Showing papers in "Optics and Laser Technology in 2002"
TL;DR: In this article, sinusoidal linear fringes are projected on a micro-component surface by a grating phase shifting projector and a long working distance microscope (LWDM), and the image of the fringe pattern is captured by a high-resolution camera and another LWDM and processed by phase-shifting technique.
Abstract: This paper describes the use of optical fringe projection method for 3D surface profile and deformation measurement of micro-components. In this method, sinusoidal linear fringes are projected on a micro-component surface by a grating phase shifting projector and a long working distance microscope (LWDM). The image of the fringe pattern is captured by a high-resolution CCD camera and another LWDM and processed by phase-shifting technique. A simple procedure is described which enables calibration of the optical set-up for subsequent quantitative measurement of micro-components of unknown shapes. This method is relatively simple and accurate, and is capable of conducting fully automated measurements. In this paper, two micro-components, a micro-mirror ( 0.1 mm ×0.1 mm ) and a micro-electrode pad are used to demonstrate deformation measurement and microscopic surface contouring.
87 citations
TL;DR: In this paper, the plasma and spatter generated during laser welding were measured using UV and IR photodiodes and a system was also formulated to perform real time evaluations of the weld quality using a fuzzy multi-feature pattern recognition with the measured signals.
Abstract: Laser welding is one of the most precise welding processes in joining sheet metals. In laser welding, performing real time evaluation of the welding quality is very important to enhance the efficiency of the welding process. In this study, the plasma and spatter, which are generated during laser welding, are measured using UV and IR photodiodes. The factors that influence weld quality are classified into five categories; optimal heat input, slightly low heat input, low heat input, partial joining due to gap mismatch, and nozzle deviation. The data number deviated from reference signals and their standard deviations were also considered to evaluate the qualities. A system was also formulated to perform real time evaluations of the weld quality using a fuzzy multi-feature pattern recognition with the measured signals.
77 citations
TL;DR: A novel approach is proposed to generate the sufficient calibration points with high accuracy for structured light 3D vision inspection based on a flexible calibration target, composed of a photo-electrical aiming device and a 3D translation platform.
Abstract: Structured light 3D vision inspection is a commonly used method for various 3D surface profiling techniques. In this paper, a novel approach is proposed to generate the sufficient calibration points with high accuracy for structured light 3D vision. This approach is based on a flexible calibration target, composed of a photo-electrical aiming device and a 3D translation platform. An improved algorithm of back propagation (BP) neural network is also presented, and is successfully applied to the calibration of structured light 3D vision inspection. Finally, using the calibration points and the improved algorithm of BP neural network, the best network structure is established. The training accuracy for the best BP network structure is 0.083 mm , and its testing accuracy is 0.128 mm .
74 citations
TL;DR: In this paper, an optical method of vortex shape measurement based on Fourier transform profilometry (FTP) and verified it by experiment is proposed. And the results of the experiment proposed in this paper show that FTP can efficiently reconstruct the vortex shape at a free surface and this method is suitable for wide use in studying such problems as liquid shear flow, wake of an object, flow behind a bluff body, and wetting angle.
Abstract: We have proposed an optical method of vortex shape measurement based on Fourier transform profilometry (FTP) and verified it by experiment. The results of our experiment proposed in this paper show that FTP can efficiently reconstruct the vortex shape at a free surface and this method is suitable for wide use in studying such problems as liquid shear flow, wake of an object, flow behind a bluff body, and wetting angle.
66 citations
TL;DR: In this article, the authors measured the refractive indices of eight standard oils from Physikalisch Technische Bundesanstalt, Germany with an accuracy of ± 1×10−4 by using Abbe Refractometer.
Abstract: The refractive indices (n) of eight standard oils from Physikalisch Technische Bundesanstalt, Germany were determined with an accuracy of ±1×10−4 by using Abbe Refractometer. The measurements were performed at temperature 20°C in the spectral range 0.4– 0.7 μm . The experimental data were fitted to the simple Cauchy dispersion formula and the results were found to be consistent within the limits of experimental error. In all cases, the refractive index decreased monotonically with increasing wavelength. The refractive indices (n) of these oils have been measured as a function of the temperature t (20° C up to 50°C) at λ=0.589 μm and were found to have linear temperature dependencies. The refractive indices of the studied oils and the uncertainty in their values are calculated at λ=0.589. The Lorentz–Lorenz (L–L) formula has been tested and it was found to be valid with a maximum deviation of 0.4% and was used to calculate the molecular polarizability θ.
58 citations
TL;DR: In this paper, the authors used femtosecond laser pulses on Si surfaces to create a periodic surface structure in the form of ripples, and the spacing of these ripples was between 0.5 and 2 μm and increased with increasing power density or number of pulses.
Abstract: Laser-induced damage morphology using femtosecond laser pulses on Si surfaces is reported. Damage morphology shows the ablation of material. A magnified view of the ablated portion shows a periodic surface structure in the form of ripples. The spacing of these ripples was between 0.5 and 2 μm and increased, on increasing the power density or number of pulses, and finally broke into parts, leaving well-ordered grains of approximate diameter 5 μm. Also for 100 or larger number of pulses, an amorphous ring in the periphery was formed. The diameter of this ring increased, on increasing either the laser fluence or the number of pulses. The formation of ripples has been explained with the help of the hypothesis of Boson condensation proposed by Van Vechten (Solid State Commun 39 (1981) 1285).
45 citations
TL;DR: In this paper, a femtosecond pulsed laser was used for micromachining on 1000 nm -thick gold film using femto-cond laser pulses of various energies.
Abstract: Laser micromachining on 1000 nm -thick gold film using femtosecond laser has been studied. The laser pulses that are used for this study are 400 nm in central wavelength, 150 fs in pulse duration, and the repetition rate is 1 kHz . Plano-concave lens with a focal length of 19 mm focuses the laser beam into a spot of 3 μm (1/e2 diameter). The sample was translated at a linear speed of 400 μm / s during machining. Grooves were cut on gold thin film with laser pulses of various energies. The ablation depths were measured and plotted. There are two ablation regimes. In the first regime, the cutting is very shallow and the edges are free of molten material. While in the second regime, molten material appears and the cutting edges are contaminated. The results suggest that clean and precise microstructuring can be achieved with femtosecond pulsed laser by controlling the pulse energy in the first ablation regime.
43 citations
TL;DR: In this article, an analytical expression to determine the strongest wavefront curvature which can be measured with a defined micro-lens array of an SHS is derived, which allows to calculate the microlens parameters required to measure the wavefront of a test lens.
Abstract: Aspheric lenses and surfaces are increasingly used in modern high-quality optics. Therefore, new measuring methods for an accurate quantification of these aspheres are also necessary. The current approach to quantify aspheres is to apply null systems such as computer-generated holograms as a part of a null lens in a interferometer. An alternative to this method is the Shack–Hartmann wavefront sensor. The dynamic range of this sensor can be adjusted by the optical parameters of the applied microlens array. Hence, large wavefront aberrations can be measured directly without a null lens. However, there are basic limitations in the dynamic range of a Shack–Hartmann sensor (SHS) depending on the curvature of the incident wavefront. In this paper, an analytical expression to determine the strongest wavefront curvature which can be measured with a defined microlens array of an SHS is derived. It allows to calculate the microlens parameters required to measure the wavefront of a test lens. Particularly, the influence of rotational symmetric aspherical wavefront shapes to the dynamic range of an SHS has been studied. A comparison between interferometry and the SHS has been accomplished. Numerical solutions using scalar diffraction theory illustrate the analytical predictions.
41 citations
TL;DR: In this paper, the authors used femtosecond pulsed laser ablation to produce sub-micron holes with diameters less than 200 nm with a focused laser spot of 1.7 μm.
Abstract: The ability to machine very small features in a material has a wide range of applications in industry. We ablated holes into thin film of 100 nm thickness made from various metals by femtosecond pulsed laser ablation. Using a Ti:Sapphire laser which supplies a laser pulse of 150 fs duration at central spectrum wavelength of 400 nm , we have produced a series sub-micron holes, whose diameters are less than 200 nm with a focused laser spot of 1.7 μm . We found that the material damage threshold has a great influence on the quality of the produced features. Experimental results shows that the heat-affected zone and the degree of being affected reduce with the increase of threshold value.
38 citations
TL;DR: In this paper, a formula for accurate calculation of the absorption coefficient of optical material is deduced by the relationship of its transmissivity, refractive index and absorption coefficient, which can be determined by the instruments or obtained directly from the references.
Abstract: In this paper, a formula for accurate calculation of the absorption coefficient of optical material is deduced by the relationship of its transmissivity, refractive index and absorption coefficient. Because the values of transmissivity and refractive index of the optical material with a higher accuracy can be determined by the instruments or obtained directly from the references, the calculated results of the absorption coefficients with a higher accuracy is certified. The absorption coefficients of some optical materials are calculated with it, and the results are discussed.
34 citations
TL;DR: A substantial increase in the photostability of pyrromethene 567 laser dye solutions and in solid polymer media has been achieved by the addition of coumarin C540 laser dye as mentioned in this paper.
Abstract: A substantial increase in the photostability of pyrromethene 567 laser dye solutions and in solid polymer media has been achieved by the addition of coumarin C540 laser dye. Up to five times increase in photostability of pyrromethene 567 in solid and two times in solution has been observed. The enhanced photostability is attributed to reduction in the effectiveness of in situ oxygen degradation of pyrromethene by the addition of the coumarin.
TL;DR: A new data processing and calibration method for a pronunciation system of an eye-tracking device using both head mounted display (HMD) technology and remote operation capabilities and can be adapted to provide a digital speech function.
Abstract: In this paper, a new data processing and calibration method for a pronunciation system of an eye-tracking device is described. The eye-tracking device was created using both head mounted display (HMD) technology and remote operation capabilities. A pattern recognition computer program was used to distinguish the pupil position and calculate its coordinates. This system can be adapted to provide a digital speech function. A new method for processing the image of the eye in the PC-based system was also developed. With one video CCD camera and frame grabber analyzing a series of human pupil images while the subject is gazing at the screen, an auto-calibration algorithm is used to obtain the direction of the eye gaze in real time. The computers provide the speech sound according to the location where the eye gazes exceed 0:5 s. The availability of multipurpose in this eye-tracking system with very simple equipment will be recon=rmed for future advanced research. ? 2002 Elsevier Science Ltd. All rights reserved.
TL;DR: In this article, the transient deformation of thin grade 304 stainless steel metal sheets heated by a single pulse of a CO2 laser beam is simulated in a three-dimensional thermo-elastoplastic.
Abstract: The transient deformation of thin grade 304 stainless steel metal sheets heated by a single pulse of a CO2 laser beam is simulated in this paper. The laser beam is assumed to be line-shaped and the problem is treated as three-dimensional thermo-elastoplastic. The temperature field, deformation pattern, stress–strain states and the residual stress distribution of the specimens have been calculated numerically and the transient response of the bending angle has been validated by experiments. Good agreement has been obtained between the numerical simulation and the experiments under various operating conditions. The numerical study reveals that a high temperature gradient exists for a positive bending angle and a low one for a negative angle. It transpires that the mechanisms of pulsed laser forming are dependent mainly upon the laser power, the heating time, the clamping arrangement, as well as the geometry, the thermal properties and the original stress states of the specimen.
TL;DR: In this article, an acousto-optically Q-switched intracavity second-harmonic generation of 106 μm in a 19mm-long BiB3O6 crystal, cut for type-I phase-matching direction of (θ,ϕ)=(1689°,90°), performed in a diode-end-pumped Nd:YVO4 laser was investigated.
Abstract: We have investigated the acousto-optically Q-switched intracavity second-harmonic generation of 106 μm in a 19-mm-long BiB3O6 crystal, cut for type-I phase-matching direction of (θ,ϕ)=(1689°,90°), performed in a diode-end-pumped Nd:YVO4 laser When the incident pump power was 43 W at 30 kHz of pulse repetition frequency, a maximum average green output power of 480 mW , the shortest pulse with FWHM width of 72 ns , the highest single pulse energy of 16 μJ and the maximum peak power of 222 W were obtained, giving the corresponding optical conversion efficiency of 112% The effect of varying temperature in BIBO crystal on the average green output power was also investigated
TL;DR: In this article, the propagation formulae of elliptical Gaussian beam through misaligned optical systems in spatial domain and spatial-frequency domain are investigated analytically by using tensor method.
Abstract: The propagation formulae of elliptical Gaussian beam through misaligned optical systems in spatial domain and spatial-frequency domain are investigated analytically by using tensor method. The derived formulae provide a powerful tool for treating the propagation and transformation of elliptical Gaussian beam through misaligned optical systems. As an application example, the propagation properties of elliptical Gaussian beam through a misaligned thin lens are illustrated.
TL;DR: A simple two ordinary lens system is proposed to realize the fractional Fourier transform of continuously variable order while keeping the scaling factors of both the input and output functions as the same constant independent of the geometric parameters of the system and the FRT orders.
Abstract: A simple two ordinary lens system is proposed to realize the fractional Fourier transform (FRT) of continuously variable order while keeping the scaling factors of both the input and output functions as the same constant independent of the geometric parameters of the system and the FRT orders. It can remove the necessity and inconvenience of using input masks of different scales or any other special devices, and then is helpful to those who want to observe the FRT but have no specific facilities.
TL;DR: In this article, a phase shifting Fizeau interferometry was used to measure the refractive index and wedge angle of transparent plates used as optical components in different experiments, and a near IR external cavity diode laser having spectral resolution up to 10−7 was employed to measure a test plate by introducing amplitude modulation technique.
Abstract: It is shown that Fizeau interferometry provides an accurate optical method to measure the refractive index and wedge angle of transparent plates used as optical components in different experiments. A near IR external cavity diode laser having spectral resolution up to 10−7 has been employed to measure the refractive index of the test plates by introducing amplitude modulation technique in the detection system of our phase shifting Fizeau interferometry. Detection of spatial fringes has been performed to find out the wedge angles of the plates by using a He–Ne laser along with the CCD-image sensor.
TL;DR: In this paper, a distributed fiber optic sensor for petroleum hydrocarbon leak detection and localization based on the measurement of transmitted and Rayleigh backscattered power is presented, which includes a sensitive polymer, which reversibly expands in hydrocarbon presence and induces the bending losses in the fiber.
Abstract: A novel type of distributed fiber optic sensor for petroleum hydrocarbon leak detection and localization based on the measurement of transmitted and Rayleigh backscattered power is presented. The sensor structure includes a sensitive polymer, which reversibly expands in hydrocarbon presence and induces the bending losses in the fiber. The location of the loss region is determined from unique relationships between normalized transmitted and Rayleigh backscattered powers for different positions of the disturbance along the test fiber. The localization of a strong disturbance with an estimated accuracy of ±1 m along a 2.844 km -length single-mode fiber was demonstrated.
TL;DR: In this article, a general model to predict and correct the displacement measurement error and error phase map interpretation taking into account the target shape, illumination geometry, and in-plane displacement information is presented.
Abstract: Out-of-plane configurations used in electronic speckle pattern interferometry (ESPI), introduce phase error interpretation in extended target objects due to spatial variation of the sensitivity vector. In this paper, a general model to predict and correct the displacement measurement error and error phase map interpretation taking into account the target shape, illumination geometry, and in-plane displacement information, is presented. This model generalizes and extends previous analyses with respect to the sensitivity vector variations. The model is based on a relationship between variable sensitivity vector and the constant one. The importance of illumination geometry and in-plane displacement as factors that introduce the biggest error in the interpretation of the phase map are stressed. An analysis with practical parameters using divergent and collimated beams is presented. In order to predict and correct the error of phase interpretation, the finite element method should be used to obtain in-plane proportional factors to build up the correction function. The analysis shows that the error can be large for common configurations even when using collimated beam. To compute the measurement directly from the phase map, a general sensitivity function taking into account the shape and in-plane displacement information is naturally obtained from the presented analysis.
TL;DR: In this paper, a path-independent phase unwrapping algorithm is presented, which is based on a parallel elimination of local phase jumps and the subsequent shifts of them, through iterations, to the boundary or to cancel with others in the midway.
Abstract: A newly developed path-independent phase unwrapping algorithm, which is simple and concise, is presented. The algorithm is based on a parallel elimination of local phase jumps and the subsequent shifts of them, through iterations, to the boundary or to cancel with others in the midway. The number of iterations never exceeds the sum of the width and height of the processed map, whereas for cellular automata algorithm, a multiplier of the cycle of iterations by the proposed algorithm herein is easily needed for successful treatment of a same map. The proposed noise-immune algorithm is applied to a phase map of electronic speckle pattern interferometry (without any filtering work) to prove its effectiveness.
TL;DR: In this paper, the effects of the angle of inclination on the flow structure of a straight nozzle on a substrate with varying inclined angles have been simulated numerically and visualized experimentally.
Abstract: In laser cutting, the flow structure around a substrate significantly affects the material removal rate, the cutting depth and the surface finish of the cutting front. In this paper, the phenomena of shock wave that is induced by a supersonic impinging jet emanating from a straight nozzle onto a substrate with varying inclined angles has been simulated numerically and visualized experimentally. The numerical model offers fairly good prediction in comparison with the experiments. It transpires that the angle of inclination has a significant and dramatic effect on the flow structure and that a large wall pressure with a steep gradient can be built up when the angle is large.
TL;DR: In this paper, a laser shadowgraphy method is presented to measure the dynamic contact angle of a sessile drop on a nontransparent metal substrate and simultaneously visualize flow motions inside the drop.
Abstract: A new laser shadowgraphy method is presented to measure the dynamic contact angle of a sessile drop on a nontransparent metal substrate and simultaneously visualize flow motions inside the drop. A collimated laser beam is refracted into the drop, then reflected on the substrate surface and finally refracted out of the drop to form a shadowgraphic image on a screen. The instant diameters of the refracted-shadowgraphic image, cooperated with the corresponding instant contact-diameters of the drop measured from the magnified top view, are used to determine the instant contact angles of the sessile drop. At the same time, flow motions, if any, in the drop can be visualized from the refracted-shadowgraphic image. The new method is demonstrated to be a very simple, accurate, and unique optical technique for simultaneous measuring of the dynamic contact angle of a liquid drop spreading on a nontransparent metal substrate with flow visualization in the drop.
TL;DR: In this paper, a method for tracking boundary layer height from micro-pulse Lidar data is presented, for a continuous 16-hour study conducted on the east coast of the United States.
Abstract: Atmospheric aerosols exhibit a high degree of variability in their properties and their spatial and temporal distribution. Mapping atmospheric aerosols is of great importance for monitoring the effects of anthropogenic activities and natural processes upon local air quality, as well as for producing accurate input for radiative transfer models. To help enhance our understanding of radiative, physical, chemical, and dynamic processes in the atmosphere, laser radar is used to provide systematic monitoring of the temporal evolution of the aerosol rich boundary layer. The Micro Pulse Lidar (Light Detection and Ranging) System is capable of long-term autonomous mapping of vertical aerosol structure. We present a new automated method for tracking boundary layer height from Micro Pulse Lidar data and show the results of this method for a continuous 16 h study conducted on the east coast of the United States.
TL;DR: In this paper, a polymer passive switch based on polyurethane composite and organic dye BDN was developed for the yttrium aluminate laser for the first time, achieving an energy of 0.98 J for a single pulse at passive Q-switching.
Abstract: Stable highly efficient polymer passive switch based on a polyurethane composite and organic dye BDN were developed for the neodymium lasers. The maximum energy of 0.98 J was obtained for a single pulse at passive Q-switching of these lasers. Repetition of single pulses at 50 Hz was possible. Repetitively pulsed operation with a peak output power up to 2 MW and an energy of train of nanosecond pulses 14.1 J were achieved in an yttrium aluminate laser for the first time. Variation of the initial switch transmittance made it possible to vary the pulse (spike) duration in the range 28– 90 ns . The maximum pulse repetition rate in a train was 350 kHz when the Q-switching efficiency was 98%. The damage threshold of the investigated polymer matrix was achieved 14 and 18 J / cm 2 for single pulse duration (15 and 35 ns correspondingly) and 52 J / cm 2 in multi-spike generation regime (duration 80 ns ).
TL;DR: In this paper, a procedure for optimizing the choice of materials for a broad-band retarder is presented, where a combination of three plates of different birefringent materials with properly chosen thicknesses is used.
Abstract: Apochromatic retarders can be constructed by using a combination of three plates of different birefringent materials with properly chosen thicknesses. However, when dealing with a broad wavelength range, their performance depends very much on the materials chosen. A procedure is presented for optimizing the choice of materials for such a broad-band retarder.
TL;DR: In this paper, a long distance alignment technique using the combination of a singlemode optical fiber and a phase plate was developed using the characteristics of the diffraction pattern of a Gaussian beam passing through a π step phase plate.
Abstract: A long distance alignment technique is developed using the combination of a single-mode optical fiber and a phase plate. The characteristics of the diffraction pattern of a Gaussian beam passing through a π step phase plate are analyzed theoretically. The feasibility of the method is validated in theory and with computer-simulation, and the factors affecting the alignment precision are discussed. The reliability of the alignment technique is demonstrated when it is used in the measurement of the straightness of a 12 m -track, in which measured results using the new technique coincide very well with those using an HP5528 dual frequency laser interferometer.
TL;DR: In this article, a diode-pumped high-efficiency Nd:YVO4/LBO red laser was designed using critical phase matching (CPM) LBO, 671 nm red laser from 1342 nm light by intracavity frequency doubling.
Abstract: A design of diode-pumped high-efficiency Nd:YVO4/LBO red laser is reported. Using critical phase-matching (CPM) LBO, 671 nm red laser was obtained from 1342 nm light by intracavity frequency doubling. With an incident pump laser of 800 mW , using type-I and type-II CPM LBO, 97 and 52 mW TEM 00 mode red laser outputs were obtained, with optical-to-optical conversion efficiencies of up to 12.1% and 6.5%, respectively.
TL;DR: In this paper, a simple approach is described and used for on-line measurement of the fractional heat load parameter ξ in an operating diode-pumped Nd:YVO4 laser at 1.06 μm wavelength for different doping concentrations.
Abstract: A simple approach is described and used for on-line measurement of the fractional heat-load parameter ξ in an operating diode-pumped Nd:YVO4 laser at 1.06 μm wavelength for different doping concentrations. The method is based on the fact that if the thermo-optical properties of the sample are known then the ξ-parameter can be estimated from the measured effective focal length induced by the pump beam and any other lensing effect due to mechanical mounting of the sample for a given pumping configuration. The value of the fractional heat-load parameter estimated by our technique was in excellent agreement with the earlier reported values.
TL;DR: In this article, a method is described and used for determination of the effective stimulated emission cross-section ( σ e ) in an operating diode pumped Nd:YVO 4 micro-laser at 1064 nm with various doping concentrations.
Abstract: A practical method is described and used for determination of the effective stimulated emission cross-section ( σ e ) in an operating diode pumped Nd:YVO 4 micro-laser at 1064 nm with various doping concentrations. In this method a micro-laser is formed by keeping a small piece of the sample in a plane–plane resonator under semi-monolithic configuration and a fiber coupled diode laser ( 808 nm ) was used for pumping. The pump power induced thermal lensing effect was used to make the cavity stable. In thermally stabilized solid-state lasers the cavity parameters change dynamically with the pump power and hence the overlap integrals become a function of the absorbed pump power. In our method the overlap integrals were estimated by measuring the thermal lens focal length at the threshold. The value of σ e of Nd:YVO 4 crystal with different doping concentrations obtained by this method were in well agreement with the reported values.
TL;DR: In this article, the temporal speckle pattern interferometry (TSPI) has been applied to measure the displacement caused by low-frequency vibration in TSPI.
Abstract: In this paper, the time sequence phase method (TSPM) has been applied to measure the displacement caused by low-frequency vibration in temporal speckle pattern interferometry (TSPI). The principle is that by capturing the temporal speckle patterns related to the object vibration, the whole-field displacement responses (amplitude and phase) of the vibrating object can be calculated through scanning these fluctuations. Thus, quantitative measurement can be carried out using a conventional ESPI system without a camera synchronized to the object vibration or a phase shifting system. The elaboration on the method is given and experimental results are presented.