Showing papers in "Optics and Laser Technology in 1997"
TL;DR: In this article, an optical system for the parallel evaluation of in-and out-of-plane dynamical deformations is described, where a double pulse laser with pulse separation in the microsecond range is used for the investigations.
Abstract: An optical system for the parallel evaluation of in- and out-of-plane dynamical deformations will be described. A double pulse laser with pulse separation in the microsecond range is used for the investigations. Two separate interferograms of an object under test, in its undeformed and deformed state, are recorded in a few microseconds. The object is illuminated from two different directions and imaged onto a CCD sensor. This produces two sensitivity vectors. The reference beams have different directions in order to produce two directional spatial carriers. The Fourier method is used for quantitative evaluation, and the measurements along different sensitivity vectors are separated in the Fourier domain. The phases of the two interferograms are obtained from the complex amplitudes and the two dimensional deformation is calculated from the phases. Experimental results are presented.
74 citations
TL;DR: In this article, the authors described developments in the CO2 laser cutting of thick ceramic tiles, that is thicknesses of 8.5 mm and 9.2 mm, at a combination of different cutting speeds.
Abstract: This paper details developments in the CO2 laser cutting of thick ceramic tiles, that is thicknesses of 8.5 mm and 9.2 mm. These tiles were cut at a combination of different cutting speeds to determine the necessary cutting parameters for various tile geometries. Different cutting modes were used in conjunction with different cutting speeds to investigate cut quality after laser processing. The work also looked into the effects on cutting through using various shield gases. Multipass cutting and underwater cutting were performed to examine their effects on thermal load during processing.
45 citations
TL;DR: In this paper, a phase-shifted Sagnac interferometer for ultrasound detection has been developed, which is a truly path-matched device, and therefore requires no path stabilization or heterodyning.
Abstract: A compact fibre, phase-shifted Sagnac interferometer for ultrasound detection has been developed. The interferometer is a truly path-matched device, and therefore requires no path stabilization or heterodyning. It is a less expensive and more robust alternative to the heterodyne or path-stabilized Michelson interferometer. The device provides high spatial resolution of ultrasonic detection. It has been used in conjunction with conventional piezoelectric transducers (PZT) to detect Rayleigh and Lamb waves and to image a crack in a thin plate, rivet cracks in riveted plates, and for ultrasonic beam profiling.
36 citations
TL;DR: In this article, the authors describe the experimental results obtained on the Cr 4+ :YAG crystal used as a passive Q-switch in Nd: YAG lasers and investigate the combination of a Cr 4 + : YAG passive Q switch with an acousto-optical Q switch operating simultaneously in one cavity.
Abstract: This work describes the experimental results obtained on the Cr 4+ :YAG crystal used as a passive Q-switch in Nd: YAG lasers. In addition, the combination of a Cr 4+ : YAG passive Q-switch with an acousto-optical Q-switch operating simultaneously in one cavity was investigated. More than 180 W average output in the passive Q-switched mode was obtained with the C 4+ : YAG crystal. The pulse-to-pulse stability was better than 1%. A mode selection occurred when the laser system operated near threshold.
33 citations
TL;DR: In this paper, a dual trap design was proposed for lifting, orienting and depositing of micrometre sized particles as required in the area of micro-machining.
Abstract: Trapping of micro-optical particles in the minimum waist region of highly focused laser beams has been observed for structures such as spheres, cylinders, rings, stars, etc, with dimensions in the 1 to 10 μm range. The non-contact, controlled manipulation and orientation of these objects shows considerable promise for simplifying the assembly, activation, and possibly repair, of micro-machines. A simple model is presented and used as the theoretical foundation for discussing the behaviour of these objects in the beams. The model may also be employed to predict the behaviour of other object geometries not discussed here. A dual trap design is discussed which appears suitable for the lifting, orienting and depositing of micrometre sized particles as required in the area of micro-machining.
25 citations
TL;DR: In this article, an initial study of the use of holographic mensuration, otherwise known as hologrammetry, for the enumeration, sizing and spatial distribution determination of plankton is presented.
Abstract: The distribution and dynamics of particles in the aquatic environment play an important role in the modelling of bio-geochemical processes. Previous work on the measurement of such particles, which vary in size from tens of micrometres (individual cells) to several centimetres (aggregates such as ‘marine snow’), has mainly used electronic counting or conventional photography coupled with image analysis. Here we report on an initial study of the use of holographic mensuration, otherwise known as hologrammetry, for the enumeration, sizing and spatial distribution determination of plankton. We present results on imaging plankton in water tanks using both in-line and off-axis pulsed-laser holography. In this work, we have recorded in-line holograms in a volume of 2400 cm 3 of water with a resolution of better than 20 μm and off-axis holograms in a volume of 36000 cm 3 with a resolution of 140 μm. In both cases, identifiable images of plankton were obtained and precise spatial coordinates determined from the in-line holograms.
24 citations
TL;DR: The possibility of applying adaptive optical technology to underwater imaging is discussed in this article, where an introduction to the history and problems associated with imaging through turbulence is outlined and trends in low-cost adaptive optical technologies and results from a system applied to the correction of water generated turbulence are presented.
Abstract: The possibility of applying adaptive optical technology to underwater imaging is discussed. An introduction to the history and problems associated with imaging through turbulence is outlined. Trends in low-cost adaptive optical technology and results from a system applied to the correction of water generated turbulence are presented. The aim of this paper is to demonstrate the current solutions used in the correction of atmospheric turbulence in the hope of applying these same techniques to underwater imaging and communications.
24 citations
TL;DR: Green Compact Laser Sintering (GCLS) as mentioned in this paper is a new technique for sintering powder metallurgical components by laser irradiation, where powders are pressed into a green compact, which can then be sintered by laser radiation.
Abstract: Green Compact Laser Sintering (GCLS) is a new technique for sintering powder metallurgical components by laser irradiation. After mixing; powders are pressed into a green compact; which can then be sintered by laser irradiation. The properties of powder metallurgical alloys for GCLS and conventional sintering are compared.
19 citations
TL;DR: Here, image restorations of actual physically degraded images are presented, based on a constrained least squares improvement of the original Wiener filter, and it is shown that even for extreme vibrations where the blur extent is much larger than the blurred detail, restoration is quite complete.
Abstract: A method of numerically calculating the optical transfer function appropriate to any type of image motion and vibration, including random, has been recently developed. This method has been verified experimentally with real vibrations, and the close agreement justifies implementation in image restoration from blur deriving from any type of image motion, including random displacement. Here, image restorations of actual physically degraded images are presented, based on a constrained least squares improvement of the original Wiener filter. Even for extreme vibrations where the blur extent is much larger than the blurred detail, restoration is quite complete. The key to restoration is the determination of the optical transfer function unique to the particular image motion and vibration causing the blur. Results are also presented for low vibration frequency motion of random blur extent, as well as for high vibration frequencies.
19 citations
TL;DR: The criteria for determining the theoretical feasibility of LD is discussed, and issues related to future industrial implementation by introducing the process's basic principles are discussed, to compare LD with classical laser processing, which differs not only in the consideration of cutting quality and speed, but also in the cutting irregularities that could be accepted.
Abstract: As the applications of laser processing progress, new fields of use are being investigated, including dismantling with power lasers. To fulfil our dismantling requirements we propose a new laser method that we have called the laser dismantling (LD) process. This cutting method uses a high-power laser at a long distance, without an assist gas, and with a focal length of the system of 1 m to 10 m. Precision and accuracy in the process are not the same as for laser cutting for production and assembly. The first application of the laser dismantling process, on which we demonstrate our method, is the dismantling of obsolete nuclear plants with remote controlled, or automatic, robots in irradiated environments. For our demonstrator, the beam from a Nd:YAG laser was focused by a multimode optical fibre. The objectives of this paper are: to discuss the criteria for determining the theoretical feasibility of LD; to discuss issues related to future industrial implementation by introducing the process's basic principles; and to compare LD with classical laser processing, which differs not only in the consideration of cutting quality and speed, but also in the cutting irregularities that could be accepted.
17 citations
TL;DR: In this article, a high resolution measuring system based on confocal microscopy has been developed for the evaluation of microlens arrays; in particular for applications in confocal imaging itself.
Abstract: A new; high resolution measuring system based on confocal microscopy has been developed for the evaluation of microlens arrays; in particular for applications in confocal microscopy itself. Lenslet arrays for parallel scanning and processing in confocal microscopy were designed as phase-matched Fresnel lenslets and fabricated by direct laser writing. Replica arrays were produced by ultraviolet embossing and hot embossing techniques. Fabricated arrays with a numerical aperture of 0.28 exhibited near diffraction limited performance and a focal length standard deviation of 120 nm in a nominal value of 250 μm. The technique developed represents a convenient and powerful technique for the characterization of lenslet arrays in general.
TL;DR: It will be shown that through the use of CMSD representation, the number of symbolic substitution rules in an optical content-addressable memory (CAM) based system is significantly reduced.
Abstract: A single-step optoelectronics symbolic substitution scheme to handle parallel modified signed-digit (MSD) arithmetic operations is proposed. Conversion algorithms from MSD numbers into a canonical MSD representation are provided. The canonical MSD numbers have the property that no two consecutive digits are non-zero. The addition operation of two CMSD numbers is performed in one step. It will be shown that through the use of CMSD representation, the number of symbolic substitution rules in an optical content-addressable memory (CAM) based system is significantly reduced. The number of symbolic substitution rules can be further reduced to an optimum value through a proposed shared content-addressable memory optical set-up. Further, the proposed optical scheme doubles the storage efficiency of the shared content-addressable memory.
TL;DR: A holographic real image can create an optical replica of an underwater scene, thus allowing measurements of the scene to be undertaken in air in the laboratory, and has many applications, including the study of marine particles and the inspection of offshore oil and gas installations.
Abstract: A holographic real image can create an optical replica of an underwater scene, thus allowing measurements of the scene to be undertaken in air in the laboratory. The methods used to record and replay the holograms are discussed together with an introduction to the problems caused by recording underwater and replaying in air. This technique has many applications, including the study of marine particles and the inspection of offshore oil and gas installations.
TL;DR: In this article, the authors measured the refractive index of pure polyvinyl alcohol (PVA) film and five PVA films, doped with lead acetate of concentrations of 5, 10, 15, 20 and 25% by weight, before and after irradiation by doses of 2, 4, 6, 8 and 10 Mrad gamma rays.
Abstract: Non-localized interference fringes, resulting from illuminating a film of PVA with a laser point source, have been used for measuring the refractive index of such a film. The refractive index of pure polyvinyl alcohol (PVA) film and five PVA films, doped with lead acetate of concentrations of 5, 10, 15, 20 and 25% by weight, have been investigated before and after irradiation by doses of 2, 4, 6, 8 and 10 Mrad gamma rays. It is found that, before irradiation, the refractive index increases with increasing the concentration of doped lead acetate. After irradiation the refractive index increases with increasing the dose up to a certain limit then decreases again. This indicates that the radiation deformation of gamma radiation is a chain scission effect.
TL;DR: In this paper, a fast z-scan method involving a fast-scanning sample holder was proposed to obtain real-time z-scanned traces and greatly improves experimental efficiency and applicability.
Abstract: Traditional z -scan techniques have been used to determine the non-linear optical coefficients of semiconductors. This is usually carried out by scanning a sample along the optical z -axis using a manual or computer-controlled linear translation stage. We report upon a novel z -scan method involving a fastscanning sampleholder: This gives real-time z -scan traces and greatly improves experimental efficiency and applicability. The technique is used here to study the two-photon absorption coefficient of ZnSe.
TL;DR: In this article, the performance of a holographic set-up with a Bi12SiO20 (BSO) photorefractive crystal for measuring vibration amplitudes in a time average holography system was reported.
Abstract: We report the performance of a holographic set-up with a Bi12SiO20 (BSO) photorefractive crystal for measuring vibration amplitudes in a time average holography system. The volume hologram is recorded with the 514.5 nm wavelength of an Ar+ laser. In this set-up the reference beam is sinusoidally phase-modulated with the same frequency of the vibrating object. By increasing the value of the phase modulation, the fringes of the time average pattern run along the object surface, so that the vibration amplitude mapping is carried out. This technique allows the improvement of the measurement sensitivity compared with conventional time average holography, even for interferograms with poor visibility.
TL;DR: In this article, the authors present an approach to the design of such apochromatic combinations which automatically minimizes the residual chromatic aberration over a specific wavelength range, by combining three lenses made of different materials with properly chosen powers and dispersions.
Abstract: Apochromatic objectives are constructed by combining three lenses made of different materials with properly chosen powers and dispersions. This paper presents a novel approach to the design of such apochromatic combinations which automatically minimizes the residual chromatic aberration over a specific wavelength range.
TL;DR: In this paper, a power rippling method was proposed to improve the cut edge quality by disturbing the natural frequency of the periodic striations in high power C02 laser cutting.
Abstract: A power rippling method was proposed in this study to improve the cut edge quality by disturbing the natural frequency of the periodic striations in high power C02 laser cutting. A pilot study was also designed and set up to examine the power responsibility of the laser system, which is externally controlled by a modulated analogue signal from a signal generator. Several aspects were examined in this study. The effects of different power rippling frequencies on the cut surface roughness is the first such aspect, and the different power modulation depth on cut surface roughness is another. The power rippling shape is the third important parameter examined in this study. It was found that the amplitude and frequency of the striation pattern on the cut surface were significantly affected by the characteristics of the rippling power. Cutting quality can be significantly improved by rippling the laser power.
TL;DR: In this paper, a white-light interferometric system with two Michelson interferometers linked by a 100 μm diameter core multimode step index fiber has been investigated, where a signal processing scheme, using curve fitting, has been introduced to suppress the noise induced in the system.
Abstract: A white-light interferometric system, which comprises two Michelson interferometers linked by a 100 μm diameter core multimode step index fibre has been investigated, where a signal processing scheme, using curve fitting, has been introduced to suppress the noise induced in the system. The theoretical resolution of such a sensor with the use of an appropriate curve fitting signal processing scheme has been discussed. The experimental results obtained show the short term repeatability (to three standard deviations) to be better than 5 nm after signal processing, under conditions where the fibre is constantly vibrated in a known and reproducible way.
TL;DR: In this article, the thickness and refractive index of a thick transparent plate are measured by using an unexpanded HeNe laser beam, where the laser beam is incident at different angles onto the plate; and then two reflected beams; from the front and back surfaces; are received on a distant screen: the corresponding separations between them are measured.
Abstract: The thickness and refractive index of a thick transparent plate are measured by using an unexpanded HeNe laser beam. The laser beam is incident at different angles onto the plate; and then two reflected beams; from the front and back surfaces; are received on a distant screen: the corresponding separations between them are measured. A theoretical relation between the refractive index; thickness; angle of incidence and separation is derived. This relation is experimentally verified and shows good agreement. The errors in the measured thickness and refractive index are analysed. The method is non-contact; non-destructive and low cost.
TL;DR: The agreement between the general description of imaging with quasimonochromatic spatially coherent optical fields and the concept of the Schell-model beam is analyzed in this paper.
Abstract: The agreement between the general description of imaging with quasimonochromatic spatially partial coherent optical fields and the concept of the Schell-model beam is analysed. Radiator pairs of object Schell-model beams at the entrance window of the imaging system yield interferograms with different periods, visibilities and fringe orientation onto the entrance pupil, whose superposition determines the intensity distribution there. Furthermore, the structure of the optical field in the entrance pupil will be modified by the properties of the imaging system through their transfer to the exit pupil. Radiator pairs in the exit pupil generate interferograms onto the exit window, whose superposition yields the image intensity distribution. In the case of ideal imaging, the optical field in the exit window will also be constituted by image Schell-model beams, which are a scaled, inverted and proportional version of the object Schell-model beams, and the superposed interferograms in the exit window will be Young's interferograms.
TL;DR: In this paper, the authors describe a new submersible instrument which makes simultaneous measurements of chlorophyll fluorescence, beam attenuation and wide-angle scattering using a single xenon flashlamp as the light source.
Abstract: This paper describes a new submersible instrument which makes simultaneous measurements of chlorophyll fluorescence, beam attenuation and wide-angle scattering using a single xenon flashlamp as the light source Cross-calibration against single-parameter commercial instruments shows satisfactory linear correlations, comparable resolution and enhanced dynamic range The instrument package includes microprocessor control of data acquisition and a rechargeable battery pack It is capable of acquiring high-resolution vertical profiles when deployed from a ship, or bio-optical time series from moorings Results are presented here from initial deployments in inshore waters and in a deck tank at sea
TL;DR: In this article, the authors improved the time averaged frame subtraction technique by subtracting two Bessel fringe patterns at two different force levels, which enabled significant enhancement of fringe contrast and increased measurement sensitivity.
Abstract: The time averaged frame subtraction technique is improved by subtracting two Bessel fringe patterns at two different force levels. The technique enables significant enhancement of fringe contrast and increased measurement sensitivity. The contrast and sensitivity of the fringes obtained at different force ratios are investigated. Both theoretical and experimental results are presented.
TL;DR: In this article, the four-detector photopolarimeter is operated using the compact and easier-to-align corner-cube configuration, and theoretical and experimental instrument matrices are given.
Abstract: The four-detector photopolarimeter is operated using the compact and easier-to-align corner-cube configuration, and theoretical and experimental instrument matrices are given. Experimental results are consistent with theory. Light-beam deviation effects are also analysed and some improvement in the field of view is reported.
TL;DR: In this paper, a grating pattern modulated by deformations, such as dents on the surface of a rotating cylindrical object, is recorded using a TDI camera.
Abstract: This paper explains the application of scanning moire in association with TDI (Time Delay and Integration) imaging for complete peripheral inspection of cylindrical objects. Based on the structured light technique, a grating pattern modulated by deformations, such as dents on the surface of a rotating cylindrical object, is recorded using a TDI camera. The illumination system consists of an intensity modulated, line generating laser diode aligned at an angle to the camera axis. By using the TDI option for recording every nth line, an online scanning moire pattern is generated. After providing a simple explanation of the scanning moire, the effects of object rotation speed and TDI scan speed on the fringe pattern are discussed and demonstrated. The techniques presented here offer low cost solutions to industrial machine vision tasks related to peripheral imaging and inspection of cylindrical objects.
TL;DR: By introducing bipolar carries, a unified negabinary symbolic arithmetic for the two operations can be derived, using only the same six substitution rules.
Abstract: Conventional algorithms process addition and subtraction in different ways. In this paper, by introducing bipolar carries, a unified negabinary symbolic arithmetic for the two operations can be derived, using only the same six substitution rules. Based on the polarization-encoded optical shadow-casting technique, the encoding and decoding patterns for half-addition, half-subtraction and unified arithmetic are designed, with the fixed LED pattern and separate and simultaneous generation of the multi-outputs. The architecture is simple, programmable, cost-efficient, and the addition and subtraction of multiple pairs of bipolar numbers can be handled in parallel in the same manner.
TL;DR: In this article, the characteristics of a 940 nm pumped Cr 4+ :forsterite laser have been investigated using a pulsed color center laser as the excitation source.
Abstract: The characteristics of a 940 nm pumped Cr 4+ :forsterite laser have been investigated using a pulsed colour centre laser as the excitation source. Laser threshold, slope efficiency and temporal behaviour have been determined for high and low Cr 4+ doped material. 940 nm pumping is found to be more efficient than 532 and 730–770 nm excitation. Discrepancies with 1064 nm pumping are attributed to excited state absorption. Absorption saturation measurements have been used to assess the potential applications of Cr 4+ :forsterite, Cr 4+ :YAG and Cr 4+ : Lu 3 A1 5 O 12 (LuAG) as passive Q-switches for Nd lasers in the 940 nm region.
TL;DR: In this article, a system of roughness measurements using a CCD camera and a liquid crystal spatial light modulator (LCSLM) was developed, where scattered light patterns from the surface, which is covered by liquids with several different refractive indices, were acquired by the camera and stored in a frame grabber in a computer.
Abstract: A system of roughness measurements using a CCD camera and a liquid crystal spatial light modulator (LCSLM) has been developed. The scattered light patterns from the surface, which is covered by liquids with several different refractive indices, are acquired by the CCD camera and stored in a frame grabber in a computer. The superposition of two arbitrary patterns is calculated by the computer and displayed on the LCSLM. It is then illuminated by coherent light to produce interference fringes of equal inclination at infinity. The surface roughness can be determined through the relationship between the fringe visibility and the difference of refractive indices. The performance of this system is estimated by experiments.
TL;DR: In this paper, Fan-out energy distribution for substrate-guided wave optical interconnects with a surface-normal configuration is addressed, where up to nine optimized waveguide holograms are independently fabricated on the same substrate.
Abstract: Optimization of fan-out energy distribution for substrate guided wave optical interconnects with a surface-normal configuration is addressed in this paper. Up to nine optimized waveguide holograms are independently fabricated on the same substrate. Energy fluctuation affected by the deviation of the designed diffraction efficiency is theoretically analysed. Using DuPont photopolymer film HRF-600X001-20, we demonstrate 1-to-5 and 1-to-9 surface-normal fan-out devices operating at 850 nm. The output non-uniformities of ±4% and ±10% are experimentally confirmed for the two devices, respectively.