Materials with on-demand refractive indices in the terahertz range

We demonstrate the possibility to create materials with chosen refractive indices and a strong birefringence in the terahertz range by etching of patterns with appropriate filling factors in a dielectric substrate. We show that by using deep inductive plasma etching of silicon wafers, it is possible to achieve a birefringence as high as 1.2 in an 80 microm thick layer. The resulting stacks were used as building blocks for a photonic crystal displaying sharp defect mode peaks in transmittance.     

Mid-infrared wire-grid polarizer with silicides

An infrared (IR) polarizer with tungsten silicide (WSi) wire grid was fabricated by two-beam interference exposure and reactive ion etching. To enhance TM transmittance, silicon monoxide was deposited between the WSi wire grid (400 nm period) and a Si substrate. The transmittance was over 80% in the 4-5 microm wavelength range. The ratio of TM and TE transmittances was over 100 (20 dB) in the 2.5-6 microm wavelength range. The fabricated polarizer has higher durability and better compatibility with microfabrication processes compared with conventional IR polarizers.     

Surface modification of doped ZnO thin films

Effects of photo-assisted electrodeless and ion RF-sputter etching on the structural and optical properties of sputtered ZnO:Al thin films were investigated. Photo-assisted electrodeless etching was appropriate for getting “smooth” surfaces and ion RF-sputter etching by high power has significantly modified the surface roughness with an increase of the light diffuse transmittance.     

Demonstration of a single-layer meanderline phase retarder at infrared

Meanderline wave plates are in common use at radio frequencies as polarization retarders. We present initial results of a gold meanderline structure on a silicon substrate that functions at a wavelength of 10.6 microm in the IR. The measured results show a distinct change in the polarization state of the incident beam after passing through the device, inducing a 74 degrees phase retardance between horizontal and vertical components. A high degree of polarization (88%) is maintained in the transmitted beam with an overall power transmittance of 38% and a beam profile that remains essentially unchanged.     

Imprint lithography of pyramidal photonic pillars using hydrazine etching

An inexpensive method to produce a pyramidal-type 2D photonic structures in the silicon substrate was proposed. The method is based on the combination of imprint lithography and wet Si1 0 0 etching in water solution of hydrazine, which etches 1 1 1 faces much more slowly than others. Thermally grown SiO₂ mask for the hydrazine etching was used, because single Al mask cannot be well bonded to the substrate and tends to peel during the etching. It was revealed that transmittance in the infrared spectrum region of the patterned silicon decreases by about five times compared with that of flat silicon substrate and this decrease is almost independent of the angle of the incident beam. In the infrared region, decrease of transmittance of the patterned samples is directly proportional to the wave number. The shape of formed pyramids has strong influence on the transmittance. Decrease of the transmittance is much more rapid and larger in the case of sharpless pillars.     

Fabrication of two-dimensional organic photonic crystal filter

A high quality two-dimensional photonic crystal filter made of polystyrene is fabricated by the method of focused ion beam etching. Scanning electron microscopy (SEM) and transmittance spectrum are used to characterize the properties of photonic crystal filter. The measured transmittance spectrum is in agreement with the theoretical one. It is found that the filtering properties of photonic crystal filter, including the position and quality factor of optical channel, can be tuned by adjusting the width of line defect. PACS 42.70.Qs; 61.46.+w; 81.15.-z     

Anti-reflective effect of transparent polymer by plasma treatment with end-hall ion source and optical coating

The surface of poly(methyl methacrylate) (PMMA) was treated by plasma with an end-Hall ion source in vacuum in order to enhance its anti-reflectivity. The cone-shaped bumps induced by the plasma etching have shown an antireflective effect. Moreover, PMMA has poor thermal durability due to its low melting point; therefore, the etched PMMA was further coated by a 5 nm thick SiO₂ film after 900 and 1300 s plasma etching. Samples after SiO₂ coating were thermally annealed at temperature of 70°C for 1 h. Experiments show that transmittance was increased after 5 nm thick SiO₂ coating. The of transmittance of PMMA after both sides treated by 900 s plasma etching and 5 nm SiO₂ coating was not changed after thermal annealing. However, without SiO₂ coating the transmission was reduced 1% after annealing. Atomic force microscope (AFM) demonstrated that the nano-structures of cone-shaped bumps were formed on the PMMA after plasma etching and a smoother nano-structured pattern preserved the transmittance of the PMMA after both sides treated by 900 s plasma etching and 5 nm SiO₂ coating. Three dimensional photonic crystal formed by uniformly distributed cone-shaped bumps was assumed to result in the reduction of the anti-reflectivity of treated PMMA.     

Effects of hydrogen etching process on the structural and optical properties of nano-crystalline diamond films

In this work, hydrogen etching method is applied to improve the quality of nano-crystalline diamond (NCD) films grown from hot-filament assisted chemical vapor deposition (HFCVD) system. From the characteristics of the structure and optical property, the grain size and surface roughness decrease while the optical transmission increase obviously under certain deposition parameters (gas pressure and substrate temperature) and longer etching time. Soft X-ray transmission measurements by synchrotron radiation are also carried out on the NCD films. The result shows that the X-ray transmission has an obvious improvement when the NCD film is fabricated from the hydrogen etching method. And the transmittance reaches 53.3% at X-ray photon energy of 258 eV, which has met the requirement for X-ray mask materials.     

New method to measure whole-wavelength transmittance of TCO substrates for thin-film silicon solar cells

High transmittance of transparent conductive oxide (TCO) substrates is one of the most important factors for achieving high efficiency in thin-film silicon solar cells. Immersion (IM) method with CH₂I₂ liquid is widely used for the evaluation of optical properties (transmittance, reflectance and absorption) for TCO substrates with textured surface in order to reduce the scattering at the TCO surface. However, in order to measure transmittance accurately, three problems have been found. (1) CH₂I₂ liquid itself absorbs the light in short wavelength region. (2) The transmittance around the absorption edge of CH₂I₂ liquids is very sensitive to its amount. (3) Scattering cannot be suppressed when the scattering surfaces are more than 2 surfaces (for example, TCO on reactive ion etching (RIE) processed glass). To overcome these problems, we proposed a new setup to measure optical properties of TCO substrates by holding the samples inside the integral sphere. As the results, we have confirmed that their absorption in all wavelength could be measured accurately and the transmittance measured by the new method was well consistent with the external quantum efficiency (EQE) of the fabricated cell while the transmittance measured with conventional IM method showed differently. Therefore, this new method could be a useful tool to evaluate TCO substrates for thin-film silicon solar cells.     

Effect of Cr and V dopants on the chemical stability of AZO thin film

The effect of the dopants of Cr and V on the optoelectronic properties of AZO thin film by pulsed DC magnetron sputtering has been investigated. We also use HCl and KOH solutions to conduct the chemical stability of AZO:Cr:V thin film. The experimental results show that the optimum AZO optoelectronic properties without Cr and V doping obtain the resistivity of 9.87 × 10⁻⁴ Ω cm, optical transmittance of 84% and surface roughness rms value of 2.6 nm. The chemical stability of AZO will increase after Cr and V doping. Under the added V = 0.19 wt.%, Cr = 0.56 wt.%, AZO:Cr:V thin film showed 52% increased chemical stability and 128% decrease in surface roughness after etching (the resistivity was 3.62 × 10⁻³ Ω cm and optical transmittance 81%). From the experimental results, the higher resistivity obtained after KOH etching compared with after HCl etching. The reason is that the Zn/Al ratio will reduce after etching and cause the AZO film carrier density to reduce as well. However, the optical transmittance obtained after KOH etching will be higher than that after HCl etching. This is because that a better surface roughness after KOH etching obtained than after HCl etching.     

Characterization of asymmetric polymeric membranes by gas permeation

Polycarbonate films (thickness 18, 25 and 38 microm) were irradiated by a beam of 100MeV Ni7+ ion. The permeability for hydrogen and carbon dioxide was measured from both sides of membrane at increasing etching time. These membranes show larger permeability from the irradiation side, than the reverse side indicating the formation of conical tracks and asymmetrical membrane. The stopping range (Se) of 100MeV Ni7+ ion beam in polycarbonate is 22microm, for 18microm thick membrane the etching time at which the permeability increases rapidly is less than that of 38microm thick membrane, for both the gases. The difference in permeability from the two sides is attributed to the conical shape of the track generated by the ions. The controlled flow rate of the membrane leads to the design of a special type of gas filter.     

一种新型的低角度效应的滤波器

低角度效应的滤波器由高折射率的介质膜和金属膜交替的奇数层膜组成.这种滤波器使用于斜入射光和大光锥角照明时,不仅中心波长移动显著减少,而且特性仍能保持良好.理论和实验表明, 这种新型滤波器能突破现用滤波器对入射角和光锥角的限制.实现低角度效应的主要原理是高折射率材料的使用及其诱导透射的实现. 关键词： 光学薄膜 新型滤波器 低角度效应     

Fabrication of Two-Dimensional Organic Photonic Crystal Microcavity

A two-dimensional polystyrene photonic crystal microcavity is fabricated by the method ot tocused ion Oeam etching. The scanning electron microscopy and the transmittance spectrum are used to characterize the properties of the photonic crystal microcavity. The quality factor and the transmittance of the photonic crystal microcavity is more than 530 and 90%, respectively. The measured results are in agreement with the theoretical predictions.     

ZnS衬底表面亚波长增透结构的设计及制备

ZnS是长波红外窗口优选材料之一,而其表面反射率较高;为了减小表面反射,利用耦合波理论,对ZnS衬底表面的亚波长结构参数进行优化设计,得到了具有良好增透效果的最佳亚波长结构参数;并利用掩膜光刻、反应离子刻蚀技术在ZnS衬底表面制备出在8—12 μm波段范围内有明显增透效果的二维亚波长结构,这为ZnS衬底的增透提供了一种新的方法. 关键词： 耦合波理论 表面亚波长增透结构 反应离子刻蚀 硫化锌     

酸蚀与紫外激光预处理结合提高熔石英损伤阈值

采用HF酸刻蚀和紫外激光预处理相结合的方式提升熔石英元件的负载能力,用质量分数为1%的HF缓冲溶液对熔石英刻蚀1~100 min,综合透过率、粗糙度和损伤阈值测试结果,发现刻蚀时间为10min的熔石英抗损伤能力最佳。采用355 nm紫外激光对HF酸刻蚀10 min的熔石英进行预处理,结果表明:紫外预处理能量密度在熔石英零损伤阈值的60%以下时,激光损伤阈值单调递增;能量到达80%时,阈值反而低于原始样片的损伤阈值。适当地控制酸蚀时间和紫外激光预处理参数能有效提高熔石英的抗损伤能力。     

High frequency attenuation measurements of lipid encapsulated contrast agents

A number of recent studies have indicated the potential of ultrasound contrast agent imaging at high ultrasound frequencies. However, the acoustic properties of microbubbles at frequencies above 10 MHz remain poorly understood at present. In this study we characterize the high frequency attenuation properties of (1) BR14, (2) BR14 that has been mechanically filtered (1 and 2 microm pore sizes) to exclude larger bubbles, and (3) the micron to submicron agent BG2423. A narrowband pulse-echo substitution method is employed with a series of four transducers covering the frequency range from 2 to 50 MHz. For BR14, attenuation decreases rapidly from 2 to 10 MHz and then more gradually from 10 to 50 MHz. For 2 microm filtration, the attenuation peaks between 10 and 15 MHz. For 1 microm filtration, attenuation continues to rise until 50 MHz. The agent BG2423 exhibits a diffuse attenuation peak in the range of 15-25 MHz and remains high until 50 MHz. These results demonstrate a strong influence of bubble size on high frequency attenuation curves, with bubble diameters of 1-2 microm and below having more pronounced acoustic activity at frequencies above 10 MHz.     

Tuning the negative electromagnetic response in periodically perforated metal-dielectric-metal structures

We fabricate Ag-SU-8-Ag sandwich metamaterials perforated with a periodic array of dipoles. The transmittance spectra of both experiment and modeling have indicated the existence of low- and high-intensity transmission bands in midinfrared frequencies. The position of these transmission bands depend on the dipole length, and lattice structure. The high-intensity transmission bands are due to the excitation of the external surface plasmon plartion (SPP) modes and the localized modes, while the low-intensity transmission bands are from the excitation of the internal SPP modes. The transmittance of the low transmission bands can be increased by decreasing the relative position of the two transmission bands, and the negative electromagnetic response of the metamaterials is also increased. However, if we further decrease the relative position of the two bands, the low transmission band will be merged in the high transmission band, and no negative electromagnetic response can be retrieved.     

EVOH树脂薄膜制备及其保温性能的红外光谱研究

采用平挤上吹成膜工艺制备了EVOH,PE,EVA薄膜,并利用红外光谱仪、透光率/雾度测定仪等分别研究了以EVOH,PE,EVA树脂为基材生产的薄膜的透光率、雾度、红外阻隔率和温室增温、保温性能的关系.结果表明在光学性能上,EVOH树脂薄膜比常用的PE和EVA农膜的雾度分别下降10%和5%左右;从红外透射率来看,EVOH...     

In-fiber polymer-glass hybrid waveguide Bragg grating

A 1.2 microm (height) x 125 microm (depth) x 500 microm (length) microslot along a fiber Bragg grating was engraved across the optical fiber by femtosecond laser patterning and chemical etching. By filling epoxy in the slot and subsequent UV curing, a hybrid waveguide grating structure with a polymer core and glass cladding was fabricated. The obtained device is highly thermally responsive with linear coefficient of 211 pm/ degrees C.