Spectacle-type wearable display

A holographic spectacle-type wearable display (SWD) is proposed. In the proposal, partial coherent illumination and large-off axis hologram are applied to the optical layout in order to enhance resolution and simplify the optical system. The SWD bench model consists of six optical components, that is, LED light source, graded index (GI) lens, pinhole, hologram, substrate (spectacle glass), and test target. Here, the thickness of the spectacle glass fabricated is about 5 mm. The resolution of its reconstruction image on the bench model is measured by using a CCD camera. The MTF measured on SWD bench model is not less than 0.5 in spatial frequency 40 lp/mm, experimentally. Its value is enough resolution to display SXGA level. It is expected that the proposed optical system is useful as a wearable computer display unit.     

Confocal microscopy with a volume holographic filter

We describe a modified confocal microscope in which depth discrimination results from matched filtering by a volume hologram instead of a pinhole filter. The depth resolution depends on the numerical aperture of the objective lens and the thickness of the hologram, and the dynamic range is determined by the diffraction efficiency. We calculate the depth response of the volume holographic confocal microscope, verify it experimentally, and present the scanned image of a silicon wafer with microfabricated surface structures.     

Studies on aperture synthesis in digital Fresnel holography

Aperture synthesis can improve image resolution in digital holography by increasing the numerical aperture of the system. In this paper, we show that both the lateral resolution and image field of view can be enhanced at the same time using a more general Fresnel holography setup and hologram stitching. The impact of aperture synthesis on the lateral resolution is investigated both theoretically and experimentally. In the experiment, the synthesis is executed by moving the compact digital holographic system in two directions. Nine holograms are recorded and stitched into one hologram. The reconstruction results show that expanding aperture improves the lateral resolution. The lensless Fresnel holography used in this paper is demonstrated to have the ability to provide a larger numerical aperture and can compress the object spectrum in recording process.     

预放大数字全息显微系统的特点

为了提高预放大数字全息显微系统的成像质量,采用理论分析与实验验证相结合的方法,分别对采用平面及球面参考光记录的预放大数字全息显微系统进行了研究和比较。结果表明:在通常的实验条件下,系统的横向分辨力主要取决于显微物镜的成像分辨力;记录距离较小时,两种系统的横向分辨力均随着记录距离的增大略有降低;但当记录距离较大时,球面参考光预放大数字全息系统的横向分辨力降低得更为明显,即平面参考光预放大数字全息显微系统较为优越;在记录距离为0的情况下,即像面数字全息成像情况下,两种系统的再现像均具有最高的分辨力,在利用普通工业用传感器条件下,横向分辨力远超过了2.19 m,且像质较好。因此,尽可能减小全息图的记录距离,或者采用像面数字全息系统,可以有效提高数字全息系统的成像分辨力。     

A holographic image printing technique with high resolution

A method is shown to obtain a real image with a large image field and high resolution from an image hologram, which is produced by a large aperture lens with large amount of aberration. The resolution of the reconstructed serial image is estimated to be within the range from 450 to 500 lines/mm in 2 inch diameter image field.     

Fraunhofer holography of small particles

The reconstruction of an in-line Fraunhofer (far-field) hologram is re-examined, and an analytical solution of the intensity distribution throughout the entire reconstructed image is presented. The solution bridges the gap between previously documented solutions which are limited to the plane-of-focus image and distant out-of-focus images. The analysis is motivated by a particle velocity measurement technique which attempts to distinguish the focussed image by photographic thresholding. The general methodology is presented for objects of one- and two-dimensional cross-section. Specific results are presented for the single exposure holograms of a long wire and a small particle of circular cross-section. The one-dimensional solution is verified experimentally. The results show precisely how the Fresnel diffraction term creates peaks in the intensity distribution, both upstream and downstream of the focussed image. This characteristic limits the resolution of methods which use thresholding as a means of distinguishing focussed images from their out-of-focus neighbors.     

X射线激光全息的可见光再现

Ｘ射线激光全息是Ｘ射线激光一个非常重要的应用。本文模拟了Ｇａｂｏｒ全息的记录和再现过程，分析了Ｇａｂｏｒ全息和无透镜傅立叶变换全息用可见光再现过程中再现象的放大率、象差等对再现象的影响，提出了减小象差和获得高分辨再现象的方法，认为无透镜傅立叶变换全息是当前Ｘ射线激光全息的重要记录方式。     

垂直分割视场制作合成动态全息图

从理论上及实验上分析了利用垂直视场分割法制作合成动态全息图的方法。将二步彩虹全息术中的主全息图Ｈ１分成若干全息单元,在各单元中分别记录了物体一系列连续变化状态的二维图像,利用该主全息图制作像面全息图Ｈ２,从而获得合成动态全息图。该方法用银盐干版记录主全息图Ｈ１,节省了大量的曝光时间。     

Polychromatic reconstruction for volume holographic memory

We propose a method of reconstructing an image from a volume hologram at a wavelength different from the recording one. Spectrally broad but spatially coherent light was used as a probe beam. Each angular spectral component of the recorded hologram could be Bragg matched at one particular wavelength within the broadband spectrum. We experimentally demonstrated that a whole image could be reconstructed by using polychromatic light, whereas only a partial image was obtained by using single-mode laser light. We discuss the required bandwidth of the probe beam and the deformation of the reconstructed image.     

Spatial-frequency-filtering effect of multiphase holograms

A well-designed hologram can be used as a spatial frequency filter to remove moiré fringes in a digital imaging system. However, it also degrades the resolution of the image. We have used a homemade program to design holograms with better filtering characteristics. We have designed holograms with two, four, eight, and 16 phases and compared their diffraction efficiencies and modulation transfer functions (MTFs). The four-phase hologram showed a diffraction efficiency and MTF characteristics similar to those of the binary hologram. The eight-phase hologram, however, showed much better diffraction efficiency than the previous two, and thus higher MTF values. The 16-phase hologram was still better, but the improvement was marginal. We have manufactured binary and eight-phase holograms and measured their MTFs. We have also observed directly their filtering effects by attaching them to a digital camera and taking pictures of test charts. The Moiré-fringe-removing effects of the two holograms were similar, but the eight-phase hologram showed better resolution.     

A scheme for recording a fast process at nanosecond scale by using digital holographic interferometry with continuous wave laser

A scheme for recording fast process at nanosecond scale by using digital holographic interferometry with continuous wave (CW) laser is described and demonstrated experimentally, which employs delayed-time fibers and angular multiplexing technique and can realize the variable temporal resolution at nanosecond scale and different measured depths of object field at certain temporal resolution. The actual delay-time is controlled by two delayed-time fibers with different lengths. The object field information in two different states can be simultaneously recorded in a composite hologram. This scheme is also suitable for recording fast process at picosecond scale, by using an electro-optic modulator.     

Measurement of the size and position of aerosol droplets using holography

positions and diameters of aerosol particles are measured using Gabor's holographic system. The influence on image quality of the homogeneity of the holographic material, resolution, hologram processing method and optical reconstructing system are considered. The best experimental procedure is suggested.     

On-axis diffuse directional screen based on a transmission Gabor hologram

Holographic single-component diffuse screens based on on-axis transmission holograms are studied theoretically and experimentally. The configurations of extra holographically reconstructed images of the diffuse screen (conjugate image, halo, and zeroth-order spot) are analyzed. A so-called centered hologram is suggested in which the conjugate image of the diffuse screen spatially coincides with the main image, thereby eliminating distortions inserted by the conjugate image. Also, hologram recording using a Mach-Zender interferometer is suggested and implemented. Such an approach makes it possible to eliminate the shadow of an object on the hologram. It is noted that, in recording a planar diffuse screen, the presence of the halo does not distort the image of an object projected through the screen: only the light intensity is partially lost. Analysis of the images projected shows that the luminance of the zeroth-order spot, while relatively low, should be diminished in one way or another.     

Submicrometer digital in-line holographic microscopy at 32 nm with high-order harmonics

Soft-x-ray digital in-line microscopic holography is achieved using a fully coherent high-order harmonic source emitting at 32 nm. Combination of commercial-grade soft-x-ray optics and a back-illuminated CCD detector allows a compact and versatile holographic setup. Different experimental geometries have been tested by imaging calibrated 50 nm tips and 1 microm wires. Spatial resolution of 800 nm is measured with magnifications ranging from 30 to 110 and a numerical aperture around 0.01. Finally, the potentiality of three-dimensional numerical reconstruction from a single hologram acquisition is shown experimentally.     

周视彩虹全息图中共轭像的抑制

本文从理论和实验两方面分析了共轭像的干扰问题,求得了共轭像强度对记录介质厚度及物光—参考光夹角的依赖关系,并对普通6μm干板给出了抑制共轭像的条件.     

微粒场远场同轴全息术

本文从一般模型出发,导出了微粒场远场同轴全息图和再现实象面上的光强分布的普遍表达式.给出了全息图条纹对比度、记录介质的分辨率要求和可允许的微粒最大位移的普遍公式.完善和普遍化了微粒场同轴全息术的理论体系.     

传像光纤束单丝芯径大小对光纤像面全息图的影响

光纤像面全息可以获得较高衍射效率的全息图和再现较大的物像。文中分析了相干光激励下传像光纤束单丝芯径的大小对其输出光场的影响，以及输出光场中低阶模与高阶模对全息照相的不同作用，在此基础上，提出缩小传像束单丝芯径，增多单丝根数，可以提高光纤像面全息图衍射效率和分辨率的观点，并通过实验进行了验证。     

基于离散Fourier变换的内源全息图重构计算方法

对基于离散Fourier变换的内源全息图重构计算方法作了深入系统的分析，讨论了如何计算整个球面全息图对原子重构像的贡献，克服了以往该方法只能计算半个球面全息图的不足，并运用采样定理知识，分析了全息图的采样率、重构像的空间范围和分辨率等问题. 关键词： 内源全息术 离散Fourier变换 采样定理 同步辐射     

Recording and reconstruction of digital Gabor hologram

This paper looks at some as yet undisclosed observations in the recording and reconstruction of digital Gabor hologram. Small particles on the specimen plane diffract the illuminating spherical wave to form the object wave which interferes with the un-diffracted reference to form the in-line hologram. The interference is similar to that between two spherical wavefronts. It is shown that resolution enhancement can be achieved in the recording process through the use of wavefronts with different curvature. Numerical reconstruction of this hologram with a conjugate of the illuminating (reference) wave provides the in-focus real image at the object plane. It is exemplified that the proper choice of the reconstruction wavefront can optically magnify the reconstructed image enabling one to better visualize the resolution enhancement. Both theoretical analysis and experimental confirmation are provided for these observations.     

Three-dimensional holographic lithography by an iterative algorithm

We have applied an iterative algorithm for hologram design with multiple output image planes arranged in close proximity to create continuous patterns within an imaging volume. These holograms have been designed for photolithography on three-dimensional surfaces. The influence of simulated image plane separation on the final image, and its suitability for lithography, is assessed. Results are presented and the most suitable case is demonstrated experimentally.