The effects of working pressure on the properties of 355nm Al<sub>2</sub>O<sub>3</sub>/MgF<sub>2</sub> HR coatings were investigated. A series of
samples were deposited by electron beam evaporation using the same deposition process at different working pressure.
Transmittance of the HR coatings was measured by Lambda 900 spectrometer. Structure of the samples had been
characterized by X-ray diffraction (XRD).The stress was measured by viewing the substrate deformation before and after
coatings deposition using an optical interferometer, the stress results range from 223MPa to 315MPa. Laser-induced
damage threshold (LIDT) was measured by a 351 nm Nd:YAG laser with a pulse width of 7 ns, the LIDT results range
from 2.69 J/cm<sup>2</sup> to 11.03 J/cm<sup>2</sup> with the working pressure changing. It was found that working pressure has important
effects on the absorption, stress and LIDT of 355nm Al<sub>2</sub>O<sub>3</sub>/MgF<sub>2</sub> HR coatings. (351nm, 7ns).The working pressure was
no clear effect on the crystalline structure of the HR coatings.
The effect of deposition temperature on the properties of 355-nm high-reflectivity (HR) coatings was investigated. A series of 355-nm HR coatings were deposited by electron-beam evaporation using the same deposition process, but different deposition temperatures: 200, 250, 280, and 320 °C. Transmittance and high reflectance of the samples were measured with a Lambda 900 spectrometer, and the highest reflectance, 98.7%, was achieved at a deposition temperature of 280 °C. The laser-induced damage threshold (LIDT) was measured with a 355-nm pulsed laser with a pulse width of 8 ns. It was found that the deposition temperature had a significant effect on the LIDT of coatings. LIDTs up to 18.5 J/cm2 were achieved when the deposition temperature was 280 °C. The LIDT of the coating deposited at 280 °C is about three times greater than that of coatings deposited at the other temperatures. Damage morphologies of samples at different deposition temperatures were observed with a Leica-DMRXE microscope. Microstructures of the samples were characterized by x-ray diffraction (XRD). An absorptance-dominated model is proposed, which agrees very well with the damage threshold results.
The Laser-induced damage behavior of single-Crystalline Silicon was investigated with a Nd:YAG laser at 1064nm under single-pulse mode and free-running mode. It was found that the damage behavior of the SCS showed strong dependence on the output mode of the incident laser. From the experimental and theoretical analysis, the damage mechanism under the two laser modes were given based on thermal and thermal-stress coupling models.
Zirconium oxide films were prepared with and without ion beam assisted deposition (IBAD) by an electron beam. The effects of Ar-ion bombardment on the optical inhomogeneity of ZrO<sub>2</sub> films deposited at room temperature were investigated. The results show that all samples are amorphous, and the refractive index of sample A without IBAD randomly changed with the film thickness, while the relative inhomogeneity of samples B, C, D with IBAD nearly zero. It was found that the energy of depositing molecule or atom had an important effect on the optical inhomogeneity of films, and the optical inhomogeneity of amorphous ZrO2 films could be improved by IBAD.
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.
Laser-induced damage threshold (LIDT) of 355nm was a more severe problem than that of 1064nm. This work had been carried out to obtain high LIDT and high reflectance for Al<sub>2</sub>O<sub>3</sub>/MgF<sub>2</sub> quarter wave multilayer stacks (35 layers). All the samples were deposited by electron beam evaporation using the same deposition process at different deposition temperatures. LIDT was measured by using a 355 nm Nd:YAG pulsed laser with a pulse width of 8 ns. It was found that deposition temperature had a fundamental effect on the thresholds of HR coatings. LIDT up to 18.5J/cm<sup>2</sup> was achieved when the deposition temperature was 280°C. Transmittance and high reflectance of the samples were measured by Lambda 900 Spectrophotometer and the high reflectance of 98.7% was achieved. An absorption dominated model was proposed which met the results of damage thresholds.
ZrO<sub>2</sub> thin films were deposited using an electron beam evaporation technique on two kinds of LiB<sub>3</sub>O<sub>5</sub> (LBO) substrates having the surfaces prepared by cutting at specified crystalline orientations. The results tested by the spectrophotometer indicated that all films had optical anisotropy, which was attributed to the film microstructure with preferred orientation from GXRD (grazing X-ray diffraction) analysis. The film microstructure difference deposited on LBO substrates with different crystalline orientation resulted in film refractive index change, namely, the ZrO<sub>2</sub> thin film with the <b>m</b>-(-212) preferred orientation had lower refractive index than that with the <b>o</b>-(130) preferred orientation.