一种新型多波长绝对距离干涉测量系统的研究

介绍了一种新型多波长绝对距离干涉测量系统。系统采用633nm的双纵模He-Ne激光器和629nm的He-Ne激光器,组成三级合成波长链对较大距离进行精密测量,并作了误差分析。系统采用高稳定度的声光晶体对各波长分别进行偏频,再用外差探测法测量出光束通过参考光路和测量光路后的位相差。简要介绍了629nm的He-Ne激光器的设计方案。     

Low-noise-figure optical parametric amplifier with a continuous-wave frequency-modulated pump

We present what are to our knowledge the first gain and noise-figure measurements of a fiber optical parametric amplifier pumped by a simple frequency-modulated source. The maximum gain was 27.2 dB and the average noise figure was 4.2 dB. We achieved the low noise figure by filtering the pump to remove the broadband amplified spontaneous-emission pedestal on the pump spectrum.     

干涉测距仪中光纤的特性分析

提出一种由定位干涉仪和测量干涉仪组成的光纤干涉绝对距离测量方法 ,将对光程的定位过程和对距离的测量过程分别进行 ,实现对大距离的高精度绝对测量 ,同时在测量系统中引入光纤和光纤干涉仪 ,以改善系统结构和性能。详细分析了光纤损耗特性、色散特性和偏振特性对测量系统的影响 ,并特别给出了有关色散特性影响的量化分析结果。分析表明色散特性对于系统的测量范围有较大的影响     

Phase measurements of a twisted nematic liquid crystal spatial light modulator with a common-path interferometer

We present a novel and high accuracy (±1°) technique for measuring the difference in phase delay between the positive and negative eigenvectors of a twisted nematic liquid crystal spatial light modulator (LCSLM) as a function of applied voltage. We show a new architecture for a common-path interferometer where we simultaneously generate both the positive and negative eigenvectors of the LCSLM. We use an electro-optic light modulator to provide a time varying phase shift between the two eigenvectors and measure the phase delay difference between the two eigenvectors. We compare the phase delay values with those obtained using a Mach–Zehnder interferometer and find good agreement.     

Effect of copropagating and counterpropagating directions on a semiconductor optical amplifier-Mach-Zehnder interferometer based wavelength converter using a continuous-wave assist light

We experimentally investigate and compare the effects of copropagating and counterpropagating directions on a semiconductor optical amplifier-Mach-Zehnder interferometer based wavelength converter. When an assist light is not used, the copropagating scheme induces a long rise-fall time and small timing jitter, whereas the counterpropagating scheme induces a short rise-fall time and large timing jitter. The results show that the copropagating scheme with a backward assist light yields the best performance.     

Test measurements with a perfect crystal neutron interferometer

Two widely separated coherent neutron beams from dynamical diffraction in a perfect Si-crystal are used for neutron interferometric measurements. Al and Bi samples cause phase shifts within the individual beams which result in a marked intensity oscillation of the interfering beams behind theE-shaped interferometer crystal. With this interferometer interesting features of various physical quantities can be investigated in a new way, e.g. refracting index, scattering amplitudes, magnetic domain structures, density inhomogeneities, and coherence properties of the neutron beams.     

Analysis of nonlinearity in a high-resolution grating interferometer

Metrological feasibilities of a high-resolution grating interferometer (GI) based on a transverse Zeeman laser are investigated. When the grating pitch equals 20 μm, a resolution of 0.7 nm is obtained by means of a heterodyne signal processing method. The comparison of two approaches for determining the residual nonlinearity is presented. One is to evaluate the maximum residual error by determining the amplitude modulation degree of the measurement signal. The other is to do a high precision calibration with a differential dual-frequency interferometer that has a higher precision. The experimental results show that the nonlinearity is no more than 25 nm which fits well with the estimating result. Analysis of the depolarization effect of the grating indicates that it has little influence on the measurement accuracy.     

Tomographic imaging of absolute optical absorption coefficient in turbid media using combined photoacoustic and diffusing light measurements

We present a new method that can provide high resolution images of absolute optical absorption coefficient in heterogeneous turbid media. In this method, acoustic measurements in conventional photoacoustic tomography are combined with diffusing light measurements to separate the product of absorption coefficient and optical fluence or photon density. We validate this method using a series of tissuelike phantom experiments. The experimental results show that targets as small as 0.5 mm in diameter with optical absorption contrasts as low as 1.5 relative to a 50 mm diameter scattering background medium can be clearly detected.     

利用透射光栅寻找迈克耳孙干涉仪的白光干涉条纹

介绍了借助透射光栅调整迈克耳孙干涉仪的白光干涉条纹的方法和原理，并讨论了其中的有关现象．     

Frequency-modulated continuous-wave laser radar using dual vertical-cavity surface-emitting laser diodes for real-time measurements of distance and radial velocity

Optical Review - A frequency-modulated continuous-wave (FMCW) laser radar capable of real-time displaying the distance to a target object and its radial velocity as their corresponding frequency...     

Many-wavelength interferometry with thousands of lasers for absolute distance measurement

We demonstrate a new technique for absolute distance measurement with a femtosecond frequency comb laser, based on unraveling the output of an interferometer to distinct comb modes with 1?GHz spacing. From the fringe patterns that are captured with a camera, a distance is derived by combining spectral and homodyne interferometry, exploiting about 9000 continuous wave lasers. This results in a measurement accuracy far within an optical fringe (λ/30), combined with a large range of nonambiguity (15?cm). Our technique merges multiwavelength interferometry and spectral interferometry, within a single scheme.     

Performance and testing of a four channel high-resolution heterodyne interferometer

When studying complex vibrations, simultaneous measurements at several points are indispensable if one is dealing with objects whose vibrational behavior is not guaranteed to be stable over longer periods of time, such as biological specimens, micro-mechanical elements or objects characterized by nearly resonant normal modes with different vibrational patterns. Obviously, both amplitude and phase need to be measured at each point to obtain a full characterization of the vibration. We introduce birefringent beam displacers as a highly efficient beam multiplying method to create a system of four heterodyne interferometers operating in parallel from a single laser source. The design and the performance characteristics (resolution, cross-talk) of the instrument will be discussed. The system revealed the existence of running vibrational modes on an electrically driven plate clamped along its outer edge.     

Fabry-Perot interferometer with diffraction-scattered reflection of light

The incorporation of a phase grating into the optical system of a Fabry-Perot interferometer makes it possible to transform the incident beam of light so that the major part of energy in the reflected wave is contained in the side lobes in the far-field diffraction pattern and radiation in the zero order of diffraction along the optical axis is suppressed. Experimental results are presented, which are obtained with a grating produced by evaporating a thin-layer dielectric coating onto the input mirror of the interferometer.     

Characterization and validation of the frequency-modulated continuous-wave technique for assessment of photon migration in solid scattering media

The frequency-modulated continuous-wave (FM-CW) technique, based on the beat signal of a Mach?CZehnder interferometer employing a frequency-ramped light source, is studied for solid scattering media applications. The method is used to evaluate the mean time-of-flight (MTOF) of light traveling in scattering media, specifically polystyrene foams. We assume that each the time-of-flight (TOF) time corresponds to different light scattering paths resulting in a different phase shift. The phase shift variations produce a speckle pattern, which together with the frequency leakage induced by the discrete Fourier transform (DFT) cause ??spikes?? in the power spectrum of the beat signal, thus decreasing the accuracy of the measured MTOF values in solid scattering media. For comparison, time-of-flight spectroscopy (TOFS) is also employed to evaluate the MTOF for the same samples, while the geometrical difference between these two techniques is compensated for by using diffusion theory. The MTOFs measured by the FMCW and TOFS techniques agree well, which demonstrates a great potential to develop a robust FMCW setup for simplified MTOF assessment.     

A nanomeasuring machine based white light tilt scanning interferometer for large scale optical array structure measurement

White light vertical scanning interferometry (VSI) has been well developed during the past two decades and it is well suited for optical component evaluation due to its non-contact nature. However, because of its inherent limits in the field of view, the VSI is incapable of performing large range measurements. For large surfaces, stitching must be employed. In this paper, a nanomeasuring machine (NMM) based white light tilt scanning interferometer (TSI) is described, which can evaluate an optical array component in one round, without the need for stitching. By integrating a NMM, the tilt angle in the TSI no longer will require to be calibrated, easing in this way the realization of the TSI. With a tilt stage mounted on the NMM, the proposed system has two angles related to the measurement, which can provide excellent “fringes slipping out” correction ability. The analysis and the experiments are given.     

Stark-width measurements of argon-ion lines with a Fabry-Pérot interferometer

Stark widths of optically thin line profiles of the 4806 and 4426 Å Ar(II) lines in an atmospheric cascade arc plasma have been measured with a Fabry-Pérot interferometer. These experimental results are significantly lower than all other experimental data and differ about a factor of 2 from theoretical calculations.     

Signal processing techniques for absolute displacement/strain sensing using a fiber interferometer

We present two displacement sensing techniques which rely on amplitude variations of Bessel frequency components contained in the photodetected output of a phase modulated two-beam interferometer. Experimental results demonstrate demodulated output signals that correspond to the absolute optical path difference between the two arms of an interferometer. Optical displacements over a 50 mm range have been recorded with a resolution of 25 microns. Both approaches are suitable for passive remote sensing applications.     

Vibration-displacement measurements with a highly stabilised optical fiber Michelson interferometer system

A highly stabilised vibration-displacement measurement system, which employs fiber Bragg gratings (FBGs) to interleave two fiber Michelson interferometers that share the common-interferometric-optical path, is presented. The phase change in the interferometric signals of the two fiber Michelson interferometers have been tracked, respectively, with two electronic feedback loops. One of the fiber interferometers is used to stabilise the system by the use of an electronic feedback loop to compensate the environmental disturbances. The second fiber interferometer is used to perform the measurement task and employs another electronic feedback loop to track the phase change in the interferometric signal. The measurement system is able to measure vibration-displacement and provide the sense of direction of the displacement. The frequency range of the measured vibration-displacement is from 0.1 to 200 Hz and the measurement resolution is 10 nm.     

Single-shot wave-front measurements of high-intensity ultrashort laser pulses with a three-wave interferometer

A simple new three-wave interferometric technique is used to measure, for what is believed to be the first time, the wave front of femtosecond ultrahigh-peak-power pulses carrying a strong B integral (B = 5.26+/-0.15) in a single shot. Wave-front distortions of a terawatt-class laser system are measured with good accuracy (lambda/50) and discussed. These distortions can significantly reduce the focused peak intensity, emphasizing the necessity of implementing adaptive optics in ultrahigh-intensity chirped-pulse amplification lasers.