Influences of SiO2 laser-induced protective layers and damage threshold of annealing on the Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition. The effects of SiO2 protective layers and annealing on the laser-induced damage threshold （LIDT） of the films are investigated. The results show that SiO2 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 SiO2 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 Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

多层介质膜脉冲宽度压缩光栅与超短脉冲作用时的性能分析

基于啁啾脉冲放大技术的超短脉冲激光系统是提供超快、超强激光的重要途径，具有良好输出波形和高损伤阈值的多层介质膜脉冲宽度压缩光栅是获得高峰值功率脉冲激光的关键. 基于傅里叶谱变换方法和严格模式理论，分析了多层介质膜光栅(MDG)在超短脉冲作用下的光学特性. 结果表明，当MDG的反射带宽小于具有高斯分布的入射脉冲的频谱宽度时，-1级反射脉冲呈非对称高斯分布，其前沿出现振荡，并且-1级反射脉冲能量开始剧烈下降. 讨论了MDG结构参数对其反射带宽的影响. 分析了MDG与超短脉冲作用时的近场光分布，对提高其抗激光损 关键词： 脉冲压缩光栅 傅里叶谱变换 模式理论 损伤阈值     

Surface relief resonant Brewster filters with multiple channels

In this paper, a new type of resonant Brewster filters （RBF） with surface relief structure for the multiple channels is first presented by using the rigorous coupled-wave analysis and the S-matrix method. By tuning the depth of homogeneous layer which is under the surface relief structure, the multiple channels phenomenon is obtained. Long range, extremely low sidebands and multiple channels are found when the RBF with surface relief structure is illuminated with Transverse Magnetic incident polarization light near the Brewster angle calculated with the effective media theory of sub wavelength grating. Moreover, the wavelengths of RBF with surface relief structure can be easily shifted by changing the depth of homogeneous layer while its optical properties such as low sideband reflection and narrow band are not spoiled when the depth is changed. Furthermore, the variation of the grating thickness does not effectively change the resonant wavelength of RBF, but have a remarkable effect on its line width, which is very useful for designing such filters with different line widths at desired wavelength.     

Influence of Different Substrates on Laser Induced Damage Thresholds at 1064nm 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 12 h. 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.     

反射型导模共振滤波器设计

导模共振滤波器由于其高峰值反射率,低旁带反射,窄带以及带宽可控等优良特性引起了人们极大的关注,采用亚波长光栅的导模共振效应可以实现传统基于高低折射率介质的多层膜滤波器所无法实现的特殊功能,在弱调制模式下,其共振带宽可以被压缩到零点几纳米,但是由于介质表面和空气层的菲涅耳反射,使得偏离或者远离共振区时的反射率偏高,根据等效介质理论,亚波长光栅在远离共振区可以被看为均匀的薄膜,本文通过对导模共振光栅进行单层、双层以及三层抗反射设计,有效的降低了导模共振光栅的旁带反射率,从而在可见光波段获得了性能优良的共振滤波 关键词： 导模共振 平面波导 傅里叶模式理论 窄带滤波     

基于泄漏模共振的多层介质膜光栅宽角谱特性实现

基于泄漏模共振产生多层介质膜光栅（MDG）的-1级高衍射效率的理论,重点分析了产生MDG的-1级宽衍射角谱的物理机理,提出薄匹配层能有效提高MDG的-1级衍射角谱带宽.采用傅里叶模式理论计算MDG的衍射效率,给出了中心波长为1040 nm,Littrow角37.9°附近±11°范围内衍射效率大于90%的宽角谱MDG设计结果,且设计参数具有良好的工艺宽容度. 关键词： 介质膜光栅 泄漏模共振 匹配层 宽角谱     

Laser-induced damage threshold in n-on-1 regime of Ta_2O_5 films at 532,800,and 1064 nm

Ta_2O5 films were prepared with conventional electron beam evaporation and annealed in O_2 at 673 K for 12h.Laser-induced damage thresholds(LIDTs)of the films were performed at 532 and 1064 nm in 1-on-1 regime firstly,and then were performed at 532,800,and 1064 nm in n-on-1 regime,respectively- The results showed that the LIDTs in n-on-1 regime were higher than that in 1-on-1 regime at 532 and 1064 nm.In addition,in n-on-1 regime,the LIDT increased with the increase of wavelength.Furthermore, both the optical property and LIDT of Ta_2O_5 films were influenced by annealing in O_2.     

Surface plasmon resonance transmission filters at 1053nm based on metallic grating with narrow slit

Metallic gratings with narrow slits can lead to special optical properties such as strongly enhancing the transmission and considerably strengthening the polarized effect. A narrow-band filter suitable for application in optical communication is designed by sandwiching a metallic grating between two identical dielectric films. The maximum transmission can reach 96% after optimizing the parameters of films and grating at a central wavelength of 1053 nm. It is the first time, to our knowledge, that such high transmission has been reported since the discovery of the extraordinarily high transmission through periodic holes or slits; moreover, the extremely polarized effect is also found in P mode of this symmetric grating.     

Guided-mode resonant Brewster filter consisting of two homogenous layers and a single grating with an equal refractive index

In this paper,a new type of resonant Brewster filter(RBF) consisting of two homogenous layers and a single grating with an equal refractive index is presented.The properties are studied by using the plane waveguide method(PWM) and rigorous coupled-wave analysis(RCWA).It is found that the variation of the grating thickness does not effectively change the position of the resonant wavelength,however it has a remarkable effect on the line width,and the resonant peak can be adjusted back to its original position by slightly tuning the grating period.Moreover,by simultaneously tuning the thicknesses of the homogeneous layers above and beneath the grating structure,multiple channels can also be obtained when the RBF is illuminated at the Brewster angle calculated with the effective medium theory(EMT) of subwavelength grating.The adjacent optical thickness for acquiring the multiple channels is about three-quarters of the resonant wavelength.Furthermore,it is demonstrated that the line width at the operating resonant wavelength can be appreciably narrowed by tuning the thickness of the homogenous layer to its corresponding thickness without fine tuning the grating period or the thickness.Therefore,it is very useful for designing filters with different line widths at the desired wavelength.In addition,it is shown from our calculations that the symmetrical line feather can be obtained if the total optical thickness for the homogeneous layer meets the special condition.     

反射型导模共振滤波器设计

导模共振滤波器由于其高峰值反射率，低旁带反射，窄带以及带宽可控等优良特性引起了人们极大的关注，采用亚波长光栅的导模共振效应可以实现传统基于高低折射率介质的多层膜滤波器所无法实现的特殊功能，在弱调制模式下，其共振带宽可以被压缩到零点几纳米，但是由于介质表面和空气层的菲涅耳反射，使得偏离或者远离共振区时的反射率偏高，根据等效介质理论，亚波长光栅在远离共振区可以被看为均匀的薄膜，本文通过对导模共振光栅进行单层、双层以及三层抗反射设计，有效的降低了导模共振光栅的旁带反射率，从而在可见光波段获得了性能优良的共振滤波