Cascaded mode-locking of a spectrally controlled Yb:KYW laser

Self-starting and stable mode-locking of an Yb:KYW laser in the picoseconds pulse regime has been achieved by exploiting a positive cascaded Kerr lens in periodically poled KTP. The use of a volume Bragg grating (VBG), for locking the output spectrum of the laser, was essential to achieve a stable mode-locked operation in this wide gain bandwidth laser material. The laser emitted stable, nearly transform-limited pulses with a duration of 16 ps, at a repetition rate of 210 MHz, and with an energy of 3.2 nJ. The mode-locked spectrum was centred at 1,029.1 nm and featured a FWHM bandwidth of 85 pm, which was effectively determined by the VBG. Combination of a large cascaded Kerr nonlinearity with spectral limiting by a VBG represents so far the best opportunity for stable mode-locking of a broadband laser to produce near-transform-limited picosecond pulses.     

Stripe patterns in degenerate optical parametric oscillators

We experimentally demonstrate the stripe (or roll) patterns in a broad-aperture degenerate optical parametric oscillator in a plane-mirror minicavity. The stabilization of stripes is achieved by seed injection at a subharmonic frequency. We measure the temporal spectra of the stripe pattern and obtain the 1/f-like noise spectra.     

Application of time-resolved digital holographic microscopy in studies of early femtosecond laser ablation

We studied evolution of femtosecond laser ablation by employing novel method of time-resolved off-axis digital holographic microscopy. Phase and amplitude profiles of early shock front and ablation plume dynamics of irradiated tempered steel were reconstructed from the digital holograms. In order to gain additional information, digital holographic microscopy was combined with plasma emission imaging. By using both techniques simultaneously we studied material response to multi-pulse irradiation, shock wave propagation, ablation plume formation and plasma emission. The significant changes in ablation performance were observed when using multi-pulse irradiation if compared to widely investigated single-shot regime.