共查询到20条相似文献,搜索用时 15 毫秒
1.
V. A. Bushuev A. I. Frank G. V. Kulin 《Journal of Experimental and Theoretical Physics》2016,122(1):32-42
A multiwave dynamic theory of diffraction of ultracold neutrons from a moving phase grating has been developed in the approximation of coupled slowly varying amplitudes of wavefunctions. The effect of the velocity, period, and height of grooves of the grating, as well as the spectral angular distribution of the intensity of incident neurons, on the discrete energy spectrum and the intensity of diffraction reflections of various orders has been analyzed. 相似文献
2.
We demonstrate a novel approach to the moving grating technique for removal of velocity ambiguity in a laser Doppler velocimeter. The method replaces the continuous motion of a moving grating with a grating which can be positioned or switched to three distinct phase positions. Advantages of this approach are its potential for compact implementation and high stability of the velocity offset. 相似文献
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A new scheme for recording a dynamic phase grating with an asymmetric profile in C60-doped homeotropically aligned nematic liquid crystal(NLC) was presented.An oblique incidence beam was used to record the thin asymmetric dynamic phase holographic grating.The diffraction efficiency we achieved is more than 40%,exceeding the theoretical limit for symmetric profile gratings.Both facts can be explained by assuming that a grating with an asymmetric saw-tooth profile is formed in the NLC.Finally,physical mechanism and mathematical model for characterizing the asymmetric phase holographic grating were presented,based on the photo-refractive-like(PR-like) effect. 相似文献
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We report a novel kind of all-optical dynamic grating based on Brillouin scattering in a polarization maintaining fiber (PMF). A moving acoustic grating is generated by stimulated Brillouin scattering between writing beams in one polarization and used to reflect an orthogonally polarized reading beam at different wavelengths. The center wavelength of the grating is controllable by detuning the writing beams, and the 3 dB bandwidth of approximately 80 MHz is observed with the tunable reflectance of up to 4% in a 30 m PMF. 相似文献
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Surface profile inspection of a moving object by using dual-frequency Fourier transform profilometry
The 2π phase ambiguity caused by surface isolations and large height step can be solved by dual-frequency projection grating profilometry. However, in the Fourier transform profilometry (FTP) of a moving object, only one single deformed fringe pattern can be obtained. In order to introduce the dual-frequency technique into the FTP of moving object, a novel experimental system is designed to capture two fringe patterns with different frequency at the same time. A grating structure comprising two regions with different frequencies is projected upon the surface of the detected object. Two line-scan CCD cameras are used to capture the surface images encoded by the two kinds of patterns, respectively. By getting the corresponding image intensity at the same point of the object surface in the two acquired images, the dual-frequency technique is applied to extract the real phase without phase ambiguity. The surface profile of a specimen with a large height step is measured to prove the feasibility of the proposed method. The experimental results show that the proposed method can solve the 2π phase ambiguity problem successfully in the surface profile inspection of a moving object. 相似文献
9.
Alon Bahabad 《Optical and Quantum Electronics》2014,46(8):1065-1077
A first-principles tutorial account is given for the diffraction of either light or free, non-relativistic, massive particles from a moving grating. Discussion on the properties of the moving grating including non-reciprocity is followed by considering both Raman-Nath (thin grating) diffraction and Bragg (thick grating) diffraction in either transmission or reflection geometry. Use of four-momentum conservation with dispersion relations yield the angles of diffraction. The increase in the angle of diffraction for grazing incident by using a moving grating relative to using a static grating is calculated. It is shown that this increase is possible only for Raman-Nath geometry. 相似文献
10.
In the course of processing deformed grating patterns and obtaining an object's height distribution with a digital filter, several factors, such as dynamic and frequency ranges of phase signal, background luminance and reflection coefficient of the measured object, grating period, filter passband, time drift of image data, etc., may exert an influence on the phase measurement accuracy. Through simulation and experiment, the influence is discussed and the conclusion is that, by choosing a suitable grating period and filter frequency characteristic according to the frequency range of the phase signal, the phase measurement error will be reduced. 相似文献
11.
The dynamic behavior of a holographic grating induced in a homeotropically aligned dye-doped liquid-crystal film is investigated. In the presence of an applied dc voltage, photoexcited azo dyes induce a photorefractive grating and then diffuse and are adsorbed onto cell substrates. The reorientation of liquid crystals as a result of adsorbed dyes leads to a phase grating that is phase shifted 90 degrees from the photorefractive grating. Competition of these two gratings induces two-beam coupling of the writing beams, initially transferring energy from beam 1 to beam 2 and then, after a pause, from beam 2 to beam 1. 相似文献
12.
Yang Li Yi-Ping Cao Zhen-Fen Huang De-Liang Chen Shun-Ping Shi 《Optics Communications》2012,285(21-22):4285-4289
A three-dimensional on-line measurement method based on five unequal steps phase-shifting with phase measuring profilometry is presented. While only one sinusoidal grating pattern is projected onto the measured object moving with the pipe-line, five arbitrary deformed patterns are captured by CCD as the measured object moves within a duty cycle of the grating pattern. The modulation distribution based on Fourier transform profilometry is introduced to realize pixel matching so as to calculate the corresponding equivalent shifted phase on the deformed patterns. A five unequal steps phase shifting algorithm is developed, which is suitable for non-uniform motion of the pipeline. The experiments verify its feasibility and validity. 相似文献
13.
T. Malinauskas S. Nargelas R. Aleksiejunas K. Jarasiunas 《Optics Communications》2008,281(24):6061-6064
A novel heterodyne detection scheme for light-induced transient grating technique is presented. The heterodyne detection is achieved coherently mixing the picosecond pulses of diffracted and scattered light. A phase difference between these pulses is controlled by moving a holographic beam splitter along its grating vector. This approach is employed to study a competition of coexisting electronic and thermal optical nonlinearities in CVD grown diamond films in sub-nanosecond time domain and to determine carrier parameters. 相似文献
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Improvement of holographic recording property of a Ce: KNSBN crystal by the moving grating technique
The moving grating technique is applied to improve the holographic recording property of the Ce: KNSBN crystal. In the case of extraordinarily polarized recording, the diffraction efficiency at large fringe modulations is enhanced by a factor of up to 35% at the optimum fringe velocity and the fringe modulation dynamic range is improved from m = 0.2 to m = 0.6. In the case of ordinarily polarized recording, a linear holographic reconstruction in the range of m ≤ 0.8 can be achieved by the moving grating at a fringe velocity of 9.6 nm/s. These results are significant in holography where a grey-level object needs to be recorded and reconstructed with high fidelity. 相似文献
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光栅平动式光调制器结构参量的优化分析 总被引:4,自引:0,他引:4
提出的光栅平动式光调制器是一种基于微机电系统(MEMS)工艺的光调制器,利用其表面具有的变形部分(可动光栅)提供衍射光栅,通过控制可动光栅的位移实现光调制器的两种工作状态,即亮态和暗态。根据衍射理论和傅里叶光学对光栅平动式光调制器工作状态的光学特性进行了详细的理论分析和仿真。重点讨论了可动光栅占空比、长度L1、垂直光栅周期方向上边框长度、光栅栅条宽度、整个器件的光栅周期数等对光调制器工作性能的影响。结果表明,可动光栅与反射镜的距离为入射波长的一半时,调制器工作在暗态;而当可动光栅向反射镜方向下移入射波长的1/4时,光调制器工作在亮态;要达到最佳的衬比度,需满足可动光栅的栅条宽度为光栅周期的一半,L1应该为光栅周期的整数倍;在不满足L1为光栅周期d的整数倍时,可动光栅在垂直于光栅周期方向上的边框越小越好;光栅栅条越宽、光栅周期数越多,衬比度越高。 相似文献
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X射线光栅相衬成像存在系统复杂、成像效率低、步进精度要求高、光栅加工难度大等问题.本文设计了一种双能阵列X射线源和双能分析光栅,并应用于X射线光栅相衬成像,提出了一种双能X射线光栅相衬成像系统,阐述了该成像系统的成像原理和相位信息提取方法.提出的成像系统不需要精密步进平台,精简了成像系统,避免了步进误差导致的成像质量降低问题;两次曝光就可以成像,提高了成像效率;双能阵列X射线源、双能分析光栅的应用避免了源光栅、分析光栅难以加工的问题.对提出的成像系统及其相位提取方法进行了仿真,仿真结果显示成像系统可以正常成像,提取到的检测样本的X射线相衬成像相位一阶导数分布与相关文献实验所得结果一致. 相似文献
17.
The possibility of time focusing for very slow neutrons is considered. This focusing may prove very useful in solving the problem of accumulating ultracold neutrons in a trap that are generated by a pulsed source. Diffraction at a phase grating moving across a beam or resonance neutron-spin flip is proposed to implement time-controlled changes in the neutron energy. 相似文献
18.
S. Balasubramanian I. Lahiri Y. Ding M.R. Melloch D.D. Nolte 《Applied physics. B, Lasers and optics》1999,68(5):863-869
The photorefractive response to an applied electric field is measured in a photorefractive quantum well, providing evidence
in favor of the nonlinear transport in the device due to the hot electrons. The reduced mobility of the hot electrons limits
the drift length, and thereby limits fringe overshoot. Thus the nonlinear transport prevents the slowing down of the grating
writing rate for increasing fields which is common in bulk photorefractives. The photorefractive phase shift in transverse-field
photorefractive quantum wells is measured as a function of the frequency offset between two laser writing beams that generate
moving gratings. The two-wave mixing passes through a maximum at an optimum frequency which depends on the magnitude and the
sign of the applied dc electric field. The phase shift associated with the moving grating adds or subtracts from the static
phase shift induced by hot-electron transport in the semiconductor quantum wells, depending on the sign of the field and the
sign of the dominant photocarriers. We observe a linear relationship between the roll-off frequency and the power of the writing
beams.
Received: 26 November 1998 / Revised version: 22 January 1999 / Published online: 12 April 1999 相似文献
19.
The possibility of creating a time lens, an analogue of the zone plate in X-ray optics, for ultracold neutrons is experimentally demonstrated. The neutron energy was changed by means of a purely quantum effect: the phase modulation of a neutron wave at a variable modulation frequency. The modulator was a phase grating with variable spatial period moving across the neutron beam. 相似文献