Fabrication of high-spatial-frequency gratings through computer-generated near-field holography

We demonstrate an innovative method for fabrication of high-spatial-frequency grating structures. This technique makes use of the near-field diffraction patterns from computer-generated phase holograms for lithographic fabrication of grating structures with periods that are one half that of the phase hologram mask. Linear, rectilinear, and circular gratings were fabricated with this technique. Experimental results from gratings with periods to 0.5 mum and feature sizes to ~0.2 mum are presented.     

平场全息凹面光栅制作结构与使用结构之间误差补偿作用的数值模拟与实验验证

通过对优化计算出的平场全息凹面光栅制作结构(曝光记录结构)和使用结构(光谱仪分光结构)之间各个参数进行联合数值模拟,得出如下结论：在优化设计参数值附近一个较大范围的误差区域内,平场全息凹面光栅的制作结构参数误 差和使用结构参数误差可以相互补偿,最终补偿的结果可以使光谱成像质量达到与原设计结构相当的水平,满足光谱仪器的使用要求。文章给出了数值模拟结果以及与其相符的实验验证结果。此补偿作用有利于降低平场全息凹面光栅制作 中各个参数精度的调节难度,并且可以对实际使用过程中光谱仪器的设计和装调进行理论上的指导。     

全息光栅实时显影监测曲线的理论模拟

在特定的工艺条件下,光刻胶的非线性效应非常显著;合理地利用非线性效应,能够制作出近似矩形的全息光栅掩模。为了分析清楚非线性效应对光栅沟槽成形的作用机理,有必要建立一个显影理论模型。模拟得到的光栅轮廓和实验样片的扫描电子显微镜照片结果很吻合。根据这个模型,进而使用光栅严格理论,得到其主要特征与实时监测实验曲线一致的理论模拟监测曲线。理论分析和实验证实,该模型基本表征了工艺条件对光栅沟槽形状的影响,并揭示了光刻胶呈现显著非线性效应时,必然对应着明暗条纹中心位置之间的显影刻蚀速率相差很大。这个模型为全息光栅的工艺研究提供了一个有效的理论分析工具。     

高密度光盘存储中的梯形光栅设计和误差分析

为了符合实际加工情形，推导了梯形相位光栅衍射效率，与矩形光栅作了比较，设计其用作高密度光盘存储光学头分光束器件时的各参数，并分析推导了系统和随机加工误差对光栅性能的影响及设计原则。     

全息离子束刻蚀衍射光栅

全息离子束刻蚀衍射光栅集中了机械刻划光栅的高效率和全息光栅的无鬼线、低杂散光、高信噪比的优点．全息离子束刻蚀已作为常规工艺手段应用于真空紫外及软x射线衍射光栅的制作．文章对全息离子束刻蚀衍射光栅的制作方法、主要类型、研究现状和应用进行了综述．     

金纳米颗粒掺杂光致聚合物的体全息混合光栅模型

金纳米颗粒掺杂光致聚合物在全息曝光过程中,光产物周期分布会形成折射率调制相位型主光栅,同时金纳米颗粒周期分布形成由局域表面等离子体共振引起强吸收的振幅型辅助光栅。研究基于耦合波理论的一种混合光栅模型,分析了光栅的体全息光学特性。结果表明,混合光栅中的折射率光栅和吸收光栅都能够提升体光栅的衍射效率; 体光栅的角度选择性也可以得到明显的改善。     

Holographic formation of dynamic transmission diffraction gratings in a photopolymer material in the process of two-beam interaction at low contrasts

In the present study, the process of formation of holographic transmission diffraction gratings in photopolymer media is investigated at low contrasts with allowance for self-diffraction of recording waves. A theoretical model for the first spatial harmonics of the refractive index grating is constructed based on a solution of the coupled kinetic photopolymerization and diffraction equations. The temporal dynamics of amplitude and phase spatial profiles of harmonics, diffraction efficiency, and angular selectivity of recorded gratings is theoretically investigated. The calculated and experimental data are compared. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 35–42, November, 2006.     

光聚合物中全息光栅的温度依赖性研究

在Polyacrylic Acid(PPA)光聚合物中用双光束相干的方法成功地写入了全息光栅,用He-Ne 激光器作为探测光对光栅的写入过程进行了实时监测.分两种情况重点研究了温度对光栅成栅过程的影响,一是在不同的温度下写入光栅;二是在室温下写入光栅,待光栅强度达到最高时再改变温度来研究温度对光栅的影响.实验中温度的变化范围为25 ℃~100℃.     

New methods of fabricating gratings for deformation measurements: A review

Gratings have been widely accepted as practical and effective deformation carriers/sensors and are commonly used in many deformation measurement methods. Since the deformation measurement sensitivity is directly proportional to the grating frequency, and the measurement accuracy is strongly affected by the grating quality. Thus, it is crucial to prepare an appropriate grating on the specimen surface that is to be measured. Over the past few decades, an increasing number of grating fabrication methods have been developed, including holographic photolithography, electron beam lithography, focused ion beam etching, nanoimprinting, soft lithography, and others. Although substantial literature regarding grating fabrication can be found, a comprehensive review is still necessary to promote the application of these methods. This review introduces the technical details and characteristics of recently developed grating fabrication methods and provides suggestions of which grating fabrication methods to use in correspondence with different deformation measurement methods. Emphasis is placed on the introduction of grating fabrication processes and the quality and applicability of the resulting gratings.     

I型全息凹面光栅制作误差对光谱像的影响分析

通过对I型全息凹面光栅制作参量误差对光谱像的影响进行数值计算发现|1)两记录臂长的相对误差而不是绝对误差决定光谱像的展宽程度,即使绝对误差较大,只要两记录臂长的误差值相同,像宽也没有明显改变|2)由于I型光栅的记录臂一般较长,记录角度误差对像宽的影响不大,但会影响光栅的刻线密度,导致光谱成像位置的偏移|3)曲率半径误差对像宽的影响较大.通过数值模拟明确了I型全息凹面光栅制作的误差容许范围,找到了对光谱像宽度影响较大的误差来源,从而为此类光栅的制作提供理论指导,有助于制作出高质量光栅,降低罗兰圆光谱仪的调节难度.     

平面全息光栅刻线密度的倍频式调整方法

刻线密度准确与否直接影响光栅色散及给定波长的衍射方向,进而影响光谱仪器结构设计.为了提高全息光栅刻线密度的制作精度,提出了平面全息光栅刻线密度的倍频式调整方法.将给定刻线密度的基准光栅放在干涉场曝光区域内,调节光束干涉角,干涉场曝光光束经基准光栅衍射后,根据调整光栅刻线密度的不同选择不同的衍射级次相互叠加形成莫尔条纹,...     

Exact solution of stationary holographic four-wave mixing in photorefractive crystals: two-level model

Based on the two-level model of recording and read-out of dynamic holographic gratings, precise expressions for wave amplitudes, diffraction efficiency and the gain coefficient representing the generalization of the corresponding formula by Kukhtarevet al. have been obtained. This model allows one to take into account the effect of the read-out beam on the holographic grating and to solve a problem of four-wave mixing in transmission geometry with wave depletion and arbitrary value of the spatial phase shift between the holographic grating and the interference pattern.     

Diffraction properties of ultrashort pulsed beams with arbitrary temporal profiles by a reflection volume holographic grating

The diffraction properties of reflection volume holographic gratings are studied when the gratings are illuminated by an ultrashort beam with arbitrary temporal profiles. The modified Kogelnik's theory of coupled waves is used. Simple analytical expressions for spectral and temporal distribution of the transmitted and diffracted are obtained. The dependences of the diffraction bandwidth, the Bragg selectivity bandwidth and the total diffraction efficiency of the reflection volume grating on the temporal profiles of the input ultrashort pulse are investigated. Study shows that the bandwidth of the reflection volume holographic gratings varies with the grating parameters more slowly than the transmitting volume holographic gratings. For three different temporal profiles, numerical results about diffraction properties of the reflection volume holographic gratings are given and compared with the transmitting volume holographic gratings.     

大角带宽高衍射效率体全息光栅的设计和制备

高性能体全息光栅是全息波导的重要耦合元件,角带宽小、平均衍射效率不高是制约体全息光栅性能的重要因素.以不对称倾斜记录为出发点,设计并制备了大角带宽高衍射效率的体全息光栅.首先讨论在横电模式光和横磁模式光下体全息光栅的记录参数与其衍射效率的关系,找到平均衍射效率较高的记录参数范围,随后进一步分析在此范围内的记录参数与体全...     

Diffraction gratings: aberrations and applications

Diffraction grating is an optical instrument, which is advantageously used for scientific research in spectroscopy and spatial filtering. It has many other applications in science and technology such as wavelength selectors for tuneable lasers, selective surfaces for solar energy, masks for photolithography, beam sampling mirrors for high power lasers, spectrometers in extreme UV and X-ray regions for space optics, metrology, phase measuring interferometry and pattern recognition, etc. Although the holographic gratings have many advantages over the ruled gratings but they have not yet eliminated completely the classical ruled gratings as the ruled gratings have their own importance in many applications. Therefore, in this article, both the ruled and holographic gratings will be discussed, in particular, their focusing properties, aberrations, and their applications.     

基于共振异常的消偏振型窄带滤波器分析

亚波长光栅因光栅参量的不同而具有不同的衍射特性,通过对亚波长光栅参量的合理设计来实现消偏振窄带滤波是一种新的方法与途径。首先分析了基于共振异常的窄带滤波的物理机制及存在条件,讨论了二维亚波长光栅实现消偏振窄带滤波的可能性。然后,利用严格模式理论进行了计算模拟,其计算结果与导波理论所得结果基本吻合,其衍射特性表现出周期性共振异常、敏感的角度依赖性和波长依赖性。最后,讨论了由工艺误差对滤波特性所带来的影响。为具体工艺制作提供了一定的指导。     

Modified phase contrast for recording of holographic optical elements

A modified phase contrast method is described for the fabrication of holographic optical elements with in-line diffraction patterns. In this method, a liquid crystal phase modulator is addressed by computer-generated holograms to achieve variable phase gratings. The phase gratings are imaged onto photosensitive material by a phase contrast method without a Fourier filter. We show the analytical treatment of the modified phase contrast method and demonstrate the application in holographic recording.     

Direct Fabrication Methods of Surface Relief Electro-Optic Gratings in Azo-Polymer Films

Two fabrication methods of surface relief electro-optic (EO) gratings in azo-polymer films are described: surface deformation by a continuous wave laser and laser ablation by a pulse laser. In the fabrication process, the periodic intensity modulation of laser beams is formed by an interference fringe or a phase mask. The surface relief EO grating is fabricated by poling the surface relief grating (SRG) after the SRG fabrication process. The linear dependence of an applied voltage in the modulation efficiency of the first-order diffraction beam is observed. The proposed methods are effective for highly-efficient surface relief EO grating fabrication.     

On the Fresnel diffraction pattern of phase holographic gratings

The Fresnel diffraction pattern of phase diffraction gratings is studied on the example of idealized sinusoidal relief-phase plane holographic thermoplastic gratings. It is shown that, in the region of low spatial frequencies, which are more than two times lower than the inverse wavelength of the reading coherent radiation, the intensities of the main diffraction maxima, the diffraction efficiency, and the light-scattering power are independent of the spatial frequency of the phase gratings under investigation, which are characterized by a sinusoidal law of modulation of the reading-radiation phase. It is established that the range of spatial frequencies at which a plateau is observed in these dependences increases with decreasing amplitude of the phase modulation of the reading light. These dependences are also observed to have similar character for the thermoplastic holographic gratings under study. Calculations were performed to analyze the influence of real profiles of thermoplastic strain on the diffraction efficiency and light-scattering power of such gratings. On the basis of analysis of the results obtained, recommendations on using holographic and raster techniques of recording data on phase carriers are given that make it possible to improve the quality of the restored optical image.     

Formation of positive and negative anisotropic holographic gratings depending on recording energy in photoreactive liquid crystalline copolymer films

Anisotropic diffractive gratings formed by birefringent molecular alignment are fabricated by a holographic technique using a photo-cross-linkable liquid crystalline copolymer (PLCCP). Depending on the exposure energy used for holographic recording, bright or dark regions of the interference fringe can be chosen for the molecular-aligned region, analogous to positive- and negative-type photoresist processing in photolithography. In conjunction with simultaneously generated surface relief gratings, the anisotropic refractive index modulation inherent in the PLCCP film exhibits different diffraction properties depending on the incident beam polarization. The anisotropic refractive index grating profiles are quantitatively presented for two cases determined by the exposure energy, based on the Fourier analysis of diffractive optics. The selection of different grating formations selected by varying only the exposure energy could provide a strategy for the fabrication of functionalized diffractive optical elements.