Laser Interference Method Research Articles

Method improving low Signal-to-noise ratio of velocity test signals for Laser-induced shock waves

When laser-induced shock (LIS) wave characteristics testing is carried out using laser interference methods, the electrical noise, vibration noise, jitter or offset of the diffuse reflective surface during high-speed motion and other factors can lead to superposition or offset of the noise signal frequency with the low-frequency phase of the useful signal. As a result, problems such as phase shift of the useful signal and difficulty in extracting the initial position of the wavelet ridge may appear, and the initial position cannot be zeroed. By introducing a measurement factor through multi-resolution singular value decomposition and adaptively determining the optimal number of decomposition layers, zero-phase offset filtering is achieved and the signal-to-noise ratio (S/N) of the data is improved. According to the waveform decay characteristics of laser-induced shock wave velocity signals, the Shannon wavelet entropy method is proposed to accurately optimise the Morlet wavelet basis parameters to enhance the aggregation of wavelet scale spectrum time–frequency distribution. Simulation and test results show that: the proposed method overcomes the background noise interference and enables the initial velocity to be zeroed; the relative singular value points of the pulse are accurately symmetrically distributed and no phase shift occurs; the denoising performance is better than that of the wavelet method, the root mean square error is only 0.046, and the repeatability is strong; the error of the elastic wave velocity of the laser-induced shock wave at different power densities is within 3.2%; the relative velocity resolution remains constant at low/high frequencies, effectively avoiding false peaks and misclassification of the velocity profile.

Investigation of partially transparent and high-density two-phase liquids using laser interference method

The purpose of the present work was to investigate partially transparent and high-density two-phase liquids using the laser interference method to establish the limits of applicability of this method. The results of the work include the interference fringe patterns of drops when using various kinds of liquids, the calculated drop sizes. The calculation of inaccuracies was also carried out to further establishing the limits of applicability of this method.

Investigation of the interference pattern from a spherical particle at different viewing angles

The work aim is to investigate the influence of the parameters of the laser interference method experimental setup on the obtained images. Using computer modeling based on the diffraction theory and physical experiment, the change in the parameters of the interference pattern for different viewing angles had been shown. The results can be used to develop a single algorithm for processing images of the laser interference method.

High-precision optical fiber pressure sensor using frequency-modulated continuous-wave laser interference

This work presents a high-precision fiber optic pressure sensor based on frequency-modulated continuous-wave (FMCW) laser interference. The pressure sensor is primarily composed of a diaphragm-type Fabry–Pérot (F–P) cavity, with the diaphragm fabricated using high-elasticity SUS631 stainless steel. The external air pressure causes the center of the elastic diaphragm to deform, and this deformation results in a change in the F–P cavity length. The FMCW laser-interference method was used to demodulate the change in the length of the cavity and realize high-precision pressure measurements. The experimental results showed that when the pressure measurement is in the range of 0 kPa–600 kPa, an accuracy of 3.8 Pa can be obtained. In addition, the sensor had very good linearity with pressure change (R2 = 0.999 94), repeatability, and stability.

Research of free oscillations of the Earth dynamics with a period of 20.5 minutes by laser interference method

Research of free oscillations of the Earth dynamics with a period of 20.5 minutes by laser interference method

Research on Two-dimensional Fabry-Perot Ultrasonic Sensing Technology

According to the laser interference method, a two-dimensional Fabry-Perot fiber optic sensor is used as the core, and the difference between the propagation speed of the ultrasonic transverse wave and the longitudinal wave in the solid medium is used to measure the ultrasonic wave propagating in the solid to realize the ultrasonic positioning. An F-P interference cavity is formed with a coated quartz film, the end face of the fiber end, and air. At the same time, the cantilever beam design can be used to simultaneously extract longitudinal ultrasonic waves based on Fabry-Perot cavity interference and transverse ultrasonic signals based on cantilever fibers in a solid rod-shaped acoustic waveguide. In this paper, the position of the ultrasonic wave is determined by the difference of the longitudinal and transverse ultrasonic wave speeds in the detected ultrasonic signals.

超声换能器表面振动的激光干涉测量

超声换能器表面振动的激光干涉测量

Crystallization of amorphous‐Si using nanosecond laser interference method

AbstractLaser crystallization of a 50‐nm thick amorphous‐Si (a‐Si) thin film on glass substrate was examined by a Nd:YAG (λ = 1064 nm) nanosecond laser and a two‐beam laser interference method. In spite of the low absorption rate of the laser wavelength in the a‐Si, crystallized Si ripple patterns were observed following a single laser pulse irradiation. The atomic force microscope (AFM) measurement revealed that surface ripple arrays are protruded as high as 120 nm at the positions corresponding to the maximum laser intensity and the ripples are composed of narrow double peaks with a separation of 1 μm. Raman image mapping was used to plot the spatial distribution of the crystallized Si phase. It was found that a 1064‐nm‐wavelength nanosecond laser could crystallize an a‐Si thin film into polycrystalline‐Si (poly‐Si) by nonlinear absorption under high laser energy irradiation.

Measurements of interfacial dynamics of gas–liquid displacement in a capillary

Measurement of liquid film thickness in gas–liquid plug/slug flows is a challenging task. A novel laser interference method for measuring the interfacial film thickness of gas–liquid displacement in a plug flow has been developed. This novel technique utilizes light scattering from different liquid/gas interfaces in forming interference fringes. The interference fringes are used for calculating the film thickness. A set of simultaneous equations is derived based on geometrical optics. The experiment set up is not complex and is easy to install. The fringes are recorded by a charge-coupled device high speed camera and the image data are calculated using fast Fourier transform (FFT) and a non-linear least squares Levenberg–Marquardt algorithm. The uncertainty of this measurement technique is quite small (0.3 μm) and the entire film thickness profile can be measured at the same time.

Fabrication of honeycomb texture on poly-Si by laser interference and chemical etching

In this paper, we present a laser-interference method to fabricate honeycomb textures on poly-Si wafer for reflection reduction. When exposed to three interfering pulsed laser beams at 532nm, the Si surface was periodically melted in accordance with the interference pattern. As a result, concave holes were generated on the surface because the melted material overflowed and condensed at the periphery. Subsequent acid etching revealed uniform and clean honeycomb textures. The texture depth could be controlled by varying the irradiation condition and a minimum reflectance of 10% was obtained. Transmission electron microscopy analysis showed that no irradiation-induced damage remained after etching. This approach can be a cost-effective alternative to lithographic processes for fabricating high-efficiency poly-Si solar cells.

Influence of Flowfield on CO<sub>2</sub> Hydrate Film Thickness

In order to realize of CO2 ocean sequestration, it is important to reveal the knowledge of CO2 hydrate film thickness which forms on the interface between CO2 and water. However, knowledge of CO2 hydrate film thickness under various parameter conditions such as temperature, flow velocity on CO2 hydrate film, and elapsed time from hydrate formation is little. The objective of the present study is to investigate the influence of temperature and flow velocity on CO2 hydrate film thickness. CO2 hydrate film thickness is measured under differential temperature and flow velocity conditions. In this study, CO2 hydrate film thickness is measured with laser interference method. And, CO2 hydrate film thickness is estimated based on duality of CO2 saturated solubility under CO2 hydrate formation condition. As the result, the measured CO2 hydrate film thickness decrease with increase in temperature and flow velocity. And, the estimated CO2 hydrate film thickness denotes the same tendency of measured CO2 hydrate film thickness.

Length Determination of a Fixed-Path Cylindrical Resonator with the Dual Wavelength Laser Interference Method

The length is one of the key parameters for a cylindrical acoustic resonator used for measurement of the Boltzmann constant. A research project has been conducted in the National Institute of Metrology (NIM), China, for the re-determination of the Boltzmann constant with a fixed-path cylindrical acoustic resonator. This paper describes the procedure for the length determination. The excess fraction method was applied to accurately obtain the length of the resonator. This method is performed in a two-step procedure. First, the length is coarsely determined as L1 with an uncertainty of 1.5 μm in the length division of NIM. Second, the result of the coarse measurement is further interpolated by the dual wavelength laser interferometer with a resolution of 1 nm, which is composed of a 633 nm He–Ne laser and a 657 nm semiconductor laser. A Michelson wavemeter has been constructed for calibration of the wavelength of the semiconductor laser. The length variation of the resonator has to be measured from room temperature to the triple point of water (TPW). As a result, the laser interferometer can be also used as a precise dilatometer. The result and the measurement uncertainty of the length measurement are given in this paper.

H111 CO_2ハイドレート膜厚に及ぼす流れ場の影響(OS11 温暖化対策とCO_2削減技術)

The objective of the present study is to investigate the influence of temperature and flow velocity on CO_2 hydrate film thickness. CO_2 hydrate film thickness is measured under differential temperature and flow velocity conditions. In this study, CO_2 hydrate film thickness is measured with laser interference method. And, CO_2 hydrate film thickness is estimated based on duality of CO_2 saturated solubility under CO_2 hydrate formation condition. As the result, the measured CO_2 hydrate film thickness decrease with increase in temperature and flow velocity. And, the estimated CO_2 hydrate film thickness denotes the same tendency of measured CO_2 hydrate film thickness.

Laser interference method of determining the parameters of gas bubbles

The fundamentals of the laser interference method of determining the parameters of gas bubbles in liquids and solids are considered. The role of polarization in the development of interference bands is analyzed. Features in the realization of an experimental plant and a technique for performing experiments are presented.

In-situObservation of Lubrication Dynamics between Soft Elastomer and Glass Substrate

Direct observation is done for the thin lubrication layer in the friction between glass plate and soft elastomer using laser interference method. A poly(dimethylsiloxane) (PDMS) rubber having very ...

The use of laser interference methods for acoustic field diagnostics

The limits of applicability of different schemes of experimental equipment and methods of processing the dynamic signal, which adapt laser interference technologies for acoustic-field diagnostics in a liquid, depending on the extent of the medium and the frequency and intensity of the acoustic field are determined. The results of measurements of the intensity of an acoustic field are presented and their errors are estimated.

20305 レーザー干渉法を用いたCO_2ハイドレート膜厚の光学計測(流れの計測と制御(1),OS6 流れの計測と制御)

20305 レーザー干渉法を用いたCO_2ハイドレート膜厚の光学計測(流れの計測と制御(1),OS6 流れの計測と制御)

Laser-crystallized microcrystalline SiGe alloys for thin film solar cells

Thin films of crystalline silicon–germanium (SiGe) alloys could be an interesting material for next generation solar cells. SiGe alloys with a Ge content of approximately 80 at.% have an indirect band gap only slightly smaller than that of Si. However, the first direct optical transition occurs at approximately 1.5 eV, leading to a strongly enhanced optical absorption compared to Si. Thin μc-SiGe films were prepared by crystallization of evaporated amorphous or nanocrystalline alloys with a pulsed Nd:YAG laser, using homogeneous as well as laser interference methods to achieve lateral grain growth. Structural properties were characterized by atomic force microscopy and transmission electron microscopy. Raman measurements were performed to study possible phase separation and to analyze residual strain in the recrystallized films.

Topographical evaluation of optical disks with polycarbonate substrates in the manufacturing process

An optical contour mapping with a laser-interference method was carried out to evaluate the topographical deformation of optical memory disks. The dynamics of the deformation in a manufacturing process was studied. Reflective films and a protective resin coating increased the dishing, irrespective of the original shape of a substrate. A bonding process decreased the dishing and contributed to mechanical stability that lasted for a long period in daily use. In the case of a 0.6-mm-thick substrate, as with a DVD disk, the large dishing of the single substrate was suppressed by the bonding to less than 100 microm. In addition, it was shown that distortions arising from the molding process remained in the final product and that the initial process should be carefully controlled.

Optical method of determining the components of the relative displacement vector

The theory of a laser interference method of determining in real time the relative displacement of two scattering objects in space is put forward and an experimental verification is described.