标量衍射理论模拟蚀刻衍射光栅

讨论用于光通信的集成波分复用/解复用器件蚀刻衍射光栅（EDG）,它是波分复用光通信的核心器件的一种。EDG基于平面波导的Rowland圆结构,光栅面是平面。光栅的每一个齿面都垂直于齿面中心和输入波导端点的连线。基于标量散射场满足的Hemholtz方程,推导出Rowland圆上场分布的精确表达式。利用这个模型对设计好的器件参数进行了模块形状、谱响应、色散等复用性能的模拟,并对插入损耗和串扰进行了简要分析。     

Generalized groove density equation concerning bending-grating-related imaging properties

Varied-line-spacing gratings are used in soft-x-ray monochromators and spectrometers because of their ability to correct various aberrations by varying the groove density. A curved grating blank in a Rowland circle mounting could eliminate primary aberrations. Bending a plane constant-groove-density grating into a desirable surface can eliminate higher-order aberrations as a result of the change in surface profile and groove density. This provides a simple means for improving the imaging properties. When used in a monochromator, the grating can be bent to different degrees to minimize aberrations at all wavelengths. General formulas concerning the transformations of groove function, groove density, and groove spacing are presented for the bending grating. Analytic results with a numerical example show the significant properties of the system.     

Off-plane anastigmatic imaging in Offner spectrometers

In this paper, the imaging performance of an Offner concentric imaging spectrometer is analyzed when the spectrometer entrance slit is disposed arbitrarily on the plane that is parallel to the grating grooves and contains the common center of curvature. Astigmatism-corrected designs are obtained for off-plane incidence on the grating if one point on the slit is located on the Rowland circle of the primary mirror. In this case, the combined system of primary mirror plus diffraction grating provides two astigmatic line images oriented parallel and orthogonal to the plane of diffraction, with the former located on the same plane as the slit. Consequently, these images can be brought to a single focus on this plane by the tertiary mirror if its radius of curvature is chosen properly. In addition, coma aberration is simultaneously removed. These results can be applied to the design of two-mirror or three-mirror spectrometers, generalizing the concept of the best imaging circle and providing solutions to get anastigmatic imaging for two object points and two wavelengths.     

Image Evaluation of the High Resolution VUV Spectrometer at SURF II by Ray Tracing

A high resolution VUV spectroscopic facility has been in use for several years at SURF II, the Synchrotron Ultraviolet Radiation Facility at the National Institute of Standards and Technology in Gaithersburg, Maryland. At this facility, a combination of three cylindrical mirrors is utilized to focus the light originating in the storage ring onto the horizontal entrance slit of the spectrometer. The spectrometer uses a 6.65 m concave grating having a groove density of 4800 lines/mm in the off-plane Eagle mounting. In preparation for the installation of an array detector in the exit image plane, a ray tracing program has been formulated and spot diagrams have been constructed by plotting the coordinates of the points of intersection of the diffracted rays with the image plane, which is tangent to the Rowland circle. In creating the spot diagrams, we have considered both parallel and tilted configurations of the entrance slit with respect to the grating grooves. It is shown that the line widths of the spectral images can be reduced when the entrance slit is properly tilted. Finally, we have estimated the spectral widths of the images when they are recorded on an array detector placed tangent to the Rowland circle. We conclude that an image spectral width of 0.41 pm to 0.88 pm in first order can be achieved over the wavelength region of 40 nm to 120 nm.     

Third-generation holographic Rowland mounting: fourth-order theory

The third-generation holographic Rowland mount consists of a Rowland-mounted, optimally recorded holographic spherical grating, referred to as an optimized Rowland grating (ORG), whose recording sources are aberrated by two auxiliary ORG's. The main purpose of this mount is to avoid any aspherical surface while providing control over all the parameters needed to correct the aberrations up to and including the fourth order. Earlier [Appl. Opt. 30, 4019-4025 (1991)], we considered the case of a moderate coma c2. We now give the fourth-order theory, apply it to the high-dispersion (4600 grooves/mm) grating considered previously, and obtain for it diffraction-limited images.     

Narcissistic Ghosts in Rowland-Mounted, Concave Gratings with nu = 0 degrees : a Cautionary Note

Narcissistic ghost lines in a Rowland-grating spectrograph have been identified as arising from the reimaging of bright spectral features, which are incident on the face of a detector photocathode [Cesium iodide (CsI) on a microchannel plate], back onto the detector by the grating in zero order. The mean of the wavelength of the diffracted light and the apparent wavelength of the ghost allows the angle of the grating normal with respect to the input beam (alpha) to be determined. Measurements of ghost intensity as a function of wavelength are presented and are found to range between 7 x 10(-4) and 7 x 10(-3) of the parent line. We find that the sum of the CsI photocathode reflectivity and quantum efficiency <1/2, showing the bulk of the light incident upon the detector, is neither reflected nor detected. We caution that any Rowland circle spectrograph with a detector normal nearly aligned with the grating normal and with a sufficiently reflective detector face (or surrounding mounting structure) will suffer from these narcissistic ghosts.     

Single-element imaging spectrograph

A spectrograph concept designed for both high wavelength and high spatial resolution (in one dimension) is briefly described. This design is referred to as a single-element imaging spectrograph (SEIS). It is a one-bounce diffractive system that combines the spectral properties of a Rowland mount spectrograph with the imaging (spatial resolution) properties of a Wadsworth mount spectrograph through the use of a toroidal diffraction grating. No primary optics are necessary, making the system especially attractive for use in the extreme and far ultraviolet, where low reflectivity of common optical coatings can severely limit instrument sensitivity.     

Recording high-dispersion spherical holographic gratings in a modified Rowland mounting by use of a multimode deformable mirror

To reduce the uncorrected higher-order aberrations for holographic gratings requiring an extreme dispersion, we have modified the Rowland mounting by moving the recording laser sources away from the grating. Then, with a multimode deformable plane mirror to record the grating, the correction of all the aberrations up to the fourth order inclusive is found sufficient to obtain a high-quality image. Applied to the FUSE-LYMAN grating, with a groove density of as much as 5740 grooves/mm, for which a resolution of 30,000 was required, this new recording device produces a resolution from 139,000 to 222,000 over the spectral range.     

Design, fabrication and performance evaluation of a 22-channel direct reading atomic emission spectrometer using inductively coupled plasma as a source of excitation

The indigenous design, fabrication and performance evaluation of a polychromator, using inductively coupled plasma (ICP) as a source of excitation, are described. A concave holographic grating is used as the dispersing element and a Paschen — Runge mount is chosen to focus the spectra over a wide range along the Rowland circle. Twenty-two exit slits, mounted along the circle, precisely correspond to the wavelengths used for determination of up to twenty elements present in the plasma. Radiations emerging from the exit slits are detected by photomultiplier tubes placed behind them. The photomultiplier signal is recorded by an electronic system consisting of an integrator and a PC-based data acquisition system. The performance of the spectrometer has been evaluated with an ICP excitation source. Synthetic standards in deionized water containing a mixture of twenty impurities have been analysed. Typical determination limits observed for elements range from sub-ppm to ppm levels. All the elements present as impurities can be detected simultaneously. It is also observed that each element has a different emitting region in the ICP flame for which the maximum signal to the background is obtained. The determination limits obtained corresponding to these zones are the lowest. A study of the sensitive emitting zones for several elements has been carried out and the results are demonstrated by photographs of the ICP flame. The study will help in achieving the minimum value of determination limit for an impurity element.     

Fabrication of holographic blazed grating with Fourier synthesis exposure

A simple, direct, and universal fabrication method for holographic blazed gratings is proposed and a 79 lines/mm holographic echelle grating with 4 μm depth quasi-triangular grooves experimentally demonstrated as an example of a blazed grating fabricated directly by Fourier synthesis exposure. With the method, we converted a periodic grating groove profile into the exposure energy spatial distribution on the surface of a photoresist with the response characteristics of the particular photoresist. Then the exposure energy could be decomposed into a series of sinusoidal functions using Fourier series, and realized by superposing a series of two-beam interference patterns. In contrast with mechanically ruled gratings, the fabrication process of holographic gratings is quite quick and low cost, and especially no Rowland ghosts appear in their dispersion spectrum. The reported work will offer a new approach for blazed grating fabrication with a holographic process.     

圆光栅检测仪的研制

介绍了一种高精度、精密、自动化、动态测量的光栅检测仪,测量光栅盘的扩展不确定度为０．０８”。该仪器采用了高回转精度的空气静压轴承及多头均化技术,减小了参考盘刻划误差的影响,同时,采用了计算机系统控制测量过程,进行数据处理,实现了自动化测量,检测结果和误差曲线由打印机打印输出。     

High-dispersion spherical holographic gratings in a modified rowland mounting

For holographic gratings requiring an extreme dispersion, I consider a modified Rowland mounting, in which the recording laser sources are moved away from the grating, to reduce the uncorrected higher-order aberrations. In addition, I choose the geometric parameters such that first-type coma is corrected. Then a plane multimode deformable mirror (MDM) or two auxiliary spherical holographic gratings (R3 device) are used to aberrate the grating's recording sources; correction up to the fourth order is sufficient to obtain high image quality. Applied to the FUSE-Lyman (FUSE is Far Ultraviolet Spectroscopic Explorer) grating, with a groove density as high as 5767 grooves/mm, these recording devices produce a resolution (chromatic resolving power) as great as 611,000 with the MDM and 3,030,000 with the R3 device. These results far exceed the specified performance of 30,000. Since diffraction limits the resolution to 482,000, the images are diffraction limited with both devices.     

High-resolution x-ray imaging of extended lasing plasmas

An x-ray imaging system with a bent focusing crystal was used for time-resolved one-dimensional imaging of a long plasma column of highly ionized aluminum. This scheme uses a focusing geometry with a spherically bent crystal and a slit on the Rowland circle. Alternative schemes of x-ray monochromatic imaging are briefly discussed. The homogeneity of the up to 40-mm-long laser-generated plasma column was studied with a temporal resolution of 100 ps. The potential spatial resolution of the instrument is 90 mum or better. Monochromatic images taken on the resonance Healpha line of Al XII characterize the homogeneity of a plasma generated to study a recombination x-ray laser scheme, giving an amplified spontaneous emission in AlXI.     

The Diffuse Interstellar Cloud Experiment: a high-resolution far-ultraviolet spectrograph

We have designed, assembled, and launched a sounding rocket payload to perform high-resolution far-ultraviolet spectroscopy. The instrument is functionally a Cassegrain telescope followed by a modified Rowland spectrograph. The spectrograph was designed to achieve a resolving power (R=λ/δλ) of 60,000 in a compact package by adding a magnifying secondary optic. This is enabled by using a holographically ruled grating to minimize aberrations induced by the second optic. We designed the instrument to observe two stars on opposing sides of a nearby hot/cold gas interface. Obtaining spectra of the O VI doublet in absorption toward these stars can provide new insight into the processes governing hot gas in the local interstellar medium. Here we present the optical design and alignment of the telescope and spectrograph, as well as flight results.     

Design of Dyson imaging spectrometers based on the Rowland circle concept

We aim to show that Dyson imaging spectrometers can be easily designed by applying the concept of the Rowland circle to refracting surfaces. This allows us to conceive an analytical procedure that is based on the removal of astigmatism at two wavelengths. Following this procedure, high-optical-quality spectrometers can be designed even for high speeds. Root-mean-square spot radii less than 2.5 μm are obtained for speeds as high as f/1.5, slit lengths of 15 mm, and wavelength ranges of 0.4-1.7 μm. Design examples are presented for classical Dyson spectrometers in which the detector is glued to the glass plane surface and for spectrometers with an air gap between this surface and the image plane.     

滚压印圆柱母光栅的微刻划制造

精密长光栅作为高档数控机床中的核心部件,其制造能力和精度直接决定高精密机床的制造水平．本文对纳米滚压印技术制造长光栅中的核心部件——圆柱母光栅的制造开展研究,建立了高精度的母光栅刻划制造平台,保证了母光栅制造的精度要求;分析了微尺度毛刺的形成机理和抑制方法,对母光栅材料选择及微尺度刻划工艺参数进行了优化,实现了直径110mm,周期分别为20μm、10μm和4μm整圈圆柱母光栅的高精度微刻划制造．母光栅刻划总条数为数万条,4μm周期母光栅连续刻划时间超过62h,最终实现母光栅的首尾拼接误差控制小于300mm．另外,针对滚压印加工中的填充问题,利用聚焦离子束（FIB）技术制备了V形、梯形等形状金刚石刀具,获得了良好的光栅压印结果．     

Cylinder and metal grating polarization beam splitter

We propose a novel and compact metal grating polarization beam splitter (PBS) based on its different reflected and transmitted orders. The metal grating exhibits a broadband high reflectivity and polarization dependence. The rigorous coupled wave analysis is used to calculate the reflectivity and the transmitting spectra and optimize the structure parameters to realize the broadband PBS. The finite-element method is used to calculate the field distribution. The characteristics of the broadband high reflectivity, transmitting and the polarization dependence are investigated including wavelength, period, refractive index and the radius of circle grating. When grating period d = 400 nm, incident wavelength λ = 441 nm, incident angle θ = 60° and radius of circle d/5, then the zeroth reflection order R₀ = 0.35 and the transmission zeroth order T₀ = 0.08 for TE polarization, however, T₀ = 0.34 and R₀ = 0.01 for TM mode. The simple fabrication method involves only single etch step and good compatibility with complementary metal oxide semiconductor technology. PBS designed here is particularly suited for optical communication and optical information processing.     

Far-ultraviolet spectrographs: the impact of holographic grating design

One of NASA's major scientific initiatives in astrophysics, the Far Ultraviolet Spectroscopic Explorer, is an orbiting observatory designed to perform high-resolution spectroscopy of stellar objects between 910 and 1150 ?. To achieve the 100 cm(2) of effective area required to observe faint quasars, the mission has adopted an unconventional design that couples grazing-incidence Wolter optics and an aberration-corrected Rowland circle spectrograph. The projected cost of the satellite has, however, become very high, driven in large part by the cost of the grazing optics and the side effects of compensating for their relatively poor performance. The logic that leads to the current design is reanalyzed, and it is argued that because of the technical developments of the last 7 years, grazing incidence is no longer the most attractive alternative. In particular, the application of aberration-corrected, spherical substrate, holographic gratings now greatly simplifies the design and thereby reduces the cost. A new is presented that substantially outperforms the old and that is easier to fabricate.     

集成光栅干涉微位移测量方法

介绍了一种新型集成光栅干涉微位移测量方法,设计加工了微位移敏感芯片,并进行了初步的性能测试．敏感芯片利用硅-玻璃键合体硅工艺制作而成,在玻璃上制有金属光栅,光栅上方有由铝梁支撑的可动结构．实验系统由敏感芯片、半导体激光器、光电二极管以及相应的驱动、检测电路组成入射激光照射到光栅上产生衍射光斑,衍射光的光强随可动结构与光栅之间的距离变化,通过测量衍射光强的变化可以得到位移．测试实验结果表明,所制作的集成光栅干涉微位移敏感芯片可实现位移检测,最小可检测的位移约0．2nm．