Analysis of period and visibility of dual phase grating interferometer

Dual phase grating interferometer may simultaneously achieve large field of view and high x-ray dose efficiency. Here, we develop a simple theoretical method to better understand the imaging process of the dual phase grating interferometer. The derivation process of fringe period and the optimal visibility conditions of the dual phase grating interferometer are given in detail. Then, we theoretically prove that the fringe period and optimal visibility conditions of the dual phase grating interferometer include that of the Talbot interferometer. By comparing our experimental results with those of other researchers, we find that when the positions of phase gratings are far away from the positions where the fringe visibility is optimal, the fringe period of the dual π -phase grating interferometer is twice the theoretical results under the illumination of polychromatic x-ray. This conclusion may explain the contradictory research results of dual phase grating interferometer among different researchers.     

高灵敏度的量子迈克耳孙干涉仪

迈克耳孙干涉仪不仅可以用来研究物理学的基本问题,而且能够用于精密测量,比如引力波信号的测量.因此,构建高灵敏度的迈克耳孙干涉仪是实现微弱信号测量的关键.目前,人们利用压缩态可以降低迈克耳孙干涉仪的噪声;通过光学四波混频过程能够放大马赫·曾德尔干涉仪中的相位信号,从而提高干涉仪的信噪比和灵敏度.本文研究了一种用于高灵敏度相位测量的量子迈克耳孙干涉仪.在迈克耳孙干涉仪中,利用非简并光学参量放大器取代干涉仪中的线性光学分束器;并且将压缩态注入干涉仪的真空通道,可以得到高信噪比和高灵敏度的干涉仪.由于存在不可避免的光学损耗,分析了迈克耳孙干涉仪内部和外部的损耗对相位测量灵敏度的影响.通过理论计算研究了干涉仪的相位测量灵敏度随系统参数的变化关系,得到了高灵敏度的相位测量量子迈克耳孙干涉仪的实现条件,为用于精密测量的干涉仪的设计提供了直接参考.     

Polarization phase-shifting Jamin shearing interferometer

The Jamin shearing interferometer is very useful in wavefront testing, especially for the low coherent light. Based on this interferometer, a polarization phase-shifting Jamin shearing interferometer is proposed to improve the performance. In the interferometer, two interference beams are linearly polarized and a polarization phase shifter is applied to realize the phase shifting. Different types of configurations of the interferometer are given. With phase-shifting interferograms, the precision of the interferometer can be improved. The interferometer is kept as an equal optical path system and its shearing amount remains changeable with simple structure and easy operation. In experiments, phase-shifting interferograms are obtained by rotating the analyzer. The usefulness of the interferometer is verified.     

克服光纤Mach-Zehnder干涉仪信号衰落的新方法及分析

为了克服光纤Mach-Zehnder干涉仪易受环境因素影响而引起偏置相位漂移从而导致输出信号衰落(波动)的问题,提出一种新的简单方法,即:将干涉仪输出信号分为直流和交流两个分量,通过直流分量的大小来计算交流信号的补偿因子,以达到克服交流信号衰落、稳定检测传感信号的目的在小信号测量情况下,该方法在很大范围内能有效抑制随机温度涨落等因素引起的信号衰落的问题文中对补偿方法的误差和局限性也做了分析和讨论.     

Wavelength-Tunable Laser-Diode Interferometer

Laser diodes (LDs) have been applied to a phase-measuring interferometer through the wavelength tunability of LDs by controlling their currents. Laser-diode interferometers based on a heterodyne technique are reviewed. A two-wavelength laser-diode interferometer is demonstrated with current control of dual LDs in opposite directions. A synthetic wavelength makes it possible to extend the range of interferometric measurements. The wavelength is controlled by the laser injection current and is stepwise or rampwise changed to introduce a time-varying phase difference between the two beams of an interferometer with unbalanced optical path lengths. The optical output is demodulated with a phase-extraction algorithm. Systematic phase errors caused by the LD-power variation and by the difference between the beat frequency and ramp frequency are analyzed. A feedback interferometer with electronics is used to eliminate the phase error by locking the interferometer on a preset phase. Typical experimental results are shown.     

Digital phase-shifting interferometer with an electrically addressed liquid-crystal spatial light modulator

A digital phase-shifting interferometer with a liquid-crystal-display coupled, parallel aligned, nematic liquid-crystal spatial light modulator is developed. The optical phase shift in the Michelson-type polarization interferometer is achieved by a digital phase shift of a grating displayed on the spatial light modulator. Accurate experimental results of using the heterodyne system for pi/2 phase steps were demonstrated. A phase-shifting interferometer with no moving parts and no requirement for calibration of the value of the phase shift was achieved.     

Determining the phase-energy coupling coefficient in carrier-envelope phase measurements

For f-to-2f interferometers based on white-light generation in sapphire plates, the accuracy of the carrier-envelope (CE) phase measurement and stabilization is affected by the laser energy fluctuation. The coupling coefficient between the CE phase and the laser energy has been determined by modulating the pulse energy in an in-loop f-to-2f interferometer while measuring the CE phase variation with an out-loop interferometer. When the total spectral phase measured by the in-loop interferometer was locked, a 1% change in laser energy caused a 160 mrad shift in the CE phase of the output pulses.     

Compulsorily Phase Locked Interferometer Using Orthogonally Polarized Light Source of a Modulated LD with High Extinction Ratio

This paper describes a compulsorily phase locked differential interferometer using an orthogonally polarized light source of a modulated LD with high extinction ratio to reduce non-linearity of the interferometer caused by polarization cross-talk. The current modulated LD is used as a light source to make the interferometer compact and for the scanning phase of the interferometer. The interferometer is operated compulsorily at the maximum inclination point of the fringe intensity curve by fringe scanning and an electric system. A Wollaston prism of high extinction ratio (50 dB) is used to combine the polarizing beams and to make the polarization cross-talk very small. In one light source the polarized output beams are on the same propagation axis; in the other they have a small crossing angle (2.5 mrad ∼ 10 mrad) to completely exclude non-linearity of the interferometer causded by polarization cross-talk. Using jets of a gas mixture of nitrogen and ethylene, this interferometer was demonstrated to be useful in detecting the photothermal effect of a photothermal velocimeter under phase fluctuation in a turbulent flow.     

Mach–Zehnder interferometer with squeezed and EPR entangled optical fields

We study a scheme for Mach-Zehnder(MZ) interferometer as a quantum linear device by injecting two-mode squeezed input states into two ports of interferometer.Two-mode squeezed states can be changed into two types of inputs for MZ interferometer:two squeezed states and Einstein-Podolsky-Rosen(EPR) entangled states.The interference patterns of the MZ interferometer vary periodically as the relative phase of the two arms of the interferometer is scanned,and are measured by the balanced homodyne detection system.Our experiments show that there are different interference patterns and periodicity of the output quantum states for two cases which depend on the relative phase of input optical fields.Since MZ interferometer can be used to realize some quantum operations,this work will have the important applications in quantum information and metrology.     

Comment on "Phase-shifting shearing interferometer"

The role of the liquid-crystal layer in the phase-shifting shearing interferometer that was proposed by Griffin [Opt. Lett. 26, 140 (2001)] is analyzed. An extra voltage-dependent phase difference is produced when the phase retarder is oriented at an angle from the optical axis of the laser beam such that the interferogram will not repeat itself after a 2pi phase change of the liquid-crystal retarder in either the common Mach-Zehnder interferometer or the phase-shifting shearing interferometer.     

Passively stabilized single-photon interferometer

A single-photon interferometer is a fundamental element in quantum information science. In most previously reported works, single-photon interferometers use an active feedback locking system to stabilize the relative phase between two arms of the interferometer. Here, we use a pair of beam displacers to construct a passively stable single-photon interferometer. The relative phase stabilization between the two arms is achieved by stabilizing the temperature of the beam displacers. A purely polarized single-photon-level pulse is directed into the interferometer input port. By analyzing and measuring the polarization states of the single-photon pulse at the output port, the achieved polarization fidelity of the interferometer is about 99.1 ±0.1%. Our passively stabilized single-photon interferometer provides a key element for generating high-fidelity entanglement between a photon and atomic memory.     

基于π/4相移平均的多光束干涉相位提取算法

菲佐干涉仪中如存在多光束干涉现象,干涉光强将不再是严格的余弦分布形式.在导出菲佐干涉仪中多光束干涉光强公式的基础上,给出了将其近似为理想多光束干涉光强公式的条件.推导了对多光束相移干涉图用四幅算法求解的相位计算误差,并据此提出了基于π/4相移平均的多光束干涉相位提取算法:通过采集相移间隔π/4的两组干涉图序列,将两次计...     

相干合成子光束一致性检测研究

分析了激光相干合成装置及其光路调整要求,提出利用剪切干涉检测合成光路中子光束一致性的方法。分析剪切干涉原理,建立了剪切板干涉物理模型,以相干合成中两路矩形光束拼接组束为例,数值模拟并研究了子光束的整体倾斜、离焦所对应的剪切干涉条纹,得到了条纹图像与子光束光轴误差、离焦误差之间的对应关系,用于相干合成光路中子光束光轴和发散角误差的判断。光轴倾斜大于5μrad时,可以直接观察互干涉和自干涉条纹变化,发散角在大于10μrad时,干涉条纹变化明显。此外,剪切干涉的自干涉条纹平移可用来检测子光束间的活塞误差,可作为光束拼接相干合成中闭环相位检测和控制的手段。     

Phase detection at the quantum limit with multiphoton Mach-Zehnder interferometry

We study a Mach-Zehnder interferometer fed by a coherent state in one input port and vacuum in the other. We explore a Bayesian phase estimation strategy to demonstrate that it is possible to achieve the standard quantum limit independently from the true value of the phase shift and specific assumptions on the noise of the interferometer. We have been able to implement the protocol by using parallel operation of two photon-number-resolving detectors and multiphoton coincidence logic electronics at the output ports of a weakly illuminated Mach-Zehnder interferometer. This protocol is unbiased, saturates the Cramer-Rao phase uncertainty bound, and, therefore, is an optimal phase estimation strategy.     

双光路测量红外飞秒激光脉冲的载波包络相位稳定性

描述了利用双光路自参考技术测量红外飞秒脉冲载波包络相移的方法,并通过建立的红外飞秒脉冲载波包络相移测量装置,实验测量了自主搭建的可调谐光学参量放大系统输出的红外飞秒激光脉冲的载波包络相移.对于1.6 μm的激光脉冲,测量得到在100 s内其相位抖动为115 mrad（rms）.实验结果表明双光路法具有易于调节、测量方便、应用性强等优点. 关键词： 飞秒激光测量 自参考技术 双光路 载波包络相位     

Stable single-photon interference in a 1 km fiber-optic Mach-Zehnder interferometer with continuous phase adjustment

We experimentally demonstrate stable and user-adjustable single-photon interference in a 1 km long fiber-optic Mach-Zehnder interferometer, using an active phase control system with the feedback provided by a classical laser. We are able to continuously tune the single-photon phase difference between the interferometer arms using a phase modulator, which is synchronized with the gate window of the single-photon detectors. The phase control system employs a piezoelectric fiber stretcher to stabilize the phase drift in the interferometer. A single-photon net visibility of 0.97 is obtained, yielding future possibilities for experimental realizations of quantum repeaters in optical fibers and violation of Bell's inequalities using genuine energy-time entanglement.     

一种新型高灵敏度光纤干涉仪

本文提出并分析了一种新型的光纤干涉仪,该仪器对Mach-Zehnder干涉仪作了适当的改进,使灵敏度提高近6倍.通过对干涉仪臂长的适当调节,还可以实现对“共模”噪声的抑制,减小光源波长波动及环境干扰对系统的影响.     

光和原子关联与量子计量

物理量的测量与单位标准的统一推动了计量学的发展.量子力学的建立,激光技术的发明以及原子与分子物理学的发展,在原理与技术上进一步刷新了计量学的研究内涵,特别是激光干涉与原子频标技术的发展,引起了计量学革命性的飞跃.基于激光干涉的引力波测量、激光陀螺仪,基于原子干涉的原子钟、原子陀螺仪等精密测量技术相继诞生,一个以量子物理为基础,探索与开拓物理量精密测量方法与技术的新的科学分支——量子计量学(Quantum Metrology)已然兴起.干涉是计量学中最常用的相位测量方法.量子干涉技术,其相位测量精度能够突破标准量子极限的限制,是量子计量学与量子测量技术的核心研究内容.本文重点介绍近几年我们在量子干涉方面所取得的新开拓与新发展,主要内容包括基于原子系综中四波混频过程的SU(1,1)型光量子关联干涉仪和基于原子系综中拉曼散射过程的光-原子混合干涉仪.     

用于原子干涉仪的拉曼光的制备

原子干涉仪是利用原子物质波的特性而实现的干涉仪,广泛应用于精密测量领域.在原子干涉仪中,通过拉曼光对原子进行相干操作,拉曼光的质量直接影响着干涉仪的技术指标.基于注入锁定技术,采用普通半导体激光器、声光调制器,实现了功率、频率和位相稳定的拉曼光的制备,并对拉曼光的相位噪声技术指标进行了测试.     

迭代最小二乘法用于非线性移相器的标定

针对移相干涉仪中移相器的非线性会影响测量结果准确性的问题,提出了一种基于迭代最小二乘拟合的标定干涉仪移相器的新方法。对移相器加电压并采集若干幅干涉图后,通过在帧间和帧内迭代开展最小二乘拟合可计算出干涉图间移相值,从而得出了电压值与移相值的对应关系曲线,通过对曲线作非线性拟合并对电压值进行精密调整,完成移相器的精确标定。在改造后的干涉仪上对此标定方法进行验证,与Zygo干涉仪相比,相同元件下两者测量结果之差的RMS值为1.726 nm。该标定方法可以降低高精度面形测量干涉仪对移相器线性度的要求。