Preparation of high laser induced damage threshold antireflection film using interrupted ion assisted deposition

Single layers and antireflection films were deposited by electron beam evaporation, ion assisted deposition and interrupted ion assisted deposition, respectively. Antireflection film of quite high laser damage threshold (18J/cm(2)) deposited by interrupted ion assisted deposition were got. The electric field distribution, weak absorption, and residual stress of films and their relations to damage threshold were investigated. It was shown that the laser induced damage threshold of film was the result of competition of disadvantages and advantages, and interrupted ion assisted deposition was one of the valuable methods for preparing high laser induced damage threshold films. (c) 2007 Optical Society of America

Effect of SiO2 protective layer on the femtosecond laser-induced damage of HfO2/SiO2 multilayer high-reflective coatings

Two kinds of HfO2/SiO2 800 nm high-reflective (HR) coatings, with and without SiO2 protective layer were deposited by electron beam evaporation. Laser-induced damage thresholds (LIDT) were measured for all samples with femtosecond laser pulses. The surface morphologies and the depth information of all samples were observed by Leica optical microscopy and WYKO surface profiler, respectively. It is found that SiO2 protective layer had no positive effect on improving the LIDT of HR coating. A simple model including the conduction band electron production via multiphoton ionization and impact ionization is used to explain this phenomenon. Theoretical calculations show that the damage occurs first in the SiO2 protective layer for HfO2/SiO2 HR coating with SiO2 protective layer. The relation of LIDT for two kinds of HfO2/SiO2 HR coatings in calculation agrees with the experiment result. (c) 2006 Elsevier B.V. All rights reserved.

Effects of annealing on laser-induced damage threshold of TiO2/SiO2 high reflectors

The mechanism of improving 1064 nm, 12 ns laser-induced damage threshold (LIDT) of TiO2/SiO2 high reflectors (HR) prepared by electronic beam evaporation from 5.1 to 13.1 J/cm(2) by thermal annealing is discussed. Through optical properties, structure and chemical composition analysis, it is found that the reduced atomic non-stoichiometric defects are the main reason of absorption decrease and LIDT rise after annealing. A remarkable increase of LIDT is found at 300 degrees C annealing. The refractive index and film inhomogeneity rise, physical thickness decrease, and film stress changes from compress stress to tensile stress due to the structure change during annealing. (c) 2007 Elsevier B.V. All rights reserved.

Avaliação da trealose como crioprotetor natural de células-tronco hematopoiéticas de sangue de cordão umbilical e placentário

O sangue do cordão umbilical e placentário (SCUP) tem sido usado como fonte de células-tronco hematopoiéticas (CTH) para reconstituir a função medular (hematopoiese). A maioria das vezes, esta modalidade de transplante requer a criopreservação das CTH, que permanecem congeladas até uma possível utilização futura. Na criopreservação de CTH, o reagente químico dimetilsulfóxido (DMSO) tem sido utilizado como um crioprotetor. No entanto, tem sido provado que DMSO tem efeitos tóxicos para o corpo humano. Muitos organismos na natureza possuem uma capacidade de sobreviver ao congelamento e à desidratação acumulando dissacarídeos, como a trealose e sacarose, por isso a trealose, tem sido investigada como um crioprotetor alternativo para diversos tipos celulares. Outro dano muito comum durante o congelamento é a formação de espécie reativas de oxigênio (ERO) que diminui a viabilidade celular, por isso a adição de bioantioxidantes na solução de criopreservação das células é passo muito importante. Este estudo foi dividido em duas fases na primeira foram avaliados os resultados obtidos com a adição de antioxidantes na solução de criopreservação das células de SCUP e na segunda fase avaliou-se a hipótese que a solução de criopreservação contendo trealose intracelular e extracelular melhora a recuperação e a viabilidade das células-tronco do SCUP, após a criopreservação. SCUP foi processado e submetido à criopreservação em soluções contendo na primeira fase: soluções com diferentes concentrações de DMSO (10%, 5% e 2,5%), assim como as combinações de DMSO (5%, 2,5%) com um dos dissacarídeos (60mmol/L) e ácido ascórbico e/ou catalase (10mg/mL); e na segunda fase: soluções contendo diferentes concentrações de DMSO (10% e 2,5%), assim como as combinações de DMSO (2,5%) com trealose intra (a trealose foi introduzida na célula por meio de lipossomas) e extracelular e soluções contendo trealose intra e extracelular sem DMSO, armazenados por duas semanas em N2L, e descongeladas. As células descongeladas foram avaliadas por citometria de fluxo, pelo ensaio metabólico pelo MTT e de unidades formadoras de colônias (UFC). Na primeira fase do estudo, a catalase, melhorou a preservação das células CD34+ e CD123+, a UFC e a viabilidade celular, em comparação com a solução padrão de criopreservação. Já na segunda fase do estudo, após as análises de todos os testes vimos que a solução que continha trealose intra/extracelular e DMSO mostrou uma capacidade de manutenção da viabilidade/integridade celular superior a todas as outras testadas. A solução que continha trealose intra e extracelular sem DMSO, obteve um resultado comparável com seu controle (2,5%DMSO), porém quando avaliamos a solução que continha apenas trealose intracelular não obtivemos resultados satisfatórios. A catalase pode atuar sobre a redução dos níveis ERO na solução de criopreservação das CTH de SCUP, diminuindo os danos por ele causados e a trealose deve estar presente em ambos os lados das células durante o processo de congelamento. Portanto, em testes clínicos futuros, ela poderá ser um potencial crioprotetor das células-tronco de SCUP, podendo substituir totalmente o DMSO da solução de criopreservação, minimizando com os efeitos colaterais provenientes da infusão de produtos criopreservados nos pacientes.

Investigation of damage threshold to TiO2 coatings at different laser wavelength and pulse duration

Laser-induced damages to TiO2 single layers and TiO2/SiO2 high reflectors at laser wavelength of 1064 nm, 800 run, 532 urn, and pulse width of 12 ns, 220 ps, 50 fs, 8 ns are investigated. All films are prepared by electron beam evaporation. The relations among microstructure, chemical composition, optical properties and laser-induced damage threshold (LIDT), have been researched. The dependence of damage mechanism on laser wavelength and pulse width is discussed. It is found that from 1064 nm to 532 nm, LIDT is mainly absorption related, which is determined by film's extinction coefficient and stoichiometric defects. The rapid decrease of LIDT at 800 nm is due to the pulse width factor. TiO2 coatings are mainly thermally by damaged at long pulse (tau >= 220 ps). The damage shows ablation feature at 50 fs. (C) 2007 Elsevier B.V. All rights reserved.

Laser-induced damage of Ti O2 Si O2 high reflector at 1064 nm

A high laser-induced damage threshold (LIDT) TiO2/SiO2 high reflector (HR) at 1064 nm is deposited by e-beam evaporation. The HR is characterized by optical properties, surface, and cross section structure. LIDT is tested at 1064 nm with a 12 ns laser pulse in the one-on-one mode. Raman technique and scanning electron Microscope are used to analyze the laser-induced modification of HR. The possible damage mechanism is discussed. It is found that the LIDT of HR is influenced by the nanometer precursor in the surface, the intrinsic absorption of film material, the compactness of the cross section and surface structure, and the homogeneity of TiO2 layer. Three typical damage morphologies such as flat-bottom pit, delamination, and plasma scald determine well the nanometer defect initiation mechanism. The laser-induced crystallization consists well with the thermal damage nature of HR. (C) 2008 American Institute of Physics.

Influences of CO2 laser annealing on mechanical and laser-induced damage properties of ZrO2 thin films

Zirconium dioxide (ZrO2) thin films were deposited on BK7 glass substrates by the electron beam evaporation method. A continuous wave CO2 laser was used to anneal the ZrO2 thin films to investigate whether beneficial changes could be produced. After annealing at different laser scanning speeds by CO2 laser, weak absorption of the coatings was measured by the surface thermal lensing (STL) technique, and then laser-induced damage threshold (LIDT) was also determined. It was found that the weak absorption decreased first, while the laser scanning speed is below some value, then increased. The LIDT of the ZrO2 coatings decreased greatly when the laser scanning speeds were below some value. A Nomarski microscope was employed to map the damage morphology, and it was found that the damage behavior was defect-initiated both for annealed and as-deposited samples. The influences of post-deposition CO2 laser annealing on the structural and mechanical properties of the films have also been investigated by X-ray diffraction and ZYGO interferometer. It was found that the microstructure of the ZrO2 films did not change. The residual stress in ZrO2 films showed a tendency from tensile to compressive after CO, laser annealing, and the variation quantity of the residual stress increased with decreasing laser scanning speed. The residual stress may be mitigated to some extent at proper treatment parameters. (c) 2007 Elsevier GmbH. All rights reserved.

Mechanism initiated by nanoabsorber for UV nanosecond-pulse-driven damage of dielectric coatings

A model of plasma formation induced by UV nanosecond pulselaser interaction with SiO2 thin film based on nanoabsorber is proposed. The model considers the temperature dependence of band gap. The numerical results show that during the process of nanosecond pulsed-laser interaction with SiO2 thin film, foreign inclusion which absorbs a fraction of incident radiation heats the surrounding host material through heat conduction causing the decrease of the band gap and consequently, the transformation of the initial transparent matrix into an absorptive medium around the inclusion, thus facilitates optical damage. Qualitative comparison with experiments is also provided. (C) 2008 Optical Society of America.

High temperature annealing effect on structure, optical property and laser-induced damage threshold of Ta2O5 films

Ta2O5 films were deposited by conventional electron beam evaporation method and then annealed in air at different temperature from 873 to 1273 K. It was found that the film structure changed from amorphous phase to hexagonal phase when annealed at 1073 K, then transformed to orthorhombic phase after annealed at 1273 K. The transmittance was improved after annealed at 873 K, and it decreased as the annealing temperature increased further. The total integrated scattering (TIS) tests and AFM results showed that both scattering and root mean square (RMS) roughness of films increased with the annealing temperature increasing. X-ray photoelectron spectroscopy (XPS) analysis showed that the film obtained better stoichiometry and the O/Ta ratio increased to 2.50 after annealing. It was found that the laser-induced damage threshold (LIDT) increased to the maximum when annealed at 873 K, while it decreased when the annealing temperature increased further. Detailed damaged models dominated by different parameters during annealing were discussed. (C) 2008 Elsevier B. V. All rights reserved.

Influence of SiO2 additional layers on the laser induced damage threshold of Ta2O5 films

A series or Ta2O5 films with different SiO2 additional layers including overcoat, undercoat and interlayer was prepared by electron beam evaporation under the same deposition process. Absorption of samples was measured using the surface thermal lensing (STL) technique. The electric field distributions of the samples were theoretical predicted using thin film design software (TFCalc). The laser induced damage threshold (LIDT) was assessed using an Nd:YAG laser operating at 1064 nm with a pulse length of 12 ns. It was found that SiO2 additional layers resulted in a slight increase of the absorption, whereas they exerted little influence on the microdefects. The electric field distribution among the samples was unchanged by adding an SiO2 overcoat and undercoat, yet was changed by adding an interlayer. SiO2 undercoat. The interlayer improved the LIDT greatly, whereas the SiO2 overcoat had little effect on the LIDT. (C) 2007 Elsevier Ltd. All rights reserved.

Impact of organic contamination on laser-induced damage threshold of high reflectance coatings in vacuum

The influence of organic contamination in vacuum on the laser-induced damage threshold (LIDT) of coatings is studied. TiO2/SiO2 dielectric mirrors with high reflection at 1064 nm are deposited by the electron beam evaporation method. The LIDTs of mirrors are measured in vacuum and atmosphere, respectively. It is found that the contamination in vacuum is easily attracted to optical surfaces because of the low pressure and becomes the source of damage. LIDTs of mirrors have a little change in vacuum compared with in atmosphere when the organic contamination is wiped off. The results indicate that organic contamination is a significant reason to decrease the LIDT. N-2 molecules in vacuum can reduce the influence of the organic contaminations and prtectect high reflectance coatings. (C) 2008 Elsevier B.V. All rights reserved.

Influence of different substrates on laser induced damage thresholds at 1064 nm of Ta2O5 films

Ta2O5 films are prepared on Si, BK7, fused silica, antireflection (AR) and high reflector (HR) substrates by electron beam evaporation method, respectively. Both the optical property and laser induced damage thresholds (LIDTs) at 1064 nm of Ta2O5 films on different substrates are investigated before and after annealing at 673 K for 12h. It is shown that annealing increases the refractive index and decreases the extinction index, and improves the O/Ta ratio of the Ta2O5 films from 2.42 to 2.50. Moreover, the results show that the LIDTs of the Ta2O5 films are mainly correlated with three parameters: substrate property, substoichiometry defect in the films and impurity defect at the interface between the substrate and the films. Details of the laser induced damage models in different cases are discussed.

Laser induced damage threshold at 355 and 1064 nm of Ta2O5 films of different phases

Ta2O5 films are deposited on fused silica substrates by conventional electron beam evaporation method. By annealing at different temperatures, Ta2O5 films of amorphous, hexagonal and orthorhombic phases are obtained and confirmed by x-ray diffractometer ( XRD) results. X-ray photoelectron spectroscopy ( XPS) analysis shows that chemical composition of all the films is stoichiometry. It is found that the amorphous Ta2O5 film achieves the highest laser induced damage threshold ( LIDT) either at 355 or 1064 nm, followed by hexagonal phase and finally orthorhombic phase. The damage morphologies at 355 and 1064 nm are different as the former shows a uniform fused area while the latter is centred on one or more defect points, which is induced by different damage mechanisms. The decrease of the LIDT at 1064nm is attributed to the increasing structural defect, while at 355nm is due to the combination effect of the increasing structural defect and decreasing band gap energy.

Influence of oxygen post-treatment on laser-induced damage of antireflection coatings prepared by electron-beam evaporation and ion beam assisted deposition

Antireflection coatings at the center wavelength of 1053 nm were prepared on BK7 glasses by electron-beam evaporation deposition (EBD) and ion beam assisted deposition (IBAD). Parts of the two kinds of samples were post-treated with oxygen plasma at the environment temperature after deposition. Absorption at 1064 nm was characterized based on surface thermal lensing (STL) technique. The laser-induced damage threshold (LIDT) was measured by a 1064-nm Nd:YAG laser with a pulse width of 38 ps. Leica-DMRXE Microscope was applied to gain damage morphologies of samples. The results revealed that oxygen post-treatment could lower the absorption and increase the damage thresholds for both kinds of as-grown samples. However, the improving effects are not the same. (c) 2008 Elsevier B.V. All rights reserved.