Showing papers in "Optics and Laser Technology in 1994"
TL;DR: In this paper, the phase detection technique can be implemented using a special purpose video processor for phase determination at video rates, making it a very fast algorithm with the main advantage that the traditional phase unwrapping process is not required.
Abstract: An innovative technique for obtaining automatic three-dimensional shape information of a diffuse surface is presented. The technique is based on a new approach of phase measuring from a fringe pattern. The target to be studied is first modulated by projecting a linear grating onto its surface. The linear fringes are deformed according to the surface shape. Demodulation is carried out by determining the phase of these deformed fringes using a novel digital phase locked loop demodulation algorithm. The technique has the main advantage that the traditional phase unwrapping process is not required. The phase is determined continuously as the algorithm scans the two-dimensional fringe pattern. Owing to its sequential nature, this phase detection technique can be implemented using a special purpose video processor for phase determination at video rates, making it a very fast algorithm. The algorithm along with experimental results of real surface profiles are presented.
43 citations
TL;DR: In this article, a non-contact laser (tissue) blood flow meter capable of measuring local blood flow per unit tissue volume is proposed, which utilizes the polarization of laser light to eliminate the light specularly reflected from the tissue surface and an electronic circuit to reduce artefacts caused by temporal changes in the distance between the probe and tissue.
Abstract: A non-contact laser (tissue) blood flowmeter capable of measuring ‘tissue blood flow’ (local blood flow per unit tissue volume) is proposed. The non-contact flowmeter utilizes the polarization of laser light to eliminate the light specularly reflected from the tissue surface, and an electronic circuit to reduce artefacts caused by temporal changes in the distance between the probe and tissue. The probe of the non-contact laser blood flowmeter (LBF) consists of optical fibres and a special polarizer. The tissue sample is illuminated by linearly polarized light, and the light, which is polarized perpendicularly with respect to the polarization of the incident light, is detected by the probe. The non-contact LBF was evaluated using a tissue blood flow model and human fingers. The results show that the values obtained by the non-contact LBF were not influenced by the intensity of the light reflected from the model surface and were hardly affected by temporal changes in the distance between the probe and model. In addition, the values obtained by the non-contact LBF agreed very well with those of a conventional LBF instrument for measurements on human fingers.
25 citations
TL;DR: The trinary logical operations required in MSD additions can be considered as the ‘signed’ version of the logical XOR and AND operations performed in binary addition to achieve efficient design of optical arithmetic and logic unit (ALU) as the binary logic gates can be commonly used to perform both logic and arithmetic operations.
Abstract: We propose here the realization of modified signed-digit (MSD) addition using traditional binary logical operations. The trinary logical operations required in MSD additions can be considered as the ‘signed’ version of the logical XOR and AND operations performed in binary addition. Therefore, MSD additions can be implemented by binary logic gates if the sign information is extracted first and then restored to the binary output. This approach results in an efficient design of optical arithmetic and logic unit (ALU) as the binary logic gates can be commonly used to perform both logic and arithmetic operations.
21 citations
TL;DR: In this paper, a technique called multiple-exposure shearography is presented for direct determination of second-order derivatives of displacements in a plate. But the optical set-up is similar to that of conventional Shearography, and the curvatures and twist of the deflected surface are computed directly from the fringe orders.
Abstract: A technique, called multiple-exposure shearography, is presented in this paper for direct determination of second-order derivatives of displacements in a plate. The optical set-up is similar to that of conventional shearography. Four exposures of the illuminated test specimen on the same photographic film are made. The first exposure is made when the specimen is in its unloaded state, and the second after an incremental load is applied. The third exposure is made when the specimen is shifted slightly whilst it is still under load. Finally, the fourth exposure is made after the specimen is unloaded. The fringe pattern, reconstructed in the same way as in conventional shearography, is related to the second-order derivative of displacements. Hence, the curvatures and twist of the deflected surface are computed directly from the fringe orders.
19 citations
TL;DR: The p -RB (packed redundant binary) number representation introduced in this work has efficiency greater than both RB and MSD (modified signed digit) representations.
Abstract: A family of redundant binary number representations, obtained by generalization of the RB (redundant binary) number representation, is introduced. All these number representations are suitable for optical computing and have properties similar to the RB representation. In particular, the p -RB (packed redundant binary) number representation introduced in this work has efficiency greater than both RB and MSD (modified signed digit) representations. With p -RB numbers the algebraic sum is always permitted in constant time for any efficiency value. p -RB representations also fit in a natural way the 2's complement binary number system. Symbolic substitution truth tables for the algebraic sum and several examples of computation are also given.
17 citations
TL;DR: It has been shown that the methods developed have the potential for use as reflection analysis systems suitable for applications to non-stationary objects and complicated fringe fields.
Abstract: This paper describes the application of a digital Fourier transform to phase encoded intensity distribution. Attention is drawn to a method of extracting quantitative information automatically from the interferometric fringe data. To achieve this, a set of carrier fringes has been added to interferometric fringe data. This has made it possible to form a phase map using a FFT (fast Fourier transform) algorithm. A minimum spanning tree (MST) phase unwrapping strategy has been used to create a contiguous map of the whole fringe field. Finally, the measurement parameter related to the fringe field has been calculated from one single image. Experimental results are given for the burner flames, a compressible flow and photoelastic fringe data. It has been shown that the methods developed have the potential for use as reflection analysis systems suitable for applications to non-stationary objects and complicated fringe fields.
14 citations
TL;DR: In this article, an evanescent field fiber-optic sensor for detecting chlorine in water is proposed and studied experimentally, which is based on the color development of reacting diethyl phenylene diamine with chlorine, forming an azo compound.
Abstract: An evanescent field fibre-optic sensor for detecting chlorine in water is proposed and studied experimentally. The technique is based upon evanescent field absorption through the colour development of reacting diethyl phenylene diamine with chlorine, which forms an azo compound. Sensor systems with single and multi-fibre sensing elements were designed, constructed and evaluated for linearity of response, sensitivity, and reproducibility of results. The experimental results establish the feasibility of detecting low concentration chlorine in water using the proposed method. The results for an improved design are indicative of reasonably good reproducibility and linearity of the sensor response.
13 citations
TL;DR: In this paper, a digital speckle pattern interferometer with optical fibres is proposed for composite materials diagnostics in an operative environment, which can detect disbonds, delaminations and cracks in aircraft components.
Abstract: A digital speckle pattern interferometer with optical fibres is proposed for composite materials diagnostics in an operative environment. Detection of a variety of flaws, such as disbonds, delaminations and cracks in aircraft components, is reported. Additional fringes are introduced for linearizing the fringe pattern and obtaining quantitative deformation measurements by Fourier transform analysis.
13 citations
TL;DR: In this article, beam sampling mirrors, which are basically shallow gratings, are applied to give an accurate sample of the original beam without deteriorating it, and first results using these elements are presented.
Abstract: In laser machining great interest has been shown in diagnostic tools for on-line testing and correcting. We present here beam sampling mirrors, which are basically shallow gratings, and which can be applied to give an accurate sample of the original beam without deteriorating it. The method compares favourably with other techniques for beam diagnostics. First results using these elements are presented.
11 citations
11 citations
TL;DR: A 2-bit trinary full adder using a restricted set of a modified signed-digit trinary numeric system is designed, which is able to operate at a speed independent of the size of the operands.
Abstract: A 2-bit trinary full adder using a restricted set of a modified signed-digit trinary numeric system is designed. When cascaded together to design a multi-bit adder machine, the resulting system is able to operate at a speed independent of the size of the operands. An optical non-holographic content addressable memory based on binary coded arithmetic is considered for implementing the proposed adder.
TL;DR: Time analysis indicates that order statistics can be done more efficiently on a linear array with a pipelined optical bus than with an electronic bus, suggesting that optical buses may emerge as a powerful communication mechanism for connecting large parallel computer systems in the near future.
Abstract: Processor arrays with an optical bus are introduced for parallel computation in this paper. We use the order statistics problem as an example to demonstrate how to design efficient parallel algorithms on such systems. Besides proposing a new algorithm on the model, some basic data movement operations involved in the algorithm are discussed. We believe that these operations can be used to design other parallel algorithms on the same model. Time analysis indicates that order statistics can be done more efficiently on a linear array with a pipelined optical bus than with an electronic bus. The initial results are promising, and the author believes that optical buses may emerge as a powerful communication mechanism for connecting large parallel computer systems in the near future.
TL;DR: In this paper, a hybrid optical/digital joint-Fourier correlation system using a liquid crystal light valve is presented for fingerprint identification using a Mach-Zehnder interferometer as the fingerprint negative input device.
Abstract: A hybrid optical/digital joint-Fourier correlation system using a liquid crystal light valve is presented for fingerprint identification. A Mach-Zehnder interferometer is used as the fingerprint negative input device and characteristics of real fingerprints are investigated in detail. The definitions of the cross-correlation peak as well as the identification criteria are modified by introducing the power density. A spatial band-pass filtering is adopted to surpress effectively the background noise, and the identification performance is significantly improved. Experimental results are given.
TL;DR: The peak pressure in the unfocused shock was found to be 3.2 MPa and 4.6 MPa for the Schlieren and piezoelectric transducer measurements respectively as mentioned in this paper.
Abstract: Schlieren photography has been used to analyse quantitatively the acoustic field of an electromagnetic acoustic transducer (EMAT). By measuring the angle through which the rays are refracted it is possible to compute the refractive index gradient and thus determine both the absolute and complex pressure related structures of the images. Using this method, planar and focused shock transients generated by the EMAT have been evaluated and compared with transducer derived pressure measurements. The peak pressure in the unfocused shock was found to be 3.2 MPa and 4.6 MPa for the Schlieren and piezoelectric transducer measurements respectively. Corresponding values for the focused shock-wave agreed to within experimental error at about 19 MPa.
TL;DR: Simulation results are presented showing the benefits of using error-correcting codes with digital partitioning, and an analysis of the time requirements for encoding and decoding the error-Correcting codes and the effect on system throughput.
Abstract: Digital partitioning is a promising new technique for achieving high accuracy computations on analogue optical matrix-vector processors. One potential drawback of digital partitioning is its sensitivity to errors. Error-correcting codes can enhance the performance of the digital partitioning algorithm by reducing the sensitivity to errors. Simulation results are presented showing the benefits of using error-correcting codes with digital partitioning. In addition, an analysis of the time requirements for encoding and decoding the error-correcting codes and the effect on system throughput is presented.
TL;DR: A fully functional optical pipeline adder based on systolic arrays and optical symbolic substitution (OSS) is demonstrated and the design concept includes the possibility of microintegration by adapting the modular system design to features of typical micro-optical devices.
Abstract: A fully functional optical pipeline adder based on systolic arrays and optical symbolic substitution (OSS) is demonstrated. By pupil division four OSS-rules are applied to a dataplane in one single optical path. The design concept includes the possibility of microintegration by adapting the modular system design to features of typical micro-optical devices.
TL;DR: In this article, a two-dimensional time-dependent model, based on heat transfer and energy conservation theory, has been developed to simulate the transient material behaviour in laser microspectral analysis (LMA).
Abstract: The interaction between laser radiation and target material plays an important role in understanding and controlling any material processing technique involving lasers. In this paper, a two-dimensional time-dependent model, based on heat transfer and energy conservation theory, has been developed to simulate the transient material behaviour in laser microspectral analysis (LMA). The spatial and temporal profile of the laser beam and the temperature dependent properties of the material, such as absorptivity, heat capacity and thermal conductivity, are considered. Finally, the experimental and computational results are compared and the interaction between the laser radiation and workpiece are discussed.
TL;DR: In this article, a supersonic chemical oxygen-iodine laser of 5 cm long active medium has been operated utilizing a simple sparger-type O 2 (1 Δ) chemical generator and a medium size pumping system.
Abstract: A supersonic chemical oxygen-iodine laser of 5 cm long active medium has been operated utilizing a simple sparger-type O 2 ( 1 Δ) chemical generator and a medium size pumping system. A grid nozzle was used for iodine injection and supersonic expansion. 9 W of cw laser emission at 1315 nm were obtained in the present experiments. The small size and the simple structure of the laser system and its stable operation for long periods make it a convenient tool for studying parameters important for high-power supersonic iodine lasers.
TL;DR: In this paper, a spatially resolved temperature measurement in a spinning pipe gas lens of aperture 2.25 cm and length 1 m was performed, where Ray tracing through the measured refractive index profile was performed.
Abstract: A spatially resolved temperature measurement in a spinning pipe gas lens of aperture 2.25 cm and length 1 m, is presented. Ray tracing through the measured refractive index profile was performed. We show that by reducing the optical aperture of the lens (to 1 cm), an angular resolution of twice the diffraction limited is obtainable.
TL;DR: In this paper, an improvement of the single line output power of a tunable cw CO laser was described, which reached 9.16 W m -1, which was almost twice the best reported value.
Abstract: Enhancement of the single line output power of a tunable cw CO laser is described. With the methods of fast flow and better precooling, the specific output power of line 9-8P (14) reaches 9.16 W m -1 , which is almost twice the best reported value. The consumption of working gas is greatly reduced by combining fast recirculation with slow exchange.
TL;DR: In this article, the authors attempted to optimize the flashlamp pumping of a titanium-doped sapphire rod, which is 8 mm diameter by 152.4 mm (6 inches) length.
Abstract: In this work, we attempted to optimize the flashlamp pumping of a titanium-doped sapphire rod. The dimensions of this rod are 8 mm diameter by 152.4 mm (6 inches) length. First, we realized a fast discharge circuit (2 μs FWHM) with six flashlamps. Afterwards, we used a four-flashlamp system with an enlarged discharge being shaped by a PFN (Pulse Forming Network). The first set-up yielded 530 mJ of output energy with an electrical-to-optical efficiency of 0.265%, whereas the second set-up yielded 3 J with an efficiency of 0.8% in the relaxed mode centred at 782 nm.
TL;DR: A simple angle-limited integrated scattering (ALIS) measurement technique is described in this article, where the relation between the measured scattering within a limited solid angle and the root-mean-square (RMS) roughness of the surface under test is investigated.
Abstract: A simple angle-limited integrated scattering (ALIS) measurement technique is described. The relation between the measured scattering within a limited solid angle (ALIS) and the root-mean-square (RMS) roughness of the surface under test is investigated. The technique is applied to the in-workshop inspection of the optical polishing process.
ENEA1
TL;DR: In this article, the influence of the current return geometry on the electric field uniformity in the discharge laser chamber is studied, and a suggestion for better electrode profiles, giving lower electric field spatial gradients, is proposed.
Abstract: The influence of the current return geometry on the electric field uniformity in the discharge laser chamber is studied, and a suggestion for better electrode profiles, giving lower electric field spatial gradients, is proposed.
TL;DR: In this article, the use of optical correlation of speckle patterns to detect and analyse the metallic oxidation phenomena in real time at environmental temperatures is reported, and preliminary results are reported.
Abstract: The aim of the present paper is to report preliminary results on the use of optical correlation of speckle patterns to detect and analyse the metallic oxidation phenomena in real time at environmental temperatures.
TL;DR: In this paper, the coupling coefficient contour map of a five-layer slab waveguide structure having a general trapezoidal grating was computed, for both the first and second-order Bragg diffraction gratings.
Abstract: The coupling coefficient contour map of a five-layer slab waveguide structure having a general trapezoidal grating has been computed. Calculations have been carried out for both the first and the second-order Bragg diffraction gratings.
TL;DR: The intrinsic slope efficiency has been determined to be 8.84, 2.25%, and 1.25% from Nd: KGW, YAG, and SGGM.
Abstract: Laser emission at 1.06 μm has been observed from Nd: doped YAG, KGW and SGGM crystals pumped by a linear Xe-gas filled flashlamp in the input energy range of 1–25 J. The intrinsic slope efficiency has been determined to be 8.84%, 2.25% and 1.25% from Nd: KGW (Nd: 3% atomic), Nd: YAG (Nd: 1.0% atomic) and Nd: SGGM (Nd: 4% atomic), respectively.
TL;DR: In this article, a finite element method is described that enables the modelling of the non-linear dual waveguide structure for arbitrary waveguide shapes, and nonlinearity is handled by iteration and assuming an equivalent nonlinear relative permittivity.
Abstract: Optically controlled two-way optical switches are useful for high-speed photonic switches and rapidly reconfigurable optical interconnection networks. A directional coupler forms such a switch because the field can be switched from one waveguide to the other by altering the optical length of the waveguide. Nonlinear materials are incorporated in the waveguide so that the optical path length may be altered by using an optical control beam to vary the intensity of light. A finite element method is described that enables the modelling of the non-linear dual waveguide structure for arbitrary waveguide shapes. Spurious modes are avoided in the transverse magnetic field method and non-linearity is handled by iteration and assuming an equivalent non-linear relative permittivity.
TL;DR: It is found that the application of fuzzy set theory in grating manufacturing reduces the cost of the process and improves the quality of the grating.
Abstract: In this paper a fuzzy model for fabricating planar-grating is given. In the model, the diffraction efficiency of the holographic grating (predicted by computer simulation) has a reasonable match with the experimentally verified results. The method can be summarized in three steps: first, a choice of the grating characteristics, which are closely related to the diffraction efficiency factors, is made; secondly, according to our experience, we construct the fuzzy matrix from the grating manufacturing parameters and the grating characteristics; finally, we use the fuzzy matrix composition to obtain the diffraction efficiency factors. Then, coupled wave theory is used to predict the diffraction efficiency. The comparisons between the results of this fuzzy model and experiments are given. It is found that the application of fuzzy set theory in grating manufacturing reduces the cost of the process and improves the quality of the grating.
TL;DR: In this paper, the authors investigated the gas stabilities of a CO laser using electrodes of several kinds of metal materials, including aluminium, phosphorus copper, OFHC copper, silver copper, stainless steel, nickel and tantalum.
Abstract: Laser gas stabilities of a CO laser using electrodes of several kinds of metal materials are investigated. These materials are aluminium, phosphorus copper, OFHC copper, silver copper, stainless steel, nickel and tantalum. From analysis of the adhesion on the surface of the electrode after discharge, we get the information about the surface variation, and this can be the basis according to which we can select a suitable electrode material. We find that tantalum is a relatively good electrode material for CO lasers.
TL;DR: In this paper, a compact, reduced-cost optical fiber sensor is presented for the combined measurement of the size, density, and relative refractive index of monodispersive particulates.
Abstract: A compact, reduced-cost optical fibre sensor is presented for the combined measurement of the size, density, and relative refractive index of monodispersive particulates. The sensor uses multimode optical fibres and GRIN rods to analyse scattering and absorption at multiple wavelengths and detection angles. The particle size, density and refractive index values were obtained through calibration.