利用保角变换实现环形光栅的Talbot效应

Talbot效应是一种近场自成像效应,通常只有周期光栅可以产生Talbot效应,而环形光栅无法产生.本文通过引入保角变换,发现可以在环形光栅外部设计适当的折射率渐变层介质,使得其中也能够产生严格的Talbot效应,并计算了对应的自成像半径表达式.本文利用FDTD软件分别将一个环形光栅放置在真空中以及人工设计的折射率渐变层中进行了模拟,并对二者的结果进行了比较分析,发现这种折射率渐变层介质确实对点光源入射的环形光栅的自成像情况有着很好的改善.希望这一工作能够推广Talbot效应的应用范围.     

Influence of the size of the grating on Talbot effect

The Fresnel theory of the Talbot effect of the grating is reviewed in this paper, and the general formula of the Fresnel diffraction of the grating with finite aperture size is presented. The aperture effect of the grating on the Talbot image is discussed and a number of numerical calculations are performed. The variation rule of the diffraction intensity distribution at the Talbot distance with the aperture size of the grating and the case at different Talbot distances are obtained through the calculations, and the corresponding explanations of these phenomena are given in this paper. We think that these discussions provide the theoretic basis for the practical application of the Talbot effect of the actual grating.     

Talbot effect of a high-density grating under femtosecond laser illumination

The Talbot effect of a high-density grating under femtosecond laser illumination is analyzed with rigorous electromagnetic theory which is based on the Fourier decomposition and the rigorous coupled-wave analysis (RCWA). Numerical simulations show that the contrast of the Talbot images steadily decreases as the transmitted femtosecond laser pulses propagate forward and with wider spectrum width of the femtosecond laser pulses. The Talbot images of high-density gratings have much higher sensitivity of the spectrum widths of the incident laser pulses than those of the traditional low-density gratings. In experiments, the spectrums and the pulse widths of the incident pulses are measured with a frequency-resolved optical grating (FROG) apparatus. The Talbot images are detected by using a Talbot scanning near-field optical microscopy (Talbot-SNOM) technique, which are in coincidence with the numerical simulations. This effect should be useful for developing new femtosecond laser techniques and devices.     

Borman effect in resonant diffraction of X-rays

A dynamic theory of resonant diffraction (occurring when the energy of incident radiation is close to the energy of the absorption edge of an element in the composition of a given substance) of synchronous X-rays is developed in the two-wave approximation in the coplanar Laue geometry for large grazing angles in perfect crystals. A sharp decrease in the absorption coefficient in the substance with simultaneously satisfied diffraction conditions (Borman effect) is demonstrated, and the theoretical and first experimental results are compared. The calculations reveal the possibility of applying this approach in analyzing the quadrupole-quadrupole contribution to the absorption coefficient.     

啁啾超短脉冲光波照射下光栅Talbot效应的研究

应用傅里叶频谱分析法，给出了光栅在啁啾超短脉冲光波照射下菲涅耳衍射方程并分析了其Talbot效应. 数值计算表明，在Talbot距离处的衍射光强不仅与照射的超短脉冲光波的宽度有关，而且与脉冲光波的啁啾有关. 根据光栅在Talbot距离处衍射光强的变化，给出了一种检验超短脉冲光波是否含有啁啾的简单方法. 关键词： 光栅 菲涅耳衍射 Talbot效应 啁啾超短脉冲激光     

To measure chirped ultrashort laser pulse by the Talbot effect of a grating

We study the Fresnel diffraction of a phase grating under the illumination of a chirped femtosecond laser pulse. Using spatial spectrum theory, first we extract the central wavelength signal from the diffraction wave of the chirped pulse through a diaphragm. Then the central wavelength waves are directed to interfere in remote regions by two reflectors. The interference stripes at different distance will be exactly the same in interference region. Since the intensity distribution of the stripes is related to the chirp parameter of the femtosecond pulse, through measuring the stripe intensity distribution, we can indirectly detect the chirp parameter of the femtosecond pulse.     

双光栅白光衍射干涉的消色效应

本文提出和研究了白光点源照明下的双光栅衍射干涉效应,报道了白光照明下剪切干涉的“消色效应”,给出了完整的菲涅耳线性标量衍射原理的数学推导和几何光学的解释.     

The effect of arbitrary small discrepancy between normal directions of grating planes in Talbot interferometry

The effect of nonparallel grating planes in Talbot interferometry is discussed when an arbitrary relative inclination exists between the normal directions of the two grating planes. The inclination can be composed of the two angles, and β, which are generated by rotating the beam splitter grating about the two axes parallel to and perpendicular to the line direction of the grating. Theoretical analyses indicate that the tilt angle of the moiré fringes is very sensitive to but not to β. Experimental results coincide well with the theoretical analyses. Methods of judging and removing the two small angles are briefly discussed.     

X-ray resonant powder diffraction

X-ray resonant diffraction can be applied in structural chemistry studies on powder samples. It enables an important limitation of powder diffraction to be overcome. This limitation is related to the low ability of powder diffraction to differentiate elements with close atomic numbers when they occupy the same or close crystallographic sites (mixed occupancy case) and also to discriminate cations with different valence states in different sites. However the resonant effect usually has a second order influence on the measured intensity. As a consequence, the efficiency of this method directly implies the need for excellent quality data collection and has generally been better assessed on elements present in single phase powder samples. In recent years, instrumental developments have been made in synchrotron radiation facilities which allow easier use of resonant powder diffraction for site-specific contrast and valence i.e. oxidation state analyses. Moreover, resonant contrast diffraction tools also have been proposed for better visualization of the anomalous effect both in direct and reciprocal space by using differences between electron density maps or diffraction patterns. Finally the potentialities of this technique for de novo structure solution on macromolecular systems are mentioned.     

反射型导模共振滤波器设计

导模共振滤波器由于其高峰值反射率，低旁带反射，窄带以及带宽可控等优良特性引起了人们极大的关注，采用亚波长光栅的导模共振效应可以实现传统基于高低折射率介质的多层膜滤波器所无法实现的特殊功能，在弱调制模式下，其共振带宽可以被压缩到零点几纳米，但是由于介质表面和空气层的菲涅耳反射，使得偏离或者远离共振区时的反射率偏高，根据等效介质理论，亚波长光栅在远离共振区可以被看为均匀的薄膜，本文通过对导模共振光栅进行单层、双层以及三层抗反射设计，有效的降低了导模共振光栅的旁带反射率，从而在可见光波段获得了性能优良的共振滤波     

反射型导模共振滤波器设计

导模共振滤波器由于其高峰值反射率,低旁带反射,窄带以及带宽可控等优良特性引起了人们极大的关注,采用亚波长光栅的导模共振效应可以实现传统基于高低折射率介质的多层膜滤波器所无法实现的特殊功能,在弱调制模式下,其共振带宽可以被压缩到零点几纳米,但是由于介质表面和空气层的菲涅耳反射,使得偏离或者远离共振区时的反射率偏高,根据等效介质理论,亚波长光栅在远离共振区可以被看为均匀的薄膜,本文通过对导模共振光栅进行单层、双层以及三层抗反射设计,有效的降低了导模共振光栅的旁带反射率,从而在可见光波段获得了性能优良的共振滤波 关键词： 导模共振 平面波导 傅里叶模式理论 窄带滤波     

Novel optical comb filter based on full-duty-cycle sampled fiber Bragg grating with spectral Talbot effect

Spectral Talbot effect in full-duty-cycle sampled fiber Bragg grating is proposed and numerically demonstrated for the first time. Based on analysis and simulations, it is shown that high-performance comb filters can be realized with the proposed structure. Moreover, it is found that channel count scales linearly with the number of samples and that high-quality filtering is still available with some fabrication errors.     

Soft X-ray resonant magnetic diffraction

We have conducted the first soft x-ray diffraction experiments from a bulk single crystal, studying the bilayer manganite La2-2xSr1+2xMn2O7 with x=0.475 in which we were able to access the (002) Bragg reflection using soft x rays. The Bragg reflection displays a strong resonant enhancement at the L(III) and L(II) manganese absorption edges. We demonstrate that the resonant enhancement of the magnetic diffraction of the (001) is extremely large, indeed so large that it exceeds that of the nonresonant Bragg diffraction. Resonant soft x-ray scattering of 3d transition metal oxides is the only technique for the atomic selective measurement of spin, charge, and orbital correlations in materials, such as high temperature superconductors, colossal magnetoresistance manganites, and charge stripe nickelates.     

反射式单级衍射光栅

介绍了单级衍射光栅的发展趋势, 从理论上论证了单级衍射光栅的可行性, 引入了一种新型衍射光学元件—-准正弦反射式单级衍射光栅(QSRG). 它能有效抑制高级衍射, 可用于提高光谱系统的信噪比和精度. 而通过QSRG的实验结果也验证了此新型色散元件确实具有良好的单级衍射特性, 二级及以上的高级衍射被有效地抑制, 与理论预测几乎一致. 本文的结果可望在反射式光谱测量系统中得到广泛应用.     

Planar dielectric grating diffraction theories

Various planar dielectric grating diffraction theories are reviewed for the case of a general sinusoidal permittivity planar grating with slanted fringes and plane wave incidence at an arbitrary angle. Exact formulations without approximations (rigorous coupled-wave analysis and rigorous modal analysis) are developed first. Then, using a series of fundamental assumptions, rigorous theory is shown to reduce to the various approximate theories in the appropriate limits. The implications of these fundamental assumptions are discussed.     

Fractional second-harmonic Talbot effect

We demonstrate the fractional second-harmonic (SH) Talbot effect in a hexagonally poled LiTaO3 crystal. We carefully record the SH Talbot images at 1/2, 1/3, and 1/4 Talbot lengths, which are well matched with the simulated images by using the modified Rayleigh-Sommerfeld diffraction formula. A simplified model with a hexagonal array is adopted in the simulations. Also, we use a modified reciprocal vector theory to analytically explain the evolution of the SH array at fractional Talbot lengths. Our results show that the images are sensitive to the duty circle and the background of the array.     

The spectral combination characteristic of grating and the bi-grating diffraction imaging effect

This paper reports on a new property of grating, namely spectral combination, and on bi-grating diffraction imaging that is based on spectral combination. The spectral combination characteristic of a grating is the capability of combining multiple light beams of different wavelengths incident from specific angles into a single beam. The bi-grating diffraction imaging is the formation of the image of an object with two gratings: the first grating disperses the multi-color light beams from the object and the second combines the dispersed light beams to form the image. We gave the conditions necessary for obtaining the spectral combination. We also presented the equations that relate the two gratings’ spatial frequencies, diffraction orders and positions necessary for obtaining the bi-grating diffraction imaging.     

On the resonant diffraction of X-rays

Il Nuovo Cimento D - Data on the absorption by a crystalline powder of Ge and on the intensities diffracted by the (111) planes of a perfect Ge crystal were collected in the laboratory at...     

基于Talbot效应的掺镁铌酸锂二维六角位相阵列光栅的研究

本文系统研究了基于泰伯效应(Talbot) 的位相可调掺镁铌酸锂二维六角位相阵列光栅及其光衍射成像, 对光栅占空比D、不同位相差Δφ、及泰伯分数β条件下的光栅近场光衍射强度分布进行了理论研究, 结果表明当光栅占空比D=52%、位相差Δφ=0.75 π、 泰伯分数β=0.2时, 光栅近场衍射光图像效果最佳. 实验设计与 制备了掺镁铌酸锂二维六角位相阵列光栅, 并对其进行了Talbot衍射光成像实验研究, 得到了不同位相差和不同泰伯分数β条件下光栅近场衍射 光图像, 实验结果与理论研究结果相符. 关键词： 二维六角位相阵列光栅 掺镁铌酸锂晶体 泰伯效应