Use of step-scan FT-IR to obtain the photoacoustic/photothermal response phase

This paper describes the extraction of photoacoustic (PA)/photothermal (PT) or other experimental response phase from data measured by step-scan FT-IR. The signal processing used with step-scan FT-IR is discussed and contrasted to the signal processing used to extract the experimental phase from data acquired by conventional continuous-scan FT-IR methods. Step-scan operation decouples the FT-IR spectral multiplexing from time, simplifying a variety of time-dependent spectroscopic measurements both conceptually and practically. A consequence of the decoupling is the separation of the temporal phase from the FT-IR instrument (beamsplitter) phase. Data are presented which show clearly that the temporal phase is completely separated from the FT-IR phase by step-scan. This is in contrast to the case of continuous-scan FT-IR, in which the phases are added together. In continuous-scan operation, a single interferogram, which is the average of a number of scans, is recorded. Typically, in step-scan operation, two interferograms, the in-phase and quadrature responses, are recorded simultaneously point-by-point. The beam splitter phase is the same for both of the step-scan interferograms, while the temporal response (sample) phase appears as their relative intensities, specifically, the arctangent of their ratio. Photoacoustic and photothermal beam deflection data are presented here as illustrations of the points discussed.     

基于多普勒非对称空间外差光谱技术的多普勒测速仿真

阐述了多普勒非对称空间外差光谱仪用于被动式多普勒测速的基本原理,通过综合考虑干涉条纹对比度和仪器测速灵敏度等关键因素,建立了效率函数,分别针对高斯线型和洛伦兹线型发射谱线,从理论上推导了最优单臂偏置量的选择依据,并以高斯线型目标谱线为例进行了仿真验证.同时,提出了一种基于部分干涉条纹反演多普勒速度的数据处理方法,简化了多谱线目标源的数据处理过程.结合自适应频率跟踪算法对单谱线目标源和多谱线目标源进行了仿真比较,仿真结果表明,在不考虑噪声的情况下,该方法针对多谱线目标源的多普勒测速最大绝对误差在0.004 m/s以内,与针对单谱线目标源的处理精度相当,可以满足实际应用的精度要求.     

Novel Ghost Imaging Method for a Pure Phase Object

We propose a novel ghost imaging scheme which is especially served to a pure phase object. A spatially incoherent beam is mixed with a coherent beam of the same frequency field by a beamsplitter. Then we perform the ghost imaging scheme using the mixed beam. Our theoretical result shows that this approach is capable of reconstructing a pure phase object in joint-intensity measurement. The visibility of the images is also analysed for two pure phase objects, an optical wedge and a phase grating.     

平面全息光栅曝光系统中的分光器件特性分析

分光器件是全息光栅曝光系统中的关键光学元件,它将入射激光光束分成两束,两相干光束叠加后形成干涉条纹。曝光系统的稳定性不但影响干涉条纹对比度,还影响光栅衍射波前像差、杂散光水平以及光栅掩模刻槽质量。为了提高曝光系统的稳定性,分析入射光束角度偏离与两相干光束夹角(2θ)的关系,并结合干涉条纹周期公式,分别导出了以光栅和棱镜作为分光器件时入射激光束角度偏离量与待制作光栅空间相位差的解析表达式,据此分析了光栅和棱镜曝光系统的稳定性。结果表明,采用光栅分光的曝光系统的稳定性比棱镜分光曝光系统稳定性提高5~6个数量级,这对长时间曝光制作全息光栅具有实际意义。     

In-plane ESPI using an achromatic interferometer with low-coherence laser source

The use of an achromatic interferometer is explored as a means of doing in-plane ESPI measurements using a laser diode as the light source. This interferometer type, which uses a diffraction grating in place of the conventional beamsplitter, has two features that make it suitable for making ESPI measurements over extended areas, even when using a low-coherence laser diode source. First, the parallelogram optical geometry of the interferometer causes all rays passing through to have the same optical path lengths. Second, the interferometer is achromatic, whereby the piezo-actuated mirror that steps the illumination light does so by the same phase angle, independent of wavelength. This latter feature accommodates the spectral impurity of a laser diode source. A periodic variation of fringe visibility is observed in experiments, where narrow ranges of high visibility occur at regular spatial intervals. This behavior derives from the clustered discrete spectral character of laser diode light output. A method to “tune” the interferometer by slightly rotating the diffraction grating is described so as to achieve consistent high fringe visibility throughout the measured images.     

成像光谱仪星上光谱定标的数据处理

为了提高仪器光谱定标精度,降低谱线偏移对地物反射光谱数据反演精度的影响（特别是大气吸收峰附近）,根据星上光谱定标的特点,介绍了星上光谱定标数据处理的常用方法。通过对实验室光谱定标时两种典型工况的比较,实现了星上定标数据处理算法的地面仿真,验证了算法的可行性,并比较了各自的优缺点。结果表明,基于谱线匹配的标准差法、相关系数法和最小差值法计算精度较高,但计算效率较低;基于多项式拟合的极值法计算精度较低,但是计算效率较其他算法提高1个数量级。用极值法对数据进行预处理,快速确定谱线偏移量,再用谱线匹配算法在小范围内精确计算谱线偏移量,可以在不影响计算精度的前提下提高运算速度,计算精度优于1 nm,满足成像光谱仪星上光谱定标的精度要求。     

基于单一分光棱镜干涉仪的双通路定量相位显微术

仅仅使用一个单独的分光棱镜(BS),实现了一种用于生物细胞三维成像的双通路定量相位显微术.不同于传统的使用方法,将BS倾斜放置,使中央半反射层与入射光光轴之间存在一个非常小的角度.这样基于BS的分光特性,经过BS后的透射光束和反射光束将会叠加在一起并形成干涉.调节样品位置,利用相机拍摄同时获得了存在π相移的双通路干涉图.这种离轴干涉模式,只需要记录单幅干涉图就可以获得真实的相位信息,方法结构简单,易于操作,适用于微小透明样品的三维形貌测量.     

Entangling single photons on a beamsplitter

We report on a scheme for the creation of time-bin entangled states out of two subsequent single photons. Both photons arrive on the same input port of a beamsplitter and the situation in which the photons leave the beamsplitter on different output ports is post-selected. We derive a full quantum mechanical analysis of such time-bin entanglement for emitters subject to uncorrelated dephasing processes and apply this model to sequential single photons emerging from a single semiconductor quantum dot. Our results indicate that the visibility of entanglement is degraded by decoherence effects in the quantum dot, but can be restored by use of CQED effects, namely the Purcell effect.     

Phase retrieval from spectral interferograms including a stationary-phase point

We report on a simple processing procedure to retrieve the phase from spectral interferograms including a stationary-phase point. First, the numerical simulations are performed to demonstrate high precision of the phase retrieval from the spectral interferogram. Second, the feasibility of the procedure is confirmed in processing the experimental data from a dispersive Michelson interferometer comprising a cube beam splitter and a plate made of BK7 optical glass. From the retrieved spectral phase, the effective thickness of the BK7 optical glass is determined precisely.     

Method for measuring the phase shift introduced by a phase plate with an interference ellipsometer

A new method for measuring the phase delay introduced by a phase plate is substantiated. The method uses an interference ellipsometer that does not require preliminary determination of the direction of the principal axes of the plate. Sources of error in the method are analyzed and components of error are quantitatively estimated. Requirements for the polarization characteristics of a beamsplitter used in the interference ellipsometer are formulated and conditions for decreasing the measurement error are found.     

Spectral interferometry and reflectometry used to measure thin films

A new method for a precise measurement of the oscillatory part of phase change on reflection (interferometric phase) from a thin-film structure is presented. The method, which is based on phase retrieval from the spectral interferograms recorded at the output of a slightly dispersive Michelson interferometer, is combined with reflectometry. The interferometric phase of the thin-film structure is measured precisely using a reference sample of known phase change on reflection. The spectral reflectance of the thin-film structure is also measured in the interferometer. The feasibility of the method is confirmed in processing the experimental data for SiO₂ thin film on a silicon wafer of known optical constants. Four samples of the thin film are used and their thicknesses are determined. We confirm very good agreement between the thicknesses obtained from the interferometric phase and reflectance measurements. PACS  07.60.Ly; 68.55.Jk; 78.20.Bh     

Spectral interferometric technique to measure the relative phase change on reflection from a thin-film structure

A two-step white-light spectral interferometric technique to measure the relative phase change on reflection from a thin-film structure is presented. The technique is based on recording of the channeled spectra at the output of a Michelson interferometer and their processing by using a windowed Fourier transform to retrieve the phase functions. In the first step, the phase difference between the beams of the interferometer with a thin-film structure is retrieved. In the second step, the structure is replaced by a reference sample of known phase change on reflection and the corresponding phase difference is retrieved. From the two phase differences, the relative phase change on reflection from the thin-film structure is obtained. The feasibility of the simple method is confirmed in processing the experimental data for a SiO₂ thin film on a Si wafer of known optical constants. Four samples of the thin film are used and their thicknesses are determined. The thicknesses obtained are compared with those resulting from reflectometric measurements, and good agreement is confirmed.     

Fast f-to-2f interferometer for a direct measurement of the carrier-envelope phase drift of ultrashort amplified laser pulses

We propose a novel method to directly extract the phase from spectral interferograms, without the need for digital signal processing. This method is demonstrated with single-shot measurement and stabilization of the carrier-envelope phase of a 3 kHz amplifier system. Our scheme allows for real-time monitoring of the carrier-envelope drift and an increased loop width for stabilization. We find that in our amplifier laser system fast carrier-envelope phase jitter is mainly inherited from the oscillator stabilization loop but we also find previously unreported indications for a rapid pulse-to-pulse jitter from the amplifier pump laser.     

紫外真空紫外傅里叶变换光谱仪

研制了新型的由分束耦合器、“猫眼”后向反射光学系统、稳频激光辅助采样系统和光电探测器等组成的紫外真空紫外傅里叶变换光谱仪 ,光谱测量范围为 170nm～ 6 0 0nm ,30 0nm处分辨率高于 1.5× 10 5。光谱仪结构紧凑 ,可精确探测紫外真空紫外波段物质的发射及吸收光谱 ,尤其适合与同步辐射源对接完成相关的光谱分析。     

Physical foundations of achromatic nulling interferometry for stellar coronagraphy

We propose an achromatic interferometer for the observation of a faint off-axis light source against the background of a bright on-axis light source. The on-axis source and its copy acquire an achromatic phase shift by 180° and interfere with a phase difference of π. The achromatic phase shift is attributable to the geometric phase in the three-dimensional interferometer scheme. Interference spatially separates the nulled and bright fields of the on-axis source, redirecting them on opposite sides of the beamsplitter. Interference does not attenuate the field of the off-axis source and redirects it with an equal intensity on both sides of the beamsplitter. We consider the principle of operation of the nulling interferometer and constraints on the attenuation of an extended source due to the decrease in coherence. The laboratory breadboard and experiment are briefly described.     

A Quantum Interpretation of Light Scattering near the Boundary between Transparent Media with Kerr Nonlinearity

The transformation of light by a nonlinear beamsplitter is considered. The beamsplitter is formed by a plane interface between two transparent dielectrics, at least one of which has a Kerr nonlinearity; i.e., its refractive index depends on the intensity of the penetrating radiation. It is shown that the interpretation of the result of calculation of quantum fields at the outputs from such a beamsplitter indicates a violation of the principle of causality in the sense that a subsequent event affects the previous one.     

Speedmeter scheme for gravitational-wave detectors based on EPR quantum entanglement

We propose a new implementation of a quantum speed meter QND measurement scheme. It employs two independent optical readouts of the interferometer test masses with different values of the bandwidths and of the optical circulating power, whose outputs have to be combined by an additional beamsplitter. Signals at the two outputs of the beamsplitter are proportional to the position and the velocity of the test masses, respectively. The influence of the position meter-like back action force associated with the position signal can be cancelled using the EPR approach by measuring the amplitude quadrature of the beamsplitter common output.     

Oscillations of the soliton parameters in nonlinear interference phenomena

Applying the inverse scattering transform method, we show that a soliton modified by an amplitude or phase filter can evolve into several solitons. The oscillation period upon subsequent propagation follows from the wavenumbers of the emerging solitons and the radiation. Our results clarify spectral variations observed in recent supercontinuum experiments.     

共焦生物芯片扫描仪光束分离器设计探讨

指出激光共焦生物芯片扫描仪的光束分离器设计最终影响系统分辨率,简要给出了采用波长光束分离器和几何光束分离器的优缺点.为满足仪器扫描分辨率和灵敏度这对互相受牵制的因素,系统地分析了几何光束分离器中,采用的反射镜孔径的定量分析计算方法.所得的结果对几何光束分离器的设计和性能的评价有重要的意义,最后给出实验结果.     

非对称空间外差光谱技术研究

传统空间外差光谱技术存在光谱分辨率、光谱范围与探测器象元数之间的制约关系。非对称空间外差光谱技术相比传统空间外差光谱技术主要区别在于增加单臂光栅到分束器的距离,能够在系统参数不变的情况下大大的增加光谱分辨率。首先阐述了非对称空间外差光谱技术的基本原理,并给出相应的系统参数计算公式推导结果,从理论上推导出单臂光栅偏置量增加和光谱分辨率增加之间的关系。偏置量作为非对称空间外差光谱技术的重要参数,受短双边象元数和光谱分辨率需求的制约。根据实验室现有实验平台参数,给出偏置量选择原则及结果。在元器件参数相同的情况下,分别计算了两种形式的理论光学性能参数,并且进行了仿真验证,得出非对称空间外差光谱仪与传统空间外差光谱仪光谱范围相同,但具有更高的光谱分辨率,并且分辨率提高与偏置量增加关系与理论计算相符。最后通过单色光扫描方法对非对称空间外差光谱仪实验室装置进行光谱范围和光谱分辨率的定标,定标结果与理论计算值吻合较好。