Lau effect: OTF theory

The Lau effect is an interference phenomenon involving two gratings and incoherent illumination. Here the Lau effect is described in terms of the OTF theory. It is shown that this analysis is equivalent to that given in terms of coherence theory.     

Rotation sensitivity of Lau fringes: an analysis based on coherence theory

An analysis based on coherence theory is presented, which explains the experimentally observed rotation sensitivity of the contrast of Lau fringes obtained under spatially incoherent illumination.     

ANALYSIS OF THE GENERAL EFFECTS IN DOUBLE-GRATING DIFFRACTION-INTERFERENCE SYSTEM

Based on the ambiguity function, the optical phenomena of the double-gearing diffraction-interference system are analysed with partially coherent illumination. Different patterns are observed on the observation plane when the optical elements are placed in their proper positions. Detailed discussions on the two extremes of coherence are given. Conclusions could be obtained about the Lau effect, the generalized Lau effect, the incoherent grating-lens imaging, the Talbot effect, the joint-Talbot effect and the generalized joint-Talbot effect. Some special cases are also verified by experiments.     

Lau fringes and subjective refraction

Lau fringes formed in the far field of a pair of gratings illuminated by spatially incoherent light are known to disappear when one grating is rotated slightly (+/-3 degrees ) with respect to the other. We observed that a cylindrical lens that was appropriately rotated could restore the high-contrast Lau fringes by bringing together the rays that are coherent with respect to each other. We have developed a new refractometer based on this phenomenon, the details of which are presented. Measurement of the cylinder power and axis of the human eye is possible with good accuracy and repeatability with this instrument.     

Application of source encoding to incoherent Talbot imaging and the Lau effect

We demonstrate a technique to generate Talbot images by a spatially incoherent source using a source encoding technique. We further show that a Talbot image can be formed in the optical set-up for the Lau effect following source encoding theory.     

Automated collimation testing in Lau interferometry using phase shifting technique

We demonstrate an automated procedure for detection of collimation position of an incoherent beam in Lau interferometry using phase shifting technique. The experimental arrangement consists of a Lau-based interferometer in which light from a source grating illuminates a set of two coarse gratings separated by self-imaging distance. Phase shifting procedure is incorporated by translating the detector grating, corresponding to different positions of the collimating lens. The phase map is plotted corresponding to each position. The slope of the phase map is indicative of the collimation position of the optical beam. The technique is fully automatic and provides good accuracy and high precision.     

衍射相关和Lau干涉

本文用离轴傅里叶变换系统的模型和菲涅耳衍射理论分析了衍射受限下的离焦相关器的系统特性,证明是第一模板和第二模板衍射像之间的强度相关积分。推导了衍射相关器作为测量相位物体的干涉仪的一般理论,这时要求编码板函数能衍射自成像并且相关函数为周期性函数。讨论了平行光栅作为编码板时的干涉仪的横向剪切干涉特性,给出了实验结果。本文还证明了衍射相关器是推广到任何平面物体在任何观察距离上的Lau效应装置。衍射相关干涉仪产生Lau干涉条纹,并且是直接应用Lau效应的干涉仪。 关键词：     

Incoherent all-optical NAND-, NOR-, and XOR-gate using photorefractive fanning effect

An all-optical computing device is proposed to perform incoherent digital operations, including the NAND, NOR, and XOR gates. Instead of using interferometer-based methods, making use of self-generating noise gratings and the erasure of them by another beam in two photorefractive self-pumped phase conjugators (SPPC), the device is able to process mutually incoherent as well as mutually coherent inputs. Changing the orientations of two polarizers and a photorefractive crystal, we are able to perform incoherent parallel NAND, NOR, and XOR operations with this proposed setup. Received: 18 November 1998 / Revised version: 10 February 1999 / Published online: 12 April 1999     

Phase shifting grating-slit test utilizing a liquid crystal display

A quantified focal plane testing method, termed phase-shifting grating-slit test, is demonstrated by utilizing a micro liquid crystal display. In contrast to the setup in the Ronchi Test, an incoherent illuminating grating is used and an optical slit is located at the image plane of the tested lens to modulate the aberrated wavefront. With the micro liquid crystal display generating and phase shifting the incoherent illuminating grating with variable frequency, a higher measurement dynamic range can be achieved on demand.     

Photonic temporal integration of broadband intensity waveforms over long operation time windows

We propose and experimentally demonstrate a novel design for temporal integration of microwave and optical intensity waveforms with combined high processing speed and a long operation time window. It is based on concatenating in series a discrete-time (low-speed) photonic integrator and a high-speed analog time-limited intensity integrator. This scheme is demonstrated here using a cascaded fiber-based interferometers' system (as a passive eight-point discrete-time integrator) and an analog time-limited intensity integrator. The latter is based on temporal intensity modulation of the input waveform with a rectangular-like incoherent energy spectrum followed by linear dispersion. Using this setup, we experimentally achieve accurate time integration of intensity signals with ~36 GHz bandwidths over an operation time window of ~4 ns, corresponding to a processing time-bandwidth product of >144.     

Real-time one-step incoherent level slicing of optical images

A modification of a real-time subtraction setup enables the performance of the level slicing operation of optical images. The operation is done with incoherent sources for both read-in and read-out illuminations. The enhanced (sliced) intensity level is displayed on top of a uniform background level.     

Inelastic and elastic scattering differential cross‐sections of 59.5 keV photons for Cu and Zn targets

Differential cross‐sections for incoherent and coherent scattering of 59.54 keV photons were measured for Cu and Zn targets at scattering angles of 40–135° in a reflection geometry setup with a graded shielding arrangement. The ratio of these cross‐sections, which can be determined with higher precision than absolute values, is given. A method was used to determine differential incoherent and coherent scattering cross‐sections of elements. This method is based on simultaneous measurement of fluorescence radiation and scattered radiation, thus avoiding problems with measuring source strength and source‐to‐detector solid angle. The measurements were performed using a point source of Am‐241 radioisotope and an Si(Li) detector. The experimental results, which complement earlier results, were compared with the theories of incoherent scattering function and form factor. Copyright © 2004 John Wiley & Sons, Ltd.     

非相干背景光辐照对LiNbO3∶Fe与LiNbO3∶Fe∶In晶体中二波耦合的控制

理论分析和实验观测了非相干背景光辐照下掺杂LiNbO₃晶体中的二波耦合,发现非相干背景光能够在很大范围内灵活有效地控制信号光增益,抑制扇形效应,提高信噪比,缩短光栅的建立时间.入射光光强比一定时,适当地增大背景光光强可以使光栅响应时间减小一个数量级.尤其对于抽运光光强远大于信号光光强的情况下,上述作用更为明显. 关键词： 光折变 二波耦合 非相干背景光     

Speckle characteristics of a broad-area VCSEL in the incoherent emission regime

We present a technique to reduce the speckle contrast of a NIR broad-area VCSEL based on the spatially incoherent emission regime that can be obtained when using the proper driving conditions. We evaluate the efficiency of this technique to reduce the speckle contrast by comparing it with the speckle characteristics in multimode emission under cw operation. Depending on the illumination setup, the incoherent emission regime can lead to a strongly reduced speckle contrast down to 1.3%. This is in agreement with estimates of the expected speckle contrast reduction when three contrast reducing effects are taken into account. These low contrast values make the investigated sources attractive for several applications that suffer from speckle noise.     

Production of vector mesons in ultraperipheral nucleus-nucleus interactions

Theoretical models describing the production of vector mesons in coherent ultraperipheral nucleus-nucleus interactions are considered. The experimental data on the coherent and incoherent production of ρ⁰ mesons at the STAR setup (BNL, USA) are analyzed.     

Dynamic and static position control of optical feedback solitons

We report on the experimental implementation of an external control for optical feedback solitons using incoherent spatial intensity distributions in a liquid crystal light valve (LCLV) optical single feedback system. The external control provides excellent experimental possibilities for static and dynamic control of the lateral positions of the optical feedback solitons which will be demonstrated. Particularly, the influence of different gradients onto the drift motion of spatial solitons is experimentally investigated in detail. In agreement with theoretical predictions, the drift velocity of the soliton increases according to the steepness of the gradient. Additionally, a completely incoherent addressing scheme including creation and erasure of feedback solitons is demonstrated for the LCLV setup.     

Sensitive high-resolution white-light Schlieren technique with a large dynamic range for the investigation of ablation dynamics

We developed a modified Hoffman contrast technique with a 12 ns pulsed incoherent extended white-light source that enables an easily interpretable visualization of ablation plumes with high resolution, a large dynamic range, and color information. By comparison, a conventional dark-field setup with a slitlike laser light source provides large sensitivity but a small dynamic range, and it is difficult to interpret the filtered images.     

相干谐波辐射的测量方法和系统

 研究了光学速调管自发辐射谱,其调制率已达0.80,即将进行相干谐波辐射实验。介绍了相干谐波辐射实验的主要考虑因素、相干增强因子的测量方法和测量系统以及种子激光与电子束的准直和同步。     

平面周期物体的Lau效应

基于部分相干理论中交叉谱密度函数的概念研究了平面周期物体的Lan效应文章导出了平面物体Lau像光强分布式,求得了平面周期物体的Lau像光强分布及其Lau成像条件,并进行了实验验证,给出了实验结果.     

超低温下掺Er3+玻璃的相干拍频调制效应研究

采用非相干光时延四波混频(TDFWM-IL)实验装置,在7K温度下,利用波长为800 nm的飞秒脉冲激光,观测到掺Er3+玻璃的光子回波效应,发现信号随延时变化的拍频调制结构.根据TDFWM-IL多能级理论,运用其非均匀加宽占主导时的公式拟合实验结果,从最佳拟合获得的退相时间T2=300 fs,这与由相干控制实验测得的...