Radio-frequency matched filtering by photorefractive optical holography

Matched filtering of megahertz-bandwidth signals by use of holograms recorded in a photorefractive crystal is demonstrated. Holographic recording of rapidly varying signals has heretofore been hampered by the relatively slow response of photorefractive crystals. For the first time, to our knowledge, synchronization between waveforms and short optical sampling pulses is used with acousto-optic electrical-to-optical conversion to build up static holograms of rf waveforms in a SBN crystal. Readout with a continuous input signal yields a time-resolved correlation with stored waveforms.     

High-speed 3D imaging using photorefractive holography with novel low-coherence interferometers

The paper reports recent progress in developing high speed 3D imaging systems based on low coherence photorefractive holography with high-speed depth-sectioned imaging at 476 frames per second. It is demonstrated that photorefractive holography can utilize a wide variety of sources of differing spatial and temporal coherence, including a novel all-solid-state broadband laser. Also presented is a novel real-time optical sectioning technique based on structured illumination combined with photorefractive holography that provides real-time optical sectioning when imaging with reflected light or with fluorescence.     

Immersion holography based on amorphous chalcogenide films

A solid immersion holographic method for the recording of refractive index and surface-relief modulated gratings with a period of 0.1–1 μm in amorphous films of chalcogenide semiconductors As₂S₃ and As–S–Se has been developed and studied. The laser immersion interference lithography can be used as a low-cost method for the exposure of large surfaces with regular patterns like subwavelength-gratings and microsieves. The polarization sensitive properties of the subwavelength refractive-index modulated transmission gratings were studied. The possibility to use the amorphous chalcogenide films as a media for holographic recording and storage of information with high density is discussed.     

Thick dye-doped poly(methyl methacrylate) films for real-time holography

Molding and direct-polymerization techniques are used for the fabrication of holographic materials based on dye-doped poly(methyl methacrylate). The thickness of the samples obtained ranges from several micrometers to several millimeters. Pump-signal cross modulation is studied experimentally, and photophysical mechanisms responsible for refractive-index and absorption changes are discussed. Self-developing intensity and polarization holographic recording capability, strong anisotropy of diffraction, and high angular selectivity are demonstrated in thick samples.     

Magnetostatic analog for the calculation of phase contours inelectron holography of magnetic films

A method is presented for predicting the electron holographic interference pattern from a given magnetization distribution, and it is explained how phase contours can be sketched using magnetostatic intuition. The presented method is derived from the classical Lorentz force and the de Broglie relation between momentum and wavelength. The calculation of the electron phase to a two-dimensional magnetostatics problem is also mapped to which engineering experience and familiar mathematical methods can be applied. The result is considered simple to state and to remember     

Collinear holography

A novel reading and writing technology for a holographic storage system called collinear holography is developed. With this method, two-dimensional page data can be recorded as volumetric holograms generated by a reference beam and a signal beam that are bundled on the same axis and irradiated on the recording medium through a single objective lens. The multiplex recording and reconstructing process is demonstrated, and it is presented that optical configuration and the dichroic media disk structure are suitable for a compact system. This method enables us to construct a small volumetric optical disk storage system with CD and DVD upper compatibility.     

球面波散射因子对光电子全息的影响

用于研究物质结构的光电子全息 ,其物理机制是光电子波在固体中的散射。在电子能量为 5 0～ 2 0 0eV的中低能量下 ,不能用通常的平面波近似方法加以研究 ,必须考虑到光电子波的球面波本质。即使在电子能量大于 5 0 0eV的高能情况下 ,用平面波近似的方法也应对前向散射进行修正。本文以铜单晶薄膜为例 ,利用单重散射模型讨论了球面波近似模型下校正因子对光电子全息函数的影响 ,并与平面波近似作了比较。结果表明 ,对能量低于 2 0 0eV的光电子全息来说 ,球面波近似校正因子对前向散射和背向散射的振幅和相位都有较明显的修正。而在高能条件下 ,球面波近似校正因子主要影响光电子的前向散射 ,对背向散射的影响较小。进一步研究发现 ,球面波近似校正可以提高光电子全息的重现图的质量。     

Phase-error correction in digital holography

The quality of images computed from digital holograms or heterodyne array imaging is degraded by phase errors in the object and/or reference beams at the time of measurement. This paper describes computer simulations used to compare the performance of digital shearing laser interferometry and various sharpness metrics for the correction of such phase errors when imaging a diffuse object. These algorithms are intended for scenarios in which multiple holograms can be recorded with independent object speckle realizations and a static phase error. Algorithm performance is explored as a function of the number of available speckle realizations and signal-to-noise ratio (SNR). The performance of various sharpness metrics is examined in detail and is shown to vary widely. Under ideal conditions with >15 speckle realizations and high SNR, phase corrections better than lambda/50 root-mean-square (RMS) were obtained. Corrections better than lambda/10 RMS were obtained in the high SNR regime with as few as two speckle realizations and at object beam signal levels as low as 2.5 photons/speckle with six speckle realizations.     

Optical aperture synthesis imaging with fractional Fourier-domain filtering

The fractional Fourier transform, which is a generalization of the classical Fourier transform, is introduced into an optical aperture synthesis (OAS) system by which imaging of an astronomical object can be achieved. We introduce fractional Fourier optical imaging and fractional Fourier-domain filtering (FFDF), and then present the schematic diagram of an OAS imaging system with FFDF. The modulation transfer function of an OAS system with FFDF is compared with that of an OAS system in the same condition. The result indicates that the OAS system with FFDF has larger practical cutoff frequency when the fill factor is smaller. Furthermore, the quality of imaging and restoration also demonstrates this conclusion.     

One-step two-wavelength holography

One-step two-wavelength holography is obtained with twointerferometric beams with different wavelengths by means of apolarizing modulation produced by a liquid-crystal lightvalve. This holographic method eliminates the need for preliminarystatic recording of the hologram and permits one-step two-wavelengthholographic testing to produce results easily in real time.     

Disk-type multiplex holography

A theory for making a disk-type multiplex hologram is derived. This theory relates the final image point, as seen by the observer, to a point on the original three-dimensional object through a set of equations. From these equations the distortion of the image and the wavelength as seen by each individual eye can be evaluated. Computer simulation shows the characteristics of this hologram. Some experimental results also confirm these characteristics. By reversing the process and specifying a desired image, we generated a set of distorted two-dimensional originals. The hologram fabricated with these distorted images can generate nearly distortion-free images.     

Large-viewable-angle rainbow holography

A new, to our knowledge, method for recording rainbow holograms of three-dimensional diffused objects in one step without the use of slits is proposed. No lens is needed for recording in this kind of holography; instead, multiple synthetic slits are created by displacement and multiple exposure of an object to expand the horizontal and the vertical viewing angles of the hologram.     

Fourier-domain digital holographic optical coherence imaging of living tissue

Digital holographic optical coherence imaging is a full-frame coherence-gated imaging approach that uses a CCD camera to record and reconstruct digital holograms from living tissue. Recording digital holograms at the optical Fourier plane has advantages for diffuse targets compared with Fresnel off-axis digital holography. A digital hologram captured at the Fourier plane requires only a 2D fast Fourier transform for numerical reconstruction. We have applied this technique for the depth-resolved imaging of rat osteogenic tumor multicellular spheroids and acquired cross-section images of the anterior segment and the retinal region of a mouse eye. A penetration depth of 1.4 mm for the tumor spheroids was achieved.     

Short-time Fourier transform and wavelet transform with Fourier-domain processing

We discuss the semicontinuous short-time Fourier transform (STFT) and the semicontinual wavelet transform (WT) with Fourier-domain processing, which is suitable for optical implementation. We also systematically analyze the selection of the window functions, especially those based on the biorthogonality and the orthogonality constraints for perfect signal reconstruction. We show that one of the best substitutions for the Gaussian function in the Fourier domain is a squared sinusoid function that can form a biorthogonal window function in the time domain. The merit of a biorthogonal window is that it could simplify the inverse STFT and the inverse WT. A couple of optical architectures based on Fourier-domain processing for the STFT and the WT, by which real-time signal processing can be realized, are proposed.     

Generalized Bragg selectivity in volume holography

The diffraction efficiency of holographically recorded volume gratings was extensively studied, and it can be accurately predicted as long as the recording wave fronts are simple. The derivation of the diffraction efficiency when complicated wavefronts or images are involved is much more tedious and less explored. In this work we derive operator expressions that can be used to analyze these processes regardless of the shape of the wavefront and the nature of the optical systems through which they propagate. The compact expressions derived are directly applicable to the analysis of volume holographic processes, and the deterioration of the holographic reconstruction quality is derived as a function of the deviations from the recording parameters. The generalized results obtained reduce to the conventional Bragg effect for plane wave recording and reconstruction. Previously unexplored phenomena are discussed and demonstrated through some simple, and practically useful paradigms, including hologram recording and reconstruction in the Fresnel, Fourier transform, and image plane regions, as well as recording with plane and spherical waves. Some prior experimental results are also interpreted mathematically. In subsequent publications the analysis will be explored further to facilitate its application to more complicated architectures.