共查询到20条相似文献,搜索用时 15 毫秒
1.
本文论述光波场的时问、空间对称性,包括拍频导致的“空间放大”与“时间放大”;多束光干涉提高条纹细锐度“空间压缩”、锁模技术中脉冲的“时间压缩”;空间调制与时间调制;非线性效应中的时间倍频与空间倍频;空间相干性与时间相干性;时域测不准与空域测不准。 相似文献
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《声学学报:英文版》2015,(2)
The research is about the effect of a layer of varying density of sea-bottom sediments on spatial correlation of sea-bottom backscattering.The relationship between scattering cross section and spatial correlation is that backscattering cross section decreases quickly and the spatial correlation becomes stronger as the incident angle increases.Therefore,the densitydepth profile is introduced into sea-bottom high-frequency backscattering echo model,which is used to simulate sea-bottom backscattering and calculate the function of spatial correlation.The influence of the density gradient on spatial correlation of sea-bottom backscattering is investigated by analyzing the relations between vertical gradient of density and the scattering cross section.As can be seen from the simulation results,the impact of the density gradient on the spatial correlation is found more significant.While the density gradient increases,the scattering cross-section and the radius of the spatial correlation broaden,the spatial correlation becomes stronger.At the same time,the scattering cross-section decreases more quickly as the incident angle increases. 相似文献
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为避免啁啾脉冲堆积宽带激光的空间调制对光学元件的损坏,数值研究了其非线性传输过程中时域调制对光束空间调制产生与增长的影响。结果表明:光束未叠加空间调制时,若B积分在实际工作范围内,堆积子脉冲间干涉引入时间调制外,叠加与未叠加时间调制,正反常色散情况下光束空间上均不会产生调制,因而也没有调制增长,然而,当B积分进一步增加时,光束空间将产生调制,并能快速增长;当光束引入空间调制后,在反常色散情况下,与时间未额外叠加调制相比,时间额外叠加调制时空间调制增长速度明显加快,而在正常色散时,额外添加时间调制与不添加调制,空间调制增长的差别很小。 相似文献
4.
D. Walter S. Eyring J. Lohbreier R. Spitzenpfeil C. Spielmann 《Applied physics. B, Lasers and optics》2007,88(2):175-178
We demonstrate the spatial homogenization of intense laser pulses by adaptive minimization of spatial chirp of the spectrally
broadened output pulses of a filament. A liquid-crystal-based two-dimensional spatial light modulator is used to control the
spatial phase of the driver pulse. An evolutionary algorithm finds the optimal spatial laser phase distribution that introduces
minimal distortions during filamentation and enhances the beam quality of the output pulse. A homogeneous intensity distribution
favours efficient temporal compression close to the bandwidth limit without the need for spatial filtering after the filament.
PACS 42.65.-k; 42.65.Re; 41.85.Ct 相似文献
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We experimentally investigate the spatial and temporal properties of a nonlinear optical system composed of an optically addressed spatial light modulator and a two-dimensional optical feedback. The system property is examined using fringes with only one spatial wave vector. The fringes are spontaneously generated using a spatial frequency filter in the optical feedback. We also experimentally investigate the properties of the spatial light modulator in the system using ordinary interference fringes in order to compare with the system property. We demonstrate that the spatial frequency response of the nonlinear optical system is identical to that of the spatial light modulator. We also demonstrate the distinctive temporal behavior of diffraction lights from the fringes generated in the system. 相似文献
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In this paper we present a new approach allowing the surpassing of the diffraction based limitation for the achievable resolution provided by imaging systems. It is based on an encoding-decoding process of various spatial pixels or regions in the field of view of the imaged object by orthogonal and differently time varying polarization states.The reconstruction of the original spatial information is obtained by applying a decoding process in a way similar to the encoding one. Although all the spatial information is summed and mixed together by the system, the decoding provides super-resolved imaging since in every spatial position the undesired spatial information having time varying polarization dependence, that is uncorrelated to the decoding sequence applied on that specific spatial position, is averaged to zero and, on the other hand, the information which corresponds to that specific spatial region is being reinforced.The proposed approach can be used not only for super-resolved imaging but also for imaging module that maintains the same spatial resolution while providing enlarged field of view. 相似文献
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Gaoping Huang Jia Sun Weikang Feng Jiamin Yuan Zhenkun Wu Mengzhe Qin Yiqi Zhang Yanpeng Zhang 《Applied physics. B, Lasers and optics》2013,112(2):267-278
We report the self- and external-dressed Autler-Townes (A-T) splittings of the images of the generated four-wave mixing signal (FWM) and electromagnetically induced transparency (EIT) of probe images in cascade three-level atomic system. Such spatial properties of probe and FWM signals are induced by the enhanced cross-Kerr nonlinearity. We demonstrate the controlled electromagnetically induced spatial dispersion (EISD), splitting and focusing of probe and FWM signals images by adjusting self- and external-dressing fields. Studies on such controllable A-T spatial splitting and spatial EIT effect can be very useful in applications of spatial signal processing and optical communication. 相似文献
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A method of calibrating the spatial distribution of photosensitivity of matrix photodetectors without the use of reference optical radiation intensity distributions has been developed and experimentally verified. A scheme of the experimental setup implementing the method, an experimental procedure, and two modifications of the algorithm that reconstructs spatial distributions of photosensitivity using the measurement results have been developed. Experiments on calibrating the spatial distributions of photosensitivity of CCD matrices have been performed. It is shown that, using the presented method, calibration of the spatial distribution of photosensitivity of matrix photodetectors permits one to almost eliminate systematic error when detecting spatial distributions of the optical radiation intensity. 相似文献
12.
We investigate the role of the spatial pattern and temporal dynamics on the population properties of a diffusive Gause–Lotka–Volterra system. The average total population size is insensitive to the temporal dynamics, whereas a significant decrease of the population size can be found as the spatial diffusion effect is increased, implying that the spatial pattern plays an important role. At large diffusion coefficients, a saturation of the spatial pattern variation is observed, which can be understood by a spatial scaling analysis of the system. The existence of multiple attractors can also indicate that spatial patterns play a more important role than temporal dynamics in dominating the population size. 相似文献
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The implementation of the angular spectrum approach based on the two-dimensional fast Fourier transform is evaluated for near-field pressure simulations of square ultrasound transducers, where the three-dimensional pressure field is calculated from the normal velocity distribution on the transducer surface. The pressure field is propagated in the spatial frequency domain with the spatial propagator or the spectral propagator. The spatial propagator yields accurate results in the central portion of the computational grid while significant errors are produced near the edge due to the finite extent of the window applied to the spatial propagator. Likewise, the spectral propagator is inherently undersampled in the spatial frequency domain, and this causes high frequency errors in the computed pressure field. This aliasing problem is alleviated with angular restriction. The results show that, in nonattenuating media, the spatial propagator achieves smaller errors than the spectral propagator after the region of interest is truncated to exclude the windowing error. For pressure calculations in attenuating media or with apodized pistons as sources, the spatial and spectral propagator achieve similar accuracies. In all simulations, the angular spectrum calculations with the spatial propagator take more time than calculations with the spectral propagator. 相似文献
14.
Kota Chaen 《Optics Communications》2007,280(1):165-172
Liquid crystal spatial light modulators, which are widely used as display devices for computer-generated holograms, have modulation characteristics that depend on spatial frequency. We describe a method for displaying a computer-generated hologram on a liquid crystal spatial light modulator with compensation of its spatial frequency response. Using this method, we demonstrate a binary phase grating with smaller dependence on the spatial frequency. We also demonstrate application of the display method to holographic femtosecond laser processing. 相似文献
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Tatsuki Tahara Yasuhiro Awatsuji Kenzo Nishio Shogo Ura Toshihiro Kubota Osamu Matoba 《Optical Review》2010,17(6):519-524
We comparatively analyzed and quantitatively evaluated the field of view and the viewing zone of single-shot phaseshifting
digital holography that uses space-division multiplexing, for the first time. We formulated the sampling intervals in the
techniques in which the phase of the reference wave is spatially divided into two and four steps, and numerically simulated
the areas. It was clarified that each area of the spatial two-step phase-shifting technique was twice as wide as that of the
spatial four-step phase-shifting technique. We also experimentally investigated the areas. The ghost appeared for the spatial
four-step technique when the object was between the boundary of the field of view of the spatial two-step technique and that
of the spatial four-step technique, but did not appear for the spatial two-step technique. 相似文献
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凝视阵列型热像仪的空间噪声制约着热像仪对远距离目标的探测、分辨、跟踪性能。为解决热像仪空间噪声实际测量问题,分析了热像仪的空间噪声测量原理,给出了热像仪基于信号传递函数的空间噪声测量数学模型,介绍了热像仪某一组、某一区域或全部像素如何剔除时间域NETD,再通过统计计算得到其空间NETD的数学模型。对制冷型MCT320256凝视列阵热像仪的SiTF和空间NETD进行测量,当背景黑体温度为5 ℃时,FOV区域中心信号传递函数(SiTF)为27.29 mV/℃,NETD为0.128 ℃,20 ℃时FOV区域中心SiTF为29.03 ℃,NETD为0.121 ℃。测量结果表明:该方法可评估空间噪声对热像仪性能的影响。 相似文献
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在超声背散射骨质评价中,不同测量感兴趣区域(ROI)的超声背散射信号会有波动,致使诊断准确度降低。该文目的是研究超声背散射信号随测量区域的变化规律。采用空间扫描方法离体测量了35块骨样本,将超声背散射参数从空间域变换到空间频率域。结果表明,超声背散射参数的主要空间频率成分集中于低频部分;空间频率域超声背散射参量最大值(MASF)与骨矿密度等参数具有中高度显著相关性(R2=0.45~0.83,p0.001);空间频率域超声背散射参量衰减系数(AC)也与松质骨密度及结构特征有显著相关性(R2=0.41~0.72,p0.001)。研究表明空间频率域变换方法有助于明确超声背散射信号随测量ROI的变化规律,空间频率域的超声背散射相关新参量评价松质骨状况具有可行性。 相似文献
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《Journal of Electrostatics》2007,65(9):582-592
The spatial sensitivity, spatial filtering effect, temporal frequency response characteristics and bandwidth are important parameters influencing the accuracy and response speed of a ring-shaped electrostatic inductive sensor. In this paper, the charge induced on the ring-shaped sensor with different geometric sizes from a single particle having a unity charge was modeled mathematically. And from the numerical solution obtained using the finite element analysis software ANSYS, the spatial sensitivity of the sensor was derived. The effect of the geometric size of the sensor on the spatial sensitivity was also investigated, and its spatial filtering fundamental theory and spatial filtering effect were also analyzed quantitatively. The temporal frequency response characteristics of the sensor were also derived. The experimental results on a gravity-fed conveyor were presented. The theoretical and experimental results obtained demonstrate that the ring-shaped sensor acts as a low-pass filter in the spatial frequency domain and its spatial frequency characteristics are closely related to the radial position of the charged particle and the axial length of the electrode. The measurement system, including the probe and signal conditioning circuit, acts as a band-pass filter, and the radial position, the axial length of the electrode, particle velocity and particle size have important effects on the temporal frequency characteristics of the measurement system. 相似文献
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为了解决空间滤波器滤波针孔堵孔问题,提出了一种新型柱面镜空间滤波器,新型柱面镜空间滤波器由柱面镜和狭缝构成。利用线性传输理论,对高功率激光束在新型柱面镜空间滤波器中的传输特性进行了数值模拟。结果表明:新型柱面镜空间滤波器的焦斑面积比传统滤波器大,而焦斑功率密度较小;新型柱面镜空间滤波器的滤波效果与传统滤波器相同,近场均匀性也相同。因此新型柱面镜空间滤波器能够抑制空间滤波器堵孔效应,可以缩短空间滤波器系统透镜焦距,从而提高功率装置的整体性价比。由此,采用新型柱面镜空间滤波器替换传统球面镜空间滤波器具有可行性。 相似文献