Bifocal-polarization holographic lens

We present a holographic lens with novel features recorded in an azopolymer film. Two holographic modulations, bulk birefringence and surface relief, are induced in the medium at the same time. The resultant holographic element has two focal planes, and the polarization of light in the focal points depends on the polarization of the incident light. Applications of this device for writing-reading information in two planes simultaneously or separately are described.     

Agitation-free multiphoton microscopy of oblique planes

The scanning two-photon fluorescence microscope produces optically sectioned images from the focal plane. It is sometimes desirable to acquire images from other planes of the specimen that are inclined with respect to the focal plane. In this Letter, we discuss the issues concerned with acquiring such images together with the effects of the inclination angle on image resolution and sectioning strength. To obtain images from oblique planes at high speed, a two-photon system was built wherein a novel optical system is used to provide aberration-free scanning.     

Optical method of determination of stress at a point

A method of determining stress at a point is suggested here. The effect of bending of a wave front that is due to variations of the refractive index is used to measure different aspects of stresses. A Fourier lens with a cross slit at its front focal plane is used to form interference fringes at planes near its back focal plane. The sample, illuminated by a plane-parallel coherent beam of light, is placed close to a cross slit, and the change in fringe pattern due to axial shift of the spectrum planes of the slits is measured to relate it to the state of stress.     

长焦距傅里叶变换透镜的小型化

随着光学信息处理的不断发展,傅里叶变换透镜的应用也日趋广泛。本文阐述了傅里叶变换透镜的性质及作用,主要研究了长焦距傅里叶透镜光学设计的特点,以及目前国内外在设计该类型透镜时常采用的结构形式:四组元对称或非对称双远距结构。为了能进一步缩短傅里叶变换透镜前后两焦点间的距离,使之小型化,本文尝试了一种新的结构形式,比起四组元双远距结构,在结构也较为简单的前提下,它不仅进一步缩短了两焦点间的距离,而且输入面、频谱面的象质均良好。     

Two approaches to three-dimensional array foci of generalized Fibonacci structures

We propose two technologies to extend the number of layers in order to complete the three-dimensional(3D)array diffraction-limited foci, which means there are two-dimensional array foci at multi-focal planes. One technology is the diffractive optical lever; the other is multi-hybrid Fibonacci structures. Based on the aperiodic Fibonacci structures and binary phase modulation, various kinds of devices can be designed to produce 3D array foci whose focusing properties approximately satisfy the mathematical characteristics of the Fibonacci sequences. With those technologies, the diffraction-limited array foci are freely designed or distributed as required at the desired multiple focal planes.     

Grid attenuators in laser machining systems

General equations for the attenuated and focused intensity distribution of a gaussian beam at the focal region are derived for two-dimensional arbitrary shaped grid attenuators. Assuming a circular aperture grid, calculations of the intensity distribution in the focal plane and at several planes of the focal region were done. Results of calculations and relevant experiments are reported and discussed, in view of the application of these types of attenuators in laser machining systems.     

多面体模具角参数自动测量方法的研究

多平面冷反光镜模具质量的好坏直接影响着出射光束照度的均匀度和出射光束的定向性，目前使用的检测方法存在测量过程繁琐费时，测量精度低等缺点。本文介绍了一种利用ＣＣＤ线阵光电探测器研制的多面体模具角参数自动测量系统。该装置采用光学方法，将待测的几何参数——两相邻平面间夹角α转化为测量该两平面反射光聚焦光斑的距离，然后用ＣＣＤ图像数据采集系统处理数据。使整个系统简单、紧凑，适用范围广，对不能接触测量或因面形太小或因形状复杂而难以测量的平面夹角均可进行测量。本文亦讨论了实验数据处理，并根据实际情况，采用重心法计算光斑中心位置，使测量精度有了很大提高。最后给出了利用该系统测量的结果。     

Towards dualband megapixel QWIP focal plane arrays

Mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) 1024 × 1024 pixel quantum well infrared photodetector (QWIP) focal planes have been demonstrated with excellent imaging performance. The MWIR QWIP detector array has demonstrated a noise equivalent differential temperature (NEΔT) of 17 mK at a 95 K operating temperature with f/2.5 optics at 300 K background and the LWIR detector array has demonstrated a NEΔT of 13 mK at a 70 K operating temperature with the same optical and background conditions as the MWIR detector array after the subtraction of system noise. Both MWIR and LWIR focal planes have shown background limited performance (BLIP) at 90 K and 70 K operating temperatures respectively, with similar optical and background conditions. In addition, we have demonstrated MWIR and LWIR pixel co-registered simultaneously readable dualband QWIP focal plane arrays. In this paper, we will discuss the performance in terms of quantum efficiency, NEΔT, uniformity, operability, and modulation transfer functions of the 1024 × 1024 pixel arrays and the progress of dualband QWIP focal plane array development work.     

A method for quantitative analysis of clump thickness in cervical cytology slides

Knowledge of the spatial distribution and thickness of cytology specimens is critical to the development of digital slide acquisition techniques that minimise both scan times and image file size. In this paper, we evaluate a novel method to achieve this goal utilising an exhaustive high-resolution scan, an over-complete wavelet transform across multi-focal planes and a clump segmentation of all cellular materials on the slide. The method is demonstrated with a quantitative analysis of ten normal, but difficult to scan Pap stained, Thin-prep, cervical cytology slides. We show that with this method the top and bottom of the specimen can be estimated to an accuracy of 1 μm in 88% and 97% of the fields of view respectively. Overall, cellular material can be over 30 μm thick and the distribution of cells is skewed towards the cover-slip (top of the slide). However, the median clump thickness is 10 μm and only 31% of clumps contain more than three nuclei. Therefore, by finding a focal map of the specimen the number of 1 μm spaced focal planes that are required to be scanned to acquire 95% of the in-focus material can be reduced from 25.4 to 21.4 on average. In addition, we show that by considering the thickness of the specimen, an improved focal map can be produced which further reduces the required number of 1 μm spaced focal planes to 18.6. This has the potential to reduce scan times and raw image data by over 25%.     

多焦距多通道全息光学元件

本文介绍了由不同焦距与不同衍射方向的全息透镜组合而成的一种新型全息元件。这种元件中的每个透镜具有相同的物方光轴和不同的象方光轴。它可以把物方空间沿光轴方向上的不同物距上的物面分别成像在对应的通道上,从而把一个三维物场变为多个二维像进行显示。文中给出了应用此元件对三线粒子场进行检测的初步结果。     

球面端面的锥形梯度折射率透镜的近轴成像特性

本文根据光线在球面上的折射公式及光线微分方程,研究了光线经两端面为球面的锥形梯度折射率透镜的传播和变换,基于光线传递ABCD矩阵,提出了球面端面的锥形梯度折射率透镜的一种等效光学系统.文中给出了该透镜的主平面、焦平面和焦距计算公式,以及近轴成像高斯公式.当锥度为零时即得到球面端面的柱形或径向梯度折射率透镜的相应结果.     

同时实现多角度非垂轴面均匀照明的衍射光学器件

本文利用长焦深器件设计思路,提出了通过设计衍射光学器件相位分布使得在三个垂轴面上满足均匀照明要求来间接实现非垂轴面均匀照明的设计方法,并完成了同时实现多种角度非垂轴面均匀照明的衍射光学器件设计.基于爬山法和模拟退火法相结合的混合算法,设计了器件的相位分布,在30°、45°、55°非垂轴面上光斑不均匀性分别为5.91%、4.00%、3.38%.该方法可推广至二维情形,实现任意曲面均匀照明的要求.     

Focal plane tuning in wide-field-of-view microscope with Talbot pattern illumination

We have developed a focal plane tuning technique for use in focus-grid-based wide-field-of-view microscopy (WFM). In WFM, the incidence of a collimated beam on a mask with a two-dimensional grid of aperture produced the Talbot images of the aperture grid. The Talbot pattern functioned as a focus grid and was used to illuminate the sample. By scanning the sample across the focus grid and collecting the transmission, we can generate a microscopy image of the sample. By tuning the wavelength of the laser, we can tune the focal plane of the WFM and acquire images of different depth into the sample. Images of a green algae microscope slide were acquired at different focal planes for demonstration.     

Magnetic properties of epitaxial-grown exchange-coupled FePt/FeRh bilayer films

The propagation of a laser beam through a micro-lens array (MLA) was simulated using Finite Time Difference Domain (FDTD) method. The intensity distribution at different output planes away from the micro-lens array surface was investigated. As compared to the focal plane, the intensity distribution observed at those out-of-focus planes varies, which is attributed to the interference and diffraction of output laser beams. The simulated results were counter checked by placing a physical MLA under an illumination of a 488 nm continuous wave Argon Ion laser and images were captured for different output planes. Both simulation and experimental results show a great similarity in terms of the distribution patterns. By changing the lens sag height with respect to the lens diameter, the full width at half maximum (FWHM) of the focused laser spot and its corresponding maximum energy flux were analyzed. A FWHM of 160 nm can be achieved by proper selection of lens sag height. It is also found that the energy flux is proportional to numerical aperture (NA).     

Femtosecond micromachining of symmetric waveguides at 1.5 microm by astigmatic beam focusing

We report on a new spatial beam-shaping approach for fabrication of waveguides with a circular transverse profile by femtosecond laser pulses, using an astigmatic beam and controlling both beam waist and focal position in the tangential and sagittal planes. We apply this technique to write single-mode active waveguides at 1.5microm in Er:Yb-doped glass substrates. The experimental results are well described by a simple nonlinear absorption model.     

激光波带片衍射性质的数值模拟

根据亥姆霍兹-基尔霍夫积分,对菲涅尔波带片的高斯激光场在轴向、径向强度分布进行了理论分析,研究了高斯激光束照射下波带片的衍射场规律.数值计算表明：沿轴向光场呈系列焦点,各焦点附近光强分布有振荡现象,随焦点级次的增大光强迅速增大；有焦移现象,焦移量随焦点级次的增大而增大；焦深随焦点级次的升高按平方反比律减小,随波带数减小或焦距增大而增大.在焦平面上,光斑大小与最外环宽度成正比,与焦点级次成反比.     

Depth-enhanced integral imaging system with convex and composite concave micro-lens arrays

A depth-enhanced integral imaging system is proposed by using a convex micro-lens array and a composite concave micro-lens array. The convex-micro-lens array is used to provide a virtual elemental image array for the composite concave micro-lens array. The composite concave micro-lens array which has two focal lengths is used to display integral images with the virtual elemental image array. Compared with the conventional integral imaging, the proposed system can form the 3D image around two image planes with viewing angle being enhanced remarkably. The principle of the enhancement of the image depth is explained in detail and the experimental results are presented.     

一种基于Zernike多项式的波前探测和重构方法

运用Ｎｏｌｌ建议的Ｚｅｒｎｉｋｅ多项式形式表征大气扰动的波面，求出由两个离焦面上的光强分决定的Ｚｅｒｎｉｋｅ多项式的前ｎ项在特定的探测器上的响应矩阵Ｒ。由Ｒ和输入的随机波面在两个离焦面上的光强分布，可方便地求出其Ｚｅｒｎｉｋｅ多项式的系数，从而实现了波前的探测和重构。采用光线追迹的变方法，用计算机模拟验证了这种方法的原理和可行性。     

用于光束整形的多功能衍射相位板的设计

提出一种设计多功能衍射相位板的随机搜索和模拟退火混合设计方法利用这种方法,通过采用多个评价函数,可设计出在不同观察面上同时产生所需光强分布的衍射相位板设计用于高斯光束整形的多功能衍射相位板可以在焦面上产生高能量利用率、小旁瓣的光强分布,同时在离焦面上获得具有良好顶部均匀性的光强分布该方法提高了衍射器件的设计灵活性,对于设计同一块器件在光路的不同位置产生所需的光强分布提供了新的思路,在激光武器、激光加工和激光手术等领域有广阔的应用潜力.     

Diffractive–refractive optics: low‐aberration Bragg‐case focusing by precise parabolic surfaces

Based on analytical formulae calculations and ray‐tracing simulations a low‐aberration focal spot with a high demagnification ratio was predicted for a diffractive–refractive crystal optics device with parabolic surfaces. Two Si(111) crystals with two precise parabolic‐shaped grooves have been prepared and arranged in a dispersive position (+,?,?,+) with high asymmetry. Experimental testing of the device at beamline BM05 at the ESRF provided a focal spot size of 38.25 µm at a focal distance of 1.4 m for 7.31 keV. This is the first experiment with a parabolic‐shaped groove; all previous experiments were performed with circular grooves which introduced extreme aberration broadening of the focal spot. The calculated and simulated focal size was 10.8 µm at a distance of 1.1 m at 7.31 keV. It is assumed that the difference between the measured and calculated/simulated focal spot size and focal distance is due to insufficient surface quality and to alignment imperfection.