Role of interface absorption in laser-induced local heating of optical coatings

Considering the interface absorption in optical coatings, we propose a model to simulate interface absorption. Calculations are made and the temperature field of several kinds of thin film multilayers, including those of partial reflectivity, high-reflectivity, and antireflectivity coatings are analyzed. The interface absorption is found to greatly influence the temperature distribution within multilayer coatings and to weaken the laser damage resistance of the samples. The real-time results of the photothermal deflection technique for laser induced damage to samples supports the model. (C) 1997 Society of Photo-Optical Instrumentation Engineers.

Laser-induced damage threshold of the antireflection coatings on quartz and sapphire under different laser modes

The laser-induced damage threshold (LIDT) and damage morphology of antireflection (AR) coatings on quartz and sapphire are investigated. A very interesting phenomena is found in the measurement. In the case of a single pulse laser, the LIDT of the AIR coatings on quartz is higher than that of sapphire. On the contrary, for a free-pulse laser, the LIDT of AIR coatings on sapphire is higher than that of quartz. (C) 2004 Society of Photo-Optical Instrumentation Engineers.

Microstructure and laser-induced damage threshold of ZrO2 coatings dependence on annealing temperature

ZrO2 coatings were deposited on different substrates of Yb:YAG and fused silica by electron beam evaporation. After annealed for 12 h at 673 and 1073 K, respectively, weak absorption of coatings was measured by surface thermal lensing (STL) technique, and then laser-induced damage threshold (LIDT) was determined also. The crystalline phase of ZrO2 coatings and the size of the crystal grain were investigated by X-ray diffraction. It was found that microstructure of ZrO2 coatings was dependent on both annealing temperature and substrate structure, and coatings containing monoclinic phases had higher damage threshold than others. Due to the strong absorption of Yb:YAG, damage threshold of coatings on Yb:YAG was much less than that on fused silica. (C) 2004 Elsevier B.V. All rights reserved.

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. (C) 2005 American Vacuum Society.

Investigation of laser-induced damage on multi-layer dielectric gratings

We investigate mechanisms of laser induced damage thresholds (LIDTs) of multi-layer dielectric gratings (AIDG,). It is found that the laser damage thresholds of MDGs and unstructured dielectric multi-layer coatings (the substrate of MDG) are 3.15J/cm(2) and 9.32 J/cm(2), respectively, at 1064nm (12ns) with the Littrow angle 51.2 degrees and the TEM00 mode. The laser-induced damage mechanism of multi-layer dielectric is presented with the analysis of the following factors: The dominant factor is the pollution on the corrugated surface, which is induced by the complex manufacture process of multi-layer dielectric gratings; another is the electric field distribution along the corrugated surface. The third reason is due to the reduction in stoichiometry of oxide films, resulting from the manufacture process of etching.

Laser induced damage of multi-layer dielectric used in pulse compressor gratings

Laser induced damage threshold (LIDT) of multi-layer dielectric used in pulse compressor gratings (PCG) was investigated. The sample was prepared by e-beam evaporation (EBE). LIDT was detected following ISO standard 11254-1.2. It was found that LIDTs of normal and 51.2 deg. incidence (transverse electric (TE) mode) were 14.14 and 9.31 J/cm2, respectively. A Nomarski microscope was employed to map the damage morphology, and it was found that the damage behavior was pit-concave-plat structure for normal incidence, while it was pit structure for 51.2 deg. incidence with TE mode. The electric field distribution was calculated to illuminate the difference of LIDT between the two incident cases.

Laser-induced damage morphology of high-reflective optical coatings

Two different kinds of 1064 nm high-reflective (HR) coatings, with and without SiO2 protective layer, were prepared by electron beam evaporation. Three-dimensional damage morphology, caused by a Nd:YAG pulsed laser, was investigated for these HR coatings. Development of laser-induced damage on HR coatings was revealed by both temperature field calculation and discrete meso-element simulation. Theoretical results met experimental very well. (C) 2004 Elsevier B.V. All rights reserved.

Influence of negative ion element impurities on laser induced damage threshold of HfO2 thin film

Negative ion element impurities breakdown model in HfO2 thin film was reported in this paper. The content of negative ion elements were detected by glow discharge mass spectrum analysis (GDMS); HfO2 thin films were deposited by the electron-beam evaporation method. The weak absorption and laser induced damage threshold (LIDT) of HfO2 thin films were measured to testify the negative ion element impurity breakdown model. It was found that the LIDT would decrease and the absorption would increase with increasing the content of negative ion element. These results indicated that negative ion elements were harmful impurities and would speed up the damage of thin film. (c) 2006 Elsevier B.V. All rights reserved.

Stress, absorptance and laser-induced damage threshold properties of 355-nm HR coatings

A number of 355-nm Al2O3/MgF2 high-reflectance (HR) coatings were prepared by electron-beam evaporation. The influences of the number of coating layers and deposition temperature on the 355-nm Al2O3/MgF2 HR coatings were investigated. The stress was measured by viewing the substrate deformation before and after coating deposition using an optical interferometer. The laser-induced damage threshold (LIDT) of the samples was measured by a 355-nm Nd:YAG laser with a pulse width of 8 ns. Transmittance and reflectance of the samples were measured by a Lambda 900 spectrometer. It was found that absorptance was the main reason to result in a low LIDT of 355-nm Al2O3/MgF2 HR coatings. The stress in Al2O3/MgF2 HR coatings played an unimportant role in the LIDT, although MgF2 is known to have high tensile stress.

Optical, structural and laser-induced damage threshold properties of HfO2 thin films prepared by electron beam evaporation

We prepare HfO2 thin films by electron beam evaporation technology. The samples are annealed in air after deposition. With increasing annealing temperature, it is found that the absorption of the samples decreases firstly and then increases. Also, the laser-induced damage threshold (LIDT) increases firstly and then decreases. When annealing temperature is 473K, the sample has the highest LIDT of 2.17J/cm(2), and the lowest absorption of 18 ppm. By investigating the optical and structural characteristics and their relations to LIDT, it is shown that the principal factor dominating the LIDT is absorption.

Overcoat dependence of laser-induced damage threshold of 355 nm HR coatings

A series of HR coatings, with and without overcoat, were prepared by electron beam evaporation using the same deposition process. The laser-induced damage threshold (LIDT) was measured by a 355 nm Nd:YAG laser with a pulse width of 8 ns. Damage morphologies of samples were observed by Leica-DMRXE Microscope. The stress was measured by viewing the substrate deformation before and after coatings deposition using an optical interferometer. Reflectance of the samples was measured by Lambda 900 Spectrometer. The theoretical results of electric field distributions of the samples were calculate by thin film design software (TFCalc). It was found that SiO2 overcoat had improved the LIDT greatly, while MgF2 overcoat had little effect on the LIDT because of its high stress in the HR coatings. The damage morphologies were different among HR coatings with and without overcoats. (c) 2005 Elsevier B.V. All rights reserved.

Y2O3 stabilized ZrO2 thin films deposited by electron beam evaporation: Structural, morphological characterization and laser induced damage threshold

Four kinds of Y2O3 stabilized ZrO2 (YSZ) thin films with different Y2O3 content have been prepared on BK7 substrates by electron-beam evaporation method. Structural properties and surface morphology of thin films were investigated by X-ray diffraction (XRD) spectra and scanning probe microscope. Laser induced damage threshold (LIDT) was determined. It was found that crystalline phase and microstructure of YSZ thin films was dependent on Y2O3 molar content. YSZ thin films changed from monoclinic phase to high temperature phase (tetragonal and cubic) with the increase of Y2O3 content. The LIDT of stabilized thin film is more than that of unstabilized thin films. The reason is that ZrO2 material undergoes phase transition during the course of e-beam evaporation resulting in more numbers of defects compared to that of YSZ thin films. These defects act as absorptive center and the original breakdown points. (c) 2006 Elsevier B.V. All rights reserved.

Development in laser induced extrinsic absorption damage mechanism of dielectric films

Absorption of host and the temperature-dependence of absorption coefficient have been considered in evaluating temperatures distribution in films, when laser pulse irradiates on films. Absorption of dielectric materials experience three stages with the increase of temperature: multi-photon absorption; single photon absorption; metallic absorption. These different absorption mechanisms correspond to different band gap energies of materials, which will decrease when the temperature of materials increases. evaluating results indicate that absorption of host increases rapidly when the laser pulse will be over. If absorption of host and the temperature-dependence of absorption are considered, the material temperatures in films will be increased by a factor of four.

Laser-induced damage of Ta2O5/S1O2 narrow-band interference filters under different 1064 nm Nd : YAG laser modes

The laser-induced damage (LID) behavior of narrow-band interference filters was investigated with a Nd:YAG laser at 1064 nm under single-pulse mode and free-running mode. The absorption measurement of such coatings was performed with surface thermal lensing (STL) technique. The damage morphologies under the two different laser modes were also studied in detail. It was found that all the filters exhibited a pass-band-center-dependent absorption and laser-induced damage threshold (LIDT) behavior, but the damage morphologies were diverse. The explanation was given with the analysis of the electric field distribution and the operational behavior of the irradiation laser. (c) 2005 Elsevier B.V. All rights reserved.

High laser-induced damage threshold HfO2 films prepared by ion-assisted electron beam evaporation

HfO2 films were deposited by electron beam evaporation with different deposition parameters. The properties such as refractive index, weak absorption, and laser induced damage thresholds (LIDTs) of these films have been investigated. It was found that when pulsed Nd:YAG 1064 nm laser is used to investigate LIDT of films: Metallic character is the main factor that influences LIDTs of films obtained from Hf starting material by ion-assisted reaction, and films prepared with higher momentum transfer parameter P have fewer metallic character; The ion-assisted reaction parameters are key points for preparing high LIDT films and if the parameters are chose properly, high LIDT films can be obtained. (c) 2004 Elsevier B.V. All rights reserved.