption and emission coefficients. In addition, it allows to perform predictions of some laser dynamics features, which exhibit good experimental agreement.

Frequency resolved wavefront retrieval and dynamics of diffractive focused ultrashort pulses

In this work we demonstrate the ability of the spatiotemporal characterization technique STARFISH to retrieve the wavelength dependent wavefront of focused ultrashort laser pulses. The high resolution achievable with this technique allows measuring the wavefront at the focal spot. In particular, the method is applied to study the effects of focusing with a kinoform diffractive lens. The evolution from converging to diverging wavefronts as the pulse propagates along the focal region is analyzed for each wavelength. The spatiotemporal intensity and spatially resolved spectrum structure of the pulses, as well as their profiles on axis, are also presented. Numerical simulations of the propagation of such pulses confirm the experimental results.

Spatiotemporal evolution of light during propagation in filamentation regime

The full description of the evolution of light during its nonlinear propagation represents a valuable help to the complete understanding of important nonlinear phenomena such as light filamentation. In this paper we present a comparison between theoretical and experimental results of the spatiotemporal structure of a light filament at different propagation distances. In order to obtain the experimental spatiotemporal structure, we have used a technique based on spatially resolved spectral interferometry called STARFISH, for spatiotemporal amplitude-and-phase reconstruction by Fourier transform of interference spectra of high-complex beams. We have been able to observe important nonlinear pulse dynamics during the nonlinear propagation, including pulse splitting and the subsequent competition among the pulses that result from the splitting, obtaining a full insight into the general nonlinear behavior.

Spatiotemporal characterization of few-cycle laser pulses

In this paper we apply a broadband fiber optic coupler interferometer to the measurement of few-cycle laser pulses. Sub-8-fs pulses delivered by an ultrafast oscillator were characterized spatiotemporally using STARFISH, which is based on spatially resolved spectral interferometry. The reference pulse was measured with the d-scan technique. The pulses were focused by an off-axis parabolic mirror and were characterized at different transverse planes along the focusing region. The evolution of the retrieved pulses is analyzed, exhibiting small variations in the temporal (and spectral) amplitude and phase during propagation. Finally, the peak irradiance evolution is estimated from the integration of the spatiotemporal intensity.

980 and 1480 nm EDF characterisation by ring tunable laser dynamic study

Abstract An EDF characterisation method, based on laser transient behaviour, is applied to 980 and 1480 nm pumped ring tunable fibre lasers. Absorption and emission coefficients at both, pump and laser frequencies, along the 1521–1561 nm spectral range, are obtained, as well as dopant concentration. Obtained parameters are introduced in EDF amplifier (EDFA) simulation in order to check them out, presenting good agreement with experimental measurements.