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An ion-beam sputtered film of hafnium oxide was irradiated with an intense nanosecond laser pulse above the ablation threshold. The transmitted laser power was measured as a function of time, with a resolution of a few hundred picoseconds. The spatial origin of the defect-triggered ablation was monitored for each event. A phenomenological model of a rapidly expanding, absorbing disk can explain the observed time dependent transmission and structure sizes of the affected material. The required expansion speeds, ranging from 1 to 100 km/s, and their observed dependence on the local laser intensity, are compatible with a laser-driven detonation wave as described by the Chapman–Jouget (CJ) theory. Because the energy deposited by the laser pulse is too low to explain detonation in a material with the density of hafnium oxide, we hypothesize that the detonation wave propagates in the electron–hole subspace. We modified the CJ theory to describe laser-driven detonation in an electron–hole plasma and to account for plasma expansion sideways to the laser beam. [ABSTRACT FROM AUTHOR]

A first-time demonstration of mode locking on a supersonic chemical oxygen-iodine laser uses an acoustooptic modulator (AOM) as well as a small intracavity aperture to confine lasing to TEM(sub 00) mode operation. A DC magnetic field not only enhances the number of axial modes but also raises the peak power to 2.5 kW with a pulse width of 2.1 nanoseconds. Analysis of the mode-locked pulses shows a weak sound field inside the AOM at the edges of the crystal for high second transverse mode intensity. The experiments are conducted with 160-G/180-G fields and a 1 GHz detector registers mode beats.

The amplification of femtosecond light pulses in multistage as well as in traveling-wave dye amplifiers is studied numerically, taking into account group velocity dispersion, self-phase modulation that is due to Kerr-type nonlinearity, and gain depletion. The combined action of these processes results in a spectral broadening that can be utilized for pulse compression. The results are compared with experimental findings., An amplification and compression technique for dye laser femtosecond pulses is given. The multistage amplifier (MSA) and the traveling-wave amplifier (TWA) set-ups are examined for the effects of depletable amplification, group velocity dispersion (GVD), self-phase modulation (SPM) and pulse compression. Results show that gain depletion, GVD and SPM have an effect on the generation of the pulse. This situation is common in MSAs with long amplifier cells and high saturation. The growth of the spectrum on the long-wavelength side is influenced by gain depletion and GVD. Spectral widening in TWA is a caused by SPM and saturated amplification.

In multi-pulse laser damage and ablation experiments, the laser-induced damage threshold (LIDT) usually changes with the number of pulses in the train, a phenomenon known as incubation. We introduce a general incubation model based on two physical mechanisms-pulse induced change of (i) absorption and (ii) critical energy that must be deposited to cause ablation. The model is applicable to a broad class of materials and we apply it to fit data for dielectrics and metals. It also explains observed changes of the LIDT as a function of the laser repetition rate. We discuss under which conditions the crater-size method to determine LIDTs can be applied in multi-pulse experiments. [ABSTRACT FROM AUTHOR]