Measurement of temperature and temperature profile of an axisymmetric gaseous flames using Lau phase interferometer with linear gratings

In this paper we have investigated the utility of Lau phase interferometer with linear gratings and white light source to measure temperature and temperature profile of an axisymmetric flame. The temperature measured using Lau phase interferometer is in good agreement with the temperature measured with thermocouple and datalogger. Details of theoretical analysis and experimental investigation are presented.     

光栅成像与Lau效应

本文推导了两个光栅干涉仪的光强分布。分析了光栅周期与狭缝宽度比值对Lau条纹的影响。指出有β>p/(2a)的清晰的Lau条纹存在,并在数值计算与实验上加以证实。 关键词：     

Automated collimation testing in Lau interferometry using phase shifting technique

We demonstrate an automated procedure for detection of collimation position of an incoherent beam in Lau interferometry using phase shifting technique. The experimental arrangement consists of a Lau-based interferometer in which light from a source grating illuminates a set of two coarse gratings separated by self-imaging distance. Phase shifting procedure is incorporated by translating the detector grating, corresponding to different positions of the collimating lens. The phase map is plotted corresponding to each position. The slope of the phase map is indicative of the collimation position of the optical beam. The technique is fully automatic and provides good accuracy and high precision.     

部分相干光栅衍射效应和干涉术

本文提出一种新的部分相干照明的光栅衍射干涉仪.先分析了光栅的介于Talbot和Lan效应之间的部分相干衍射效应.部分相干干涉图的特点是条纹由频率成倍的两种光栅状载波所表征.调整光源狭缝,系统在两相干性极端分别转成Talbot和Lau干涉仪.理论分析采用了模糊函数方法.最后给出了实验.     

衍射相关和Lau干涉

本文用离轴傅里叶变换系统的模型和菲涅耳衍射理论分析了衍射受限下的离焦相关器的系统特性,证明是第一模板和第二模板衍射像之间的强度相关积分。推导了衍射相关器作为测量相位物体的干涉仪的一般理论,这时要求编码板函数能衍射自成像并且相关函数为周期性函数。讨论了平行光栅作为编码板时的干涉仪的横向剪切干涉特性,给出了实验结果。本文还证明了衍射相关器是推广到任何平面物体在任何观察距离上的Lau效应装置。衍射相关干涉仪产生Lau干涉条纹,并且是直接应用Lau效应的干涉仪。 关键词：     

任意周期性物体的扩展Lau效应:基于部分相干传递函数的分析

本文基于自由空间的部分相干传递函数对效应提出了新的解释模型,给出了描述Lau条纹强度分布的普遍公式,它适用于任意周期性的振幅或位相型物体,对于几种典型周期性物体分析了Lau条纹产生的条件及输出强度.给出了不同周期的矩形光栅产生Lau效应的实验结果.     

平面周期物体的Lau效应

基于部分相干理论中交叉谱密度函数的概念研究了平面周期物体的Lan效应文章导出了平面物体Lau像光强分布式,求得了平面周期物体的Lau像光强分布及其Lau成像条件,并进行了实验验证,给出了实验结果.     

Decoherence in a Talbot–Lau interferometer: the influence of molecular scattering

This work describes the interference of C₇₀ fullerenes in a Talbot–Lau interferometer with a large separation between the diffraction gratings. This permits the observation of recurrences of the interference contrast both as a function of the de Broglie wavelength and in dependence of the interaction of background gases. An exponential decrease of the fringe visibility with increasing background pressure was observed and good quantitative agreement with the predictions of decoherence theory was found. From extrapolation of the limits of matter wave interferometry it can be concluded that the influence of collisional decoherence may be well under control in future experiments with proteins and even larger objects. PACS 03.75.-b; 03.65.Yz; 39.20.+q     

Collimation testing of a CO2 laser beam with a shearing interferometer

A shearing interferometer based on a Michelson interferometer is proposed for collimation testing of a CO₂ laser beam. The shear and tilt between the interfering wavefronts is obtained by replacing one or both mirrors of the Michelson interferometer with double mirrors arranged to act as 90 ° or near 90 ° prisms in retroreflecting mode. Detailed analysis for two experimental configurations of this system are presented.     

Analysis of Lau interferometric fringe for measurement of focal length by using wavelet filtering techniques

New filtering scheme is investigated and implemented on Lau interferometric fringes to enhance the signal-to-noise ratio (SNR) in the Lau interferograms. Towards this, the applicability of Haar, Daubechies and Symlet wavelet based filtering schemes have been tested. Of these schemes, the Symlet based filtering scheme gives the best results in terms of improved signal to noise ratio and speckle index. This scheme is then used to analyse Lau interferograms recorded in the experimental arrangement for focal length measurement. The processed interferograms yield improved accuracy and precision of measurement.     

A displacement measurement system, utilizing a Wollaston interferometer

A dual interferometric displacement measurement system is presented where a Wollaston prism interferometer is employed in conjunction with a normal Michelson interferometer. The system operates without the use of external polarizers, apart from those associated with the Wollaston prism interferometer itself. It is shown that an optical path difference induced in the Michelson interferometer can be detected using the Wollaston prism in a normal interferometer arrangement. Further, the interference pattern produced by the Wollaston prism interferometer changes in a measurable, linear fashion as the optical path difference from the Michelson interferometer alters. A simple theoretical analysis of the system is presented and used to derive a computer model of the optical arrangement. Results from an experimental implementation of the system, using a Wollaston prism with a beam separation of 0.5 degrees and a superluminescent diode, of wavelength 825 nm, as a light source, are included and compared to the results from the computer model.     

Lau effect and noncoherent processing

The Lau effect has been discussed from various points of view. In this paper, a new geometrical approach for the Lau effect is presented. This approach also shows the paradoxical result of Gori which has been obtained from coherence theory. Based on the present analysis, the two gratings are used to modify a noncoherent system as a coherent multichannel system An experimental result is shown for the edge enhancement.     

Dispersive white light combined with a frequency-modulated continuous-wave interferometer for high-resolution absolute measurements of distance

A nonincremental interferometer for the absolute measurement of distances is presented. The measuring technique is based on both dispersive white-light (DWL) interferometry and frequency-modulated continuous-wave (FMCW) interferometry. The proposed configuration integrates both techniques in the same interferometer by use of a single laser diode. This solution enables the results from the coarse measurements from the FMCW interferometer to be combined with the fine readouts from the DWL interferometer. Preliminary experimental results confirm the capability of the system to combine the advantages of the two techniques.     

A reflection interferometer with a noninverted response function based on a phase grating

It is shown that the inclusion of a simple phase grating in the optical scheme of a resonator provides the possibility of performing spectral investigations in reflected light with characteristics of a Fabry-Perot interferometer. The response function of the interferometer is examined, and experimental results are presented.     

半导体激光微小振动实时干涉测量仪

设计了一种半导体激光干涉测量仪,可以实时测量物体的微小振动。通过信号处理电路对干涉信号进行分析,得到实际振动的振幅和频率。给出了具体的理论分析,实验结果验证了该干涉仪的实用性。     

Lau phase interferometry with a vibrating object

In this paper, we have demonstrated experimentally the vibration analysis of a reflecting object in a time-averaged mode using Lau phase interferometry. Experimental results provide information about the tilt at every point of a vibrating plate. The Lau phase interferometry is robust and simple. Experimental results are compared with conventional shadow-moiré method.     

Fiber optic sensor based on a sagnac interferometer including a recirculating-ring delay line with an edfa

We present a theoretical and experimental investigation of a Sagnac interferometer incorporating a fiber optic recirculating-ring delay line with an erbium-doped fiber amplifier to increase the effective length of the Sagnac loop and thereby improve the low-frequency response. Theoretical calculations show that the low-frequency response of the interferometer is enhanced as expected. However, the noise penalty of using a fiber amplifier in the ring is quite high, especially at low frequencies. The signal-to-noise ratio at low frequencies, using a superfluorescent erbium fiber source, is demonstrated as increasing by a factor of 2 compared to a single-loop Sagnac interferometer with the same total length of fiber, but without fiber amplifier.     

Use of liquid-crystal-clad fiber as a modal filter for a two-mode fiber-optic interferometer

A novel two-mode fiber-optic interferometer employing a liquid-crystal-clad fiber as a modal filter is proposed. The liquid-crystal-clad fiber can guide one of the second-order modes, TE01, and leak out the other TM01 and HE21 modes. Thus two spatial modes, fundamental mode HE11 and second-order mode TE01 serve as the two arms of the interferometer to detect an external perturbation. The experimental results obtained when this interferometer was used to sense temperatures ranging from 20 to 100 degrees C are demonstrated.     

Using a programmable interferometer for digital phase-shifting speckle interferometry

The use of a programmable phase-shifting interferometer to detect the deformation of scattering surfaces is described. The interferometer is a commercial instrument in use for optical testing applications; the sample surface is imaged as a speckle pattern. The measuring procedure and the program are outlined, and an experimental demonstration on an aluminium plate under load is given.     

Application of wavelet filtering techniques to Lau interferometric fringe analysis for measurement of small tilt angles

This communication presents the results of investigation undertaken towards testing the viability of wavelet filtering techniques in analyzing the Lau interferometric fringes. Towards this, the applicability of Haar, Daubechies and Symlet wavelet based filtering schemes have been tested. Of these schemes, the Symlet based filtering scheme gives the best results in terms of improved signal to noise ratio. This scheme is then used to analyze Lau interferograms recorded in the experimental arrangement for tilt angle measurement. The processed interferograms yield improved accuracy and precision of measurement.