用菲涅耳衍射理论分析双光栅成像效应

从理论上对双光栅成像效应现象进行研究,分别从菲涅耳衍射理论和平面透射光栅的菲涅耳衍射公式出发,分析了物光波经过两个平行放置的平面透射光栅组成的系统衍射后的复振幅分布。分析结果表明,在理想状态下,当两个光栅的放置位置满足一定条件时,在第二个光栅后面可以观察到一个清晰的原物体图像。理论分析解释了两个光栅在双光栅成像效应中的作用,得到了双光栅成像效应发生时,两个光栅的空间频率、衍射光级数以及光栅放置位置之间的关系式,这与实验所得结果相一致。     

有限宽双光栅成像效应的分析与应用

用稳相积分法分析了点光源经过2个平行放置的有限宽平面透射光栅组成的系统衍射后的复振幅分布。当两光栅满足双光栅成像条件时,将其衍射成像与无限宽双光栅衍射成像进行对比,得到有限宽光栅对双光栅衍射像的位置没有影响,而衍射像随两光栅之间的相对距离及衍射级数而变化。文中计算了满足双光栅成像条件时,某实验参数下衍射像的大小的情形,结果有限宽双光栅成像被放大了1.22倍。并根据其原理进行白光再现普通透射全息图色彩研究。     

基于双光栅成像的RGB模型色彩还原效果的研究

基于双光栅衍射成像的实验方案,利用双光栅的色散和汇合光谱效应特性,用电脑摄像头拍摄作为物体的RGB模型,得到了RGB颜色模型的像。利用Photo shop软件将RGB颜色模型和得到的像进行颜色通道分离,再进行数据化分析处理,探究双光栅的RGB色彩模型色彩还原情况以及不同光栅组合对RGB颜色模型的色彩还原效果的影响。     

体布拉格光栅滤波片及其光谱成像应用

利用厚体布拉格光栅的波长选择特性对目标光场进行窄带滤波,是实现高光谱成像的一种新途径。基于严格耦合波理论,设计了体布拉格光栅结构,探索了厚体布拉格光栅的制作工艺,搭建系统光路验证了体布拉格光栅的光谱成像能力。研究结果表明:要获得较窄滤波谱宽,需要提高体布拉格光栅的厚度周期比,并严格控制入射光束发散角;刻写光束质量、震动和偏振会极大地影响制作的光栅条纹面质量,需要从优化写入光的光束均匀性、采用防震措施以及调整两刻写光束偏振一致性等方面优化刻写过程,以提高光栅的衍射效率和质量;验证了体布拉格光栅滤波片进行空间二维面阵成像的能力,宽谱光源透射条件下,通过对入射光束进行准直,滤波谱宽5 nm左右,空间分辨率约4 lines/mm;漫反射条件下,使用体布拉格光栅对进行色散补偿,能够实现较为清晰的成像,空间分辨率约4.9 lines/mm。     

基于双AOTF的新型成像光谱偏振探测系统

声光可调谐滤波器(AOTF)具有体积小、波长稳定性好、扫描范围宽、调制速度快等优点,在光谱成像中被广泛应用,但单独采用AOTF的成像光谱偏振探测还较少。为此提出只采用两个AOTF的成像光谱偏振探测新方法。该方法首先通过分束镜将入射光分成两束,两束光分别通过两个AOTF,而两个AOTF的正一级衍射光的偏振方向互成45°,由于AOTF的正一级衍射光的偏振方向互相垂直,因此两个AOTF的正负一级分别可得到0°,45°,90°和135°的光强,在测量中需保持两个AOTF的滤光所对应的波长完全相等。最后通过对两个AOTF的正负一级衍射成像,最终得到Stokes偏振信息中S₀(0°和90°光强和)、S₁(0°和90°光强差)和S₂(45°和135°光强差),结合相应的理论公式对被测目标的线偏振度(DoLP)和线偏振角(AoLP)实现成像。再通过对AOTF的射频驱动进行扫频,实现对被测目标不同波长偏振成像,最终实现成像光谱偏振探测。并通过对500,550和600 nm偏振成像进行实验验证。该方法具有无运动部件、无需转动、一次测量同时获得成像光谱偏振信息的优点。     

How to make femtosecond pulses overlap

Normally, femtosecond light pulses that cross at a nonzero angle overlap over only a small region in space. This limitation can be overcome by the use of diffraction orders of a grating. We consider an arrangement in which, on diffraction of a femtosecond pulse by a grating, two beams that correspond to the first-order diffraction maxima are recombined at the image plane by a system of two confocal lenses. In this arrangement the beams overlap over the their full aperture, with the short duration of the pulses being preserved. We demonstrate the use of this setup as a simple autocorrelator and discuss a possible application to time-resolved vibrational spectroscopy.     

基于光栅分光法的相干衍射成像

提出一种可以通过单次曝光实现 PIE(ptychographic imaging engine)成像的方法, 该方法用正交光栅将入射细光束衍射为传播方向不同的子光束簇以对样品进行照明, 并用CCD同时记录各个子光束所形成的衍射光斑阵列. 该方法很好地克服了现有PIE方法的成像质量易受机械扫描误差影响和数据采集时间过长两个缺点, 具有很好的实用价值. 关键词： 相干衍射成像 相位恢复 显微成像 迭代算法     

一维亚波长周期结构物成像的光子学研究

当用波长为λ的单色平行光垂直照射到光栅常数d<λ的亚波长周期结构衍射物时,会产生隐失波。由于快速衰减,这种亚波长周期物是不能成像的。但是,通过对亚波长周期结构物进行适当的编码后可得到均匀波,使这种携带了隐失波信息的均匀波通过经特别设计的光学系统并被放大到CCD所能识别的像素大小后,再进行必要的解码以滤掉编码波,即可得到原亚波长周期结构衍射物的像,最终达到超分辨的目的。基于这种新颖的成像技术,用常规仪器就实现了对亚波长周期结构物的成像。在运用光子学方法对实验和成像过程进行较为详尽的理论分析的同时,对编码器、解码器的位置以及它们相对物光栅的取向给出了设计性研究,对滤波器的选择给予了必要的说明。实验结果验证了该设计理论的正确性。     

Subwavelength Fourier-transform imaging without a lens or a beamsplitter

The fourier-transform patterns of an object are usually observed in the far-field region or obtained in the near-field region with the help of lenses. Here we propose and experimentally demonstrate a scheme of Fourier-transform patterns in the Fresnel diffraction region with thermal light. In this scheme, neither a lens nor a beamsplitter is used, and only one single charge coupled device(CCD) is employed. It means that dividing one beam out of a light source into signal and reference beams is not as necessary as the one done by the use of a beamsplitter in usual ghost interference experiments.Moreover, the coincidence measurement of two point detectors is not necessary and data recorded on a single CCD are sufficient for reconstructing the ghost diffraction patterns. The feature of the scheme promises a great potential application in the fields of X-ray and neutron diffraction imaging processes.     

超短脉冲激光光束在一维反射型体全息光栅中的衍射

基于Kogelnik的耦合波理论,研究了在色散效应的影响下,超短脉冲激光光束在反射型体全息光栅中衍射的性质.研究给出了衍射光及透射光在频谱域及时间域的振幅及强度分布、光栅的光谱宽度及衍射效率随光栅参量及入射条件的变化.数值研究的结果表明,在光栅记录介质色散效应的影响下,衍射光束的光谱宽度减小,脉冲展宽,衍射效率降低.通过适当的选取光栅参量及入射条件,可以控制衍射和透射光束的频谱和时间强度分布,得到满意的衍射和透射光束的带宽和波形,从而可以将其应用于脉冲整形等技术中.     

Quadratic grating apodized photon sieves for simultaneous multiplane microscopy

We present a new type of imaging device, named quadratic grating apodized photon sieve (QGPS), used as the objective for simultaneous multiplane imaging in X-rays. The proposed QGPS is structured based on the combination of two concepts: photon sieves and quadratic gratings. Its design principles are also expounded in detail. Analysis of imaging properties of QGPS in terms of point-spread function shows that QGPS can image multiple layers within an object field onto a single image plane. Simulated and experimental results in visible light both demonstrate the feasibility of QGPS for simultaneous multiplane imaging, which is extremely promising to detect dynamic specimens by X-ray microscopy in the physical and life sciences.     

Digital holography at millimetre wavelengths

In this paper, we describe a method for wavefront reconstruction at millimetre wavelengths using off-axis holography, a frequently used image recording technique at visible wavelengths first demonstrated in the 1960’s. Millimetre radiation has been highlighted recently in the imaging of non-conducting materials and objects, which often show significant transparency at these long wavelengths, even though opaque at visible and infrared wavelengths. Holography provides a method for recording a lens-less image of an object thus reducing loss of spatial frequency information, which is important for obtaining maximum resolution at long wavelengths. An experimental arrangement based on a simple form of Fresnel off-axis holography is described, with the object illumination and reference beams derived using two radiating horn antennas fed by a single coherent source (a Gunn diode oscillator operating at 100 GHz – wavelength 3 mm) via a 3 dB cross-guide coupler. The process is discussed in the context of imaging and in the validation of millimetre wave radiation sources (horns). We show that the entire fields from these and other components can be analysed using computational optics with data derived from a single measurement obtained using inexpensive equipment.     

基准光栅重构傅里叶变换轮廓术

应用傅里叶轮廓变换术进行三维形貌测量中,为了获得待测物体的高度相位信息,通常需要采集两幅图像.因此当光学系统发牛变动时,必须重新采集基准光栅图像,不利于快速测量.提出一种从变形光栅图像中获取基准光栅图像信息的测量方法.首先在变形光栅图像中记录基准光栅信息,然后通过傅里叶分析提取基准光栅频率信息,通过图像分析获得基准光栅相位信息,最后重构出一幅完整的基准光栅图像,实现三维物体形貌测量.实验结果验证了该方法的可行的.     

Crystal diffraction grating in LiNbO3:Fe derived from interferometric volume holography

A 90° two-beam coupling configuration was used to store an image of an extended object in a 0.032 %wt iron-doped LiNbO₃ crystal. A volume hologram was thus generated, via the photorefractive effect, within the microstructure of the crystal. The time evolution of partial spatial erasure of the hologram under illumination was studied by capturing its reconstructed image on a digital camera and performing a two-dimensional inverse Fourier transform. This produced the refractive index grating created through interference of object and reference beams. The nature, intensity distribution and dimensions of the diffraction grating were derived in order to throw light upon the movement and mechanisms of charges, which create the index grating.     

利用相位模板实现数字全息超分辨成像

为了简化数字全息超分辨记录系统,分别在其物光和参考光部分引入一块相位模板,以获得垂直和倾斜方向照明物体的光束和具有不同载波频率的参考光束.当这些具有不同照射方向的光透过物体后,可以使CCD在位置固定的情况下记录到携带低频和高频信息的物体衍射场,不同载波频率的参考光则保证了高频和低频信息在复合全息图的频谱面上能够相互分离.实验结果证明,通过将记录到的物体高频和低频信息合成,可以获得超出系统衍射极限分辨率的再现像.     

Dynamic spectral imaging with spectral zooming capability

We report a dynamic spectral imaging system with spectral band zooming and selection capability that can adapt to different application requirements and significantly reduce the size of the captured spectral image data cube. It employs a diffraction grating to disperse the spectral information of the captured image and uses a dynamic spatial filter at the Fourier plane to select the spectral channel and spectral bandwidth for each spectral image. With a limited fixed spectral channel number, it can provide both coarse and fine spectral image viewing and capture. A prototype spectral imaging system with such spectral band zooming and selection features has been constructed. Spectral zooming from 9 to 50 nm resolution has been demonstrated.     

基于像素结构空间光调制器的全息再现像问题研究

基于纯相位空间光调制器的全息显示系统在重构显示时,再现像的视觉效果受到空间光调制器像素结构引起的多级衍射光和多级再现像的干扰。在分析具有有限填充因子空间光调制器的像素结构对再现像影响的基础上,提出了一种提高全息再现像的视觉效果并且再现像成像位置和大小可调节的方法。先加载闪耀光栅到纯相位全息图,其次通过叠加会聚球面波相位,分离再现像与空间光调制器像素结构引起的多级衍射光的聚焦平面的位置,再利用光阑和高通滤波器的共同作用,消除高级衍射光、多级再现像以及零级光干扰对重构视觉效果的影响,最后引入成像透镜,调节再现像的成像位置与大小。建立了一套基于硅基液晶的全息显示系统用于实验验证。实验结果表明,最终的单一再现像清晰且可以方便地调节成像位置和大小。该方法同样适用于各种基于像素结构空间光调制器的全息光学系统。     

菲涅耳波带板X射线成像的快速计算方法

菲涅耳波带板直接成像,应用到激光等离子体或惯性约束聚变靶的X射线成像诊断,可实现μm甚至亚μm的空间分辨能力。在对成像进行数值模拟时,考虑到光源的光谱带宽和几何尺度对成像的影响,要进行菲涅耳-基尔霍夫衍射积分与卷积等数值计算,需占用大量计算机内存并且耗费运行机时。改进了数值计算方法,采用了蒙特卡罗积分法和新的卷积算法。模拟了菲涅耳波带板对大尺度多色X射线源的二维成像,新算法与以往算法相比,可显著减少运算机时,在台式机上实现模拟成像的快速计算。结果表明随着光源尺度增大、光谱带宽增加,像的背景增强,导致反衬度与成像质量下降。     

Ghost imaging of Multi-Gaussian Schell-model beams in the Z-tilt aberration corrected channels

Based on the optical coherent theory and the extended Huygens–Fresnel integral, lensless ghost imaging of Multi-Gaussian Schell-model beams through the slant non-Kolmogorov turbulence channels with Z-tilt aberration correction has been studied and the theoretical models have been derived. Our results indicate that the nearer of object to illuminant plane, the larger beam width and the more beamlet number are, the more fine of image quality is. The undersize of illumination light source will cause the quality decline of ghost imaging and the image quality of the object illuminated by the incoherent light are worse than that of illuminated by partially coherent light.     

Temporal ghost imaging of a time object,dispersion cancelation,and nonlocal time lens with bi-photon state

We present a theory of temporal diffraction, temporal imaging of a bi-photon state, and temporal ghost imaging of a time object. By applying factional Fourier transform to the bi-photon wave packet propagating in space, we could obtain a theory that shows the physical origin of dispersion cancelation, temporal imaging, nonlocal effects of time lenses, and temporal ghost imaging. We introduce the temporal diffraction distance for bi-photon wave packet and show that the bi-photon wave packet behaves like a single wave packet whose temporal diffraction distance is determined by the coherent sum of the temporal diffraction distances for the signal and the idler beams. This property yields the well known dispersion cancelation, the recovery of original bi-photon wave packet in temporal imaging, and the nonlocal combination of two time lenses placed in different arms. We also propose a method for ghost imaging of an arbitrary time object.