C. Serrat

Modulated phase matching and high-order harmonic enhancement mediated by the carrier-envelope phase

The process of high-order harmonic generation in gases is numerically investigated in the presence of a few-cycle pulsed-Bessel-beam pump, featuring a periodic modulation in the peak intensity due to large carrier-envelope-phase mismatch. A two-decade enhancement in the conversion efficiency is observed and interpreted as the consequence of a mechanism known as a nonlinearly induced modulation in the phase mismatch.

Doppler-free adiabatic self-induced transparency

The ability to render a medium transparent to a resonant laser field opens a wide range of applications, from slow light and dark state polariton physics to light-matter interfaces. In atomic vapours at room temperature, Doppler broadening plays, in general, a negative role tending to reduce transparency. In a two-level (2L) system Doppler-free transparency can be achieved by means of self-induced transparency (SIT) (Fig.1(a,d)), which consists in preparing an optical pulse propagating in the medium such that an integer number of Rabi oscillations are performed [1]. Therefore, SIT requires a very precise temporal control of the Rabi frequency, i.e. the pulse area being an integer multiple of 2π. In three- (3L) and/or multi- level atomic systems, resonant transparency could be achieved by using induced atomic coherences, e.g., by means of the coherent population trapping (CPT) [2] and the electromagnetically induced transparency (EIT) phenomena [3] or via a double-STIRAP process [4]. In all these cases, the required two-photon (or Raman) resonance condition severely restricts the applications of the previous approaches to laser fields with nearly identical frequencies.

Two-photon cavity solitons in purely active media: radiative spatial profiles

This paper deals with two-photon cavity solitons in purely active media. This study also investigates the dynamical properties and radiative spatial profiles of two-photon cavity solitons (CSs), and makes comparisons with CS arising in other nonlinear optical resonators.

Dynamics of Polarization States in a Vertical-Cavity Surface Emitting Semiconductor Laser with an Axial Magnetic Field.

Laser arrays are a method to produce intense coherent beams with low divergence in the far field. In the past years the research focussed on 1D arrays of semiconductor laws, because they can be easily realized with conventional edge emitting lasers. Recently, the advances in the technology of vertical cavity surface emitting laser, allowed for the fabrication of bi-dimensional arrays with an extremely large number of components. In this paper we generalize the coupled mode theory of [Z] to study the supermodes of a 2 0 array, i.e. the stationary solutions in which all lasers oscillate at the same frequency and the relative phases are h e d . We consider only coupling with the first and second neighbours. For each supermode the mode amplitude of every laser and the common frequency correspond respectively to the eigenvectors and the eigenvalues of a suitable tridiagonal matrix. The linear stability analysis performed in the particular case 2 x 2 shows that the only supermode which is stable for reasonable values of the parameters is the one where each laser is T out-of-phase with its first neighbours. The same result was obtained in the 1D case [3], but our analysis shows that in the 2D case the width of the stability domain is one half. Following [4] we have also considered the effects that arise when two orthogonal statu for light polarization are possible. When the array oscillates on one supermode, we have demonstrated that polarization switchings can occur, in which all lasers simultaneously switch from one polarization state to the orthogonal one.