Showing papers in "Optics and Laser Technology in 1993"
TL;DR: In this article, a single-mode linear channel waveguide array with device packaging density of 1250 channels cm-1 has been achieved, and the first 12-channel wavelength division demultiplexer working at 830, 840, 850, 860, 870, 880, 890, 900, 910, 920, 930 and 940 nm on a GaAs substrate is described.
Abstract: A myriad of passive and active guided-wave devices has been successfully demonstrated using the photolime gel polymer. These include high density linear and curved channel waveguide arrays, electro-optic modulator and modulator arrays, highly multiplexed waveguide holograms for wavelength division demultiplexing and optical interconnects, waveguide lens, and rare-earth ion-doped polymer waveguide amplifiers. A single-mode linear channel waveguide array with device packaging density of 1250 channels cm-1 has been achieved. The first 12-channel wavelength division demultiplexer working at 830, 840, 850, 860, 870, 880, 890, 900, 910, 920, 930 and 940 nm on a GaAs substrate is also described in this paper. A polymer-based electro-optic travelling wave modulator with 40 GHz electrical bandwidth is further delineated. A rare-earth ion-doped polymer waveguide amplifier working at 1.06 μm with 8.5 dB optical gain is also achieved using this polymer matrix. The tunability of the waveguide refractive index of photolime gel polymer allows the formation of a graded index (GRIN) layer. As a result, these active and passive guided wave devices can be realized on any substrate of interest. High quality waveguides (loss<0.1 dB cm-1) have been made on glass, LiNbO3, fused silica, quartz, PC board, GaAs, Si, Al, Cu, Cr, Au, Kovar, BeO, Al2O3 and AIN.
67 citations
TL;DR: In this paper, an attempt to solve the heat diffusion equation of the laser heating problem is made by suggesting a solution which satisfies the physical and mathematical requirements of the problem by considering a constant laser irradiance for the cases of constant and temperature-dependent optical absorbance of the slab front surface.
Abstract: An attempt to solve the heat diffusion equation of the laser heating problem is made by suggesting a solution which satisfies the physical and mathematical requirements of the problem This was done by considering a constant laser irradiance for the cases of constant and temperature-dependent optical absorbance of the slab front surface For both cases, expressions for the temperature profile in the slab material, its front and rear surface temperatures, the thermal penetration depth and the time required to initiate damage (melting) are obtained for intervals less or greater than the transit time As an illustrative example, computations are carried out on an Al-slab
28 citations
TL;DR: Common referencing techniques used to provide immunity against the undesirable variable optical losses in analogue intensity modulated optical fibre sensors are described.
Abstract: Common referencing techniques used to provide immunity against the undesirable variable optical losses in analogue intensity modulated optical fibre sensors are described. Major strategies are investigated using a simple analytical approach to assist in the evaluation of each scheme for its referencing effectiveness. The techniques are assessed for their operational efficiency in the areas where predominant common-mode variations are experienced; namely those areas associated with optical source variations and those variations caused by optical propagation factors.
26 citations
TL;DR: In this article, a diode-pumped Nd: YAG laser with a high repetition rate for applications in small-size lidars was developed for airborne remote sensing of clouds.
Abstract: A new diode-pumped Nd: YAG laser with a high repetition rate, for applications in small-size lidars, has been developed. In this paper first results from airborne measurements are presented. Together with a sophisticated receiver set-up for detection of multiple scattering and depolarization effects, this new laser offers a unique possibility for airborne remote sensing of clouds.
23 citations
TL;DR: In this paper, the phase fringes produced by a series of small incremental deformations are digitally added together to obtain fringes representing the total deformation, and the phase shifting speckle interferometer is used to improve the quantity and quality of phase frings.
Abstract: The phase fringes produced by a series of small incremental deformations are digitally added together to obtain fringes representing the total deformation. The development of such an interferometric method to improve the quantity and quality of phase fringes using a phase shifting speckle interferometer in the measurement of solid deformation is reported
17 citations
TL;DR: A number of optical techniques used for extracting quantitative information about the velocity components in a flow field are considered in this article, where the techniques described in this paper provide information that augment measurements using the traditional methods such as, hot-wire and laser Doppler anemometry.
Abstract: A number of optical techniques used for extracting quantitative information about the velocity components in a flow field are considered. The techniques described in this paper provide information that augment measurements using the traditional methods such as, hot-wire and laser Doppler anemometry. The principle underlying each technique is based on introducing individual flow tracers in a flow field and extracting information about their simultaneous displacements over a short interval of time. The high spatial resolution and good accuracy achieved by these techniques are mainly attributed to the significant advances made in the field of image processing technology.
15 citations
TL;DR: It is shown that principal component reconstruction can yield a remarkable improvement of accuracy and robustness of range data.
Abstract: In direct-detection imaging, laser radar speckle noise, drop-outs, and outliers have to be considered in order to ensure high accuracy and reliability of measurement data. The most common approach for the stabilization of laser radar data is temporal averaging over several shots. This, however, is not in all cases the best method for the reconstruction of noisy image data. It is shown that principal component reconstruction can yield a remarkable improvement of accuracy and robustness of range data.
14 citations
14 citations
TL;DR: In this article, the authors measured the refractive power of two flashlamp-pumped Nd:YAG rods and found that the lifetime of this non-radiative transition decreases with increasing pumping power per pulse and saturation at a value of 0.63 times the fluorescence lifetime occurs.
Abstract: The refractive power of two flashlamp-pumped Nd:YAG rods was measured as being dependent on the output coupling of the resonator. With laser oscillation, the refractive power or thermal heat is decreased by up to 15% and a minimum occurs at a specific output coupling. The experimental results could be explained by a theoretical model assuming a non-radiative transition from the upper laser level to the ground state. The lifetime of this non-radiative transition decreases with increasing pumping power per pulse and, for pumping power higher than 100 kW, saturation at a value of 0.63 times the fluorescence lifetime occurs. The results indicate that the non-radiative process is caused by energy migration to flashlamp-induced transient quenching centres.
14 citations
TL;DR: In this paper, LiF:F-2 crystal was used as a passive Q-switching modulator to achieve an average output power of 220 W from a Nd:YAG slab laser.
Abstract: By using a LiF:F-2 crystal as a passive Q-switching modulator an average output power of 220 W was achieved from a Nd:YAG slab laser. The oscillator-amplifier resonator configuration under investigation delivered a peak pulse power up to 3 MW and a pulse energy of 0.31 J, pulse width of 100 ns.
TL;DR: In this article, an alternative approach, based on accurate finite-fringe detection moire deflectometry, is described for the measurement of radius of curvature, supported by experimental verification.
Abstract: Moire deflectometry, based on infinite fringe detection, is a sensitive and advantageous method for the precise measurement of optical parameters. An alternative approach, based on accurate finite-fringe detection moire deflectometry, is described for the measurement of radius of curvature. An error estimation of the method, supported by experimental verification, is also presented. Extension of the method for the measurement of a long radius of curvature has also been suggested.
TL;DR: In this paper, laser holographic interferometry is applied to the detection of impact-induced damage and marcels in graphite-epoxy composites, and pseudo-3D images of the deformed surfaces are obtained which provide a very clear picture of the effect of the defect.
Abstract: Laser holographic interferometry is applied to the detection of impact-induced damage and marcels in graphite-epoxy composites. Real-time and two-reference-beam interferometry are implemented while the specimens are thermally strained. For small temperature increases irregular fringe patterns are observed, indicative of deformation anomalies, and consequently, of the presence of defects. For the impacted specimens, closed-shape fringes begin to form at the impacted areas, and the more damaged the specimen, the sooner their appearance and their extent. For the specimen containing the marcels the fringes appear very wavy. In both cases pseudo three-dimensional images of the deformed surfaces are obtained which provide a very clear picture of the effect of the defect.
TL;DR: Experimental results using the combination method showed better images than those obtained by the iterative method alone, when referred to results from synthesized holograms.
Abstract: Two-level quantized phase holograms produced by using a combination of an iterative method and an error diffusion method are presented. By using a previously proposed iterative method, images reconstructed from two-level quantized phase holograms are rapidly improved with small amounts of iterative operations but further improvement of the image quality is difficult even if the iterations are greatly increased. Therefore, in order to exceed the improvement limitation of the image quality, the combination of the iterative method and an error diffusion method was used for the hologram-making process. Experimental results using the combination method showed better images than those obtained by the iterative method alone, when referred to results from synthesized holograms.
TL;DR: In this article, the transmission properties of two different types of all-silica fibres, step index and graded-index fibres were investigated using a multimode high-power cw Nd:YAG rod laser.
Abstract: The transmission properties of two different types of all-silica fibres, step index and graded-index fibres, are investigated using a multimode high-power cw Nd:YAG rod laser. The reflections from the fibre surface back into the laser cavity affect the laser power and the beam parameters, waist diameter and divergence. A set-up for simultaneously measuring these values in front of and behind a fibre is presented. The maximum laser power transmitted by fibres is dependent upon the beam parameters, the fibre design and the surface conditions. An upper limit for the maximum divergence which can be coupled into a fibre with a certain numerical aperture without loss is given. The beam parameters behind the fibre, related to the input parameters, are presented.
TL;DR: In this article, a birefringent fiber-optic bio-medical sensor suitable for monitoring the human heartrate is presented, where the human finger is used as the bio-mechanical interface and the fibre is located external to the patient.
Abstract: A birefringent fibre-optic bio-medical sensor suitable for monitoring the human heart-rate is presented here. The human finger is used as the bio-mechanical interface and the fibre is located external to the patient. The heart-rate information is extracted from the fast Fourier transform of the original arterial pressure waveform and this makes the sensing technique immune to noise sources such as temperature variations and patient finger movement.
TL;DR: In this article, a method for obtaining an accurate real-time measurement of the refractive index of liquids is described based on a modification of the Pulfrich refractometer.
Abstract: A method is described for obtaining an accurate real-time measurement of the refractive index of liquids. It is based on a modification of the Pulfrich refractometer. The optical arrangement is suitable for in-line industrial applications where a continuous measurement is required. Some experimental results are presented which confirm the feasibility of the method.
TL;DR: Using fast Fourier transform and PC-based electronic speckle pattern interferometry, the out-of-plane displacement is measured by detecting the peak frequency in the spatial spectrum as mentioned in this paper.
Abstract: Using fast Fourier transform and PC-based electronic speckle pattern interferometry, the out-of-plane displacement is measured by detecting the peak frequency in the spatial spectrum. An analysis has been made to show that this method can also be applied to non-uniformly spaced fringes when the deformation can be expressed in second-order Taylor series. The accuracy is shown to be good and the measurement and computing time for one point takes 200 ms.
TL;DR: An efficient technique for the design of multiple-valued logic circuits using polarization-encoded optical shadow-casting is presented and a trinary full subtracter is designed using this technique.
Abstract: An efficient technique for the design of multiple-valued logic circuits using polarization-encoded optical shadow-casting is presented. As an illustration, a trinary full subtracter is designed using this technique. The resulting logic unit is compared with those obtained by using other algorithms.
TL;DR: In this paper, the trap density in Ta: KNbO 3 and BaTiO 3 is measured at 823 nm using a laser diode and is compared with values at 514.5 nm.
Abstract: Using the shallow-trap model, the effective trap density in Ta: KNbO 3 and BaTiO 3 is measured at 823 nm using a laser diode and is compared with values at 514.5 nm. A reduction of trap density is shown at the longer wavelengths. Exponential gain coefficients are given as a function of geometry for both crystals in the near-infra red. The effect of angular bandwidth on gain and its effect on image amplification is also examined.
TL;DR: In this paper, a three-dimensional calculation of the amplified spontaneous emission (ASE) is presented that allows rapid determination (with suitable approximation techniques) of the gain-length product (GLP) in high power slab amplifiers.
Abstract: A three-dimensional calculation of the amplified spontaneous emission (ASE) is presented that allows rapid determination (with suitable approximation techniques) of the gain-length product (GLP) in high-power slab amplifiers. These calculations include non-saturable absorption, ASE line-narrowing effects, and total internal reflections (TIR) at the pumping surfaces. A parametric study of the slab geometry is presented and compared with experimental results. A good qualitative agreement between theory and experiment is achieved.
TL;DR: In this article, a simple method to determine the fringe orders at points between fringes in holographic interferometry is presented, based on the use of two reference beams in the recording and reconstruction of the interferogram.
Abstract: A simple method to determine the fringe orders at points between fringes in holographic interferometry is presented. The method is based on the use of two reference beams in the recording and reconstruction of the interferogram. A phase difference is imposed between the reference beams on reconstruction through polarization elements. The interferogram is viewed through a polarizer to recombine the images. The fractional fringe order is obtained from the angle through which the polarizer is rotated to shift the adjacent fringe to the point of interest.
TL;DR: The MOD's use of QRA in laser safety is cited as an example of a useful tool, the use of which should not be precluded by further legislation.
Abstract: Since 1976 the United Kingdom Ministry of Defence (MOD) has used quantitative risk assessment (QRA) as a tool to manage the risks involved with airborne laser rangefinders and target designators. It has done this against the background of the Health and Safety at Work Act (1974) and the regulations made under this act. These apply equally to MOD and civilian employers. More recently there has been legislation requiring that all risks should be assessed. The MOD's use of QRA in laser safety is cited as an example of a useful tool, the use of which should not be precluded by further legislation.
TL;DR: In this paper, the authors measured the temperature dependence of the losses in a 8.5 m long commercial Nd3+ doped fiber (York, ND 95020/E) and found that reabsorption from the thermally populated 4l 11 2 level is the dominant contribution to the measured losses.
Abstract: Resonance absorption, the reabsorption of laser light by the laser transition of the dopant material itself, is found to be the limiting factor for fibre lasers when extremely long fibres are used. We report on measurements of the temperature dependence of the losses in a 8.5 m long commercial Nd3+ doped fibre (York, ND 95020/E). To determine the reabsorption losses, the threshold power has been measured as a function of temperature between 243 K and 413 K. The results are compared with theory assuming a 4l 11 2 level energy of 2110 cm-1 and an absorption cross-section of δ = 1.15 x 10-20cm2. The comparison shows that reabsorption from the thermally populated 4l 11 2 level is the dominant contribution to the measured losses.
TL;DR: In this article, a simple method of producing stable discharges with a turbulent field in an axial fast-flow cw-CO2 laser is reported. But the system has provided an output power of 600 W with a beam divergence of 1.9 mrad and an electro-optic efficiency of 14%.
Abstract: A simple method of producing stable discharges with a turbulent field in an axial fast-flow cw-CO2 laser is reported. Design features and operational characteristics of the laser are described. The system has provided an output power of 600 W with a beam divergence of 1.9 mrad and an electro-optic efficiency of 14%.
TL;DR: It is shown that, in some cases, the new rules for the classification of extended sources are too restrictive, which could seriously limit the use of light-emitting diodes (LEDs), which are now included in the scope of the standard.
Abstract: The hazard for the eye produced by extended sources depends on the size of the source and the imaging devices used between the source and the eye. Formerly, the maximum permissible exposure was described in international standards such as IEC 825, by giving a limit value for the radiance. As a result of biological data, which show that the permissible irradiance on the retina decreases in inverse proportion to the size of the image on the retina, this international standard has recently been changed. Ocular hazards associated with extended sources are discussed from these aspects and typical examples are given of how these hazards should be assessed. It is shown that, in some cases, the new rules for the classification of extended sources are too restrictive. This could seriously limit the use of light-emitting diodes (LEDs), which are now included in the scope of the standard.
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TL;DR: In this article, the concept of a pulsed gas lens is proposed and potential applications are envisaged and preliminary experiments with pulsed ray refraction are reported, but this work is limited to a single image.
Abstract: The concept of a pulsed gas lens is proposed. Potential applications are envisaged and preliminary experiments with pulsed ray refraction are reported.