Characterization of grain sizes and roughness of HfO2 single layers.

The grain sizes and their influence on the roughness of an HfO2 single layer prepared with ion-assisted deposition were investigated. Three methods, x ray diffractometry, atomic force microscopy, and the k-correlated power spectral density function model, were used to obtain the grain sizes in two HfO2 single layers with 16 and 20 nm thicknesses. X ray diffractometry showed that the grain sizes were about 7 and 9 nm, respectively, whereas the other two methods demonstrated that the grain sizes were about 14 and 16 nm. It was thought that x ray diffractometry underestimated the grain size due to micro strain or a shallow penetration depth. The grains in an HfO2 single layer lead to a rough surface, which had a significant bulge at the middle-high frequency range in a power spectral density function curve. The coating intrinsic roughness of the HfO2 single layer was separated from the substrate roughness.

Fabrication of broadband absorbing coatings for amplified spontaneous emission suppression.

Amplified spontaneous emission (ASE) is a critical factor that limits the output power of slab lasers. To suppress the ASE effect in slab lasers, this paper proposes a metal/dielectric broadband absorbing coating between the laser gain medium and the metal heat sink to suppress ASE from zero to total internal reflection angle on the facet from inside the laser medium. Based on accurate characterization of Cr metal thin films, Cr/SiO2 broadband absorbing films for 1064 nm YAG slab lasers are designed and fabricated to suppress ASE. The good agreement between experiment and design shows the reliability to suppress ASE in slab lasers.

Study of HfO2/SiO2 dichroic laser mirrors with refractive index inhomogeneity.

HfO2/SiO2 dichroic mirrors, having high reflectance at 1064 nm and high transmittance at 532 nm, play an important role in high-power laser systems. However, the half-wave hole effect, caused mainly by the refractive index inhomogeneity of hafnia, affects the spectra and application of these mirrors. Two approaches to eliminate the half-wave hole effect have been proposed. Both approaches attempt to shift the location of the half-wave hole in comparison with the original wavelength. One approach broadens the reflectance band of the first harmonic wavelength and simultaneously adjusts the central reflectance band to a longer wavelength, whereas the other approach combines the two stacks to adjust the location of the half-wave hole far away from the wavelength of interest. Two kinds of dichroic mirrors have been successfully fabricated; moreover, it was found that the method of a two-stack combination, 0.9(HL)8 and 1.1(HL)8, provides designs that can be fabricated more easily and with better quality spectral characteristics.

Interfacial damage in a Ta2O5/SiO2 double cavity filter irradiated by 1064 nm nanosecond laser pulses.

The Laser-Induced Damage Threshold (LIDT) and damage morphologies of a Ta(2)O(5)/SiO(2) double cavity filter irradiated by 1064-nm, 10-ns pulses were investigated. The depths of flat bottom pits were examined by an optical profiler and then calibrated according to the Electric-Field Intensity (EFI) distributions and the cross-sectional micrographs obtained using the Focus Ion Beam (FIB) technology. The statistics for depths of 60 damage sites suggested that the Ta(2)O(5) over SiO(2) interface was more vulnerable to Laser-Induced Damage (LID) than the SiO(2) over Ta(2)O(5) interface. After examining the morphologies of interfacial delaminations carefully, we found that the Ta(2)O(5) over SiO(2) interface instead had stronger mechanical strength. So, the higher density of susceptible defects at the Ta(2)O(5) over SiO(2) interface was considered to be the reason that LID was preferentially initiated at this type of interface. Based on the above findings, a phenomenological model was proposed to describe the formation of flat bottom pits.

Effects of substrate temperatures on the structure and properties of hafnium dioxide films.

Different HfO2 monolayers under different deposition conditions, such as substrate temperature and oxygen partial pressure, were prepared from metal hafnium using the reactive electron beam evaporation method. X-ray diffraction was applied to determine the crystalline phase of these films, the surface morphology of the samples was examined by atomic force microscopy, and the optical properties were analyzed using a spectrophotometer and the surface thermal lens technique. The relationship between substrate temperature and film characteristic was investigated, and the correlation between the observed film properties and the laser damage threshold was also discussed.