Annealing effects on residual stress of HfO_2/SiO_2 multilayers

HfO_2/SiO_2 multilayer films were deposited on BK7 glass substrates by electron beam evaporation method. The effects of annealing at the temperature between 200 and 400℃on residual stresses have been studied. It is found that the residual stress of as-deposited HfO_2/SiO_2 multilayers is compressive.It becomes tensile after annealing at 200℃,and then the value of tensile stress increases as annealing temperature increases. And cracks appear in the film because tensile stress is too large when the sample is annealed at 400℃. At the same time,the crystallite size increases and interplanar distance decreases with the increase of annealing temperature.The variation of residual stresses is corresponding with the evolution of structures.     

Study on absorbance and laser damage threshold of HfO_2 films prepared by ion-assisted reaction deposition

Using a new kind of EH1000 ion source, hafnium dioxide (HfO2) films are deposited with different deposition techniques and different conditions. The absorbance and the laser damage threshold of these films have been measured and studied. By comparing these characteristics, one can conclude that under right conditions, such as high partial pressure of oxygen and right kind of ion source, the ion-assisted reaction deposition can prepare HfO2 films with higher laser induced damage threshold.     

Study on the laser treatment of electroless Ni-P-SiC composite coatings

Effect of the laser treatment on electroless Ni-P-SiC composite coatings was investigated. The microscopic structure, surface morphology, ingredient, and performance of the Ni-P-SiC composite coatings were synthetically analyzed by the use of X-ray diffraction apparatus, scanning electron microscope, energy distribution spectrometer, micro-hardness tester, wear tester and so on. It was found that the composite coatings did make crystalloblastic transformation after laser heating. Structural analysis confirmed that some new types of phase Ni2Si or Ni3Si compound would emerge in the Ni-P-SiC coatings after laser treatment. The micro-hardness measurement results showed that when the laser power was 450 W with scanning speed of 0.5 m/min, the hardness of the coating was superior to the coating obtained by the conventional furnace heating, and wear resistance of the composite coating after laser treating could also improve.     

Laser-induced damage threshold in HfO_2/SiO_2 multilayer films irradiated by β-ray

Post-processing can effectively improve the resistance to laser damage in multilayer films used in a high power laser system. In this work, HfO_2/SiO_2 multilayer films are prepared by e-beam evaporation and then β-ray irradiation is employed as the post-processing method. The particle irradiation affects the laser induced damage threshold(LIDT),which includes defects, surface roughness, packing density and residual stress. The residual stress that is relaxed during irradiation changes from compressive stress into tensile stress. Our results indicate that appropriate tensile stress can improve LIDT remarkably. In view of the fact that LIDT rises from 8 J/cm~2 to 12 J/cm~2, i.e., 50% increase, after the film has been irradiated by 2.2×10~(13)/cm~2 β-ray, the particle irradiation can be used as a controllable and desirable postprocessing method to improve the resistance to laser induced damage.     

Effect of antireflection coatings on the peak wavelength of output spectrum from end facet of a semiconductor laser

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Effect of the laser fluence on the surface characterization of β-FeSi2 films prepared by pulsed laser deposition

Single-phase β-FeSi₂ films on silicon (1 0 0) were fabricated by pulse laser deposition. The structure and crystal quality of the samples were characterized by X-ray diffraction and Fourier transform infrared spectroscopy. The field scanning electron microscopy showed that the film thickness increases with the increasing of the laser fluence. Moreover, atomic force microscopy observations revealed the changes of surface properties with different laser fluence. Based upon all experimental results, it is found that 7 J/cm² is the most favorable for the formation of β-FeSi₂ thin films.     

0.532-μm laser conditioning of HfO_2/SiO_2 third harmonic separator fabricated by electron-beam evaporation

The 0.532-μm laser conditioning of HfO_2/SiO_2 third harmonic separator fabricated by electron-beam evaporation (EBE) was studied.The laser induced damage threshold (LIDT) of the separator determined by 1-on-1 test is 9.1 J/cm~2 and it is 15.2 J/cm~2 after laser conditioning determined by raster scanning. Two kinds of damage morphologies,taper pits and flat bottom pits,are found on the sample surface and they show different damage behaviors.The damage onset of taper pits does not change obviously and the laser conditioning effect is contributed to the flat bottom pits,which limits the application of laser conditioning.     

Enhanced laser induced damage threshold of dielectric antireflection coatings by the introduction of one interfacial layer

A new method for increasing laser induced damage threshold(LIDT)of dielectric antireflection(AR) coating is proposed.Compared with AR film stack of H2.5L(H:HfO_2,L:SiO_2)on BK7 substrate,SiO_2 interfacial layer with four quarter wavelength optical thickness(QWOT)is deposited on the substrate before the preparation of H2.5L film.It is found that the introduction of SiO_2 interfacial layer with a certain thickness is effective and flexible to increase the LIDT of dielectric AR coatings.The measured LIDT is enhanced by about 50%,while remaining the low reflectivity with less than 0.09% at the center wavelength of 1064 nm.Detailed mechanisms of the LIDT enhancement are discussed.     

Influence of coating material on laser damage threshold of TiO_2 films

The optical property,structure,surface properties(roughness and defect density)and laser-induced dam- age threshold(LIDT)of TiO_2 films deposited by electronic beam(EB)evaporation of TiO_2(rutile),TiO_2 (anatase)and TiO_2 Ta_2O_5 composite materials are comparatively studied.All films show the polycrys- talline anatase TiO_2 structure.The loose sintering state and phase transformation during evaporating TiO_2 anatase slice lead to the high surface defect density,roughness and extinction coefficient,and low LIDT of films.The TiO_2 Ta_2O_5 composite films have the lowest extinction coefficient and the highest LIDT among all samples investigated.Guidance of selecting materials for high LIDT laser mirrors is given.     

Effect of biocidal additives on the mesostructure of epoxy–siloxane bioactive coatings

We investigate the structure formation of sol–gel synthesized epoxy–siloxane compositions with a ratio of the main precursors of R _{TEOS/EPONEX 1510} = 27/27 wt %, modified with biocidal additives of detonation nanodiamonds (c _DND = 0.13, 0.27, and 0.58 wt %), titanium dioxide (\(^cTi{O_2}\) = 0.1, 0.3, and 0.5 wt %), and Photosens (c _Ph = 0.04, 0.1, and 0.27 wt %), by small-angle X-ray scattering. Based on small-angle X-ray scattering (SAXS) data, it is revealed that the synthesized epoxy–siloxane xerogels are systems with a twolevel fractal structure, in the formation of which the siloxane component plays the dominant role. It is found that the introduction of small additions of detonation synthesis, titanium dioxide, or Photosens (less than 1 wt %) into the epoxy–siloxane compositions affects both the fractal dimension D _S of the surface and the size d _c1 of primary particles, and the fractal dimension D _M and sizes d _c2 of mass fractal clusters formed from them.     

Impact of organic contamination in vacuum on laser-induced damage threshold of TiO_2/SiO_2 dielectric mirrors

The influence of organic contamination in vacuum on the laser-induced damage threshold (LIDT) of coatings is studied.TiO_2/SiO_2 dielectric mirrors with high reflection at 1064 nm are deposited by the electronbeam evaporation method and their LIDTs 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,O_2 molecules in vacuum with contamination can accelerate the laser-induced damage by observing LIDT and damage morphologies.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 in vacuum.     

Influences of SiO_2 protective layers and annealing on the laser-induced damage threshold of Ta_2O_5 films

Ta_2O_5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO_2 protective layers and annealing on the laser-induced damage threshold(LIDT)of the films are investigated.The results show that SiO_2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly. Annealing is effective on decreasing the microdefect density and the absorption of the films.Both SiO_2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta_2O_5 films is achieved by the combination of SiO_2 protective layers and annealing.     

Effect of Fe impurity on the optical loss of Nd-doped phosphate laser glass

The optical loss coefficient at 1053-nm wavelength, influenced by Fe ions in N31-type Nd-doped phosphate laser glass, was determined precisely and analyzed in detail. It is found that the optical loss coefficient per unit of Fe concentration (cm-1/ppmw) increases with Fe concentration in the range of 0-300 ppmw, but it approaches a constant as the Fe concentration is larger than 300 ppmw. Such a concentration effect is due to a shift in the redox equilibrium between Fe3+ and Fe2+ ions in the glass. The effect of oxygen pressure, temperature, and variable valence states of other metal ions in glass samples on the optical loss is also discussed.     

Effect of speckle pattern on laser Doppler velocimeters

The effect of speckle pattern on laser Doppler velocimeters is studied theoretically and experimentally. We have found that dynamic speckle patterns can cause error in velocity measurement. Increasing sampling time and using proper signal processing circuits can eliminate this bad effect caused by speckle pattern. The accuracy of velocity measurement is better than 2.1% in a wide velocity range (4.66-468.86 mm/s) when speckle effects are taken into account.     

SiO_2半波覆盖层对HfO_2/SiO_2高反射膜激光损伤的影响

研究了 Si O2 半波覆盖层对 Hf O2 /Si O2 高反射膜 1 0 64nm激光损伤的影响 ,分析薄膜的激光损伤特性及图貌得出 ,对于单脉冲 ( 1 -ON-1 )激光损伤 ,Si O2 半波覆盖层能提高 Hf O2 /Si O2 高反射膜的激光损伤阈值 ;可显著降低激光损伤程度 ,减小灾难性损伤发生的概率 ;可大幅度提高 Hf O2 /Si O2 高反射膜的抗激光损伤能力     

Influence of purity of HfO_2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO_2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO_2 was the main impurity in the two kinds of HfO_2 either in the original HfO_2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO_2 single layer films was much larger than that of the other impurities such as Ti and Fe,which showed that it was just ZrO_2 that made the difference between the optical performance of the film products including the two kinds of HfO_2.With these two kinds of HfO_2 and the same kind of SiO_2,we deposited HfO_2/SiO_2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively, which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

等离子体辅助沉积HfO_2/SiO_2减反、高反光学薄膜

本文报导了用等离子体辅助（Ｐｌａｓｍａ－ＩＡＤ）沉积技术沉积ＨｆＯ２／ＳｉＯ２减反及高反光学薄膜。在波长１０６４ｎｍ处，ＨｆＯ２／ＳｉＯ２减反膜透过率大于９９．５％，ＨｆＯ２／ＳｉＯ２高反膜反射率大于９９．５％。     

HfO_2/SiO_2高反射膜的缺陷及其激光损伤

用原子力、Normaski和扫描电子显微镜等分析仪器 ,对高损伤阈值薄膜常采用的 Hf O2 /Si O2 薄膜进行了表面显微图象研究 ,分析了薄膜常见的表面缺陷 ,如节瘤 ,孔洞和划痕等。薄膜表面缺陷的激光损伤实验表明 ,不同缺陷的抗激光损伤能力大不相同 ,节瘤缺陷最低 ,约为 1 5 J/ cm2 ,薄膜的损伤阈值主要由其决定 ,孔洞的激光损伤能力与节瘤相比较高 ,约为节瘤的 2～ 3倍。节瘤缺陷在低能量密度的激光损伤所形成的孔洞 ,与镀制过程中形成的孔洞形貌相似 ,激光再损伤能力也相似。低能量密度的激光把节瘤缺陷变为孔洞缺陷是激光预处理提高薄膜损伤阈值的原因之一     

Effects of water vapor in high vacuum chamber on the properties of HfO_2 films

The influence of water vapor content in high vacuum chamber during the coating process on physical properties of HfO_2 films was investigated.Coatings were deposited on BK7 substrates by electron beam evaporation and photoelectric maximum control method.An in situ residual gas analyzer(RGA)was used to monitor the residual gas composition in the vacuum chamber.The optical properties,microstructure, absorption and laser-induced damage threshold(LIDT)of the samples were characterized by Lambda 900 spectrophotometer,X-ray diffraction(XRD),surface thermal lensing(STL)technique and 1064-nm Q- switched pulsed laser at a pulse duration of 12 ns respectively.It was found that a cold trap is an effective equipment to suppress water vapor in the vacuum chamber during the pumping process,and the coatings deposited in the vacuum atmosphere with relatively low water vapor composition show higher refractive index and smaller grain size.Meanwhile,the higher LIDT value is corresponding to lower absorbance.     

Influence of porosity on laser damage threshold of sol–gel ZrO2 and SiO2 monolayer films

Monolayer ZrO₂ sol–gel and physical vapor deposition (PVD) films were prepared by spin method and electron beam evaporation method, respectively. Monolayer sol–gel SiO₂ films were prepared with the dip-coating method from acid and base catalyzed SiO₂ sols, respectively. Some of the SiO₂ base films were subsequently treated in saturated ammonia gas for 20 h. The laser induced damage threshold (LIDT) of each film was measured. Properties of the films were analyzed by using Stanford photo-thermal solutions (SPTSs), ellipsometer, atomic force microscopy (AFM) and optical microscopy. The experimental results showed that porous ratio is an essential factor to decide the LIDT for sol–gel films, which benefits the pressure exerted on the film or substrate by the moving particle to dissipate. The films with lower thermal absorption and higher porous ratio have higher LIDT.