The damage properties of multilayer coatings tested with 1064-nm 30-ps pulses are similar to those tested with 355 nm, nanosecond pulses. A kind of HfO2 / SiO2 high-reflective (HR) coating is prepared by electron beam evaporation. Laser-induced damage of HfO2 / SiO2 HR coatings is tested by 355-nm 7-ns pulses and 1064-nm 30-ps pulses, respectively. Damage morphologies and cross-sectional profiles are characterized using a scanning electron microscope and focused ion beam, respectively. The laser-induced damage thresholds and morphologies in the two tests are compared. The developing processes and damage mechanisms are discussed. Many similarities are found in the two tests: the typical damage morphologies in both tests appeared as micrometer-sized pits when irradiated by low-fluence pulses, while it turned out to be layer delamination when irradiated by high-fluence pulses. Damage onset is nearby the peak of the E-field in the two tests. Damage pits in both tests may be related to thermal stress caused by nanometer-sized isolated absorbers. There are also some differences in the damage properties between two tests: damage pits in 1064-nm 30-ps tests have a much higher density than that in 355-nm 7-ns tests. The detail features and the developing processes of the pits are different.
A kind of HfO2/SiO2 355nm and 1064nm high-reflective (HR) coatings were deposited by electron beam evaporation. Laser-induced damage of the coatings were tested by 355nm-7ns pulses, 355nm-1ns pulses and 1064nm-30ps pulses in 1-on-1 mode. All tests were carried out with S-polarized and P-polarized pulses in two angles of incidences (AOIs) of 30° and 50°. Damage morphologies and cross-sectional profiles were characterized using scanning electron microscope (SEM) and focused ion beam (FIB), respectively. It is shown that the typical morphologies in all the tests were μm-sized pits. In the 1064nm-30ps tests, the damage pits appeared mostly as 3-4μm ripple-like pits with a density of 13000-25000 mm<sup>-2</sup>, accompanied by a few tiny pits around. The ripple-like pits were all conical pits with a cylindrical cavity at the bottom, the depth of which was around 1μm. The tiny pits were all cylindrical shaped with a depth of about 400nm. In the 355nm-7ns tests, most of the pits were flat-pits scaled from 4 to 18μm with a density of 500-900 mm<sup>-2</sup>, few with a bulge in the bottom. The depth of the pits increased with their size, which can be 2.5μm for the largest ones. In the 355nm-1ns tests, pits appeared to be similar with those in 355nm-7ns tests, with a smaller size of 4-6 μm, The damage pits were preliminary inferred to be formed because of the material removal induced by the thermal stress.
Laser-induced damage in optical components has always been a key challenge in the development of high-power laser systems. In picosecond regime, the laser-matter interactions are quite complex and the damage mechanism is not yet understood. Therefore, it is necessary to investigate the laser induced damage of optical components in picosecond regime. Our previous study on the laser induced damage in HfO2/SiO2 high-reflective (HR) coatings in 30-ps laser pulses reported the damage morphologies to be high-density micrometer-scale pits, which are similar to the morphologies of HR coatings irradiated by 355-nm pulses in nanosecond regime. Thus, it makes sense to analyze the damage mechanism of HR coatings in picosecond regime by comparing the damage results with those tested with 355-nm pulses. In this study, laser induced damage of HfO<sub>2</sub>/SiO<sub>2</sub> HR coatings are performed by 355-nm, 7-ns pulses and 1064-nm, 30-ps pulses, respectively. Different angles of incidence (AOIs) are operated in the tests, in order to modulate the electric field (E-intensity) distributions in the coating stacks. Damage morphologies and cross-sectional profiles are characterized using scanning electron microscope (SEM) and focused ion beam (FIB), respectively. The laser-induced damage thresholds (LIDTs) and morphologies tested with two different laser pulses are compared. The damage locations are compared with corresponding E-field distributions and the damage reasons are discussed.
The effect of protective layer on the picosecond laser-induced damage behaviors of HfO<sub>2</sub>/SiO<sub>2</sub> high-reflective (HR) coatings are explored. Two kinds of 1064nm HR coatings with and without protective layer are deposited by electron beam evaporation. Laser-induced damage tests are conducted with 1064nm, 30ps S-polarized and P-polarized pulses with different angle of incidence (AOI) to make the electric fields intensity in the HR coatings discrepantly. Damage morphology and cross section of damage sites were characterized by scanning electron microscope (SEM) and focused ion beam (FIB), respectively. It is found that SiO2 protective layer have a certain degree of improvement on laser induced damage threshold (LIDT) for every AOIs. The onset damage initiated very near to the Max peak of e-field, after which forms ripple-like pits. The damage morphology presents as layer delamination at high fluence. The Laser damage resistance is correspond with the maximum E-intensity in the coating stacks.
In this paper, metallic pulse compression gratings (MPCG) with three kinds of grating structures are manufactured. The diffraction efficiency and bandwidth of samples are measured and it can be found that the different grating structure has different diffraction efficiency and bandwidth. Laser damage tests of samples are implemented by an 800±30 nm laser at pulse duration of 31 fs and it can be also found that the different grating structure has different laser-induced damage threshold. Experimental measurements illustrate that the grating structure has a great influence on bandwidth, diffraction efficiency and damage threshold. The typical damage morphologies of MPCG reveal that the damage is induced by absorption and thermal stress.
In order to study the effect of material properties on the laser induced damage of
dielectric coatings at a wavelength of 248 nm, multilayer coatings were deposited by electron beam
reactive evaporation technique onto fused silica substrates with the materials of hafnium oxide,
aluminum oxide and silicon dioxide. Laser-induced damage thresholds (LIDTs), morphologies and
profiles of damage sites of multilayer thin films were measured to investigate the damage
mechanism. Besides, with our programmed software, the temperature rise in the multilayers was
calculated to better understand the relationship between damage morphology, electric field peak
location and depth of damage sites. The results indicate that the absorption of defect and the electric
field distribution of thin film greatly contribute to LIDTs of thin films, and the control of defect,
especially defect with strong absorption, is still the only way to improve the laser radiation resistivity
of coatings in the UV spectral region.