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The focusing of double-ring-shaped radially polarized ultrashort light pulses by a high-numerical aperture objective is investigated using vectorial Debye theory. After focusing, the double-ring-shaped radially polarized ultrashort light pulses slow down near the focus, and this pulse delay induces pulse compression in the propagation direction. That is, without changing the pulse duration, the spatial pulse length of the ultrashort light pulse is decreased near the focus. The velocity of the longitudinal component of the light pulse near the focus is lower than that of the radial component. The simulation results demonstrate that control of the ratio of the pupil radius to the beam radius affects not only the longitudinal component of the light pulse, but also the velocity and spatial pulse length of the light pulse because of the destructive interference between the longitudinal components of the inner and outer rings of the light pulse.

The capability of chirped-pulse compression and beam focusing of an object-image-grating self-tiling grating compressor is demonstrated in an optical parametric chirped-pulse amplification laser for the first time. Probe lasers for tiling error adjustments, which are generally required by the traditional tiled-grating compressor, are not needed in our demonstration any more. With the aid of the double-sized effective optical aperture of the second grating in the compressor, a 490 fs near-transform-limit pulse duration and a 90 μm near-diffraction-limit focal spot are obtained, synchronously, which are very close to the ones achieved by a non-tiled grating compressor with equal-sized individual gratings.

Ultrashort pulse laser heating of a germanium nanofilm was simulated using a combined continuum–atomistic method that couples the molecular dynamics and a self-consistent energy model for ultrafast laser–semiconductor interaction. Both a single pulse and a pulse burst were considered. To accurately describe laser energy deposition, the transient optical properties were computed based on the Drude formula. It was found that for a single pulse at low fluence (e.g., 0.02 J/cm2), the pulse duration had little impact on the lattice temperature response. In contrast, a higher lattice temperature could be obtained for a longer pulse (e.g., 5 ps) at higher fluences (e.g., 0.06 J/cm2) due to lower surface reflectivity. A strong thermal stress wave could be induced by the laser heating, with its maximum compression and tension occurring in the front and rear film regions, respectively. The investigations of laser burst heating revealed that a laser burst not only can retain the advantages of ultrashort pulse lasers...

The time behaviour of ultrashort laser pulses can be changed and optimized for a specific application by the combination of pulse-compression and pulse-shaping techniques. A pulsed laser beam at a central wavelength of 800 nm and 80 fs pulse duration is guided through a hollow fibre of 70cm length, filled with argon gas. Due to the nonlinear optical effect of self-phase modulation the pulse spectrum broadens during propagation. After separating the spectral components of the modified pulse with a prism and lens setup, a deformable-membrane mirror is used to control the spectral phase. By means of an evolutionary algorithm, it was possible to remove higher-order phase contributions in the final pulse shape as well as additional dispersion.