Dongping Zhang

Employing oxygen-plasma posttreatment to improve the laser-induced damage threshold of ZrO 2 films prepared by the electron-beam evaporation method

ZrO2 films are deposited by the electron-beam evaporation method. Parts of the prepared samples are post-treated with oxygen plasma at the environment temperature. The laser-induced damage threshold (LIDT) of the films increases from 15.9 to 23.1 J/cm2 after treatment with oxygen plasma. Compared with that of the as-grown samples, significant reduction of the average microdefect density and absorption are found after oxygen-plasma posttreatment. These results indicate that the oxygen-plasma posttreatment technique is an effective and simple method for reducing the microdefect density and absorption to improve the LIDT.

Laser-induced damage threshold of ZrO2 thin films prepared at different oxygen partial pressures by electron-beam evaporation

ZrO2, films were deposited by electron-beam evaporation with the oxygen partial pressure varying from 3 X 10(-3) Pa to I I X 10(-3) Pa. The phase structure of the samples was characterized by x-ray diffraction (XRD). The thermal absorption of the films was measured by the surface thermal lensing technique. A spectrophotometer was employed to measure the refractive indices of the samples. The laser-induced damage threshold (LIDT) was assessed using a 1064, nm Nd: yttritium-aluminium-garnet pulsed laser at pulse width of 12 ns. The influence of oxygen partial pressure on the microstructure and LIDT of ZrO2 films was investigated. XRD data revealed that the films changed from polycrystalline to amorphous as the oxygen partial pressure increased. The variation of refractive index at 550 nm wavelength indicated that the packing density of the films decreased gradually with increasing oxygen partial pressure. The absorptance of the samples decreased monotonically from 125.2 to 84.5 ppm with increasing oxygen partial pressure. The damage threshold, values increased from 18.5 to 26.7 J/cm(2) for oxygen partial pressures varying from 3 X 10(-3) Pa to 9 X 10(-3) Pa, but decreased to 17.3 J/cm(2) in the case of I I X 10(-3) Pa

Laser conditioning of dielectric oxide mirror coatings at 1064 nm

Laser conditioning effects of the dielectric oxide mirror coatings with different designs were investigated. Simple quarter-wave ZrO2:Y2O3/SiO2 mirrors and half-wave SiO2 over-coated ZrO2:Y2O3/SiO2 mirror coatings at 1064nm were fabricated by E-beam evaporation (EBE). The absorbance of the samples before and after laser conditioning was measured by surface thermal lensing (STL) technology and the defects density was detected under Nomarski microscope. The enhancement of the laser damage resistance was found after laser conditioning. The dependence of the laser conditioning on the coating design was also observed and the over-coated sample obtained greatest enhancement, whereas the absorbance of the samples did not change obviously.

Investigation of laser-induced damage of dielectric optical coatings

Investigation of laser-induced damage (LID) of dielectric optical coatings was reviewed in this paper. Several methods for evaluating characters of LID were developed, especially for the determinations of laser-induced damage threshold (LIDT) and the detections of absorption based on surface thermal lensing (STL) technology of optical coatings. Defect was deemed to be the initial source of several previous damage mechanisms, and was the main factor restricting the laser damage resistance of optical coatings. A pulsed laser induced damage model with a spherical absorptive inclusion was proposed in order to obtain the nature, size and distribution of defects. Attentions were paid to find out the origins of damage mechanism transformation from one laser mode to another. Moreover, interests were focused on distinct damage behaviors of ultraviolet (UV) lasers. Deposition temperature and annealing process in vacuum chamber had obvious influences on LIDT of the third harmonic Nd:YAG laser coatings. At the end of this paper, several effective methods for improving LIDT were put forward, such as cleaning substrate, improving deposition process, adding protective layers, optimizing coating stacks based on temperature field theory, as well as laser conditioning.

Surface morphology and microstructure of zirconia thin films prepared at different deposition rates

ZrO2 films were prepared by electron beam thermal evaporation at different rate of deposition. And the variation of the surface morphology, rms roughness, crystal structure, and internal stress with the deposition rate were studied.

Nodule growth in zirconium films prepared by ion beam sputtering

Zirconium films were deposited by ion beam sputtering method. A novel substrate holder was designed to realize the approximately in-situ observation the process of the nodule growth. The method of pre-setting particle seeds on the substrates was used in the film deposition. Optical microscope and SEM were presented in observation the specimen before and after annealing. An interesting growth mode of nodules which different from the reported in science literature was found in our experiment. The molecule dynamics theory and diffusion limited aggregation (DLA) model was presented to analysis this phenomenon.

The simulation of growth process of thin film on nonplanar substrate

In (2+1) dimension, growth process of thin film on non-planar substrate in Kuramoto-Sivashinsky (K-S) model is studied with the numerical simulation approach. 15×15 semi-ellipsoids arranged orderly on the surface of substrate are used to represent initial rough surface of substrate. The results show that at the initial stage of growth process, the interface width constantly decreases with the growth time, then it reaches minimum. However, with the increase of growth time, the granules of different sizes distributes evenly on the surface of thin film. Whereafter the size of granules and the interface width gradually increase with the growth time, and the surface of thin film presents fractal properties.