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Laser-induced damage threshold (LIDT) is an essential factor in measuring the anti-laser damage of optical films. The damage threshold and morphology of the Ta2O5/SiO2 multilayer film prepared by electron beam evaporation were studied by femtosecond (50 fs) and picosecond (30 ps) laser irradiations. The results showed that the LIDT of the film was 1.7 J·cm−2 under the femtosecond laser. The damage morphology developed from surface damage to a clear layered structure, and the outline has become more transparent and regular with an increase in the laser fluence. Under the picosecond laser irradiation, the LIDT of the film was 2.0 J·cm−2. The damage morphology developed from small range to thin film layer separation, and the outline changed from blurry to clear with an increase in laser fluence. Therefore, the LIDT of the film decreased with a decrease in the laser pulse width.

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For the paper, experimental studies were performed on the damage of the Ge- and Si-based flat window by lasers out-of-band. The experimental results showed that lasers out-of-band can cause film damage and substrate damage to Ge and Si windows. The high-energy laser damage window mechanism mainly manifested as thermal effects. The composite laser damage thresholds for the substrate were an Si window of 21.6 J/cm2 and a Ge window of 3 J/cm2. Compared with continuous laser and long pulse laser experimental results, it was found that the use of long pulse-continuous composite constitution could effectively reduce the damage threshold. Compared to the long-pulse laser, the composite laser could achieve similar damage effects with a smaller energy density.

This paper investigates the heat effects of continuous high-power lasers on steel cylinders. A theoretical model combining the mechanical characteristics and heat transfer of the steel cylinder that irradiated by a high-power laser is established. Simulations in temperature fields predict the varying heat effects on steel cylinders corresponding to different laser power levels, and more importantly, the thresholds of laser penetrations. The predictions are further validated by experimental tests, which use 1.5–2.8 kW laser irradiating on 7–15 mm thick steel cylinders. It has been found that the ablation mechanism of steel cylinder is primarily dependent on either the mass transfer of vaporized ablation or liquefied material under the action of vaporized back pressing. The present 0–300 s temperature field analyses show that steel melts at 1720 K and vaporizing ablation happens at 3250 K. It has also been observed that in the contact region between the laser and steel cylinder, the melting and vaporization accompanied by the interaction of the ablation process are followed by the sharp splash phenomenon.