双焦点光子筛聚焦特性的精细测量

利用数字全息测量方法结合变采样间距的衍射传输算法实现双焦点光子筛器件焦距及焦斑的同时精细测量.给出了双焦点光子筛器件及其理论焦斑分布,采用双曝光的离轴全息方法得到了CCD接收面处光场的复振幅分布,基于此光场通过变采样间距的衍射传输算法获得具有较高分辨率的双焦点光子筛的聚焦场特征,与CCD直接测量结果相比,焦斑分辨率提高了10倍,双焦点光子筛的焦距等于自动对焦算法及强度最大值扫描方式分别求得的两段距离之和.实验结果表明测得的双焦距与设计焦距偏差分别为0.53%和0.37%,得到的两个焦斑半值全宽与设计值相比,其偏差分别为2.86%和1.86%.本文提出的测量方法除了应用于光子筛类器件的性能检测以外,还能够广泛应用于其它类衍射透镜聚焦特性的测量与性能分析.     

利用光子筛产生局域空心光束

为了寻找一种简单有效的产生局域空心光束的方法,提出了一种利用交错型光子筛产生空心光束的方法。通过光子筛的内部区域和外部区域相消达到轴上光强为零的目的。给出了光子筛的结构和设计参数,对空心光束中心暗斑尺寸和光子筛焦距、环带数、小孔调制系数的关系进行了深入的研究,发现改变焦距和环带数可以得到微米甚至亚微米的中心暗斑的局域空心光束。理论推导和仿真分析验证了方法的可行性,该方法具有结构简单和能产生极小中心暗斑的优点,特别适用于光学镊子、原子冷却等。     

斐波那契光子筛的聚焦成像特性

应用斐波那契数列,提出了一种双焦点光子筛,并基于惠更斯-菲涅耳原理,分析了斐波那契光子筛的聚焦特性。数值仿真结果表明,当单色平面波通过斐波那契光子筛时,它能够获得两个焦距比约为黄金分割比的轴向焦点。筛孔直径等于所在轨道宽度的1.165倍时,两个焦点处光强相等。与斐波那契波带片相比,斐波那契光子筛具有更高的横向分辨率。最后引入高斯切趾技术,对斐波那契光子筛筛孔个数进行调制,在两个焦平面上进一步提高横向的分辨率。由于斐波那契光子筛体积小、重量轻、设计灵活,而且具有多焦性,可以用于光学开关、纳米光刻、生物仿生眼、多焦成像和测距,甚至在X射线显微技术和太赫兹成像技术都将有新的应用。     

准相位型光子筛设计

提出了一种准相位型光子筛。该准相位型光子筛通过改变暗环上小孔直径与带宽的比值,对焦点处的相位分布进行调制,使通过亮环和暗环上小孔的光波在焦点处发生相长干涉,生成聚焦光斑。该准相位型光子筛无需对基底进行特殊处理,即可完成相位型光子筛的制作,降低了加工难度。和普通振幅型光子筛相比,在相同最小加工尺寸的条件下,准相位型光子筛具有较大的数值孔径,可降低聚焦光斑尺寸。并且,和多区光子筛相比,在同样的最小加工尺寸及数值孔径的条件下,准相位型光子筛光斑尺寸及质量均优于对方。为大数值孔径光子筛设计提供了一种新的设计方法。     

基于角谱法的振幅型光子筛的设计和分析

对光子筛的聚焦成像原理作了分析,并用平面波角谱方法对光子筛聚焦成像进行了数值模拟.模拟结果表明,光子筛聚焦具有提高分辨率和抑制高级衍射的优点.在理论分析和计算机模拟的基础上,设计并制作了Fresnel波带片、未平滑处理和平滑处理后的光子筛.用波长为532 nm激光光源对波带片和光子筛聚焦光斑进行检测.结果表明,光波通过光子筛聚焦后的光斑比波带片的光斑更细,成像对比度更高.     

具有实入瞳的远心离轴三反系统研究与设计

采用远心离轴三反成像系统的空间遥感仪器前有光束限制装置时,要求系统具有实入瞳与之匹配。为了满足这一需要,研究了孔径光阑位于主镜前与系统物方焦平面重合的离轴三反系统的设计问题,推导了主镜和三镜共面时离轴三反系统结构参数计算式及物方焦点与主镜间隔表达式,确定了实现系统物方焦点为实焦点的条件及其解法。据此,针对光谱范围为1.0～2.5μm、F数为4、有效焦距为360mm、视场为5°的设计要求,设计出整个波段全视场像质接近衍射极限的具有实入瞳的远心离轴三反系统,系统非球面最高次数为4次。设计结果表明,这种设计方法可用于实入瞳远心离轴三反成像系统的设计。     

高功率高重复频率多波长飞秒激光系统的研究

以大模场面积光子晶体光纤飞秒激光系统为基频光源,利用非线性频率上转换的方法,获得了高功率高重复频率多波长的飞秒激光脉冲.理论分析并实验验证了聚焦透镜的焦距对倍频光横向模场分布的影响,透镜焦距越长,模场质量越好.在基频光平均功率为218 W,脉冲宽度为110 fs,重复频率为50 MHz的条件下,经过二倍频、三倍频和四倍频获得波长分别为520,347和261 nm的飞秒激光,其平均功率分别达105,47和214 W.二倍频和三倍频的转换效率分别为482%和216%,二倍频到四倍频的转换效率为20 关键词： 超快光学 紫外飞秒激光 频率上转换 光子晶体光纤激光器     

X射线相衬成像光子筛

基于 Zernike相衬成像原理和光瞳切趾原理,提出一种将相位板和切趾光子筛集成为一个相衬显微物镜的 X射线相衬成像光子筛的设计方法.这种 X射线相衬成像物镜可以实现生物体组织或者其他弱吸收材料的高分辨率和高衬度成像.通过优化光子筛透镜的衍射结构,可以抑制成像系统的点扩展函数的旁瓣和消除高阶衍射焦点,从而提高成像分辨率;另外,将光子筛透镜和变相板合为一体,克服了成像透镜和变相板难以对准的缺陷.以高斯切趾光子筛为例,实验验证了设计方法的可行性. 关键词： X射线显微技术 相衬成像 光瞳切趾 光子筛     

20倍双组联动变焦距光学系统设计

针对双组联动变焦距系统结构复杂的特点,对其设计过程进行了梳理。在此基础上编制了可视化辅助设计软件,该软件具有高斯解计算、变倍补偿曲线绘制、像差与外形尺寸分析、相对孔径图输出等功能。使用该软件可以方便地完成双组联动变焦系统高斯解的合理选择,并给出各组元承担相对孔径及其变化情况,辅助进行初始结构的确定。利用该辅助设计软件,对一套焦距25~500 mm的20倍可见光波段双组联动连续变焦距系统进行了初始结构设计,并通过整体优化使系统像差得到校正。设计结果系统光学总长478 mm,各焦距位置在50 lp/mm处轴上视场调制传递函数(MTF)大于0.6,边缘视场MTF大于0.4,各项指标满足系统要求。     

螺旋光子筛用于相衬成像的模拟研究

为了提高螺旋波带片用于相衬成像的分辨率和成像对比度,因此本文将螺旋波带片的透光环带替换为透光微孔,以类-贝塞尔函数作为螺旋光子筛透过率的振幅调制窗函数设计了一种螺旋光子筛.在相同的特征尺寸下,螺旋光子筛比螺旋波带片具有更大的数值孔径,因此分辨率更高.同时基于光瞳切趾原理,经过类-贝塞尔振幅调制窗函数对螺旋光子筛透光微孔的分布进行调制,螺旋光子筛的成像对比度将高于螺旋波带片.通过数值计算和仿真分析表明:螺旋光子筛的点扩展函数主瓣宽度相对于螺旋波带片更窄,旁瓣幅值也相对更低.在相衬成像中,螺旋光子筛不仅能够消除螺旋波带片对圆盘状位相物体成像时图像的"浮雕"效应而且能够更为清晰地分辨出位相跳变更为密集的周期矩形条状物体.因此,螺旋光子筛用于相衬成像中将具有更高的成像分辨率和成像对比度,其在医学领域将具有广阔的运用前景.     

Focusing properties of a modified Fibonacci photon sieve

We propose a type of diffractive optical element, a modified Fibonacci photon sieve(MFiPS), designed by using the Fibonacci sequence with two different initial seed elements. Focusing properties of MFi PS show that it not only has less secondary foci, but also presents two equal intensity foci by optimizing the diameters of pinholes of MFi PS whose ratio of the two focal distances approaches the golden mean. Higher transverse resolution on the two focal spots is improved by using a super-Gaussian amplitude modulation technology.     

Fourier treatment to the diffractive optical element composed of Fresnel zone and pinholes

Currently, the minimum feature size fabricated is about 15-40 nm. The resolution of Fresnel zone plates is limited by the width of the outermost zone. Although the photon sieves make it possible to focus soft X-rays to spot sizes smaller than the diameter of the smallest pinhole they have low diffraction efficiency. In order to foster strengths and circumvent weaknesses of them, we propose a new model which is composed of Fresnel zone and pinholes and give its fast Fourier algorithm. The simulation results demonstrate that the resolution of photon sieves is not better than that of Fresnel zone plates in low order of local rings. In this case, we can substitute pinholes for Fresnel zone in photon sieves. Resolution is nearly a constant, and also the diffraction efficiency improves.     

Lacunar fractal photon sieves

We present a new family of diffractive lenses whose structure is based on the combination of two concepts: photon sieve and fractal zone plates with variable lacunarity. The focusing properties of different members of this family are examined. It is shown that the sieves provide a smoothing effect on the higher order foci of a conventional lacunar fractal zone plate. However, the characteristic self-similar axial response of the fractal zone plates is always preserved.     

Design and application of phase photon sieve

The imaging principle of Fresnel zone plate and photon sieve were analyzed in this paper. The design and fabrication of phase photon sieve were discussed. The feasibility of using phase photon sieve to realize nano-lithography was analyzed, a novel lithography experiment system based on phase photon sieve was presented, which not only has higher resolution and image contrast than the Fresnel zone plate lithography but also have higher diffractive efficiency than the amplitude photon sieve lithography.     

Phase zone photon sieve

A novel diffractive optical element, named phase zone photon sieve (PZPS), is presented. There are three kinds of phase plates in PZPSs: PZPS1, PZPS2, and PZPS3. Each of the PZPSs has its own structure and is made on quartz substrate by etching. The three PZPSs have stronger diffraction peak intensity than a photon sieve (PS) when the margin pinhole and zone line width are kept the same. The PZPS3 can produce a smaller central diffractive spot than the ordinary PS with the same number of zones on the Fresnel zone plate. We have given the design method for and the simulation of PZPS and PS. PZPS has potential applications in optical maskless lithography.     

Axial intensity distribution behind a Fresnel zone plate

An analytical expression based on an improved Rayleigh–Sommerfeld diffraction formula with evanescent term is derived for analyzing the axial light intensity distribution throughout the whole space behind a Fresnel zone plate. The effects of the number of Fresnel zones and the size of aperture on the axial intensity distribution are calculated for two kinds of Fresnel zone plate with larger and smaller aperture. The validity of the general formulae for calculating the focal lengths and the relative intensities of the foci of a Fresnel zone plate is analyzed.     

Focusing light with a reflection photon sieve

An advanced type of diffractive optical element is presented that combines the concept of the photon sieve with an off-axis, off-normal incidence reflection geometry. Compared to transmission optical elements, the signal-to-background ratio is significantly increased by separating the first from other diffraction orders without drastically reducing the size of the smallest diffractive element. The reflection photon sieve produces sharp foci at maximum contrast and offers the advantages of effective heat dissipation and a large working space above the focal plane. Experimental results for a device working at a photon energy of 100 eV are presented and compared to theory.     

Focussed surface acoustic waves on an anisotropic crystal, studied by optical probing

Efficient focussing of surface acoustic waves has been achieved using a properly shaped gold film deposit on the −22.3° rotated Y-cut surface of quartz. The acoustic wave field was studied with laser probing techniques. A more than threefold increase in intensity and a tenfold decrease in beam width was observed at the focal point. The focussing action was obtained with the elastic wave equivalent of the Fresnel phase-reversal zone plate of optics. The multiple foci of this device allowed a simultaneous generation of acoustic waves in nearly all directions on the surface. Consequently, the surface wave velocity anisotropy could be determined completely. The experimental results are in very good agreement with the calculated velocity anisotropy. Electromagnetic diffraction theory is adopted to the two dimensional anisotropic system to analyse the performance of the focussing device.     

菲涅尔数字全息的脉冲响应

数字全息是用CCD记录全息图并用计算机数值重建全息像的一种全息新方法.在数字全息中,通过对不同记录参数下记录的全息图的数值处理,可以消除零级光和共轭光,从而将数字全息系统看作是一个线性系统.本文依据全息理论和付里叶频谱分析,对菲涅尔数字全息系统的脉冲响应和分辨本领进行了理论分析.结果表明,在矩形等间隔抽样的情形下,菲涅尔数字全息的脉冲响应是由CCD有限大小的孔径衍射斑调制的矩形函数;菲涅尔数字全息的分辨率由CCD的孔径尺寸决定;由于CCD像素具有一定的大小,使得点光源的像发生弥散.