Laser Interference Fringes Research Articles

Optimal zero-crossing group selection method of the absolute gravimeter based on improved auto-regressive moving average model

An absolute gravimeter is a precision instrument for measuring gravitational acceleration, which plays an important role in earthquake monitoring, crustal deformation, national defense construction, etc. The frequency of laser interference fringes of an absolute gravimeter gradually increases with the fall time. Data are sparse in the early stage and dense in the late stage. The fitting accuracy of gravitational acceleration will be affected by least-squares fitting according to the fixed number of zero-crossing groups. In response to this problem, a method based on Fourier series fitting is proposed in this paper to calculate the zero-crossing point. The whole falling process is divided into five frequency bands using the Hilbert transformation. The multiplicative auto-regressive moving average model is then trained according to the number of optimal zero-crossing groups obtained by the honey badger algorithm. Through this model, the number of optimal zero-crossing groups determined in each segment is predicted by the least-squares fitting. The mean value of gravitational acceleration in each segment is then obtained. The method can improve the accuracy of gravitational measurement by more than 25% compared to the fixed zero-crossing groups method. It provides a new way to improve the measuring accuracy of an absolute gravimeter.

Multi-beam ultrafast laser processing of free-standing nanofilms

In this study, femtosecond laser-based multi-beam interference laser processing on nanofilms with nanometer thicknesses was demonstrated. The resulting multi-hole, two-dimensional lattice pattern reflected a laser interference fringe formed on the surface of the nanofilm, with no breaks or cracks. In anticipation of the actual nanostructure fabrication, additional laser processing was performed to drill additional holes in the spaces between the existing holes, resulting in high-density multi-point hole drilling beyond the interference fringe pitch. Notably, processing materials with thicknesses close to 100 nm or less is difficult even with a state-of-the-art focused-ion-beam system. The presented method, in contrast, allows instantaneous, submicrometer-scale multi-point hole drilling of nanofilms over a large area, opening up a new frontier of nanoengineering. Future applications will include the fabrication of electron phase plates, membrane-based optomechanical devices, microelectromechanical systems, and engineering of atomic layer materials.

Hyperbolic metamaterial-assisted structured illumination microscopy using periodic sub-diffraction speckles

Structured illumination microscopy (SIM), as a wide-field, rapid, super-resolution imaging technology, is widely employed in the field of biology. In this work, we propose a hyperbolic metamaterial (HMM)-assisted super-resolution structured illumination microscopy technique. By utilizing the HMM, a sub-diffraction illumination pattern of bulk plasmon polariton (BPP) with pure and higher spatial frequency replaces the conventional laser interference fringes, thus the imaging resolution of BPPSIM could surpass that of conventional SIM and reach 65 nm for HMM with 8-layers periodic structure. Moreover, an HMM with 10-layers aperiodic structure designed with particle swarm optimization was obtained, and BPPSIM could bring the imaging resolution down to 60 nm (1/9 of the fluorescence wavelength), which is a 3.3-fold improvement compared with the diffraction-limited image. This BPPSIM would provide a super-resolution, wide field of view, and good bio-compatibility approach in biological imaging.

Enhanced hot electron generation via laser interference

The interaction of two interfered picosecond laser pulses with overdense plasma and the resulting hot electron generation are studied by particle-in-cell simulation. We find that the yield and temperature of forward hot electrons can be significantly increased when laser interference fringes have a period around 3–9 μm and the angle between the two pulses is about 6°–16°. The enhancements result from local intensity increase at laser interference fringes and the plasma surface structure formed by laser pulses. The optimal angle and fringe period are analyzed, and the dependence between the optimal period and plasma density scale length is discussed. This work could be applied in hot electron generation and the resulting ion acceleration, fast ignition of laser fusion, etc.

Research on Feature Extraction of Laser Interference Fringe and Centering Measurement Technology

Research on Feature Extraction of Laser Interference Fringe and Centering Measurement Technology

An optimized fringe generator of 3D pavement profilometry based on laser interference fringe

As pavement distresses have more negative influences on the driving safety and comfortableness,pavement distress detection and maintenance becomes more significant. 3D pavement profilometry can help analyze the type and severity of the pavement distress, which provides a basis for pavement maintenance. This paper has employed laser interference fringe on 3D pavement profilometry. This new technology has great research value and prospect on improving the measurement accuracy.However,the fringe generators used in previous 3D profilometry technologies performed close-range projection (< 1 m) with laser interference fringe on the object surfaces being measured which have small sizes (diameter < 0.1 m), so the area of the fringe region was small.To extract the 3D profile information of the pavement surface,it is imperative to increase the projection distance to enlarge the area of fringe region. However, increasing the projection distance will cause the fringe spatial frequency and the measurement accuracy to decrease.In order to solve the problem,this study optimizes the configuration of the fringe generator based on previous researches, that enables it to emit interference fringes with higher spatial frequencies. It is proved that the new fringe generator makes it possible to extract the 3D pavement profile.After validation, the results show that the measurement error reaches ±0.38 mm when the fiber core interval is 0.75 mm and the projection distance is 1200 mm.

Burr removal algorithm based on interference fringe skeleton

Accurate removal of the skeletal burrs is the most critical step in the extraction of interference fringe skeleton, which can be applied in laser interference fringe detection. A burrs removal algorithm of interference fringe skeleton based on skeleton features is proposed,which includes the acquisition of feature points of skeleton and the tracking of the eight-neighborhood linked list. First, the pixel points are scanned one by one to obtain the four feature points of the skeleton: endpoints, nodes, glitch points, and backbone points. Then, the algorithm of eight neighborhood linked list based on feature points is used to extract all the glitch points and backbone points, and the difference operation was performed based on nodes to remove the burrs. Finally, the processed image is iterated until the interference fringe skeleton burrs are completely removed. The OpenCV machine vision algorithm was used to simulate the burrs image removal, the results were verified by 1 000 pieces of burrs images, and the correct rate of burrs removal is 94%. Compared with the traditional scheme, the proposed algorithm has a higher pertinence, retains the backbone of the skeleton, and removes the remaining burrs, which has a broad application prospect in interference fringe detection.

PE9 レーザー干渉縞の位相速度走査法を用いた弾性表面波発生法の高周波化(SAWデバイス,ポスターセッション1)

PE9 レーザー干渉縞の位相速度走査法を用いた弾性表面波発生法の高周波化(SAWデバイス,ポスターセッション1)

Interference comparator for laser diode wavelength and wavelength instability measurement.

Method and construction of a setup, which allows measuring the wavelength and wavelength instability of the light emitted by a laser diode (or a laser light source with a limited time coherence in general), is presented. The system is based on Twyman-Green interferometer configuration. Proportions of phases of the tested and reference laser's interference fringe obtained for a set optical path difference are a measure of the unknown wavelength. Optical path difference in interferometer is stabilized. The interferometric comparison is performed in vacuum chamber. The techniques of accurate fringe phase measurements are proposed. The obtained relative standard uncertainty of wavelength evaluation in the tested setup is about 2.5 ⋅ 10(-8). Uncertainty of wavelength instability measurement is an order of magnitude better. Measurement range of the current setup is from 500 nm to 650 nm. The proposed technique allows high accuracy wavelength measurement of middle or low coherence sources of light. In case of the enlarged and complex frequency distribution of the laser, the evaluated wavelength can act as the length master in interferometer for displacement measurement.

Wide Field Super-Resolution Surface Imaging through Plasmonic Structured Illumination Microscopy

We experimentally demonstrate a wide field surface plasmon (SP) assisted super-resolution imaging technique, plasmonic structured illumination microscopy (PSIM), by combining tunable SP interference (SPI) with structured illumination microscopy (SIM). By replacing the laser interference fringes in conventional SIM with SPI patterns, PSIM exhibits greatly enhanced resolving power thanks to the unique properties of SP waves. This PSIM technique is a wide field, surface super-resolution imaging technique with potential applications in the field of high-speed biomedical imaging.

Measurement of nanometer electron beam sizes with laser interference using Shintake Monitor

The Shintake Monitor is an essential beam tuning device installed at the interaction point (IP) of ATF2 [1], the final focus test beam line of the Accelerator Test Facility (ATF) to measure its nanometer order vertical e− beam sizes (σy⁎). The e− beam collides with a target of laser interference fringes, and σy⁎ is derived from the modulation depth of the resulting Compton signal photons measured by a downstream photon detector. By switching between several laser crossing angle modes, it is designed to accommodate a wide range of σy⁎ from 20nm to a few micrometers with better than 10% accuracy. Owing to this ingenious technique, Shintake Monitor11The Shintake Monitor, invented by Dr. T. Shintake, had first been put into practical usage at the FFTB experiment at SLAC [4].[2,3] is the only existing device capable of measuring σy⁎<100nm, and is crucial for verifying ATF2's Goal 1 of focusing σy⁎ down to the design value of 37nm. Shintake Monitor has demonstrated stable σy⁎ measurement with 5–10% stability. Major improvements in hardware and measurement schemes contributed to the suppression of error sources. This paper describes the design concepts and beam time performance of Shintake Monitor, as well as an extensive study of systematic errors with the aim of precisely extracting σy⁎ from the measured modulation.

Current Status of Nanometer Beam Size Monitor for ATF2

Abstract The Accelerator Test Facility 2 (ATF2) is an extension of the ATF beamline extraction featuring an ILC-type final focus system. Among the project's major purposes are establishment of hardware and beam handling technologies aimed at transverse focusing of ATF's electron beam to below 40 nm in the vertical. A laser-interferometer type high resolution beam size monitor named the “Shintake Monitor” is installed at ATF2's virtual interaction point, and plays a crucial role in achieving this aim. A laser interference fringe is formed by crossing two coherent laser rays. This functions as an interaction target for probing the electron beam. Beam size sensitivity of the monitor depends on the pitch of the interference fringe, and maximizes at about one fifth of the pitch. The Shintake Monitor at ATF2 is designed to be capable of measuring beam sizes ranging from 6 μm down to 20 nm in the vertical. A vertical beam size of approximately 300 nm has been measured during the run of May 2010. For this running period, ATF2 operated under a special optics configuration with ten times the nominal IP beta function. For the most recent run, due to switching beam optics back to nominal, BG levels rose about 10 times from May. Shintake Monitor had been proven in May to fulfill expectations provided BG is low. However with high BG, its accuracy decreased, which makes low S/N a major concern. In this paper, we describe the design and current status of the Shintake Monitor.

The measurement of ultraweak liquid surface wave by laser interferometry

We describe a simple experiment on the interference of refraction light by ultraweak liquid surface wave at low frequency. The surface wave profile is generated by electrically driven vertical oscillations exciters. The high visibility and stable laser interference fringes were gathered experimentally. The theoretical light intensity distribution agrees well with the observations. In particular, we show the relation between the light intensity distribution and the characteristic features of the surface wave. In addition, we can measure the amplitude and wavelength of the ultraweak liquid surface wave at low frequency by this means.

219202 集光光による光干渉縞を用いた微粒子径計測(OS10 熱流体計測の新展開2,オーガナイズド・セッション)

Fine particle size measurement technique with laser interference fringes is proposed as one of the in-line measurement techniques to the diameter of several hundred nano meter particles. The objective of this study is to examine the principle of this measurement technique with laser interference fringes. First, we visualize the laser interference fringes images with a high-speed video camera. And we identify the fringes images moving through the test cell. Finally, we measure the time variation of the intensity of the laser interference fringes by using photodiodes. It is confirmed that the voltage signal depends on fine particle size. Also, correlation between the time and the voltage signal scattered with the focused laser beam is different from that of with the parallel laser beam.

10.2478/s11814-009-0265-9

When two immiscible liquids make contact in a microchannel, the flow pattern is affected by the affinity between channel walls and liquids. In this study, microchannels (200 µm in width and 200 µm in depth) having a T-shaped bifurcation point were fabricated on PMMA plates. The inner walls of the microchannels were modified in a zone-selective manner to be either hydrophilic or hydrophobic, based on verification accomplished via a laser interference fringe technique. The microchannel was placed horizontally, and water and octane were introduced into the upper-side channel (hydrophilic) and into the lower-side channel (hydrophobic), respectively. The experimental results showed that water and octane formed a stable layered flow, and the two liquids were virtually completely separated at the T-shaped section, even when static pressure was intentionally applied to the outlets. CFD simulation, using FLUENT 6.3 software, was performed to explain the role of zone-selective modification of microchannel walls.

A nanometer beam size monitor for ATF2

We developed an electron beam size monitor for nanometer scaled beam sizes. It uses a laser interference fringe for a scattering target with the electron beam. The target beam size for the monitor is 25–6000 nm to achieve and confirm the 37 nm design beam size of ATF2, a final focus test facility for the ILC. Resolution of less than 10% for the full range is shown to be realistic, with a precise fringe control system. We describe the overall design, implementation, and performance of the monitor.

0310 光干渉縞を用いたナノサイズ微粒子径の非接触・インライン計測(OS302 ナノスケールの熱流動現象,オーガナイズドセッション)

0310 光干渉縞を用いたナノサイズ微粒子径の非接触・インライン計測(OS302 ナノスケールの熱流動現象,オーガナイズドセッション)

Layered liquid-liquid flow in microchannels having selectively modified hydrophilic and hydrophobic walls

When two immiscible liquids make contact in a microchannel, the flow pattern is affected by the affinity between channel walls and liquids. In this study, microchannels (200 µm in width and 200 µm in depth) having a T-shaped bifurcation point were fabricated on PMMA plates. The inner walls of the microchannels were modified in a zone-selective manner to be either hydrophilic or hydrophobic, based on verification accomplished via a laser interference fringe technique. The microchannel was placed horizontally, and water and octane were introduced into the upper-side channel (hydrophilic) and into the lower-side channel (hydrophobic), respectively. The experimental results showed that water and octane formed a stable layered flow, and the two liquids were virtually completely separated at the T-shaped section, even when static pressure was intentionally applied to the outlets. CFD simulation, using FLUENT 6.3 software, was performed to explain the role of zone-selective modification of microchannel walls.

Piezo-Impact-Driven X-Y Stage and Precise Sample Holder for Accurate Microlens Alignment

This paper details the development of an inertia-driven X-Y microstage and simple gripper for a pick-up lens in Blu-ray disc alignment incorporating inertia-driven microsliders on V-shaped grooves and a micropart handler. The microslider is driven by impact generated by a mass connected with a piezo element. We made a kinematic model for theoretical analysis on the X-Y microstage and gave the microinertia X-Y stage a sophisticated design.The X stage is stacked on the Y stage to provide fine in-plane positioning. Practical applications include multiple lens component assembly in which the optical lens must be centered within a tolerance of less than 100 nm. Experiments confirmed successful achievement of this microlens positioning in the center of the reference lens axis as observed by the laser interference fringe.

On continuous-line acoustic array behavior in a laser Doppler sound pressure measurement system.

Continuous-line acoustic array behavior in a laser doppler anemometry (LDA) based sound pressure measurement system is considered. Traditional LDA ultrasound measurement systems intentionally minimize the laser beam intersection or interference fringe volume to better achieve point measurements of the sound field. The large laser beam diameters due to beam spreading in remote sensing applications from space or airborne platforms make this approach impractical. Since the sound pressure signal is integrated over the interference fringe volume, continuous-line acoustic array behavior is expected to be observed proportional to the length of the laser light path through the interference fringe volume. This behavior is analyzed from a theoretical perspective and an experimental setup to test for continuous-line acoustic array behavior in a LDA sound pressure measurement system is presented.