Laser Interferometric Technique Research Articles

Laser interferometric detection of heat release rate perturbation field of acoustically perturbed laminar premixed flames

Laser interferometry, which was originally used to measure density perturbation, has been previously used to determine the heat release rate perturbation, which is a key factor in the analysis of combustion instability. However, its spatial accuracy is still unsatisfied. In the present work, an improved fringe Fourier analysis method is proposed to process the results obtained from the laser interferometry measurement, aiming to accurately determine the spatial distribution of flame heat release rate perturbation. The measurement of heat release rate perturbation was performed on a acoustic perturbed laminar premixed flame, with the burner outlet diameter of 8 mm. Interference patterns generated by two laser beams with a diameter of 70 mm were recorded at a frame rate of 6000 Hz. A spatial dependent fringe processing method, referred as the improved fringe Fourier analysis, was developed to demodulate the interference phase from the fringe patterns. The proper orthogonal decomposition analysis was performed on these results to analyze the component of interference signals. Validation of the present technique was conducted by comparing the heat release rate perturbation field resulting from the laser interferometric technique to those from the CH* chemiluminescence from the flame. Comparisons were performed both for the global and local values, and the low-frequency natural oscillation effects were analyzed. Finally, a refraction correction method based on background-oriented Schlieren is proposed to compensate the beam deflection caused by flame.

Review on Low-Noise Broadband Fiber Optic Seismic Sensor and Its Applications

Fiber optic seismic sensors have important application prospects in the field of earthquake science research and underground structure detection, due to their strong adaptability in harsh environments such as deep wells, seabeds, and glaciers. It has always been one of the key problems to achieve ultra-low noise levels over a wide measurement frequency band for fiber optic seismic sensors. This article reviews two typical low-noise broadband fiber optic seismic sensing techniques, including narrow-linewidth laser frequency scanning and frequency locking sensing technique, laser interferometric phase interrogation technique. The principles are given. The measurement frequency band and noise level are tested and discussed. Recent progresses on crustal deformation observation, earthquake monitoring, water temperature solid tide detection and deep earth structure exploration based on fiber optic seismic sensors are introduced. Finally, the possible research trends are discussed.

The Detection Scheme and Applications of Gravitational Waves

In recent years, gravitational waves have already attracted attention as the gateway to a new era in physics since they were first directly detected and observed. This paper summarizes the development of gravitational waves from the first proposed to the present and the main observation methods, as well as the main uses and significance of the detection of them. To be specific, in this paper, the most popular laser interferometer technique for the detection based on Michelson interferometer is discussed, and several purposes of the detection of gravitational waves are given. The detection signatures are available to adopt to the analysis of the collision of binary star systems. Gravitational radiation or primordial gravitational radiation can carry more information about black holes or the Big Bang than electromagnetic waves. The gravitational wave astronomy created by gravitational waves has opened a new horizon for astronomers to explore the universe, and the detection of them is an integral part of the future development of physics and astronomy. To sum up, these results shed light on guiding further exploration of gravitational waves detection as well as applications of them.

Shape resonances in photoionization cross sections and time delay

Shape resonances in photoionization of atoms and molecules arise from a particular geometry of the ionic potential which traps the receding photoelectron in a quasi-bound state in a particular partial wave. This mechanism allows us to connect the photoionization cross section in the resonant region with the photoelectron scattering phase in this partial wave by a simple formula $\sigma \propto \sin^2\delta_\ell$. Due to this relation, the phase $\delta_\ell$ can be extracted from an experimentally known cross section and then converted to the photoelectron group delay (Wigner time delay) $\tau_{\rm W} = \partial \delta_\ell/\partial E$ which is measurable by recently developed laser interferometric techniques. Such a direct connection of the photoionization cross section and the time delay is a fundamental property of shape resonances which provides a comprehensive test of novel measurements against a large body of older synchrotron data.

A Portable Compact System for Laser Speckle Correlation Imaging of Artworks Using Projected Speckle Pattern

Artworks have a layered structure subjected to alterations caused by various factors. The monitoring of defects at sub-millimeter scale may be performed by laser interferometric techniques. The aim of this work was to develop a compact system to perform laser speckle imaging in situ for effective mapping of subsurface defects in paintings. The device was designed to be versatile with the possibility of optimizing the performance by easy parameters adjustment. The system exploits a laser speckle pattern generated through an optical diffuser and projected onto the artworks and image correlation techniques for the analysis of the speckle intensity pattern. A protocol for the optimal measurement was suggested, based on calibration curves for tuning the mean speckle size in the acquired intensity pattern. The system was validated in the analysis of detachments in an ancient painting model using a short pulse thermal stimulus to induce a surface deformation field and standard decorrelation algorithms for speckle pattern matching. The device is equipped with a compact thermal camera for preventing any overheating effects during the phase of the stimulus. The developed system represents a valuable nondestructive tool for artwork diagnostics, allowing the monitoring of subsurface defects in paintings in out-of-laboratory environment.

Ultrasonic Propagation in a Dental Implant

Ultrasound techniques can be used to characterize and stimulate dental implant osseointegration. However, the interaction between an ultrasonic wave and the implant-bone interface (IBI) remains unclear. This study—combining experimental and numerical approaches—investigates the propagation of an ultrasonic wave in a dental implant by assessing the amplitude of the displacements along the implant axis. An ultrasonic transducer was excited in a transient regime at 10 MHz. Laser interferometric techniques were employed to measure the amplitude of the displacements, which varied 3.2–8.9 nm along the implant axis. The results demonstrated the propagation of a guided wave mode along the implant axis. The velocity of the first arriving signal was equal to 2110 m.s–1, with frequency components lower than 1 MHz, in agreement with numerical results. Investigating guided wave propagation in dental implants should contribute to improved methods for the characterization and stimulation of the IBI.

Dual scanning interferometric technique for measurements of the temperature and concentration dependence of the refractive index of liquids

A novel laser interferometric technique for measuring the variation of the refractive index with concentration and temperature is presented. The technique is based on the principle of ‘absolute scale’ accomplished with a Michelson interferometer. The linear motion of the scanning mirror allows simple extraction of the optical path change inside the Fabry–Perot interferometer. The measurement of the relative positions of the interference maxima reduces the sensitivity of the system to intensity noise and drift of the laser source. The sensitivity to the changes of the refractive index is of the order of 1 × 10−7 for a 20 mm optical path.

Ultrasonic guided wave propagation in a dental implant

Ultrasound techniques can be used to characterize and stimulate dental implant osseointegration. The acoustical energy transmitted to the bone-implant interface is an important parameter that must be controlled for both applications, since it should be sufficiently low to avoid damaging the surrounding tissues, but sufficiently high for stimulation purposes to enhance bone growth. However, the interaction between an ultrasonic wave and a dental implant remains unclear. The objective of this study combining experimental, analytical and numerical approaches is to investigate the propagation of an ultrasonic wave in a dental implant by assessing the amplitude of the displacements along the implant axis. An ultrasonic transducer was excited in transient regime at 10 MHz. Laser interferometric techniques were employed to measure the amplitude of the displacements, which varied between 5 and 12 nm according to the position. The results show the propagation of a guided wave mode along the implant axis with a velocity of first arriving signal equal to 2110 m s−1 and frequency components lower than 1 MHz, which was confirmed by the analytical and numerical results. This work paves the way to improve techniques for the characterization and stimulation of the bone-implant interface.

Experimental modal analysis of disk-like rotor–stator system coupled by viscous liquid

The vibrational behavior of a rotor–stator system coupled by a viscous liquid is investigated experimentally using a test bench with rotor and stator simplified as disks. The understanding of this vibration problem is of particular importance in the design of hydraulic machines such as Francis turbines, pump–turbines or hydraulic pumps, where the elastic rotor is coupled to the adjacent elastic stator by the intermediate water. The especially developed test bench enables high-resolution scan measurements of the rotor and stator disk vibrations by applying the modal analysis method in combination with the laser interferometer technique. We present the mode shapes, eigenfrequencies and damping factors measured over a large number of parameter combinations of the stator thickness, the rotor thickness, the clearance between rotor and stator as well as the rotation speed of the rotor. We identify and discuss fundamental vibration mechanisms of the system (for example, the characterization of varicose and sinuous modes, or the frequency split between co- and counter-rotating modes). The derived experimental results may serve as a benchmark for the validation of simulation models studying the linear vibration including effects of rotation, bias flow and viscous damping.

100-m standoff detection of a QCL-induced photo-vibrational signal on explosives using a laser vibrometer

Laser Doppler vibrometry is a key technology in the field of photomechanics. It allows pointwise noncontact measurements of dynamic effects. In recent years, it has been applied as a sensor in photoacoustic/photothermal spectroscopy to detect hazardous chemicals or explosive substances in an open environment. In photoacoustic spectroscopy, normally the analysis has to be conducted in a sealed space to enable signal detection, either through a high-sensitivity microphone, or a piezo-sensor coupled with a lock-in amplifier. In addition, the requirement for sample preparation prior to analysis is an impediment preventing practical adoption of the technique in real-time, standoff chemical detection deployments in an open environment. The research team has previously demonstrated the feasible use of a laser interferometric technique to detect photo-vibrational signals of trace chemicals because it was excited by an intensity-modulated quantum cascade laser (QCL). In this study, our long distance laser Doppler vibrometer developed in house was demonstrated to be able to detect the vibration amplitude and frequency of trace explosives at long standoff distances of 100 m in an open environment. Three explosives of 10 µg/mm2 concentration were tested, and the photo-vibrational spectrum obtained by scanning the output wavelength of the QCL through the mid-IR range, coincides well with the corresponding spectrum obtained using typical FTIR equipment. The experiment demonstrated that the detection of hazardous chemicals or explosive substances at a safe standoff distance can be realized through a system utilizing capable interferometric sensors like the laser Doppler vibrometer, coupled with a QCL excitation source.

Photorefractive Effect in Organic–Inorganic Hybrid Perovskites and Its Application to Optical Phase Shifter

AbstractSingle crystals of methylammonium lead trihalide perovskites with high optical transparency and well‐defined facets are grown via solution process. Using these high‐quality crystals, the photocarrier‐induced refractive‐index change is observed for the first time in organic–inorganic hybrid perovskites. The photorefractive properties are measured using a laser interferometric technique that enables to monitor the time‐resolved refractive phase shifts. It is found that these phase shifts are determined by the initial density of photogenerated carriers and they are surprisingly retained even after carrier recombination. Utilizing the extremely long‐lived phase shift, it is demonstrated that the perovskite single crystal works as a phase shifter of laser light to generate any desired polarization. Furthermore, a periodic polarization‐modulation technique is established using the time‐dependent refractive phase shift. This refractive property can be used for advanced optical applications of organic–inorganic hybrid perovskites.

Wideband dispersion removal and mode separation of Lamb waves based on two-component laser interferometer measurement**Project supported by the National Natural Science Foundation of China (Grant No. 11374230)

Ultrasonic Lamb waves are considered as a sensitive and effective tool for nondestructive testing and evaluation of plate-like or pipe-like structures. The nature of multimode and dispersion causes the wave packets to spread, and the modes overlap in both time and frequency domains as they propagate through the structures. By using a two-component laser interferometer technique, in combination with a priori knowledge of the dispersion characteristics and wave structure information of Lamb wave modes, a two-component signal processing technique is presented for implementing dispersion removal and mode separation simultaneously for two modes mixture signals of Lamb waves. The proposed algorithm is first processed and verified using synthetic Lamb wave signals. Then, the two-component displacements test experiment is conducted using different aluminum plate samples. Moreover, we confirm the effectiveness and robustness of this method.

Physical and spectroscopic properties of pure C2H4and CH4:C2H4ices

Physical and spectroscopic properties of ices of C2H4 and CH4:C2H4 mixtures with 3:1, 1:1 and 1:3 ratios have been investigated at 30 K. Two laboratories are involved in this work. In one of them, the density and refractive index of the samples have been measured by using a cryogenic quartz microbalance and laser interferometric techniques. In the other one, IR spectra have been recorded in the near- and mid-infrared regions, and band shifts with respect to the pure species, band strengths of the main bands, and the optical constants in both regions have been determined. Previous data on ethylene and the mixtures studied here were scarce. For methane, both the wavenumbers and band strengths have been found to follow a regular pattern of decrease with increasing dilution, but no pattern has been detected for ethylene vibrations. The method employed for the preparation of the samples, by vapour deposition under vacuum, is thought to be adequate to mimic the structure of astrophysical ices. Possible astrophysical implications, especially by means of the optical constants reported here, have been discussed.

Implementation of multidirectional moiré computerized tomography: multidirectional affine calibration.

To realize three-dimensional (3D) instantaneous diagnoses for flow fields, many multidirectional optical computerized tomographic (optical CT) techniques based on laser interferometry have been proposed. Projections from different directions of these tomographic systems are captured simultaneously to reconstruct the test field. These projections are independent from each other. However, due to the inevitable errors from installation and difference between optical elements, projections will be imaged with different distortion and located at different positions on the sensors. Therefore, a multidirectional calibration should be performed to remap these projections to a unified coordinate system before CT reconstruction. As far as we know, the multidirectional calibration problem for laser interferometric CT techniques has never been discussed in previous research. In this paper, a six-directional moiré tomographic system is designed. Considering the projection characteristics of moiré deflectometry, a multidirectional affine calibration method is proposed to determine the extrinsic and intrinsic parameters of tomographic projections. With the calibration results, projections can be remapped to the unified coordinate system and the 3D distributions of flow field can be reconstructed.

On the direct detection of gravitational waves, and some of the problems of improving laser interferometers

In this paper we describe an observational method for determining black holes masses. The study shows that the knowledge of the recorded low-frequency gravitational waves and the period from the beginning of registration till the moment of black holes collapse is sufficient and even preferable in determining the possible values of collapsing black holes masses. The reason for this is that the proportion of the period in the measured interval containing relativistic corrections (i.e. those ones in which the black hole speed is comparable to the speed of light), is smaller if the observed and measured time interval is longer. The values of black holes masses and the measured time interval, obtained as a result of the first observations, according to this model are in a very good agreement.We examine the problem of mirror heating in Fabry-Perot cavity of Michelson interferometer, by incident laser radiation, and we conclude that the problem of heat removal can be solved by a different approach, without use of multilayer reflective openings. As an alternative approach to the creation of highly reflective structures, we suggest using a spatially extended structure with a sinusoidal variation of the refractive index. We consider some of the possible technological methods for producing such structures based on heterogeneous media.The article describes the effects of the incident laser radiation exposure on the periodic structure, and it shows that the volume ponderomotive force may lead to a mirror polarization due to the radiation, and consequently, to appearance of an additional mechanical connection of the mirror with the surrounding mirror suspension design. The article examines the impact of the surface ponderomotive forces on the media boundary with different dielectric permeability and it shows that pressure spatial variables arising at the same time lead to deformation of the media layers, and the deformation and pressure values depend on the difference in the dielectric permeability values of the nearest layers. We also state the possible consequences of such spatially variable pressures effects (violation of synchronism conditions (misalignment) of reflective coatings, and others. It is also noted that our work, in which a laser interferometric technique for the detection of gravitational waves was first proposed, was already known to Joseph Weber in 1963.

Gravitational waves observation: brief comments

In preceding papers we have shown the fundamental aspects of the General Relativity (GR), of the emission and detection of gravitational waves (GW). With the same objective we analyze the two recent observations of the GW done by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States of America. These GW observations known as the GW150914 and GW151226 events are emitted by binary-star systems of black-holes (BBH). We present the basic principles of the laser interferometric technique that today is considered as the only one able to detect with certainty the GW. Using a simple relativistic approach we explain approximately the observed GW in the spiral stage.

Benchmarking Surface Position from Laser Velocimetry with High-Speed Video in Impact Experiments

Photonic Doppler Velocimetry (PDV) is a heterodyne laser interferometric technique for computing the velocities of free surfaces moving up to tens of kilometers per second. This information can be used to infer material properties such as equation of state and phase transitions, many of which are unknown even for common materials like steel. Broadly speaking, the methods of computing velocity from the voltages measured on an oscilloscope are either local or global in time, either frequency-based or phase-based, and formulated either statistically or deterministically. It is important to understand how velocities extracted using the different classes of methods relate to each other and how the results relate to measurements from independent diagnostics. In this work we present computed surface velocities of a flat plate of stainless steel impacted by a projectile traveling approximately 4km/s from a light gas gun, using several different extraction methods, and we benchmark the results of the different PDV analyses against high-speed video captured at 5 million frames per second with a hybrid framing-video camera. The different extraction methods all show the same large-scale structures in the computed velocity profiles–and they agree with the high-speed video at the appropriate time scale–but they each show different small-scale features. We discuss the nature of these features, including descriptions of the numerical artifacts that one would expect with each of the different analysis techniques applied. Descriptions of the methods are provided, with a focus on the Local Polynomial Approximation method, and its uncertainty quantification, developed by the authors.

Experimental investigation of acceleration of steel plates using simultaneously two laser interferometric techniques

This paper presents the results of experiments on the spalling and nonspalling acceleration of steel plates by HMX-based explosive charges of different initial thickness (with spall closure) in the presence and absence of an air gap between the explosive charge and the projectile plate. The plate acceleration dynamics was simultaneously recorded by two different independent laser interferometric techniques using lasers of different wavelengths. The experiments were carried out to perform a metrological certification of a new laser-heterodyne technique based on the data of a previously metrologically certified laser-interferometric technique based on the Fabry-Perot scheme.

Real time monitoring of laser beam welding keyhole depth by laser interferometry

The utility of a new laser interferometric technique, inline coherent imaging, for real time keyhole depth measurement during laser welding is demonstrated on five important engineering alloys. The keyhole depth was measured at 200 kHz with a spatial resolution of 22 μm using a probe beam, which enters the keyhole coaxially with the process beam. Keyhole fluctuations limited average weld depth determination to a resolution on the order of 100 μm. Real time keyhole depth data are compared with the weld depths measured from the corresponding metallographic cross-sections. With the exception of an aluminium alloy, the technique accurately measured the average weld depth with differences of less than 5%. The keyhole depth growth rates at the start of welding are measured and compare well with order of magnitude calculations. The method described here is recommended for the real time measurement and control of keyhole depth in at least five different alloys.

Optimization for sinusoidal profiles in surface relief gratings recorded on photoresist

The formations of sinusoidal surface relief structures recorded in positive photoresist (Allresist AR-P 3120) have been studied and optimized for different recording parameters of gratings with spatial frequency of ∼1200 grooves/mm. A stable sinusoidal pattern generated using a two-beam laser interferometric technique was recorded in thin films of positive photoresist deposited on glass substrates. Several gratings were generated by varying the exposure time of interference pattern and time of chemical development of exposed media. Time duration of exposure for 90 s and chemical development for 15 s were observed to be optimum for the translation of the sinusoidal interference pattern into nearly-sinusoidal profiled grooves in the gratings for a developer AR-300-26 of dilution of 2:1 (developer:de-ionized water).