Microwave pulse compression using diffraction gratings

Electromagnetic pulse compressors employing gratings of high breakdown strength in the autocollimation regime at the center frequency of the pulse for p polarization are investigated theoretically. A theory is devised on the basis of a numerical solution of the electromagnetic field equations in an integral-equation formulation. The case of the aberrationless approximation of the compression of a bell-shaped pulse with a quadratically modulated phase is considered analytically. A numerical experiment demonstrates the presence of strong distortions in the pulse after compression, which are caused by the cubic and higher terms in the expansion of the frequency dependence of the phase acquired by the wave in the compressor. The conditions for optimal pulse compression with allowance for aberrations are investigated. Zh. Tekh. Fiz. 68, 82–90 (February 1998)     

Polarization beam splitters using polarization diffraction gratings

We report a polarization beam splitter that uses polarization gratings written onto a zero-twist nematic liquid-crystal display. We show three configurations. The first two separate the diffracted light into two orthogonally polarized orders that are either linearly or circularly polarized. In the third configuration, we demonstrate a novel case for which the output is separated into two nonorthonormal polarization states. One component is linearly polarized and the second is circularly polarized.     

An image deblurring method using diffraction gratings

A method of image deblurring is described, in which the restoration filter is derived from Ronchi rulings. Although two-dimensional spatial filtering is used, the method employs a line source, resulting in significant noise reduction. Experimental results are given.     

Holographic diffraction gratings using polymer-dispersed ferroelectric liquid crystals

By controlling the morphology of holographic polymer-dispersed ferroelectric liquid crystals (FLCs), highly aligned FLC domains are obtained for diffractive optical applications. Rapid, thresholdless switching is observed for various grating pitch sizes between approximately 3 and approximately 12 microm. A simple phenomenological model is presented encompassing a distribution of domain sizes and an effective field that stabilizes the FLC domains to reflect the observed thresholdless switching and optical behavior.     

Phonon diffraction gratings

A two-dimensional diffraction grating for phonons is described. It scatters thermal phonons strongly when their dominant wavelength is equal to the grating's lattice constant. Through measurements of the Kapitza resistance between the silicon crystal carrying the grating and liquid helium, it is shown that the scattering by the grating is predominantly coherent, as expected for phonon diffraction.     

Diffusion phase diffraction gratings

Ion exchange in glass is studied. The two-dimensional diffusion equation with periodic boundary conditions that describes the formation of a diffraction grating in glass is numerically solved. The existence of the optimum diffusion time providing the maximum diffraction efficiency in the first order is demonstrated. Dependences of the optimum diffusion time and the maximum diffraction efficiency on the space factor of a mask used for ion exchange are found.     

利用泽尼克系数求取衍射光栅的分辨本领

光栅分辨本领检测设备的焦距通常达几米甚至十几米,采用直接测量法难度大、成本高,利用衍射波前间接求取光栅分辨本领是解决该问题的有效途径之一。在光栅光谱成像傅里叶变换理论基础上,建立了利用泽尼克多项式拟合系数求解衍射光栅分辨本领的归一化模型,揭示了光栅衍射波前与分辨本领的求取关系,提出了依据泽尼克多项式拟合系数求取衍射光栅分辨本领的新方法。根据该方法实测了一块衍射光栅的分辨本领,并与直接测量法进行对比测试。结果表明该方法误差小于4.42%,降低了分辨本领的测试难度,是衍射光栅分辨本领求取的有效手段,应用于ZYGO干涉仪等仪器中,通过简单的波前测试即可得到定量的衍射光栅分辨本领指标。     

Profiling of holographic diffraction gratings by using silver-arsenic triselenide interaction

Rulings of holographic gratings were profiled by interaction of silver with chalcogenide glassy semiconductors. The shape of the rulings was determined with an atomic force microscope. Angular and spectral dependences of the diffraction efficiency of the gratings were found, and a relation between these dependences and the grating surface pattern was analyzed.     

Line selection in carbon dioxide waveguide lasers using diffraction gratings

This paper treats theoretically the coupling losses which arise in square dielectric waveguide CO₂ lasers when one element of the optical resonator is a diffraction grating. These losses are due to imperfect coupling of the radiation which is launched from the end of the guide to the grating and returned from the grating back to the guide. The results of the calculations show that the coupling efficiency is a sensitive function of radiation wavelength. This result is then used to investigate the ability of a 150 lines/mm diffraction grating to resolve adjacent rotational-vibrational transitions in the CO₂ emission. It is shown that “line-hopping” places a limitation on the maximum tunability which can be obtained and is a result of the poor discrimination at the grating surface especially in the case of waveguide lasers having much reduced apertures. Computations based on the scaling laws are employed to maximise the tunability as a function of waveguide aperture taking into account limitations imposed by “line-hopping”, cut-off and the optical resonator frequency offset condition of c/4L. Comparisons are made between theory and experiment, and design guidelines for the construction of widely tunable CO₂ waveguide lasers are presented graphically.     

Thermomechanical modification of diffraction gratings

The most accurate approaches to fabrication of diffraction gratings are known to be the lithographic and holographic methods. The lithographic methods allow fabrication of arbitrarily chirped gratings whose performance, however, is degraded by stitching errors. The holographic methods are free from stitching errors; however, they are limited in the achievable spatial variations of their grating periods. We suggest a method of diffraction grating modification by nonuniform heating and stretching that is much more flexible than the holographic approach and does not suffer from the problem of stitching error. We demonstrate our approach for quartz phase masks that have a characteristic grating period of 1 microm and a length of several centimeters. Our approach allows the grating periods of the phase masks to vary in a range from a few picometers to a few nanometers and a spatial resolution of a few millimeters. It is shown that the grating period can be modified with a negligible effect on the profile of the gratings.     

Ray picture of diffraction gratings

We elaborate on a geometrical picture of diffraction gratings. Exact paraxial propagation including coherence effects is obtained by allowing the geometrical rays to transport Wigner function instead of simply specific intensity. We apply this formalism to perfect and less than perfect gratings, illuminated by plane and Gaussian waves.     

Optical testing of ultrasonic phase gratings using a Fresnel diffraction method

A simple optical method is proposed for studying the Raman-Nath parameter of plane, sinusoidal, ultrasonic beams. The Fresnel diffraction field of a continuous ultrasonic grating illuminated by a collimated laser beam is measured by a photodetector placed mid-way between the self-image planes of the grating. Measurement of the amplitude of the fundamental of the output signal enables the absolute determination of the depth of phase modulation. A comparison of the proposed method with the techniques discussed in the literature is presented.     

Profile formation in holographic diffraction gratings

A theoretical method is outlined for the calculation of the profiles of holographic diffraction gratings produced in photo-resist. This method is shown to give results in agreement with all experimental observations of such profiles. Consideration is then given to the flexibility of arrangements for the formation of holographic gratings and an experimental system is discussed which fully utilizes this flexibility. The wide range of profiles which may be generated with such a system is demonstrated. Finally a theoretical programme of investigation is suggested which may well make possible the formation of holographic gratings of greatly improved spectral performance.     

Calculations of phase reflection diffraction gratings

Intensities of principal diffraction maxima for a phase reflection diffraction grating with a rectangular groove profile were calculated by the Fresnel method, using a special algorithm. The procedure under consideration enables us to perform high-efficiency calculations of diffracted-beam characteristics and can be used extensively to optimize diffraction-grating parameters.__________This revised version was published online in May 2005 with a correction on affiliation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 38–41, November 2004.     

Light diffraction on acoustophotorefractive holographic gratings

The intermediate regime of light diffraction on acoustophotorefractive holographic gratings written in cubic photorefractive crystals according to the synchronous-detection mechanism is studied. It is shown that the diffraction efficiency in sillenite-type gyrotropic crystals only slightly depends on the incident light polarization and the external electric field. The highest diffraction efficiency in nongyrotropic crystals was achieved for p-polarized writing and reading light and at a considerable external electric field strength.     

Shape resonances in nested diffraction gratings

The diffraction problem of a plane wave impinging on a grating formed by nested cavities is solved by means of the modal method, for s and p polarization modes. The cavities are formed by perfectly conducting sheets that describe rectangular profiles. The electromagnetic response of the grating is analyzed, paying particular attention to the generation of resonances within the structure. The dependence of the resonances on the geometrical parameters of the grating is studied, and results of far and near field are shown. The results are checked and compared with those available in the literature for certain limit cases.     

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．     

Real-time diffraction gratings in DDI-methanol solutions

Nondegenerate four-wave mixing has been performed in DDI-methanol solutions using ruby laser as writing beams. The reading beam was either a pulsed one at 538.8 nm or a continuous one at 632.8 nm. Contributions from both saturation and thermal gratings were separated temporally and evaluated.