A high resolution powder diffractometer using focusing optics

In this paper, we describe the design, construction and performance of a new high resolution neutron powder diffractometer that has been installed at the Dhruva reactor, Trombay, India. The instrument employs novel design concepts like the use of bent, perfect crystal monochromator and open beam geometry, enabling the use of smaller samples. The resolution curve of the instrument was found to have little variation over a wide angular region and a Δd/d ∼ 0.3% has been achieved. The instrument provides sample environment of very low temperatures and high magnetic fields using a 7 Tesla cryogen-free superconducting magnet with a VTI having a temperature range of 1.5–320 K. The special sample environment and high resolution make this neutron powder diffractometer a very powerful facility for studying magnetic properties of materials.      

Modular optics interferometer

A waveguide interferometer is assembled using holographically formed optical elements that are constructed as individual components and can be selectively attached to an optical waveguide. The interferometer is very rugged and easy to align.     

Deformation measurement using high resolution Moiré photography

By installing a slotted mask inside the lens of a 35 mm camera the response can be tuned to resolve 300 lines/mm. The camera is used to record changes in fine grid patterns applied to engineering structures and by analysing the processed negatives in a spatial filtering system, moiré fringe maps are generated representing in detail the separate x and y displacements that have occured. Measurements have been obtained from materials ranging from concrete to soft plastics and a variety of patterns is described for treating most surfaces.     

用于位移精密测量的光外差马赫-泽德干涉仪

本文介绍了我们研制的用于位移精密测量的光外差马赫－泽德干涉仪。由于在光路设计中采用了共光路的布置，共模抑制技术得以实现，环境干扰产生的噪声得到很好的消除，相位检测的稳定性和精度大大提高。使用该干涉仪测量了一台在光学相移器内ＰＺＴ微位移驱动装置的电压－位移关系。测量结果具有良好的线性和重复性，与预期相符。根据测量数据分析，该光外差干涉仪具有３ｎｍ的位移测量精度。     

大范围高分辨率法-珀干涉仪

法 珀干涉仪有较高的分辨率 ,但是由于受到激光器模间隔的限制 ,测量范围较小。介绍了使用换模锁定法对其进行扩展 ,实现了具有较大测量范围及纳米分辨率和测量精度的法 珀干涉仪 ,扩展了法 珀干涉仪的测量范围     

使用光纤白光干涉仪测一维形变实验

光纤白光干涉仪是使用波长为1310 nm的半导体发光二极管的相位调制型光纤传感器,可用于压力、温度和应变的测量.本文介绍了光纤白光干涉仪的工作原理,设计了一维形变实验.     

The use of the Fabry-Perot interferometer for high resolution microwave spectroscopy

A simple Fabry-Perot interferometer was used for measurements of microwave spectra. Both basic experimental arrangements, absorption and emission, were tested on the rotational spectra of acetonitrile. The interferometric results obtained were compared with the spectra measured using a standard high resolution microwave spectrometer.     

Multiple-wave diffraction in high energy resolution back-reflecting x-ray optics

We have studied the effects of multiple-wave diffraction in a novel optical scheme recently published by Shvyd'ko et?al. utilizing Bragg diffraction of x?rays in backscattering geometry from asymmetrically cut crystals for achieving energy resolutions beyond the intrinsic width of the Bragg reflection. By numerical simulations based on dynamic x-ray diffraction and by experimentation involving two-dimensional angular scans of the back-reflecting crystal, multiple-wave diffraction was found to contribute up to several tens percent loss of efficiency but can be avoided without degrading the energy resolution of the original scheme by careful choice of azimuthal orientation of the diffracting crystal surface and by tilting of the crystal perpendicular to the dispersion plane.     

Differential thickness measurement using a polarization interferometer

A method for measuring the differential thickness of a thin film using a polarization interferometer is described. Theoretical estimation shows that the measurement error is less than 0.1%. Experiments performed on a PZT sample indicate high sensitivity and excellent linearity of the system. PZT expansions ranging from 300 nm to less than 1 nm could be measured with a precision better than 0.1 nm.     

Thickness measurement of GaN epilayer using high resolution X-ray diffraction technique

In this paper we propose a new method for measuring the thickness of the GaN epilayer, by using the ratio of the integrated intensity of the GaN epilayer X-ray diffraction peaks to that of the sapphire substrate ones. This ratio shows a linear dependence on the GaN epilayer thickness up to 2 μm. The new method is more accurate and convenient than those of using the relationship between the integrated intensity of GaN epilayer diffraction peaks and the GaN thickness. Besides, it can eliminate the absorption effect of the GaN epilayer.     

夜天文中的自适应光学

自1989年自适应光学首次在地基天文望远镜上成功实现衍射极限的天文观测以来,自适应光学系统已逐渐发展成为地基大口径天文望远镜必备的仪器之一。由于当今夜天文观测对仪器性能的要求越来越苛刻,为了提高夜天文观测中的适用性,自适应光学系统近20年来也在不断发展,涌现出多种新型自适应光学系统,如激光导星自适应光学系统、多层共轭自适应光学系统、极限自适应光学系统、近地层自适应光学系统等。尽管自适应光学系统的性能不断提高,但仍存在其局限性。文章分析了目前国际上已有自适应光学系统,探讨近年来夜天文当中应用的自适应光学系统及相关进展。     

Adaptive optics confocal microscopy using direct wavefront sensing

Optical aberrations due to the inhomogeneous refractive index of tissue degrade the resolution and brightness of images in deep-tissue imaging. We introduce a confocal fluorescence microscope with adaptive optics, which can correct aberrations based on direct wavefront measurements using a Shack-Hartmann wavefront sensor with a fluorescent bead used as a point source reference beacon. The results show a 4.3× improvement in the Strehl ratio and a 240% improvement in the signal intensity for fixed mouse tissues at depths of up to 100 μm.     

Adaptive optics wide-field microscopy using direct wavefront sensing

We report a technique for measuring and correcting the wavefront aberrations introduced by a biological sample using a Shack-Hartmann wavefront sensor, a fluorescent reference source, and a deformable mirror. The reference source and sample fluorescence are at different wavelengths to separate wavefront measurement and sample imaging. The measurement and correction at one wavelength improves the resolving power at a different wavelength, enabling the structure of the sample to be resolved.     

Point-diffraction interferometer for atmospheric adaptive optics in strong scintillation

This paper evaluates the performance of a point-diffraction interferometer for closed-loop adaptive optics. A point-diffraction interferometer was built using a modified Mach-Zehnder set-up. The system was used in closed-loop using a SLM to implement a square, 12 × 12, piston-only segmented corrector with a stroke of ±π. Its performance was tested for the case of atmospheric turbulence aberrations. The investigation showed, through simulation and experiment, that the point-diffraction interferometer worked in closed-loop operation in both uniform intensity and scintillated aberrations. Its robustness in the presence of phase discontinuities makes it a promising option for wavefront sensing in strong scintillation.     

利用等厚干涉条纹测量微光的调制传递函数MTF

通过对微光的调制传递函数 (MTF)的讨论 ,结合传统的“分辨率板法” ,提出了一种新的测量微光的MTF的方法。该方法直接从MTF的物理含义出发 ,利用迈克尔逊干涉仪产生一系列空间频率的等厚干涉条纹来模拟分辨率板的作用 ,在计算机的控制下 ,自动测量出连续的MTF曲线。给出的实验光路和实验结果表明 ,利用干涉条纹测量微光的MTF是一种可行的简便方法 ,在计算机的控制下 ,可快速完成夜视仪的传递函数测量     

Real-time displacement measurement with large range and high accuracy using sinusoidal phase modulating laser diode interferometer

To resolve the conflict of large measurement range and high accuracy in the existing real-time displacement measurement laser diode (LD) interferometers, a novel real-time displacement measurement LD interferometry is proposed and its measurement principle is analyzed. By use of a new phase demodulation algorithm and a new phase compensation lgorithm of real-time phase unwrapping, the measurement accuracy is improved, and the measurement range is enlarged to a few wavelengths. In experiments, the peak-to-peak amplitude of the speaker vibration was 2361.7 nm, and the repeatability was 2.56 nm. The measurement time was less than 26μs.     

Large-range displacement measurement using sinusoidal phase-modulating laser diode interferometer

A signal processing method of realizing a large-range displacement measurement in a sinusoidal phasemodulating laser diode interferometer is proposed. The method of obtaining the dynamic value of the effective sinusoidal phase-modulating depth is detailed, and the residual amplitude modulation is also taken into account.Numerical simulations and experiments are carried out to compare this method with the traditional one.We prove that, with this method, the sinusoidal phase-modulating laser diode interferometer can realize a centimeter-level displacement measurement range with high precision, which is much better than the traditional method.     

Movement measurement with a grating interferometer using sinusoidal phase-modulation

Movements of a surface profile are measured with a two-grating interferometer using sinusoidal phase-modulation. Since sinusoidal phase-modulating (SPM) interferometry can record a phase change due to the movement of an object in the interference signal, the SPM interferometer is suitable for measuring the movement of the object. Some experiments show that the two-grating interferometer can measure a sinusoidal vibration with amplitude of several tens of microns and a step movement with a magnitude of several microns.     

Tilt-insensitive film thickness measurement using a double twin-path interferometer

A lock-in amplifier detection method for measuring the film thickness on a flat substrate has been developed by using a common-path interferometer. The signal due to the film thickness has been obtained without it being affected by the tilting of the substrate. The sensitivity was better than 0.5 nm.     

光学渡越辐射测量中能量分辨精度分析

 基于光学渡越辐射原理的用于高能强流电子束束流参数在线测量及诊断系统,具有时间响应快、分辨率高等特点,可以测量电子束的束剖面、发散角、能量等多个参数。分析了测量系统的结构参数（包括了透镜的焦距、成像面位置、CCD像元尺寸）对电子束能量测量精度的影响,并在理论上模拟了电子束的发散角的影响。还根据系统数据的特点,阐述了数据噪声对能量测量结果精度的影响,指出了光学渡越辐射测量中电子束能量分辨精度受到多种因素的影响,需要在数据处理时考虑修正。