Stefano Minardi

Three-Dimensional Light Bullets in Arrays of Waveguides

We report the first experimental observation of three-dimensional light bullets, excited by femtosecond pulses in a system featuring quasi-instantaneous cubic nonlinearity and a periodic, transversally modulated refractive index. Stringent evidence of the excitation of light bullets is based on time-gated images and spectra which perfectly match our numerical simulations. Furthermore, we reveal a novel evolution mechanism forcing the light bullets to follow varying dispersion or diffraction conditions, until they leave their existence range and decay.

Far-field spectral characterization of conical emission and filamentation in Kerr media

By use of an imaging spectrometer we map the far-field (theta-lambda) spectra of 200-fs optical pulses that have undergone beam collapse and filamentation in a Kerr medium. By studying the evolution of the spectra with increasing input power and by using a model based on an asymptotic linear superposition of stationary wave modes (rather than the exact instantaneous solution), we are able to trace a consistent model of optical beam collapse highlighting the interplay between conical emission, multiple pulse splitting, and other effects such as spatial chirp.

Effective lensing effects in parametric frequency conversion

We show that, in the high wave-vector-mismatch (cascading) limit, the well-known paraxial description of parametric frequency conversion in quadratic media entails effective lensing effects, which can have a self-focusing or a self-defocusing nature, critically depending on the mismatch sign, the selected wave, and the launching condition (second-harmonic generation or downconversion). Numerical and experimental evidence of this behavior is reported.

Interferometric beam combination with discrete optics

We propose an innovative scheme exploiting discrete diffraction in a two dimensional array of coupled waveguides to determine the phase and amplitude of the mutual correlation function between any pair of three telescopes of an astrointerferometer.We explore the capabilities of discrete diffraction in phase retrieval problems and propose an innovative scheme exploiting a two-dimensional array of coupled waveguides to determine the phase and amplitude of the mutual correlation function between any pair of three telescopes of an astrointerferometer.

Accurate retrieval of pulse-splitting dynamics of a femtosecond filament in water by time-resolved shadowgraphy

By means of a time-resolved, shadowgraphic method we observed directly the development of the pulse-splitting dynamics of a femtosecond laser pulse propagating in the filamentary regime in water. For the first time to our knowledge, the relative splitting velocity was measured. We compare the experimental data with numerical simulations. A possible scenario for the splitting event and evolution of the fragments is discussed.

Three dimensional imaging of short pulses

Abstract We exploit a slightly non-collinear second-harmonic cross-correlation scheme to map the 3D space–time intensity distribution of an unknown complex-shaped ultrashort optical pulse, down to a resolution of 10 μm in space and 200 fs in time. Moreover, we directly show that the spatial phase information is not lost in the process, thanks to the coherence of the non-linear interaction. This implies that the concept of second-harmonic holography can be employed down to the sub-picosecond time scale, and used to discuss the features of the technique in terms of the reconstructed fields.

Control of the shape of the spatial mode function of photons generated in noncollinear spontaneous parametric down-conversion

We show experimentally how the spatial shape of the pump beam controls the ellipticity of the spatial mode function in noncollinear spontaneous parametric down-conversion. The degree of ellipticity depends on the pump beam width, especially for highly focused beams. We introduce an effective length, the so-called noncollinear length, that determines the importance of the ellipticity of the spatial mode function. We also discuss the ellipticity induced by the spectrum of the pump beam.

Three-dimensional photonic component for multichannel coherence measurements.

We present the experimental results of a three-dimensional integrated photonic component designed for the simultaneous determination of mutual coherence properties of three light channels. Potential applications to astronomical optical interferometry are proposed and discussed.

Pixellike parametric generator based on controlled spatial-soliton formation

We report the observation of a stable matrix of diffraction-limited solitary beams in a monolithic, single-pass, parametric amplifier pumped by a spatially modulated beam.

3D-integrated optics component for astronomical spectro-interferometry.

We present the experimental characterization of a spectro-interferometry setup based on a laser-written three-dimensional integrated optics component. By exploiting the interferometric capability of a two-dimensional array of evanescently coupled waveguides, we measure the mutual coherence properties of three different polychromatic optical fields. Direct application of our discrete beam combiner (DBC) component is astronomical interferometry. The DBC can be scaled up to combine arbitrary large number of telescopes for the determination of coherence properties of astronomical targets. Besides applications to astronomy, the DBC can be also applied to optical integrated metrology system requiring nanometric position monitoring. The working principle, the experimental setup used, and the broadband performance of the DBC are presented.