Wavelength separation from extreme ultraviolet mirrors using phaseshift reflection

A generic design and fabrication scheme of Mo/Si multilayer-grating phaseshift reflector systems is reported. Close to optimized extreme ultraviolet (EUV, λ=13.5 nm) reflectance values up to 64% are demonstrated, while the diffractive properties can be exploited in spectral filtering applications. The results can contribute to a wavelength-unspecific solution for the suppression of λ>100 nm out-of-band radiation in EUV lithography.     

Polarization holographic gratings with high diffraction efficiency recorded in azopolymer PAZO

Azopolymers are one of the most efficient materials able to record the polarization state of light. They have numerous applications, such as data storage and diffractive optical elements with unique polarization properties. An essential parameter for each diffractive element is its diffraction efficiency η. In order to optimize the recording conditions and obtain high-efficient polarization holographic gratings, in the present work we study the dependence of the diffraction efficiency on the recording angle and thickness of a series of azopolymer layers. Three recording angles are used ??10°, 20° and 30° and three series of thin films with thicknesses 470, 850 and 2400 nm from the water-soluble azopolymer PAZO. The gratings are inscribed by two plain waves with left and right circular polarization from a He-Cd gas laser (442 nm). The diffraction efficiency of the gratings is probed with a right hand circularly polarized beam from a probe laser with wavelength 635 nm. The kinetics of diffraction efficiency η(t) in the +?1 diffraction order are presented and compared. Our experimental results indicate that highest diffraction efficiency (more than 40%) is obtained for the sample with thickness 2400 nm and for recording angle 10°. As the holographic recording in azopolymers is usually accompanied by formation of surface relief gratings, the surface topography of the recorded samples is also investigated by atomic force microscopy.     

Transformation of Bessel Beams in <Emphasis Type="Italic">C</Emphasis>-Cuts of Uniaxial Crystals by Varying the Emission Source Wavelength

We investigate experimentally the transformation of zero-order Bessel beams to a second-order Bessel eam in a c-cut of a CaCO₃ crystal. We show that the output-beam shape can be controlled by varying the emission-source wavelength and using a diffractive axicon. Beams were converted nearly totally at a wavelength change of Δλ = 1.5 nm and an initial wavelength λ = 637.5 nm of a CaCO₃ crystal, 15 mm in length, and a diffractive axicon with a period of 2 μm. We estimate the required wavelength variation Δλ = 1.7 nm, which is consistent with the experimental results.     

Multilevel phase-type diffractive lenses in silica glass induced by filamentation of femtosecond laser pulses

Multilevel phase-type diffractive lenses were fabricated by translating a filament of a femtosecond laser pulse into three-dimensional space inside synthesized silica. The profile of the lenses was designed by use of a multi-level approximation to a kinoform lens. Two-level diffractive lenses with multiple layers along the optical axis provided a maximum efficiency of 37.6% at a wavelength of 632.8 nm. A four-level diffractive lens provided a maximum efficiency of 56.9%. The lenses fabricated with filamentation were free from birefringence.     

楔块调整式Talbot干涉仪改变写入Bragg波长的调谐误差

在楔块调整式Talbot干涉仪中,光纤Bragg光栅的写入区为直接由相位模板衍射的±1级衍射光束形成的干涉条纹的近场干涉区,和由±1级衍射光束经两平面镜反射后形成的可调谐写入Bragg波长的干涉条纹的远场干涉区。在改变写入光纤光栅Bragg波长的过程中,光纤光栅的Bragg波长是由平面镜的交叉角决定的,而且,影响调谐精度的三种主要因素被控制在光纤光栅生产允许的范围内,即推动机构的位移误差系数Cd为～-0.08nm/μm,楔块的倾斜误差系数Cα为-0.15～0.23nm/(′),和转动机构的传动角误差系数Cβ为～-0.08nm/(′)。     

A hybrid doubled achromat based on a photon sieve

Photon sieves are diffractive optical elements with large chromatic aberration. To correct the dispersion of a photon sieve, a novel hybrid doubled achromat combined a photon sieve and a refractive lens is proposed. The design of this achromat applies the opposite dispersive characteristics of diffractive and refractive elements. Two design examples for different bandwidths of 300 nm and 80 nm in visible spectrum are given. For analyzing their focusing properties, the intensity distributions both along the axis and at the focal plane are studied. The results illustrate that the achromatic design is achieved and the secondary spectrum can be corrected for a narrow bandwidth. And compared to traditional hybrid achromat, it can focus to a sharper spot.     

不同谐振腔分步合成法制备的固态染料P567可调谐激光器

利用新型分步合成法制备的激光染料P567掺杂有机改性凝胶玻璃,建立了基于全息光栅的两种不同腔型可调谐激光器.采用光栅零级作为输出的激光器,调谐范围近70nm (543～610nm), 获得的最高斜效率为17%;采用腔镜耦合输出方式,调谐范围超过30 nm (553～585 nm),获得的最高斜效率为9.7%.并对激光器的可调谐范围、阈值、斜效率及线宽等参数进行了深入的分析比较.     

Tunable protein harmonic diffractive micro-optical elements

Herein, tunable protein harmonic diffractive microlenses (PHDMs) have been constructed by femtosecond laser direct writing from bovine serum albumin. With excellent three-dimensional topography, PHDMs show distinct harmonic diffractive features, such as similarly good imaging performance with smaller thickness than refractive lenses and well controlled minus chromatic dispersion compared with simple diffractive lenses (～5% focal length shift against ～21% of the protein Fresnel zone plate with the same radius under light with wavelength 450-659 nm). Owing to the nature of protein molecules as "building blocks," the focal length of the PHDM can be facilely tuned within seconds by changing the pH value (focal length tunability of up to ～20%).     

非晶硅光伏电池表面高效光陷阱结构设计

提出一种应用于非晶硅光伏电池表面的光陷阱结构,该结构主要由衍射光栅、低折射率MgF₂膜层、高折射率ZnS膜层及金属Ag反射镜组成.在标准测试条件(AM1.5,100 mW/cm²和25 ℃)下,运用严格耦合波理论,通过计算400-1000 nm波段内的1 μm厚非晶硅光伏电池的吸收光子数加权平均ξ_AM1.5,优化光陷阱结构的设计参数.结果表明:对于电池前表面减反射结构,在衍射光栅周期为800 nm、高度为160 关键词： 光陷阱结构 衍射光栅 减反射膜 非晶硅光伏电池     

紫外衍射微透镜阵列的设计与制备

为了提高紫外焦平面阵列的填充因子,可以通过微透镜阵列与紫外焦平面阵列的集成,以改善紫外焦平面阵列的探测性能。根据标量衍射理论设计了用于日盲型紫外焦平面阵列的128×128衍射微透镜阵列,其工作中心波长为350nm,单元透镜F数为F/3.56。采用组合多层镀膜与剥离的工艺方法制备了128×128衍射微透镜阵列,对具体的工艺流程和制备误差进行了分析,测量了衍射微透镜阵列的光学性能。实验结果表明:衍射微透镜阵列的衍射效率为88%,与理论值95%有偏差,制备误差主要来自对准误差和线宽误差。紫外衍射微透镜阵列具有均匀的焦斑分布,与紫外焦平面阵列单片集成能较好地改善器件的整体性能。     

衍射光学元件衍射效率的测量

根据衍射光学元件衍射效率的测量原理,建立衍射光学元件衍射效率测量的双光路装置,简要介绍了双光路测量的优点。针对衍射光学元件衍射效率的测量装置,讨论了影响衍射效率测量精度的因素,合理地选择测量装置中的针孔光阑,即可以让主衍射级次的光全部通过被探测器接收,又可以滤掉次级衍射光,保证测量结果的准确度。针对所设计研制的一个折衍射混合成像光学系统,测量了可见光波段3个激光波长的衍射效率,并对测量结果进行了模拟和分析。在473～632.8nm波段范围内任意一个波长处,衍射效率的测量结果同理论值的偏差均小于5.0%。实验证明,双光路测量装置可以用于测量衍射光学元件的衍射效率。     

Transfer of continuous-relief diffractive structures into diamond by use of inductively coupled plasma dry etching

The transfer of continuous-relief diffractive structures from resist into diamond by use of direct-write electron-beam lithography followed by dry etching in an inductively coupled plasma is demonstrated. The gases used for the diamond etching are O(2) and Ar. The chemical-vapor-deposited diamond substrate is of optical quality. Our results show that the transfer process generates fairly smooth etched structures. Blazed gratings with periods of 45mum and Fresnel lenses have been manufactured. The blazed gratings have been optically evaluated with a femtosecond laser operating at 400 nm. The diffraction efficiency was 68% in the first order, with a theoretical value of 100%. We intend to investigate the transfer process further and then to fabricate diffractive and refractive elements for use with Nd:YAG high-power lasers.     

Holographic grating recorded by He–Ne laser operating at 632.8 nm in polymer film containing push–pull azo dye

Holographic gratings were optically recorded by two beams from a He–Ne laser operating at 632.8 nm in poly (methyl methacrylate) (PMMA) film containing push–pull azo dye. The holographic characteristics of the recorded gratings were dependent on the polarization direction of the recording beams and the relationship between the diffractive signals and the power density of recording beams was investigated. The formation of holographic gratings accompanied by 532 nm (double-frequency of Nd:YAG laser) irradiation was studied in detail. It was found that the effect of 532 nm laser to the holographic grating lay in two aspects. The acceleration effect of 532 nm laser to the formation of holographic grating is predominant when the power density of 532 nm laser is low. While at relatively high power density of 532 nm laser, the erasure is the main factor to the holographic grating. Moreover, the holographic grating was probed by 532 nm laser at low power density and the dependence of the first order diffractive signal on the recording beam power density was also presented.     

Design of two-dimensional apodized grating couplers with Gaussian diffractive mode

Two-dimensional apodized grating couplers are proposed with grating grooves realized by a series of nanorectangles, with the feasibility of digital tailoring the equivalent refractive index of each groove in order to obtain the Gaussian output diffractive mode in order to enhance the coupling efficiency to the optical fiber. According to the requirement of leakage factor distribution for a Gaussian output profile, the corresponding effective refractive index of the grating groove, duty cycle, and period are designed according to the equivalent medium theory. The peak coupling efficiency of 93.1% at 1550 nm and 3 d B bandwidth of 82 nm are achieved.     

Multilayer metal/metal-oxide diffractive structure for photonic temperature sensing

We designed and fabricated multilayer metal/metal-oxide surface relief diffractive grating structures by growing alternating Pt and SnO(x) layers. Optical interrogation at 633 nm reveals the temperature dependence of their reflection and transmission diffractive effects. This function is explored here in the context of a remote, spatially localized, photonic temperature sensing operation, achieving sensitivity of 10% per °C for the zeroth-order in the transmission mode. The experimental demonstration is found to be in good agreement with the results of rigorous coupled wave analysis of the composite metal/metal-oxide element.     

Investigation of laser ablation on hybrid sol–gel material applied to kinoform etching

Ultraviolet laser machining of a hybrid organic/inorganic material prepared via a sol–gel process has been studied for the fabrication of kinoforms or surface relief diffractive optical elements. The hybrid mixes silicon and titanium oxides and an organic network in order to improve the mechanical properties. Different material compositions have been investigated. Laser ablation of the hybrid material is observed at low laser fluence (measured threshold fluence of 125 mJ/cm² at 248 nm/6 ns) and shows that the process is well adapted to micro-patterning by laser machining means. The best observed depth resolution is 60± 20 nm and appears to be limited by the ablation setup. Finally, the fabrication of an effective diffractive optical element and its operation at 1.06 μm are described. PACS  81.20.Fw; 79.20.Ds; 42.79.-e     

Excimer laser patterned dielectric masks for the fabrication of diffractive optical elements by laser ablation

Masks for laser processing are generated by laser ablation patterning of dielectric layer systems. The application of these masks for the rapid fabrication of diffractive optical elements (DOEs) is presented. The diffractive optical elements are designed as phase-only elements, assuming an illumination with a plane wave. A continuous phase function is calculated using an iterative Fourier transform algorithm (IFTA). This continuous phase function is reduced to two or four levels by an iterative Fourier quantisation algorithm (IFQA) that is able to include focal power. The fabrication of the DOE is performed in a two-step process. First, a binary amplitude mask (or a set of masks for multi-level DOEs) is made by structured ablation of a highly reflective dielectric coating (HR 248 nm) from a fused silica substrate. This is accomplished by using an ArF excimer laser emitting at 193 nm, a wavelength that is sufficiently absorbed in the HfO₂/SiO₂-dielectric layer system, leading to precisely ablated mask structures. In the second step, this mask is used in a 4:1 projection configuration to generate a surface profile in a polymer substrate by ablation at 248 nm. The depth modulation can be defined by adjusting laser fluence and pulse number. Examples of DOEs ablated in polycarbonate are shown and their performance is characterised.     

Polarization conversions of diffractive wave plates based on orthogonal circular-polarization holography

A polarization holographic grating, which integrates the functions of a grating and a wave plate and is called a diffractive wave plate, is recorded by two beams(left and right circularly polarized) of a 532 nm laser in an azo polymer with a liquid-crystal structure. The polarization conversion characteristics of the diffractive wave plates are investigated with a detecting light of 650 nm by metering the polarization state of first-order diffracted light.It is confirmed that the diffractive wave plates convert the incident linear polarization into circular polarization for a linearly polarized probe laser and reverse the sense of rotation of the circular polarization when the detecting light is circularly polarized light.     

高衍射效率衍射望远镜系统的设计/加工及成像性能测试

为提高衍射效率,设计并制作了口径为300mm的衍射成像系统.该系统的物镜是由一块四台阶位相型菲涅尔波带片通过激光直写套刻和Ar离子束物理刻蚀技术在石英玻璃基板上加工而成.测试了衍射物镜的衍射效率,实验结果表明:衍射物镜在波长632.8nm处的衍射效率为66.4%,达到理论值的82%.搭建了衍射成像系统光路,分别采用10μm星点孔与分辨率板,测试了系统的成像性能.实验测得星点像直径为44μm,分辨率板的极限分辨率达到84lp/mm,接近该系统的理论计算值,表明该衍射成像系统具有较好的成像性能.