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.

To investigate the damage threshold and mechanism of a mid-infrared HgCdTe focal plane array (FPA) detector, relevant experimental and theoretical studies were conducted. The line damage threshold of a HgCdTe FPA detector may be within the range of 0.59 Jcm⁻² to 0.71 Jcm⁻². The full frame damage threshold of the detector may be in the range of 0.86 Jcm⁻² to 1.17 Jcm⁻². Experimental results showed that when the energy density reaches 1.17 Jcm⁻², the detector exhibits irreversible full frame damage and is completely unable to image. Based on the finite element method, a three-dimensional model of HgCdTe FPAs detector was established to study the heat transfer mechanism, internal stress, and damage sequence. When HgCdTe melts, we think that the detector is damaged. Under these conditions, the theoretical damage threshold calculated using the detector model is 0.55 Jcm⁻². The difference between theoretical and experimental values was analyzed. The relationship between damage threshold and pulse width was also studied. It was found that when the pulse width is less than 1000 ns, the damage threshold characterized by peak power density is inversely proportional to pulse width. This relationship can help us predict the experimental damage threshold of an FPA detector. This model is reasonable and convenient for studying the damage of FPA detectors with a mid-infrared pulse laser. The research content in this article has important reference significance for the damage and protection of HgCdTe FPA detectors.

To improve laser anti-UAV technology and UAV laser protection capabilities, research on continuous laser damage to a UAV flight control system has been carried out. Combining waveform and function monitoring, the performance of the flight control system under laser irradiation was observed in real time, and the temperature and ablation process were recorded, which were used to analyze its damage characteristics and thresholds. Our experimental results show that the flight control system had two damage modes: temporary failure and permanent damage. Temporary failure had a temperature threshold, which was on average $450.85$ K. All temporarily failed flight control system functions could be restored after cooling and a manual restart, but permanently damaged flight control systems could not be manually restarted. This experiment showed that, within K. All temporarily failed flight control system functions could be restored after cooling and a manual restart, but permanently damaged flight control systems could not be manually restarted. This experiment showed that, within $10 \mathrm{s}$, the power density required for temporary failure and permanent damage to the flight control system was ${28.4 \mathrm{W}/\mathrm{c}\mathrm{m}}^2$ and ${42.6 \mathrm{W}/\mathrm{c}\mathrm{m}}^2$, respectively. The power density required for permanent damage was ${82.0 \mathrm{W}/\mathrm{c}\mathrm{m}}^2$ within $16 \mathrm{s}$ if the flight control system was encapsulated with aluminum alloy. Based on the circuit fault diagnosis of the flight control system samples that has been permanently damaged, the laser’s thermal effects damaged the diodes and linear regulators, ultimately rendering the flight control system unable to be manually restarted.

The study used linearly and circularly polarized femtosecond pulsed lasers to irradiate a Ta₂O₅/SiO₂ film. Firstly, the damage thresholds of the film for linearly and circularly polarized femtosecond pulsed lasers were measured in 1-on-1 mode. The results showed that the damage threshold (1.70 J/cm²) under a circularly polarized laser was higher than that (1.68 J/cm²) under a linearly polarized laser. For femtosecond lasers, the multi-photon ionization cross-section under circular polarization was lower than that under linear polarization. The lower ionization rate under circular polarization led to a higher damage threshold compared to the case under linear polarization. Secondly, the damage morphology of the film irradiated by linearly and circularly polarized femtosecond lasers was observed by microscope. The damage caused by linearly polarized laser was more evident than that caused by the circularly polarized laser. Finally, the damage thresholds induced by linearly and circularly polarized femtosecond pulsed lasers were measured in S-on-1 (S = 2, 5, and 10) mode. For the same S value (2, 5, or 10), the damage threshold under the circularly polarized laser was higher than that under the linearly polarized laser. The damage thresholds under two polarized laser pulses decreased with an increase in the number of laser shots, indicating that repeated laser pulses had a cumulative effect on the damage of the film.

With the development of optoelectronic countermeasures and ultrashort pulse laser technology, the study of the interaction between ultrashort pulse laser and monocrystalline silicon has a very important theoretical and practical significance. In order to further clarify the damage mechanism of 532 nm picosecond pulsed laser on monocrystalline silicon, we have conducted an experimental study to measure the damage threshold, clarify the damage mechanism, and discuss the pulse accumulation effect at low flux. Firstly, using a laser with a wavelength of 532 nm, a pulse width of 30 ps and a metallurgical microscope based on the 1-on-1 laser damage test method, the zero damage probability threshold is determined to be 0.52 J/cm(2). Secondly, the damage effect of a picosecond laser irradiated on monocrystalline silicon was studied under different laser fluxes, and it was found that the damage of 532 nm picosecond laser to monocrystalline silicon is manifested as heated-effect damage and plasma impact damage. The increase in energy density can be divided into three stages according to the main damage mechanism: thermal effect (0.52 similar to 3 J/cm(2)), thermal ablation (3 similar to 50 J/cm(2)) and plasma effect (>50 J/cm(2)), and the damaged areas are corresponded to different growth laws with the laser energy density, respectively. Finally, an experiment for the multi-pulse cumulative effect was carried out at a low laser flux and it was found that at a laser energy density of 0.52 J/cm(2), the surface was irradiated continuously for 16 shots. The formation of a heat-affected zone confirms that the cumulative effect of multiple pulses can lower the laser damage threshold on monocrystalline silicon.

Aluminum grating has wide applications in laser systems and photoelectric equipment. Research on the laser damage characteristics of aluminum grating has guiding significance and application value for improving the laser damage resistance. The aim of this study is to investigate the characteristics of damage induced by nanosecond pulsed lasers on the aluminum grating. To better understand the laser damage characteristics of aluminum grating, herein, Maxwell’s equations were numerically solved according to the finite difference time-domain method, and the electric field model of 1,064 nm Gaussian laser damage aluminum grating was established. The simulation results showed that the light field is modulated by the grating; furthermore, the maximum value of the electric field occurred at the ridge of the grating when the laser is irradiated vertically. Analysis suggested that the electric field distribution is in accordance with the laser energy distribution, and the distribution region of the maximum electric field is a vulnerable location. To further verify the local electric field enhancement effect, based on the 1-on-1 laser damage measurement method, an experimental study of the nanosecond laser (@1,064 nm, 6.5 ns) damage to the aluminum grating was carried out. Moreover, the damage morphology was analyzed using a scanning electron microscope (SEM), and the simulation results showed good agreement with the experimental results.