Investigation of pulse-excited hydrophones for ultrasonic field measurements using laser interferometry

A comparison of the characteristics of various designs of hydrophones by means of laser interferometry is performed in a field radiated by a pulse-echo diagnostic device. The results are presented in the time and frequency domain in terms of temporal waveforms, frequency spectra and transfer functions. With regard to the measurement of characteristic ultrasonic field data, distinct differences between the various designs and units were found.     

基于圆柱定程干涉法测量气体黏度的探索

黏度是流体的重要输运性质, 实验测量是获取黏度数据的基本手段. 圆柱定程干涉法是目前测量气相声速最精确的方法之一, 其测量参数为工质的声学共振频率和共振峰半宽. 共鸣腔中气相工质的黏性会导致共振频率的偏移和共振峰半宽的增加, 是声速测量中的重要非理想影响因素. 但通过对共振频率和共振峰半宽的精确测定, 并结合热边界层、进气导管、声学传感器及壳体振动等其他非理想因素的修正, 可以精确反推获得黏度. 本文从理论上探讨了应用圆柱定程干涉法测量共振频率或者共振峰半宽来得到黏度的新方法, 以氩 (Ar) 为例进行了实验验证, 测量结果与文献值具有较好一致性, 证实了方法的可行性. 关键词： 黏度 圆柱共鸣腔 共振频率 共振峰半宽     

Accurate phase-shifting digital interferometry

In phase-shifting interferometry experiments, the accuracy of the phase shift is a major issue. Many experimental and data analyses are done to cancel phase-shift errors inherent to the modulation techniques used. We propose to remove most of the phase-shift error by recourse to a frequency-shifting method. This approach can be applied to both holography and interferometry. We validate the idea with a holographic experiment.     

Effect of target metarial on absorption measurements at short laser wavelengths

We measure the effect of target material on absorption processes for short laser wavelengths (λ = 0.53 μm and λ = 0.26 μm). The results show some increase of absorption with increasing Z-target at 0.53 μm, which can be attributed to the increase of inverse bremsstrahlung efficiency by analysing the data with a 1-D hydrodynamics code. At 0.26 μm, absorption rates are very high, ∽ (90 ± 5) %, even for low Z-targets at fluxes $\text{∽5 × 10}{}^{14}\text{W}\text{cm}{}^2$.     

Pulse-amplitude equalization using a polarization-maintaining laser resonator

For the first time to our knowledge, pulse-amplitude equalization of rational-harmonically mode-locked fiber ring laser pulses has been experimentally demonstrated using a polarization-maintaining laser resonator without any additional device. The pulse-amplitude distribution of the laser pulses was controlled by the modulator driving power, and stable pulse-amplitude-equalized pulses with repetition rates of 20, 30, and 40 GHz have been obtained in the linear region of the modulator.     

Continuous-wave fiber cavity ring-down measurements using frequency-shifted interferometry

We present a spatial-domain fiber cavity ring-down (CRD) technique that does not require optical pulses for time-resolved detection. Instead of measuring the intensity decay rate of an optical pulse in the time domain as in conventional CRD experiments, we measure the decay rate of a CW signal in a ring-down cavity (RDC) using frequency-shifted interferometry in the spatial domain, as a function of distance traveled by the light. As a proof-of-concept demonstration, we measured fiber bend loss in a loop RDC using this technique, and a cavity loss change as low as 0.0135 dB induced by every fiber turn on a mandrel was unambiguously discerned.     

Fiber ring laser for intracavity sensing using a whispering-gallery-mode resonator

Whispering-gallery-mode (WGM) microresonators are used as optical transducers for sensing applications. The typical detection scheme is based on tracking the WGM resonance shift, by scanning with a tunable laser, when a change of the refractive index in the region probed by the WGM takes place. We propose a sensing approach based instead on monitoring the position of the laser line of a fiber ring laser having a WGM microsphere in its loop. We have demonstrated that the induced shift is the same for the ring laser line and for the microsphere resonance. The proposed method requires simpler, cheaper equipment and may also improve the sensor resolution because the ring laser line is much narrower than the microsphere WGM resonance.     

Speckle interferometry methods for displacement and strain measurements using photorefractive crystal

Photorefractive crystals offer several attractive features such as high resolution and in situ processing. As the images are erasable, these crystals are suitable for read–write applications and hence find potential use in speckle photography, image processing and holography. The barium titanate (BaTiO₃) crystal as recording medium has been extensively used as a novelty filter for real-time in-plane displacement measurements employing two-beam coupling configuration. This paper presents new optical configurations in speckle shear photography to measure in-plan displacement and the strain in real time using BaTiO₃ crystal as recording medium. Speckle photography studies are made using a simple two-beam coupling configuration. In speckle shear photography, a diffused object illuminated with two parallel narrow laser beams is imaged inside the crystal, and a pump beam is added at this plane. The speckle patterns due to each beam and the pump beam produce index gratings. When the object is deformed, the speckle patterns shift consequently. We now have four speckle fields: two generated from the interaction of pump beam with the index gratings and two pertaining to deformed states directly transmitted through the crystal. Thus, the fields from respective points on the object interfere after passage through the crystal and produce the Young's fringe patterns. Due to strain, the fringes in each pattern are of different width and orientation, resulting in the generation of a Moiré pattern. The strain is obtained from the width and orientation of the fringes in the Moiré pattern. The experiments are conducted on a specimen with a notch, which is subjected to tensile loading. The in-plane displacement is measured separately in another experiment. The above studies are carried out at Nd–Yag laser.     

Diffraction losses of an asymmetric stable laser resonator using an equivalent resonator

An asymmetric stable laser resonator with one large mirror and the other mirror apertured is considered. An equivalent symmetric resonator is derived which enables the determination of the theoretical diffraction losses from Li's computations. Experiments are done to test the validity of the predictions. The experimental diffraction losses agree very well with the theoretical values and the usefulness of the concept of equivalent resonator is therefore confirmed.     

Accurate measurement of composite laminates deflection using digital speckle pattern interferometry

The modern digital speckle pattern interferometry (DSPI) technique is applied for the accurate measurement of the full-field deflection distribution of a bent composite laminates. Two kinds of powerful phase-shifting methods, phase of differences method (PDM) and difference of phases method (DPM), are described briefly and employed in DSPI to quantitatively extract the phase information, respectively. A comparison of the deflection distributions measured by DPM and PDM indicates that the former has a better measurement accuracy than the latter in laminate's static test experiment.     

Soft-x-ray laser interferometry of a pinch discharge using a tabletop laser

We have used a tabletop soft-x-ray laser and a wave-front division interferometer to probe the plasma of a pinch discharge. A very compact capillary discharge-pumped Ne-like Ar laser emitting at 46.9 nm was combined with a wave division interferometer based on Lloyd's mirror and Sc-Si multilayer-coated optics to map the electron density in the cathode region of the discharge. This demonstration of the use of tabletop soft-x-ray laser in plasma interferometry could lead to the widespread use of these lasers in the diagnostics of dense plasmas.     

高频聚焦换能器声场的激光测量法

本文描述了一种使用激光测振技术测量高频聚焦换能器声场布的方法，并给出了使用该方法对一种高频聚换能器进行测量的结果，通过理论计算对结果的正确性进行了验证。     

Holographic interferometry of laser produced plasmas using picosecond pulses

Interferograms have been obtained using a holographic system illuminated by picosecond pulses. The technique has been applied to a picosecond laser produced plasma, and the total number of electrons present in the plasma has been measured to be at least 5 × 10¹⁴for a laser energy of 0.1 joule.     

交叉棱镜腔Nd:YAG板条激光器

对稳定和非稳共焦型Nd:YAG板条激光器的特性作了理论分析和实验研究.证实了使用交叉棱镜腔的流动空气-水混合冷却板条激光器有高的光束质量和对棱镜失调的不灵敏性,可望获得某些实际应用.关键词:交叉棱镜腔,板条激光器.     

利用激光全息干涉测量梁的微小位移

全息干涉测量利用二次曝光记录物体在不同载荷状态下的相对位移场.通过在干板上记录和比较不同状态产生的光波的干涉,可以得到在不同载荷时干涉条纹随物体位移的变化情况,实现对物体微小变形、微小位移量的测量.本文利用激光全息干涉技术测量了金属梁的微小位移量,计算得到金属梁的弹性模量和挠度.     

Generation of super-high-order petal-like laser beam using Theon-sieve resonator

The Laguerre-Gaussian(LG) mode beam has very important applications in many research fields.Here,the Theon sieve is first introduced into the laser resonator to generate petal-like laser beams by coherently superimposing two high-order LG modes.The effectiveness was verified by GLAD software.The petal-like laser beam is derived from the light field redistribution and coherent superposition caused by the diffraction effect of the Theon sieve.The relationship between the order of the petal-like laser and the cavity structures has also been investigated in detail.Light field operation in the laser cavity greatly simplifies the optical structure and is more beneficial to optical diagnostics and imaging.     

Dynamic two-frequency interferometry for small displacement measurements

Two-frequency interferometry for small displacement measurements is examined from a practical point of view. A laser beam that is modulated sinusoidally in intensity by an acousto-optic Bragg cell provides signal and reference optical waves to produce dynamic interference. The output signal of a photodetector receiving the interference is composed of optical homodyne and heterodyne components. The heterodyne component carries a vibrational displacement to be detected on its amplitude. A sinusoidal vibration amplitude is measured down to 0.5 nm.     

Compact laser system for atom interferometry

We describe an optical bench in which we lock the relative frequencies or phases of a set of three lasers in order to use them in a cold atom interferometry experiment. As a new feature, the same two lasers serve alternately to cool atoms and to realize the atomic interferometer. This requires a fast change of the optical frequencies over a few GHz. The number of required independent laser sources is then only three, which enables the construction of the whole laser system on a single transportable optical bench. Recent results obtained with this optical setup are also presented. PACS 32.80.Pj; 42.50.Vk; 39.20.+q     

General relativistic measurements with satellite laser ranging, lunar laser ranging and very long baseline interferometry

Summary After a brief discussion on the experimental tests of general relativity, we describe three new measurements of Einstein theory. The first, already performed, is the test of the De Sitter or geodetic effect, for the Earth-Moon system. The second will be realized with the launch of the laser ranged satellite, LAGEOS III, and will test the existence of the, never measured, gravitomagnetic field. The third, currently being performed, is the measurement of the LAGEOS relativistic perigee advance. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.     

Accurate AC/DC voltage measurements using electrostatic comparator

The electrostatic AC-DC voltage comparator for precise voltage measurement in voltage range of 100–1000 V and frequency range of 20–100,000 Hz was designed. The equality of AC and DC voltages transforms into horizontal positioning of the beam, which is registered by two photoelectric transducers. DC voltage was measured by voltage divider, standard cell and low-voltage comparator. The construction, main characteristics, and sources of errors are described. The comparison error has been determined as having the value of 0.003% at the voltage of 100 V and the value of 0.0009% at the voltage of 1000 V.