Interference and diffraction effects in folding mirror schlieren diffraction interferometer

Experimental investigations on interference and diffraction phenomenon occurring in a folding mirror schlieren diffraction interferometer have been presented. It is shown that the well-known Lloyd mirror interferometer can easily be converted into a folding mirror schlieren diffraction interferometer. Various intermediate stages occur as the basic two-beam interference pattern in Lloyd mirror interferometer is transformed into a schlieren diffraction pattern. Study of these intermediate stages gives a good insight in understanding the transition behaviour between the fundamental phenomenon of interference and diffraction taking place as the mirror-edge approaches the Airy disk.     

Study of shockwave propagation in a metal bar by high-speed interferometry

The work described in this paper is aimed at establishing the profile of the transient displacement of a point on the side of a long metal bar when a compression wave travels along it. The part of the bar to be examined is polished optically flat and is used as one reflector in a conventional two-beam interferometer. The passage of the wave distorts the polished area. The resulting transient fringe pattern, representing the distortion in the out-of-plane direction is recorded by high-speed streak photography. From the records obtained it is easy to derive high resolution graphs of displacement against time.In many cases satisfactory results can be obtained using a small mirror attached to the bar with adhesive, so avoiding the troublesome process of optically polishing part of the surface.     

Direct visualization of Young’s boundary diffraction wave

Experimental investigations on Young’s boundary diffraction wave are presented where a wavefront division interferometric scheme is used on diffracted wavefront to generate two-beam interference fringes in the geometrically shadow region. These fringes have good visibility and are observable in the whole space, strongly advocating the physical existence of Young’s boundary diffraction wave as a separate entity. Analysis of these fringes may provide vital information about the structure and nature of boundary diffraction wave e.g. existence in whole space, dependence of amplitude on obliquity factor etc.     

点衍射干涉检测技术

本文介绍了点衍射干涉仪不同发展阶段的特点和应用。点衍射干涉仪由波长量级的针孔产生高质量的球面波作为参考波前,能够得到衍射极限性能的分辨率。按照不同的光路特点,点衍射干涉仪可分为点衍射共路干涉和点衍射非共路干涉两种结构,主要应用于高精度波前检测和面形检测。共路干涉结构简单紧凑,对环境振动不敏感,对光源相干度要求不高,可利用光束偏振态及光栅衍射分束的特性对传统点衍射板进行改造,在全共路点衍射干涉仪中引入时间相位调制技术和干涉对比度可调技术,可进一步提高波前检测精度。采用反射式针孔和各种光纤结构发展了非共路点衍射干涉仪,实现了大口径、高精度球面反射镜面形的测量。本文重点阐述了用于极紫外光刻投影物镜中高精度球面反射镜面形检测的反射式针孔点衍射干涉仪,并展望了点衍射检测技术在生物检测等领域的应用前景和发展趋势。     

毛细管干涉仪的理论分析

从几何光学出发,推导了毛细管干涉仪的从柱面透镜到接收屏的光线的光程．对光线追迹模拟,结果表明毛细管干涉仪的干涉条纹的形成可用双光束的干涉来解释．从柱面不同位置入射的两条光线可能具有相同的光程,而且从柱面透镜不同位置出发的两条光线可能到达接收屏的同一点,当它们满足相干条件时,就会形成干涉条纹．建立了干涉条纹的计算机模拟程序, 模拟了毛细管中液体折射率、毛细管内径、外径对干涉条纹的影响. 结果表明实验中应使用薄壁毛细管, 由于干涉条纹对柱面透镜到毛细管之间的距离非常敏感, 为提高精度, 建议在实验中用已知折射率的标样来确定这一距离.     

双光束干涉光谱术中的TSVD方法

本文考察了双光束干涉光谱仪中应用TSVD方法的结果,发现由于积分核cos(2πσx)的正交对称性质使得截断奇异值无法进行,而将积分核变形后再做截断,其实质是截去了积分核逆矩阵中的一部分,从而说明了双光束干涉光谱术中采用TSVD方法能够使复原光谱高波数侧具有较高信噪比的根本原因。     

Adaptive wave-front correction by means of all-optical feedback interferometry

A novel adaptive wave-front correction system based on an all-optical feedback interferometer is described. In this system the two-dimensional output fringe intensity from a Mach-Zehnder interferometer with large radial shear is optically fed back to an optically addressed phase-only liquid-crystal spatial light modulator. Consequently, without a separate aberration-free reference wave, the modulator phase approximates the conjugate of the interferometer phase that is directly related to the phase of the input aberrated wave front, so this system is applicable in adaptive optics. We successfully achieved real-time correction of aberrated wave fronts: A diffraction pattern that was seriously distorted because of aberrations was transformed into a diffraction-limited spot immediately after the feedback loop was closed.     

Breaking the far-field diffraction limit in optical nanopatterning via repeated photochemical and electrochemical transitions in photochromic molecules

By saturating a photochromic transition with a nodal illumination (wavelength, λ), one isomeric form of a small molecule is spatially localized to a region smaller than the far-field diffraction limit. A selective oxidation step effectively locks this pattern allowing repeated patterning. Using this approach and a two-beam interferometer, we demonstrate isolated lines as narrow as λ/8 (78 nm) and spacing between features as narrow as λ/4 (153 nm). This is considerably smaller than the minimum far-field diffraction limit of λ/2. Most significantly, nanopatterning is achieved via single-photon reactions and at low light levels, which in turn allow for high throughput.     

Enhancing the phase profile and contrast of an interferogram by polarization recording in bacteriorhodopsin

Interferometry is a technique for reconstructing the profiles of phase objects. We present a novel interferometric setup for generating interferograms with doubled phase profile and enhanced contrast compared with the standard interferogram. The proposed system consists of a two-beam interferometer in which the reference and test waves are circularly polarized orthogonally to each other. They are superposed upon a bacteriorhodopsin film, creating a polarization grating that is distorted by the phase of the test object. This polarization pattern is read by a polarized He-Ne beam. We show analytically and experimentally that, when the zero diffraction order is removed, an interferogram with doubled phase profile and enhanced contrast is obtained.     

Phase modulation by polarization recording in bacteriorhodopsin: application to phase-shifting interferometry

A novel phase-control method with application to phase-shifting interferometry is presented. The linear polarization state of an external (green) light beam is recorded on a bacteriorhodopsin film, and this polarization state is read by a circular polarized (red) laser beam. By reading the bacteriorhodopsin film, the original (red) wave reverses its circularity and becomes phase shifted by an amount that is dependent on the polarization of the external (green) beam. This method of phase control can be applied in a two-beam interferometer in which the test and reference waves are orthogonally polarized, which allows one to obtain phase modulation without moving parts inside the interferometer.     

Phase-difference amplification using a Sagnac interferometer

In this paper, we describe a new method for achieving phase-difference amplification, which is quick and convenient, operates in real time, and requires no photographic steps. Magnification factors of 2, 4 or 6 are achieved easily in one step. Because the system operates in real time, phase stepping may be applied to extract the amplified phase distributions. Our method is a variation on longitudinally reversed shearing interferometry, using first- or higher-order diffraction from a grating (hologram) which is in fact the interferogram of the wavefront under test. The grating is derived from a standard two-beam interferometer which is phase-stepped, and displayed in real time on a spatial light modulator in the phase-difference amplification setup. It is illuminated by the two output beams from a Sagnac interferometer, similar to the set up used by (Barnes et al. Barnes TH, Eiju T, Matsuda K. Appl Opt 1986; 25:1864). for spectral resolution enhancement, and a phase-amplified fringe pattern is obtained by spatial filtering using a Fourier transform lens. We demonstrate operation of the phase amplifier and show amplified phase maps retrieved by phase-stepping. We believe this is the first time that real-time phase amplification without photographic steps and with phase stepping has been demonstrated.     

Relative beam misalignment errors in high accuracy displacement interferometers: calculation and detection

We consider the effects of misalignment in a two-beam interferometer resulting from lateral displacement as well as angular misalignment of the beams. Furthermore, a technique to determine such misalignments is discussed and examples of measurement strategies and expected performance are given. It is found that, when the waist of the beam used to illuminate the interferometer is larger than 0.7 mm (∼1000λ), such an approach allows alignment to be made resulting in a relative interferometric error smaller than 1×10⁻¹⁰ provided that the diffraction effect is fully accounted for.     

Fabry-Perot interferometer with diffraction-scattered reflection of light

The incorporation of a phase grating into the optical system of a Fabry-Perot interferometer makes it possible to transform the incident beam of light so that the major part of energy in the reflected wave is contained in the side lobes in the far-field diffraction pattern and radiation in the zero order of diffraction along the optical axis is suppressed. Experimental results are presented, which are obtained with a grating produced by evaporating a thin-layer dielectric coating onto the input mirror of the interferometer.     

小孔干涉仪滤波孔的研究

用惠更斯-基尔霍夫公式对小孔干涉仪的滤波孔进行计算及分析后指出:尽管滤波孔小于爱里斑,滤波孔的位置对参考波的质量仍有影响。在接收面上参考波位相有较大偏移处,往往伴有较大的光强变化(变弱)。给出实验结果,并进行了讨论。     

光折变相位栅衍射动态特性的严格耦合波分析

利用严格耦合波衍射理论分析了光折变体相位光栅的衍射问题,给出了光折变二波耦合动态特性的严格耦合波分析及其对入射光束夹角和初始入射光强比的依赖关系.实验上对掺铜KNSBN晶体二波耦合的动态特性进行了测量,实验结果和数值模拟符合得很好.     

全光纤速度干涉仪设计及应用

针对冲击波物理与爆轰物理等研究领域中对高速运动物体进行连续速度测量的需求,设计了一种全光纤速度干涉仪.该干涉仪采用单模光纤作为光传输和延迟元件,对t和t-τ两个时刻由于速度变化而引起的多普勒差拍信号进行检测.由于两个时刻的两束光信号对应的待测物体速度变化不大,因而两者几乎有相等的频移量,从而大大降低了差拍信号频率.并且,通过光纤长度的改变,灵活调节条纹常量（τ值）,使差拍信号频率不超过记录系统的带宽,从原理上解决记录系统响应带宽受限问题,拓展测速的上限.单模光纤的采用,对漫反射光起到了较好的选模作用,使干涉仪实现了对漫反射靶的测量.实验设计了1.5 m·s-1和150 m·s-1两种条纹常量,对低速过程的霍普金森杆实验和高速过程的激光驱动实验分别进行了测试,取得较好结果,证明了该干涉测试技术的有效性.     

点衍射干涉仪波面参考源误差及公差分析

为了保留光纤点衍射干涉仪容易对准以及衍射光束易于控制的优点,同时又能实现大数值孔径（NA）光学系统的检测,设计了一种新型的波面参考源（WRS）,它保留了光纤点衍射和微孔点衍射的优点,可满足大NA极紫外光刻物镜系统波像差检测的要求。本文在分析各种误差的基础上,搭建了WRS原理光路并对WRS的系统误差标定算法进行详细的研究,得到WRS标定时旋转平台的角度公差为0.5°,跳径时偏离系数为0.5%。这一新型WRS误差分析及标定对于实现高精度的检测具有十分重要的意义,最终为实现WRS系统误差标定提供理论基础。     

Analysis of lateral-spread photorefractive planar lenses

The photorefractive planar lens for converting a vertical incident plane wave to a lateral-spread spherical wave and vice versa, is suggested. Using the two-beam coupled-wave theory, the coupled wave equations are derived and their half-analytical solutions are also given in terms of an infinite series. The diffraction properties (beam profiles, diffraction efficiency) of the local volume grating in the lens are presented. And the focusing property of the lens is discussed and compared with that of an ideal convergent spherical wave. It is demonstrated that the suggested photorefractive planar lens shows a good focusing effect.     

Investigation of interference field phase distribution with a lateral shearing interferometer

Problems of investigating the interference field are discussed. An investigation method is suggested which is based on using an imperfect plane-parallel plate lateral shearing interferometer for comparing aberrations in the arms of the two-beam interferometer which generates the interference field. It is demonstrated that equipartition of interference field fringes can be analyzed to an accuracy of λ/100 which exceeds the manufacturing accuracy of the lateral shearing interferometer.     

Modified polarization point diffraction interferometer with extended measurable NA for spherical surface testing

The small pinhole of point diffraction interferometer based on pinhole-point diffraction places ultra-high requirement on both the adjustment of testing system and performance of CCD camera. Besides, poor fringe contrast due to the low reflectivity of test spherical surface would limit the measurement precision in the processing of fringe pattern. A modified polarization point diffraction interferometer with extended measurable numerical aperture (NA) is presented for testing the spherical surfaces with low reflectivity. Measurement error factors as well as the corresponding calibration procedure are introduced in detail. Comparing with the results of Zygo interferometer, measurement accuracy with root-mean-square (RMS) value about 0.0026λ and peak-to-valley (PV) 0.0134λ is achieved. The system has good measurement repeatability, and the standard deviation of measurement results RMS better than 0.0010λ is obtained. The proposed interferometer reduces the difficulty in the adjustment of the system and provides a feasible way for testing the surfaces with low reflectivity and high NA.