A. Matijosius

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.

Sum-frequency mixing of optical vortices in nonlinear crystals

Results of theoretical and experimental investigation of the influence of walk-off on sum-frequency mixing of optical vortices in nonlinear crystals are presented. Various phenomena of vortex interaction such as decay of higher order vortices into singly charged vortices, formation of aligned arrays of vortices perpendicular to walk-off direction, particle-like pulling and pushing of vortices, and appearance of pairs of vortices having opposite charges were observed.

Spiraling zero-order Bessel beam

The question that we are addressing concerns the possibility of creating a zeroth-order Bessel-like beam that spirals around the axis of propagation. The analytical features of the beam propagation are studied theoretically. Approximations to such a light field can be experimentally realized by using an axicon and a hologram. The beam potentially can attract interest in microfabrication applications.

Generation and control of the spiraling zero-order Bessel beam.

We report on the generation of a spiraling zero order Bessel beam by means of conventional axicon and the phase hologram. Obtained results are in a fairly good agreement with the theoretical predictions.

Second harmonic generation of higher-order Bessel beams

Abstract Second harmonic generation of higher-order Bessel beams (Bessel vortices) formed by axicon was investigated in KTP crystal. A splitting of frequency-doubled Bessel vortex of topological charge 2 n , n =1, 2, 3, into 2 n single-charged vortices was observed. The phenomenon is caused by copropagating zeroth-order Bessel beam acting as coherent background.

Characterization of conical emission of light filaments in media with anomalous dispersion

Conical emission featuring a diminishing emission angle with increasing wavelength detuning is observed in ultrashort light filaments in fused silica at a carrier wavelength with anomalous dispersion. In the measured angularly resolved spectrum of the filament, this conical emission appears as an elliptical, or O-like, structure that fits quantitatively to the elliptical spectrum of gain in the Kerr-driven spatiotemporal instability of nonlinear plane waves.

Experimental energy-density flux characterization of ultrashort laser pulse filaments

Visualization of the energy density flux gives a unique insight into the propagation properties of complex ultrashort pulses. This analysis, formerly relegated to numerical investigations, is here shown to be an invaluable experimental diagnostic tool. By retrieving the spatio-temporal amplitude and phase we experimentally obtain the energy density flux within complex ultrashort pulses generated by filamentation in a nonlinear Kerr medium.

Generation of radially polarized beams and higher order polarization singularities by optical parametric amplification of optical vortices

Abstract. We show a method to form radially and azimuthally polarized beams as well as higher order polarization singularities by superposition of optical vortices with opposite topological charges obtained by optical parametric amplification. The proposed method could find applications in optical trapping of particles, nonlinear optics experiments, and laser material processing.

Spontaneous X-pulse generation in a Kerr medium

This study utilizes a new nonlinear 3D-mapping technique and gives the first direct experimental demonstration of spontaneous X-pulse generation in a Kerr medium with NGVD. This work also shows how an ultrashort laser pulse collapses and then relaxes to a state characterized by a definite X-shaped spatiotemporal profile. This claim is supported by numerical simulations that show a good agreement with experimental data and outline the main dynamical features of X-wave formation.

Time-gated angular-spectrum characterization of fs-beam filamentation in water

We exploited the new gated angular spectrum (GAS) technique for characterising the complex non-linear dynamics of intense fs infrared pulses underlying beam filamentation in water. The measurements allowed us to discover that the axial white-light continuum and the off-axis coloured conical emission (CCE) are generated by different temporal portions of the light filament, the red and blue-shifted continuum being produced at the trailing and leading edge, respectively, while CCE at the pulse center. Finally, by implementing a FROG type data analysis on the GAS scheme, we were able to retrieve the phase profile of the wave-packet too.