Meiqiong Zhan

Influence of deposition temperature on the properties of high-reflectivity 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 us- ing 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 high- est 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/cm 2 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.

Temperature dependence of laser-induced damage threshold of 355-nm Al 2 O 3 /MgF 2 HR coatings

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 Al2O3/MgF2 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/cm2 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.

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.

Laser-induced damage of single-crystalline silicon under different 1064-nm Nd:YAG laser modes

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.

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.

ZrO2 thin films deposited on various LiB3O5 substrates by electron beam evaporation

ZrO2 thin films were deposited using an electron beam evaporation technique on two kinds of LiB3O5 (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 ZrO2 thin film with the m-(-212) preferred orientation had lower refractive index than that with the o-(130) preferred orientation.