RESUMO
Combining electron optics, fast electronics and pulsed lasers, a transmission and a photoelectron emission microscope were built, which visualize events in thin films and on surfaces with a time resolution of several nanoseconds. The high-speed electron microscopy is capable to track fast laser-induced processes in metals below the ablation threshold, which are difficult to detect by other imaging techniques. The material response to nano- and femtosecond laser pulses was found to be very different. It was dominated by thermo/chemocapillary flow and chemical reactions in the case of nanosecond pulses, and by mechanical deformations and non-thermal electron emission after a femtosecond pulse.
RESUMO
Laser-induced birefringence patterns which break the symmetry of the experimental setup have been observed in a low molar mass anisotropic glass with nematic orientational order under a polarizing microscope. It is shown that the observed spatial modulations in birefringence can be explained by laser-induced heat flow and stress, leading to molecular reorientation which is then frozen and stored in the glassy state if the optical excitation is switched off. The experimental findings can be regarded as a manifestation of heat-flow alignment caused by a spatially inhomogeneous temperature field.
