RESUMO
Optical components with higher surface quality and higher damage threshold requirement are necessary in high-energy/power laser system, which strongly depends on the performance of optical thin films. The damage morphologies on the surface of the HfO2/SiO2 anti-reflection film, caused by focused laser pulses, were investigated in the present paper. The studies revealed that the shock wave formed with the expansion of laser plasma, and its velocity and pressure decease rapidly with the radius. The spectrum of laser plasma, recorded by EEP2000 spectrometer, shows that the wavelength of laser plasma radiation is shorter than incident laser, which will increase the probability of multi-photon absorption; the photon energy in deep ultraviolet region, higher than the band gap of HfO2, can be absorbed directly. The ionization effect of laser plasma can easily induce film damage. The combination of shock wave and ionization effect determines the damage morphology of films. In the case of laser pulse focused on the film surface, the radiation and shock wave effects are the highest, not only the film is removed, but also the quartz substrate is broken-down. When the focus point is away from the film surface to a certain distance, the radiation of laser plasma and shock wave decrease rapidly, as a result, no damage can be found except that the thin-film can be peeled away from the substrate.
RESUMO
Silicon is the basic material for electro-photonic detectors, so the studies of the laser induced damage of silicon are of great significance in laser detecting and military applications. The damage characters of silicon under high intensity nanosecond laser pulses were investigated in the present paper. The results show that laser plasma has thermal effect, shock effect and spectral radiation effect, etc. These comprehensive effects combined together determinate the damage characters. By thermal effects and shock effects of laser plasma, the material is being melt, vaporized, ionized and pushed out at the laser irradiated area. In this way, the pit can be formed and the cooled ejected effluents are radially distributed. The silicon was melt at the bottom of the pit and the temperature was modulated by the intensity of the incident laser, which interfered with scattering laser simultaneously. The periodic heat distribution generates the period stripes. N, O and Si characteristic spectrum in the laser plasma prove that the colored film is the mixture of SiOx:SiNy which were sprayed out from laser plasma under repetitive laser pulses.