共查询到20条相似文献,搜索用时 15 毫秒
1.
The Keldysh theory of above-threshold ionization (ATI) is applied to few-cycle laser pulses in order to explore the potential of a recently published new method to measure "carrier-envelope phase difference" phenomena. In this experiment, the carrier-envelope phase difference dependent left-right asymmetry of few-cycle ATI was measured and investigated with a correlation technique. Here, we explore spectral features of the asymmetry, present a theoretical analysis of the experiment, and establish a method to determine the duration of few-cycle pulses whose carrier-envelope phase differences are not controlled. 相似文献
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《Magnetic resonance imaging》1995,13(2):241-249
A technique is presented to increase the signal-to-noise ratio (SNR) in two-dimensional (2D), phase-encoded imaging at low SNR. The essence of this technique is to combine multiple echoes in the time domain. As analyzed in the paper, phase discrepancies exist among different echoes and may deteriorate the combined echo. In particular, extraneous phase shifts can be created if unshielded gradient coils are used. To overcome these phase discrepancies, a matched filter was derived from the k = 0 component of image. This matched filter has the same phase discrepancies among its echoes as the imaging signal and its magnitude decays with an average T2. In the echo summation with the matched filter, the phase of the matched filter was subtracted from the imaging signal and the magnitude of the matched filter was used as the weighting function. We have shown that this matched filter echo summation technique has better SNR than the case of 2D, phase-encoded imaging in both simulation and experiment. The SNR improvement is up to 60% in a phantom experiment. This technique is mostly useful in low SNR imaging that requires long imaging time, such as spectroscopic imaging and 19F imaging. 相似文献
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The application of digital phase shift holographic interferometry to flow-visualization and flow temperature measurement of a 2D thermal flow field was experimentally investigated. An improved recording system for two reference beam phase shift holographic interferometry is set up for this experiment, and details of this experimental technique are described. The phase distribution obtained by this technique presents an excellent picture of flow visualization. From this phase image, temperature distribution of the 2D thermal flow field is also calculated and compared with some measured values obtained using thermocouple probes. 相似文献
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RIE精确传递微光学三维结构于红外材料的方法 总被引:1,自引:0,他引:1
本文对红外光学材料锗的蚀刻性能、机制进行了深入的研究,在反应离子蚀刻(RIE)实验基础上,建立了锗材料蚀刻性能与RIE工艺参量的关系,经过大量的实验,找到了稳定蚀刻速率的方法和条件,为用RIE技术形成高精度衍射微光学元件积累了实用经验. 相似文献
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介绍了本课题组近年来在基于空间结构内部锁相的光纤激光相干合成方面的研究工作,给出了空间结构内部锁相相干合成的基本原理,搭建了七路低功率光纤激光阵列实验系统,结果表明在内部相位噪声校正基础之上,可以稳定补偿外部相位差进而实现激光阵列同相位输出,验证了内部锁相方法的可行性。进一步介绍了空间结构内部锁相技术在目标在回路相干合成、阵列光束光场调控等方面的拓展应用,通过实验论证了空间结构内部锁相技术能够有效提升目标在回路相干合成系统的相位控制带宽,并在远场有效生成轨道角动量光束阵列,其拓扑荷数可从-1到+1切换。 相似文献
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Channel spacing halving and multi-channel apodisation of sampling fiber Bragg grating (SFBG) based onSFBG. The experiment and theoretical analysis showed that the channel spacing could be halved whenfringe was twice the length of SFBG and the initial phase difference of two exposures was odd times of π.A novel method to control the initial phase difference of two exposures is presented in this paper. Usingthis technique, we fabricated two SFBGs with channel spacing of 50 and 100 G by a same phase mask andan apodized SFBG with channel spacing of 100 G. 相似文献
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以相位光栅为实验对象,开展了基于数字显微全息技术的相位物体三维显微结构信息的再现研究.在Mach-Zender透射式实验系统的基础上,分别采用显微物镜和无透镜放大方式,对相位光栅进行放大,以提高系统横向分辨率.在显微物镜放大系统中,菲涅耳近似数值再现算法与双波长技术相结合,抑制主要系统噪音,获得相位光栅的显微结构三维分布.在无透镜放大数字显微全息系统中,分别利用菲涅耳近似法和卷积方法再现原始物波前,并提出相减法消除系统主要球面误差,获得相位光栅的深度信息.实验结果与Veeco干涉仪测试结果比对表明,光栅周期和深度结构与干涉仪测试数据相符. 相似文献
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L. V. Panov D. V. Chirkov S. G. Cherny I. M. Pylev A. A. Sotnikov 《Thermophysics and Aeromechanics》2012,19(3):415-427
Numerical technique was developed for simulation of cavitating flows through the flow passage of a hydraulic turbine. The technique is based on solution of steady 3D Navier—Stokes equations with a liquid phase transfer equation. The approch for setting boundary conditions meeting the requirements of cavitation testing standard was suggested. Four different models of evaporation and condensation were compared. Numerical simulations for turbines of different specific speed were compared with experiment. 相似文献
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Profile measurement of a one-dimensional phase boundary sample using a single shot phase-step method
M. de Angelis S. De Nicola P. Ferraro A. Finizio S. Grilli G. Pierattini 《Optics and Lasers in Engineering》2005,43(12):1305-1314
Phase shifting interferometry is a preferred technique for high-resolution phase profile measurement, but the difficulty in generating the requested shifted pattern has limited the use of the technique to low-noise environment and in case accurate calibration of the phase shifting device is available. In the present experiment, a sample having one-dimensional straight phase boundary is mounted in one arm of an interferometer. One single image of the fringe pattern is recorded, a simple image process is applied generating phase shifted patterns from the original image. Using the appropriate phase shift algorithms, a phase map of the sample is obtained which gives a quantitative measurement of the topographical structure with the resolution of the phase shift method but a single shot recorded pattern. 相似文献
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Tatsuki Tahara Akifumi Maeda Yasuhiro Awatsuji Kenzo Nishio Shogo Ura Toshihiro Kubota Osamu Matoba 《Optical Review》2012,19(6):366-370
We propose a single-shot phase unwrapping technique using a single wavelength and parallel phase-shifting interferometry. In the proposed technique, an object is illuminated by two laser beams, which are emitted from the same laser, and have different illumination angles and polarizations. Two types of object waves generated by the two beams are separately and simultaneously recorded by a polarization-imaging camera. In the path of the reference wave, an array of phase retarders is placed to implement the parallel phase-shifting technique. A highly accurate three-dimensional shape is reconstructed from a single hologram. We numerically simulated the proposed technique and conducted a preliminary experiment to verify its effectiveness. It was confirmed that millimeter-order height, which was several thousand times the wavelength of the laser, can be reconstructed by the proposed technique without wrapping. 相似文献
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针对多普勒非对称空间外差干涉技术,提出一种目标信号相位自校正的方法.首先通过连续采样单色光的干涉图跟踪绝对相位漂移;然后分段线性拟合不同风速下的干涉相位,通过计算两条拟合曲线距离去除相位漂移.搭建风速模拟实验平台,获得采样干涉图,并对相位误差进行校正.结果表明,在60.37 m/s的模拟风速下,相位漂移误差达到30.78 m/s,通过相位校正风速反演误差降低至3.51 m/s,风速精度得到较大改善.最终通过几组不同风速下的反演值得到了平均2.97 m/s的风速测量精度. 相似文献
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We present results for a digital holography experiment with anisoplanatic image correction through two discrete planes of phase errors. Using a nonlinear optimization technique, we maximize a modified sharpness metric to solve for estimates of the phase errors in the system in the multiple planes where they physically exist. We show that correcting for phase errors in multiple planes gives a superior image to correction in one plane. 相似文献
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Dembowski C Dietz B Gräf HD Harney HL Heine A Heiss WD Richter A 《Physical review letters》2003,90(3):034101
A microwave experiment has been realized to measure the phase difference of the oscillating electric field at two points inside the cavity. The technique has been applied to a dissipative resonator which exhibits a singularity-called exceptional point-in its eigenvalue and eigenvector spectrum. At the singularity, two modes coalesce with a phase difference of pi/2. We conclude that the state excited at the singularity has a definitive chirality. 相似文献
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We report a Koehler-illumination-based full-field, actively stabilized, low-coherence phase-shifting interferometer, which is built on a white-light Michelson interferometer. By using a phase-stepping technique we can obtain full-field phase images of the sample. An actively stabilized phase-lock circuit is employed in the system to reduce phase noise. An application to human epithelial cells (HeLa cells) is achieved in our experiment. The advancement of this technique rests in its ability to take images of unstained biological samples quantitatively and on a nanometer scale. 相似文献
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A technique for monitoring both the pulse carving misalignment and pi phase shift in a return-to-zero (RZ) differential phase-shift keying (DPSK) system based on a phase modulator is proposed and demonstrated. By monitoring the mean-power variation of a hybrid local oscillation lightwave with the modulated signal lightwave without any deliberated control, the technique can provide the information on pulse carving misalignment and phase modulation index simultaneously, as the power variation reflects the asymmetric distribution of RZ-DPSK in a signal constellation diagram. It is characterized as transparent to signal bit rate, central wavelength, and absolute power level. Both the simulation and experiment results show that more than +/- 15% bit duration misalignment and +/- 5% phase shift deviated from pi can be detected. 相似文献