Single-shot d-scan technique for ultrashort laser pulse characterization using transverse second-harmonic generation in random nonlinear crystals.

We demonstrate a novel dispersion-scan (d-scan) scheme for single-shot temporal characterization of ultrashort laser pulses. The novelty of this method relies on the use of a highly dispersive crystal featuring antiparallel nonlinear domains with a random distribution and size. This crystal, capable of generating a transverse second-harmonic signal, acts simultaneously as the dispersive element and the nonlinear medium of the d-scan device. The resulting in-line architecture makes the technique very simple and robust, allowing the acquisition of single-shot d-scan traces in real time. The retrieved pulses are in very good agreement with independent frequency-resolved optical grating measurements. We also apply the new single-shot d-scan to a terawatt-class laser equipped with a programmable pulse shaper, obtaining an excellent agreement between the applied and the d-scan retrieved dispersions.

Femtosecond pulse propagation near a two-photon transition in a semiconductor quantum-dot waveguide.

We have studied femtosecond pulse propagation in CdS quantum-dot-doped waveguides produced by the solgel and ion-exhange methods. The observed two-photon absorption and asymmetric spectral modulation of the transmitted pulses are explained by our theoretical model, which incorporates a near-resonant two-photon transition.