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     

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.     

Agile linear interferometric method for carrier-envelope phase drift measurement

A bandwidth-independent and linear interferometric method for the measurement of the carrier-envelope phase drift of ultrashort pulse trains is demonstrated. The pulses are temporally overlapped in a resonant multiple-beam interferometer. From the position of the spectral interference pattern, the relative carrier-envelope phase between two subsequent oscillator pulses is obtained at data acquisition rates up to 200 Hz. Cross calibration has been performed by f-to-2f interferometry in two independent experiments. The optical length of the interferometer has been actively stabilized, leading to a phase jitter of 117 mrad (rms). These results indicate a reduced noise and quicker data acquisition in comparison with previous linear methods for measuring the carrier-envelope phase drift.     

In situ broadband pulse compression for multiphoton microscopy using a shaper-assisted collinear SPIDER

The characterization and control of the phase of broadband femtosecond pulses in nonlinear microscopy are successfully demonstrated with a collinear configuration of spectral shear interferometry for direct electric field reconstruction (SPIDER). A femtosecond-pulse shaper is used as a dispersionless interferometer for the measurement of the spectral phase and to actively compress a broadband supercontinuum from a photonic crystal fiber. This allows in situ online phase management and enables the application of quantum control spectroscopy in microenvironments.     

Comparative study of wide-band ultrasonic transducers

The relative performance of several types of ultrasonic transducer are assessed using reproducible acoustic transients generated from Q-switched Nd:YAG laser pulses incident on an aluminium alloy sample. A laser interferometer, a capacitance transducer, two types of electromagnetic acoustic transducers (EMATs), and a broad-band piezoelectric transducer are examined as detectors. The comparison includes a study of their rise-times, and typical signal-to-noise ratios. In the case of the interferometer and capacitance transducer, displacement measurements are shown to be highly consistent with theory.     

A new multi-channel heterodyne polarimeter for plasma current and electron density measurements

A spatially-scanning phase-sensitive heterodyne far-infrared (FIR) polarimeter/interferometer for measurement of plasma current and electron densities is described. The instrument utilizes a rotating diffraction grating wheel for the dual purpose of spatially scanning the plasma cross section and providing a Doppler frequency offset for heterodyne detection purposes. Only two detectors are required to obtain accurate interferometric and polarimetric information for 15 discrete spatial chords. A novel approach to the optical processing of the initially linearly polarized probe beam allows the Faraday rotation of the vibrational ellipse to be unambiguously encoded as a phase modulation on the intermediate frequency carrier signals extracted from the two detectors. The plasma birefringence can be recovered from the corresponding amplitude modulation.     

Bandwidth-independent linear method for detection of the carrier-envelope offset phase

We propose and demonstrate a novel linear procedure for measurement of the carrier-envelope offset (CEO) phase of femtosecond oscillators. The technique is based on a Mach-Zehnder interferometer, a ring resonator, and a spectrograph. In this scheme, interference between subsequent pulses from a pulse train may frustrate the interference between identical pulses in the Mach-Zehnder, resulting in a modification of interference contrast depending on the CEO phase. We suggest spectrally and spatially resolved interferometry for robust detection of the fringe visibility. It is shown by numerical simulations and experimentally demonstrated that the visibility of such fringes uniquely depends on the CEO phase of the pulse train. Since the method relies only on linear interactions and does not require any nonlinear conversion, it allows characterizing the CEO frequency of mode-locked oscillators with virtually arbitrarily low bandwidth and power levels.     

Femtosecond phase spectroscopy of multi-level systems: Phthalocyanines

A femtosecond frequency-domain interferometer is applied to metal-free and vanadyl phthalocyanine (H₂Pc and VOPc) thin films to measure time-resolved difference phase and transmission spectra simultaneously. For both samples, the phase-change dynamics is different from the transmission-change dynamics at 620 nm, reflecting that the phthalocyanines (Pc) cannot be modeled with a two-level system but by a multi-level or inhomogeneously broadened system, in which each level pair exhibits different relaxation dynamics. Because of this dynamical difference, a phase-change measurement is required to correct distortion of the transient spectra due to induced phase modulation of probe pulses. Near zero time delay, the phase and transmission changes show different growth behavior. This behavior is explained by antisymmetric amplitude and phase gratings which are produced by coherent coupling between frequency-chirped pump and probe pulses. Formerly V. S. Williams     

Pulsed interferometric optical fibre sensor detecting wiretapping in long transmission lines

A modified optical fibre based Mach-Zehnder interferometer was applied as a sensor to detect wiretapping in long transmission optical fibre lines. The signal consisting of short pulses (around 1?ns) was launched to the input of the interferometer based on the polarization maintaining fibres and polarization elements. When the sensing line was undisturbed, detectors registered only a single pulse. The additional two side pulses appear, if the wiretapping attempt took place. For robust detection of any alarm situation we proposed two-criteria algorithm to minimize false alarm rate. Moreover, slow environmental fluctuations were continuously monitored and compensated by polarization controllers. We measured frequency characteristics of the sensor and performed a hundred wiretapping attempts, which proved high performance of the sensor.     

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.     

Large area light-pulse atom interferometry

We report the experimental demonstration of a large area atom interferometer based on extended sequences of light pulses. We characterize the interferometer through measurement of the acceleration due to gravity and demonstrate a threefold enhancement in intrinsic acceleration sensitivity. The technique is applicable to many atom interferometer configurations, including those used for measurement of rotations, gravity gradients, and Planck's over 2pi/m.     

New data processing for multichannel FIR laser interferometer

Usually, both the probing and reference signals received by LATGS detectors of FIR interferometer pass through hardware phase discriminator and the output phase difference--hence the electron line densities is collected for analysis and display with a computerized data acquisition system(DAS). In this paper, a new numerical method for computing the phase difference in software has been developed instead of hardware phase discriminator, the temporal resolution and stability is improved. An asymmetrical Abel inversion is applied to processing the data from a seven-channel FIR HCN laser interferometer and the space-time distributions of plasma electron density in the HT-6M tokamak are derived.     

Measurement of fiber chromatic dispersion using spectral interferometry with modulation of dispersed laser pulses

We propose and experimentally demonstrate a method for fiber dispersion measurement based on the modulation of laser pulses stretched by the fiber under test. The measured spectrum of the modulated pulses is the result of the interference between the stretched pulse spectra shifted by the modulation harmonics. The interference pattern is processed as in Fourier transform spectral interferometry. Unlike to conventional spectral interferometry, environmental conditions do not affect the interferogram due to the lack of any interferometer; additionally, large dispersions can be characterized by the method proposed. Its high accuracy is demonstrated in experimental comparison with the widely used phase shift technique.     

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.     

皮秒条纹相机的标定

介绍了一种通过迈克耳孙干涉仪,产生已知延迟时间间隔的双脉冲光作为校正用的基准时间间隔,利用条纹相机对超短激光脉冲进行精确测量的方法。     

Shearing interferometer for quantifying the coherence of hard x-ray beams

We report a quantitative measurement of the full transverse coherence function of the 14.4 keV x-ray radiation produced by an undulator at the Swiss Light Source. An x-ray grating interferometer consisting of a beam splitter phase grating and an analyzer amplitude grating has been used to measure the degree of coherence as a function of the beam separation out to 30 microm. Importantly, the technique provides a model-free and spatially resolved measurement of the complex coherence function and is not restricted to high resolution detectors and small fields of view. The spatial characterization of the wave front has important applications in discovering localized defects in beam line optics.     

A novel fiber optic ring-down interferometer for sensing

A ring-down interferometer (RDI) based on a modified Mach–Zehnder structure by incorporating a pair of mirrors with very high reflectivity into each of its two arms, respectively is proposed in this paper. Launching a coherent light pulse into the interferometer, in each arm, pulse ring-down occurs between its two mirrors and outputs a chain of pulses. The two chains of pulses from the two arms combine and interfere pulse by pulse at the detector and the difference of the light phase between the two arms will be enlarged linearly in proportion to the times of ring-down.     

High sensitivity HCN laser interferometer for plasma electron density measurements

This paper describes a high sensitivity 337 μm HCN laser interferometer for plasma electron density measurements. The plasma phase shift is transferred to a low frequency signal obtained by slightly shifting the frequency of the 337 μm radiation in the reference beam of the interferometer. The frequency shift is produced by diffracting the radiation of a cylindrical rotating blazed grating. A phase shift is deduced from the time variation of the zero crossings of the low frequency signal, giving a result which is independent of amplitude fluctuations. Using pyroelectric detectors, the interferometer has a time resolution of 100 μsec and a sensitivity of 10^-2 fringe.     

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.     

All-fiber Mach-Zehnder interferometer for DWDM filter direct group-delay measurement

The group delay of the dense wavelength division multiplexing (DWDM) filter is becoming more important in optical communication. This study proposes a Mach-Zehnder interferometer based on the direct group delay measurement of an optical thin film filter. The interferometer provides a simple, accurate and physically intuitive picture of what happens to broadband optical pulses on common optical materials. A 100 GHz DWDM filter was used as an example in the measurement and showed that the time of measurement and selection of Gaussian window were two important factors.