Ta2O5 and Nb2O5 films are deposited on BK7 glass substrates using an electron beam evaporation method and are annealed at 673 K in the air. In this letter, comparative studies of the optical transmittance, microstruct...Ta2O5 and Nb2O5 films are deposited on BK7 glass substrates using an electron beam evaporation method and are annealed at 673 K in the air. In this letter, comparative studies of the optical transmittance, microstructure, chemical composition, optical absorption, and laser-induced damage threshold (LIDT) of the two films are conducted. Findings indicate that the substoichiometric defect is very harmful to the laser damage resistance of Ta2O5 and Nb2O5 films. The decrease of absorption improves the LIDT in films deposited by the same material. However, although the absorption of the Ta2O5 single layer is less than that of the Nb2O5 single layer, the LIDT of the former is lower than that of the latter. High-reflective (HR) coatings have a higher LIDT than single layers due to the thermal dissipation of the SiO2 layers and the decreased electric field intensity (EFI). In addition, the Nb2O5 HR coating achieves the highest LIDT at 25.6 J/cm^2 in both single layers and HR coatings.展开更多
The transmittance characteristics of ZnS ceramics with infrared (IR) (3-5 and 8-12um) antireflective coatings are studied. The film designs are optimized with programmed software. A double-side and double-layer scheme...The transmittance characteristics of ZnS ceramics with infrared (IR) (3-5 and 8-12um) antireflective coatings are studied. The film designs are optimized with programmed software. A double-side and double-layer scheme is employed. Two different double-layers with proper pa ameters are coated onto each side of a ZnS substrate. The measurement methods for transmittance are investigated. The measured transmittance for IR (3-5 and 8-12 um) surpasses 70%.展开更多
The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry (SIMS) equipment r...The impurities in two kinds of HfO2 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 ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films. In addition, the difference of Zr content in the two kinds of HfO2 single layer films was much larger than that of the other impurities such as Ti and Fe, which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2. With these two kinds of HfO2 and the same kind of SiO2, we deposited HfO2/SiO2 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.展开更多
We present the design of one-dimensional photonic crystal structures, which can be used as omnidirectional reflecting shields against radiative heating of space vehicles entering the Earth’s atmosphere. This radiatio...We present the design of one-dimensional photonic crystal structures, which can be used as omnidirectional reflecting shields against radiative heating of space vehicles entering the Earth’s atmosphere. This radiation is approximated by two broad bands centered at visible and nearinfrared energies. We applied two approaches to find structures with the best omnidirectional reflecting performance. The first approach is based on a band gap analysis and leads to structures composed of stacked Bragg mirrors. In the second approach, we optimize the structure using an evolutionary strategy. The suggested structures are compared with a simple design of two stacked Bragg mirrors. Choice of the constituent materials for the layers as well as the influence of interlayer diffusion at high temperatures are discussed.展开更多
The cavity ring-down (CRD) technique is adopted for simultaneously measuring s- and p-polarization reflectivity of highly reflective coatings without employing any polarization optics. As the s- and p-polarized ligh...The cavity ring-down (CRD) technique is adopted for simultaneously measuring s- and p-polarization reflectivity of highly reflective coatings without employing any polarization optics. As the s- and p-polarized light trapped in the ring-down cavity decay independently, with a randomly polarized light source the ring-down signal recorded by a photodetector presents a double-exponential waveform consisting of ring-down signals of both s- and p-polarized light. The s- and p-polarization reflectivity values of a test mirror are therefore simultaneously determined by fitting the recorded ring-down signal with a double-exponential function. The determined s- and p-polarization reflectivity of 30° and 45° angle of incidence mirrors are in good agreement with the reflectivity values measured with the conventional CRD technique employing a polarizer for polarization control.展开更多
基金supported by the Fundamental Research Funds for the Central Universities under Grant No.2009A058
文摘Ta2O5 and Nb2O5 films are deposited on BK7 glass substrates using an electron beam evaporation method and are annealed at 673 K in the air. In this letter, comparative studies of the optical transmittance, microstructure, chemical composition, optical absorption, and laser-induced damage threshold (LIDT) of the two films are conducted. Findings indicate that the substoichiometric defect is very harmful to the laser damage resistance of Ta2O5 and Nb2O5 films. The decrease of absorption improves the LIDT in films deposited by the same material. However, although the absorption of the Ta2O5 single layer is less than that of the Nb2O5 single layer, the LIDT of the former is lower than that of the latter. High-reflective (HR) coatings have a higher LIDT than single layers due to the thermal dissipation of the SiO2 layers and the decreased electric field intensity (EFI). In addition, the Nb2O5 HR coating achieves the highest LIDT at 25.6 J/cm^2 in both single layers and HR coatings.
文摘The transmittance characteristics of ZnS ceramics with infrared (IR) (3-5 and 8-12um) antireflective coatings are studied. The film designs are optimized with programmed software. A double-side and double-layer scheme is employed. Two different double-layers with proper pa ameters are coated onto each side of a ZnS substrate. The measurement methods for transmittance are investigated. The measured transmittance for IR (3-5 and 8-12 um) surpasses 70%.
基金The authors are grateful to Mr.Yongming Cao and Peiyuan Fang from National Microanalysis Center in Fudan University for the SIMS measurement
文摘The impurities in two kinds of HfO2 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 ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films. In addition, the difference of Zr content in the two kinds of HfO2 single layer films was much larger than that of the other impurities such as Ti and Fe, which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2. With these two kinds of HfO2 and the same kind of SiO2, we deposited HfO2/SiO2 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.
文摘We present the design of one-dimensional photonic crystal structures, which can be used as omnidirectional reflecting shields against radiative heating of space vehicles entering the Earth’s atmosphere. This radiation is approximated by two broad bands centered at visible and nearinfrared energies. We applied two approaches to find structures with the best omnidirectional reflecting performance. The first approach is based on a band gap analysis and leads to structures composed of stacked Bragg mirrors. In the second approach, we optimize the structure using an evolutionary strategy. The suggested structures are compared with a simple design of two stacked Bragg mirrors. Choice of the constituent materials for the layers as well as the influence of interlayer diffusion at high temperatures are discussed.
文摘The cavity ring-down (CRD) technique is adopted for simultaneously measuring s- and p-polarization reflectivity of highly reflective coatings without employing any polarization optics. As the s- and p-polarized light trapped in the ring-down cavity decay independently, with a randomly polarized light source the ring-down signal recorded by a photodetector presents a double-exponential waveform consisting of ring-down signals of both s- and p-polarized light. The s- and p-polarization reflectivity values of a test mirror are therefore simultaneously determined by fitting the recorded ring-down signal with a double-exponential function. The determined s- and p-polarization reflectivity of 30° and 45° angle of incidence mirrors are in good agreement with the reflectivity values measured with the conventional CRD technique employing a polarizer for polarization control.