In view of the fact that the weak laser damage resistance of HfO2 / SiO2 coatings at 355 nm hinders the observation of the fatigue effect, nanosecond single and multiple pulse laser damage studies on Al2O3 / SiO2 high-reflective coatings were performed at 355 nm. Relative to that at the long wavelength, the fatigue effect at 355 nm is very weak and complicated. The damage probability curves and the evolution of the laser-induced damage threshold under multiple irradiations reveal that the fatigue effect is affected by both laser fluence and shot number. As the laser fluence or number of shots increases, the fatigue effect becomes more apparent. The damage morphologies induced by single and multiple irradiations both manifest as micrometer-scale pits without plasma scalding around, with the characteristics of a high defect density and high absorption coefficient. In particular, the accumulation damage mechanism at 355 nm may be reflected not only in the newly created defects but also in the modification of the coating material around the damage precursors. Thus, the coatings at 355 nm “seem to” have no damage growth threshold, no matter what the laser fluence is; once damage occurs, the damage site will grow sharply under subsequent pulses finally resulting in catastrophic damage.
Laser processes of crystalline silicon solar cells become increasingly attractive, because they are fast, accurate and contact-free. Nanosecond and picosecond laser ablations with wavelength of 532nm were performed on the anti-reflection layers deposited on silicon. The laser ablated grooves of AR coatings on monocrystalline and polycrystalline silicon were both characterized to verify the influence on the underlying silicon. And the threshold fluences were specified by contrasting with the corresponding performances under certain laser pulse duration. More importantly, the groove edges were analyzed to further expose the laser ablation mechanism under different laser pulse durations.
To research the formation and variation principle of the weld seam and molten pool for aluminum alloy high power fiber
laser welding, the welding experiments for 5052 aluminum alloy were carried out. The influences of laser power,
scanning velocity and protection gas on the welding process were systematically researched. The results show that with
the increase of power and scanning velocity, the depth to width ratio first increases and then decreases. The ratio reaches
the maximum value at 2.6 KW and 30 mm/s, respectively. When the power located at 2.6 KW to 2.8 KW or the velocity
located at 25 mm/s to 30 mm/s, stable deep penetration welding can be obtained. The weld seam shows relative flat
appearance and the molten pool presents typical “T shape” topography. Moreover, the protection gas also influences the
appearance of the weld seam. Using the independently designed fixture, the quality of the weld seam can be well
The lifetime of optics in high power laser system is typically limited by both laser-initiated damage and the subsequent
growth of laser-initiated damage sites. The single- and multiple-shot irradiations for HfO2 /SiO2 high-reflective coatings,
deposited from hafnia and silica at 1064nm in nanosecond were investigated. It was found that when shot number
increased, the possibility of damage growth increased as well. The relationship between field distribution and damage
morphologies and inner structures was discussed to reveal mechanism of damage initiation. Additionally, the damage
morphologies under different laser fluence and shot numbers were characterized to discuss the damage growth
mechanism upon subsequent pulses. The tested results illustrated the absorbers which induced damages were random
distribution, and the second highest peak of field intensity at the fourth interface was high enough to induce the
micron-sized damage pits. It was found that defect density had a significant impact on the damage site whether growing
or not upon subsequent laser pulses. Additionally, the growth resulted in delamination, and in turn delamination
accelerated damage growth, finally the catastrophic damage happened.