A new confocal scanning beam laser MACROscope using a telecentric,f-theta laser scan lens

A new confocal scanning beam system (MACROscope) that images very large-area specimens is described. The MACROscope uses a telecentric, f-theta laser scan lens as an objective lens to image specimens as large as 7·5 cm × 7·5 cm in 5 s. The lateral resolution of the MACROscope is 5 μm and the axial resolution is 200 μm. When combined with a confocal microscope, a new hybrid imaging system is produced that uses the advantages of small-area, high-speed, high-resolution microscopy (0·2 μm lateral and 0·4 μm axial resolution) with the large-area, high-speed, good-resolution imaging of the MACROscope. The advantages of the microscope/MACROscope are illustrated in applications which include reflected-light confocal images of biological specimens, DNA sequencing gels, latent fingerprints and photoluminescence imaging of porous silicon.     

Thermal analysis on voltage responses of high-T c superconducting thin-films exposed to a pulse laser beam

One-dimensional radiation/conduction heat transfer model is employed to investigate thermal responses of HTSC thin-film detectors exposed to a pulse laser beam. The theoretical model includes local radiation absorption in the HTSC film based on the electromagnetic theory, thermal contact resistances at the interface between film and substrate, and nonuniform initial condition for the film/substrate temperature incurred by the Joule heating due to the bias current and inherent electrical resistance even before the radiation exposure. Using the steady-state conduction equation, the experimental resistance-temperature curve is corrected based on the real film temperatures instead of the substrate temperatures. The error involved in the estimation of the voltage jump based on the model without initial Joule heating could be significant near the transition temperature. Still there is a big discrepancy between the theoretical and experimental results, though the nonuniform initial condition model reduces the gap.     

Small-size terahertz spectrometer using the second harmonic of a femtosecond fiber laser

Possible implementations of a small-size terahertz spectrometer with a subpicosecond resolution on the basis of a femtosecond fiber laser are considered. An experimental sample of a spectrometer is fabricated. This spectrometer employs the method of optical rectification in a ZnTe nonlinear crystal and the Dember (photodiffusion) effect on the InAs semiconductor surface to generate terahertz radiation and the polarization-optical method to detect radiation. System operation is demonstrated by an example of measuring the terahertz absorption spectrum of water and determining the refractive index of the β-BBO crystal. The basic spectrometer parameters are found: spectral range, spectral resolution, and dynamic range of the terahertz spectrum amplitude.     

Application of convergent beam electron diffraction in the structural study of high-temperature superconducting oxides

Convergent beam electron diffraction (CBED) is a powerful technique for symmetry study of crystal. It has widespread application in physics and material sciences, as demonstrated in a recent superconducting oxide study. Using this technique, we have studied Ba-La-Cu-O superconductors with a transition temperature of about 40°K and Ba-Y-Cu-O superconductors with a critical temperature (Tc) of about 90°K. We have found that in Ba-La-Cu-O superconductors the superconducting phase La_2?xBa_xCuO_4?y has a distorted K₂NiF₄-type structure and the space group Fmmm. The two other phases in Ba-La-Cu-O superconductors have also been studied. In our Ba-Y-Cu-O superconductors, the Ba₂YCu₃O_7?x compound, which is responsible for 90°K superconductivity, has two different space groups: An orthorhombic space group Pmmm and a tetragonal space group P4mm or P4/mmm.     

A numerical study on an infinite linear elastic Bernoulli-Euler beam on a viscoelastic foundation subjected to harmonic line loads

Journal of Mechanical Science and Technology - This paper presents a numerical study on the low-amplitude responses of an infinite Bernoulli-Euler beam resting on a viscoelastic foundation...     

The effect of continuous and pulsed beam modes on cut path deviation in diode laser cutting of glass

During laser cleaving of brittle materials, with the controlled fracture technique, thermal stresses are generated which induce the crack and extend it along the cutting path, subsequently causing material separation. One of the problems in laser cutting of glass with this technique is the cut path deviation at the leading and the trailing edges of the glass sheet. Previous work with a continuous beam diode laser has shown the deviation to be partly due the high magnitudes of thermal stresses generated near the edges of the sheet. This paper reports on the effects of using a pulsed diode laser to cut soda lime glass. The effect of pulse parameters and cutting speed on the quality output variables such as cut deviation angle and surface finish are studied. Finite element modelling is also used to simulate the effects of the moving beam on stress generations to facilitate the understanding of the process mechanisms, and the results are compared with the experimental data. This work shows how to minimise the cut path deviation at the edges by reducing thermal stresses using optimum pulsed diode laser parameters and providing additional flexibility to the process.     

Effect of high-frequency orbital and vertical oscillations of the laser focus position on the quality of the cut surface in a thick plate by laser beam machining

In laser beam machining with oxygen gas, striations are formed on the cut surface due to the cyclic oxidization reaction, which is affected by the cutting conditions and the thermal properties of the workpiece. The formation of striations causes an increase in surface roughness. In order to reduce the surface roughness, we propose controlling the formation of striations by utilizing multi-DOF oscillation of the focus position of the laser. In this paper, we construct a laser machining system in which positioning control of the focus position is achieved by driving the focal lens. The effect of orbital oscillation of the laser focus position parallel to the top surface of the workpiece and vertical oscillation perpendicular to this surface on the formation of striations was evaluated by performing laser cutting tests on thick mild steel plates. The experimental results show that control of the formation of striations can be realized by choosing the appropriate oscillation conditions. The surface roughness with oscillation was less than half that without oscillation.     

A setup for visualizing the evaporation of a liquid drop using the method of frustrated total internal reflection of a laser beam

Two optical methods for visualizing physical processes that occur in an evaporating liquid drop on a horizontal substrate are considered: the method of frustrated total internal reflection and the interference method. The experimental setup that allows implementation of these methods is described. The obtained experimental data and the results of their processing are presented.     

An experimental study on damage detection of structures using a timber beam

Using vibration methods for the damage detection and structural health monitoring in bridge structures is rapidly developing. However, very little work has so far been reported on timber bridges. This paper intends to address such shortcomings by experimental investigation on a timber beam using a vibration based method to detect damage. A promising damage detection algorithm based on modal strain energy was adopted and modified to locate/evaluate damage. A laboratory investigation was conducted on a timber beam inflicted with various damage scenarios using modal tests. The modal parameters obtained from the undamaged and damaged state of the test beam were used in the computation of damage index, were then applied using a damage detection algorithm utilising modal strain energy and a statistical approach to detect location of damage. A mode shape reconstruction technique was used to enhance the capability of the damage detection algorithm with limited number of sensors. The test results and analysis show that location of damage can be accurately identified with limited sensors. The modified method is less dependent on the number of modes selected and can detect damage with a higher degree of confidence.     

A study on the mixture formation process of evaporating diesel spray by offset incidence laser beam

This paper analyzes heterogeneous distribution of branch-like structure at the downstream region of the spray. The liquid and vapor phase of the spray are obtained using a 35mm still camera and CCD camera in order to investigate spray structure of evaporating diesel spray. There have been many studies conducted on diesel spray structure but have yet only focused on the analyses of 2-D structure. There are a few information which is concerned with 3-D structure analysis of evaporating spray. The heterogeneous distribution of droplets in inner spray affects the mixture formation of diesel spray and the combustion characteristics of the diesel engines. In this study, the laser beam of 2-D plane was used in order to investigate 3-D structure of evaporating spray. The incident laser beam was offset on the central axis of the spray. From the analysis of images taken by offset laser beam, we will examine the formation mechanism of heterogeneous distribution of the diesel spray by vortex flow at the downstream of the spray. The images of liquid and vapor phase of free spray are simultaneously taken through an exciplex fluorescence method. Through this, the branch-like structure consisting of heterogeneous distribution of the droplets forms high concentrated vapor phase at the periphery of droplets and at the spray tip.     

Emission of submicron aerosol particles in operating a laser beam printer

Laser beam printers can be substantial sources of submicron particles in the indoor environment. The present work investigated particle emissions from a commercial laser beam printer (LBP), which was one of single component, non-magnetic, non-contact mode type LBPs, in various operating conditions. Size distribution and number concentration of particles were measured by a scanning mobility particle sizer (SMPS). The size distribution of particles generated from the printer was 20–200 nm in equivalent mobility diameter, regardless of the operating condition. When the fuser system was operated by fuser controller without development and the temperature of the heating roller was 190°C, particles were detected and their peak concentration was about 10³ particles/cm³. Zero percent coverage white papers and five percent coverage black papers, were used, the peak concentrations were 1.5×10⁵ particles/cm³ and 3.3×10⁵ particles/cm³, respectively. These results suggest that the sources of submicron particle generation were rubber of heating roller, paper, and toner.     

A study on eccentric behavior of discharge valve in refrigerant compressor using laser sensors

Journal of Mechanical Science and Technology - A linear compressor for household refrigerators uses a circular plate type discharge valve. The behavior of the discharge valve greatly influences the...     

A study of lubricant film thickness in compliant contacts of elastomeric seal materials using a laser induced fluorescence technique

A laser induced fluorescence technique was used to investigate the build-up of lubricant films in compliant contacts operating in the isoviscous elasto-hydrodynamic regime (I-EHL). The described technique utilises an optimised optical set-up with a relatively high signal-to-noise ratio and was shown to be able to produce film thickness maps of the complete contact area and measure a very wide span of thicknesses, from 50 nm to 100 μm. Maps of film thickness were obtained over a range of entrainment speeds and loads for three different contact configurations and two elastomer materials, polydimethylsiloxane (PDMS) and a fluorocarbon rubber (FKM) which is typically used in rotary seal applications. In a model contact of a nominally smooth PDMS ball sliding on a glass flat, a crescent shaped area of reduced film thickness was observed towards the contact exit. In contrast to typical elasto-hydrodynamic contacts, no side-lobes of reduced film thickness were recorded, while the central film region exhibited a converging wedge shape. The elliptical contact of an FKM O-ring rolling on a flat glass showed a central region of flat film while areas of minimum film thickness were located near the contact edges either side of the centre. The highly conformal contact of relatively rough FKM O-ring sliding against a concave glass lens, a geometry more representative of that found in elastomeric seals, showed discrete regions of reduced film, corresponding to surface roughness asperities. With rising entrainment speed, some lift-off was observed, with surface roughness asperities appearing to be increasingly compressed. Measured films thicknesses were compared to existing theoretical predictions for I-EHL contacts and the level of agreement was found to be highly dependent on contact geometry and applied conditions.     

A complete analysis of the laser beam deflection systems used in cantilever-based systems

A working model has been developed which can be used to significantly increase the accuracy of cantilever deflection measurements using optical beam techniques (used in cantilever-based sensors and atomic force microscopes), while simultaneously simplifying their use. By using elementary geometric optics and standard vector analysis it is possible, without any fitted or adjustable parameters, to completely and accurately describe the relationship between the cantilever deflection and the signal measured by a position sensitive photo-detector. By arranging the geometry of the cantilever/optical beam, it is possible to tailor the detection system to make it more sensitive at different stages of the cantilever deflection or to simply linearize the relationship between the cantilever deflection and the measured detector signal. Supporting material and software has been made available for download at http://www.physics.mun.ca/beauliu_lab/papers/cantilever_analysis.htm so that the reader may take full advantage of the model presented herein with minimal effort.     

A study on fuel spray of spark-ignited direct injection engine using laser image technology

One of the important research for developing a spark-ignited direct injection engine is optimization of the fuel spray distribution and air flow field in the cylinder. Therefore, spray pattern and mean fuel droplet size of swirl injector were investigated using Laser Light Sheet Photography and PDPA' respectively. And, for the formation of stratified mixture with adequate strength near a spark plug at injection mode in compression stroke, spray distribution after impingement on flat piston or bowl piston in a transparent motoring engine was visualized for the three different injector positions. KIA Motors Corp.     

Acoustic beam position monitor for microanalysis of particles in the 10 nm range in a TEM-SCAN system

This paper describes the principle and use of a simple equipment which makes it possible to keep the electron beam in the centre of a small particle analysed by X-ray microanalysis in a STEM system. A deviation from the correct beam position introduced by drift or other deficiencies is monitored by an audible change in a sound frequency and corrected for by a convenient manual operation.     

A study of the cutting modes in the grooving of tungsten carbide

In this paper, the cutting modes for grooving a tungsten carbide work material are investigated and presented. The grooving tests were carried out on an inclined workpiece surface using a solid CBN tool on a CNC lathe. The experimental results indicated that there was a transition from a ductile mode cutting to a brittle mode cutting in the grooving of tungsten carbide workpiece material as the depth of cut was increased from zero to a critical value. Ductile mode cutting is identified by the machined workpiece surface texture and the material removal ratio f _ab -ratio of the average of the volume of material removed to the volume of the machined groove. Scanning electron microscopy (SEM) observations on the machined workpiece surfaces indicated that there are three cutting modes in the grooving of tungsten carbide as the depth of cut increased: a ductile mode, a semi-brittle mode and a brittle mode. The ductile cutting mode depends on the stress in the cutting region, i.e., whether or not the shear stress in the chip formation region is greater than the critical shear stress for the chip formation ( _slip > _c ), and whether or not the fracture toughness of the work material is larger than the stress intensity factor (K ₁<K _c ). When ( _slip < _c ) and (K₁>K _c ), crack propagation dominates, the chip formation and the cutting mode are brittle.Nomenclature A ₁ , A ₂ A cross-section areas of the ridge - A _V A cross-section area of the groove - A _W The value of A _V subtracted by A ₁+A ₂ - F _X The horizontal force - F _Z The vertical force - K _C The fracture toughness - K _I The stress intensity factor - f _ab The work material removal ratio - f _n The normal cutting force - f _t The tangential cutting force - The inclined angle - _c The critical shear stress for dislocation - _slip The shear stress in chip formation zone     

A method of using the incident beam tilt as a eucentric goniometer in transmission electron microscopy

The principal difficulties in constructing and operating a eucentric specimen tilting goniometer in a transmission electron microscope are discussed, together with the goniometric function of the incident beam tilt. The latter function is found easy to operate in a eucentric manner. The imaging beam then will have a non-axial path, which will increase particularly the field chromatic aberration. Earlier, however, a technique for the compensation of the chromatic aberration during displaced aperture dark field image formation has been developed. In combination with this technique, it proved possible to use the ordinary incident beam tilt as a eucentric goniometer. Image sequences were obtained, with accurately varied diffraction conditions. The tilt angles and the direction of the tilt axis can be very accurately determined from the displacements of the diffraction pattern.     

A study of collimation and extraction of the U-70 accelerator beam using an axially oriented crystal

Extraction and collimation of the 50-GeV proton beam with a bent silicon crystal at the U-70 accelerator of the Institute for High Energy Physics (Protvino, Russia) was investigated. Until recently, proton beam extraction (and collimation) from accelerators has been effected using crystals with the (111) or (110) plane orientation, when the beam propagates far from the crystal axes. In the described experiment, the silicon crystal was oriented so that the proton beam was incident on it near the 〈110〉 axis. Under these conditions, a part of the beam was deflected by the crystal owing to the dynamic chaos phenomenon. The maximum beam extraction efficiency was as high as ~80%.