Imaging photothermal microscopy for absorption measurements of optical coatings

For absorption measurement of large-aperture optical coatings, a novel method of imaging photothermal microscopy based on image lock-in technique is presented. Detailed theoretical analysis and numerical calculation are made based on the image photothermal technique. The feasibility of this imaging method is proved through the coincidence between the theoretical results of single spot method and multi-channel method. The measuring speed of this imaging method can be increased hundreds of times compared with that of the raster scanning. This technique can expand the applications of photothermal technique.     

Rugate filters prepared by rapidly alternating deposition

A methodology for the fabrication of composite (Nb₂O₅)_1-x(SiO₂)_x thin-film rugate filters by using pulsed direct current magnetron sputtering is presented. The two materials are mixed using rapidly alternating deposition technology. The optical properties of the composite films varying with the composition of the material are studied in detail. Refractive indices between 1.50 and 2.14 can be realized in our coating system. Two designed rugate filters with a reflection band at the wavelength of 532 nm are fabricated using an automatic deposition process. The microstructure of the rugate filter is investigated by using scanning electron microscopy. The calculated and the measured transmittance spectra are in good agreement with each other. The causes of the slight differences between them are also analysed.     

基于Berreman矩阵的双折射薄膜光谱响应特性计算

采用Berreman特征矩阵方法,通过数值计算研究了双折射薄膜的反射、透射等光谱响应特性。依据电磁场理论的电场分量、磁场分量的界面连续条件,推导了光波在各向异性双轴薄膜中的Berreman转移矩阵,用以分析含有各向异性介质层的复杂薄膜系统的光学性质。这些矩阵递推关系包含了界面处的多点反射,适用于一般的各向异性的多层膜系统,包括入射媒质或基底为各向异性的情况。在文中给出了各向同性入射媒质双轴各向异性膜层一各向同性基底薄膜系统的计算结果,验证了该计算方法的可行性,以此作为进一步研究各向异性薄膜和相关光学薄膜器件设计的理论基础。     

ZnO薄膜的光学性质研究

采用直流反应磁控溅射方法在玻璃基底上成功地淀积ｃ轴取向性好的ＺｎＯ薄膜。经过优化计算，获得并分析了不同氧分压下制备的ＺｎＯ薄膜的折射率ｎ和消光系数ｋ的数值；同时得到了吸收光学带隙Ｅｏｐｔ，用能带模型解释了Ｅｏｐｔ的变化规律。     

杂质银对氧化锌薄膜气敏光学特性的影响

用反应式射频磁控溅射方法制备了纯氧化锌（ＺｎＯ）薄膜和掺Ａｇ的ＺｎＯ气敏光学传感薄膜。测量了这些薄膜在ＮＯｘ气体中的透射光谱，然后由透射光谱获得了灵敏度的变化规律，发现掺Ａｇ后的ＺｎＯ薄膜对ＮＯｘ气体的灵敏度高于纯ＺｎＯ薄膜，用俄歇电子能谱（ＡＥＳ）测试了这些薄膜的组分，发现当掺Ａｇ量为５％时灵敏度最高，并结合朗缪尔（Ｌａｎｇｍｕｉｒ）型吸附平衡关系式解释了这些现象，理论和实验结果能很好的相符。     

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.     

Effect of standing-wave field distribution on femosecond laser-induced damage of HfO_2/SiO_2 mirror coating

Single-pulse and multi-pulse damage behaviors of "standard"(with λ/4 stack structure) and "modified"(with reduced standing-wave field) HfO2/SiO2 mirror coatings are investigated using a commercial 50-fs,800-nm Ti:sapphire laser system.Precise morphologies of damaged sites display strikingly different features when the samples are subjected to various number of incident pulses,which are explained reasonably by the standing-wave field distribution within the coatings.Meanwhile,the single-pulse laser-induced damage threshold of the "standard" mirror is improved by about 14% while suppressing the normalized electric field intensity at the outmost interface of the HfO2 and SiO2 layers by 37%.To discuss the damage mechanism,a theoretical model based on photoionization,avalanche ionization,and decays of electrons is adopted to simulate the evolution curves of the conduction-band electron density during pulse duration.     

Influence of Ytterbia Content on Residual Stress and Microstructure of Y2O3--ZrO2 Thin Films Prepared by EB-PVD

Y2O3 stabilized ZrO2 （YSZ） thin films with different Y2O3 molar contents （0, 3, 7, and 12 mol%） are deposited on BK7 substrates by electron-beam evaporation technique. The effects of different Y2O3 contents on residual stresses and structures of YSZ thin films are studied. Residual stresses are investigated by means of two different techniques： the curvature measurement and x-ray diffraction method. It is found that the evolution of residual stresses of YSZ thin films by the two different methods is consistent. Residual stresses of films transform from compressive stress into tensile stress and the tensile stress increases monotonically with the increase of Y2O3 content. At the same time, the structures of these films change from the mixture of amorphous and monoclinic phases into high temperature cubic phase. The variations of residual stress correspond to the evolution of structures induced by adding of Y2O3 content.     

超声清洗与激光预处理对减反膜阈值的影响

 研究了超声清洗和激光预处理两种后处理手段对减反膜的损伤特性的影响。采用电子束蒸发技术制备了1 064 nm减反膜,利用超声清洗及激光预处理的方法分别对样品进行处理,并对处理前后的样品分别进行激光损伤阈值测试及破斑深度测量。结果表明：处理后减反膜的损伤阈值均有所提升,但激光预处理的阈值增强效果更加明显;超声清洗前后的破斑深度没有大的变化,而激光预处理后的破斑深度比处理前浅得多;原因在于超声清洗只能去除表面杂质,激光预处理可减少和抑制膜层内较深处的缺陷。