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In a 3-level system with a cascade configuration of the energy levels the process of stimulated 2-photon emission produces anisotropy and asymmetry of the amplification or absorption lineshape. In order to analyse the possibility of a tunable 2-photon laser, some properties of He-Ne cascade lasers were investigated theoretically and experimentally. The cascade oscillates simultaneously on the 3s2-3p4 transition at 3.4 μm and on the 3p4-2s2 transition at 2.4 μm. The amplification anisotropy was observed in a unidirectional ring laser, giving the first proof of strong field 2-photon gain from a continuous incoherently produced population inversion. The amplification asymmetry was measured in a standing wave laser and was used to tune the laser beyond the limits nredicted by single-photon theory. The experiments indicate the possibility of extending the tuning range into the region of "pure" 2-photon oscillation.
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Materials requirements and possible materials for optical second-harmonic generation of laser diode radiation will be discussed. It will be shown, that KNbO3 is an almost ideal material for frequency doubling Ga1-xAlxAs injection lasers operating at room temperature. In a pulsed mode of operation up to a few milliwatts of dark-blue light with λ = 430 nm can be generated.
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An investigation of intracavity selective absorbers for tunable single longitudinal mode operation of a high power CO2 TEA laser, and application of this method to optically pumped lasers is reported.
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The techniques of Laser-Raman Spectroscopy have been greatly improved during the past decade. The most promising developments involve both time-resolved spectra and microprobing or microscopy. Principles and applications of the recent instruments will be presented.
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Doping of alkali halide crystals with large amounts (10-3 to 10-2) of OH- and SH- defects can be used to drastically increase the production and stabilization of laseractive ionized F-aggregate centers like the F2+ and (F+2)A-centers. Using this technique tuneable cw laser operation is achieved for the first time with F2+ -centers in NaCl, KCl and KBr. Furthermore a short x-ray exposure reactivates centers thermally destroyed after RT storage. With F2+ -center lasers now the spectral range between o.8 and 2.o μm can nearly be covered. Slope efficiencies up to 6o % and single mode output powers in the range of 1 W have been obtained.
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We describe a coherent spectrophotometer tunable in the 1.45-20 μm range; the source is a LiNb03 optical parametric oscillator pumped by Nd-YAG laser, and AgGaSe2, GaSe or CdSe crystals as down converter of the idler and signal beams. The LiNb03 optical parametric oscillator is tunable in the 1.5-4 μm range, the peak power is higher than 200 kW and the bandwidth is 0.15 cm-1. Using a GaSe crystal we obtained a peak power better than 1 kW also in the 4-12 μm range. Using a 3.1 cm long CdSe crystal, we also obtain the down-conversion of the parametric output beams. The tunability is in the 9.5-20 μm range, and the bandwidth is 0.2 cm-1. An electronic system supplies feed-forward tuning control, output light detec-tion and absorption coefficient measurements. Tuning control is obtained by simultaneous variations of grating, LiNb03 crystal, mixer crystal and mirror angles with respect to the light beam. Further control for etalon tuning is provided. Pyroelectric detectors are used to obtain light detections and measurements on both light paths (reference and sample under test) and active filter amplifiers supplies signal to noise ratio improvement before A/D conversion.
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We report a new tunable phasematching technique for submillimeter and far-infrared difference-frequency generation by optical lasers. We use a multiple waveguide principle based on an optical waveguide embedded in a low-loss modified H-guide. The same phasematching technique also permits the development of a Gigahertz electro-optic modulator design. In order to use uniaxial electro-optic materials, the theory of the H-guide was extended to determine the appropriate crystal orientations and dispersion equations. Numerically generated design curves are presented for tunable electro-optic modulators designed for 3-10 Gigahertz operation. A brief discussion of other possible designs and applications based on the multiple-waveguide method of phasematching is also given.
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Low gas concentration measurements of some selected gaseous pollutants have been performed with high local and temporal resolution using a giant-pulse laser Raman probe. Values below loo ppm (down to 65 ppm) were measured with a local resolution of o.6 mm3 and with a temporal resolution of 2o ns (pulse width of the laser). Setup influences on the measurement accuracy are deduced.
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The new developments in acousto-optic spectrum analysis result into improved performances regarding the detection of weak and short signals. The acousto-optic spectrum analysis is based on the properties of certain cristals to behave like a phase grating when they are excited by an acoustic wave.
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The ferro-electric crystals such as Lithium Niobate have been extensively employed for high capacity information storage. A few image processing operations have also been carried out with these recording materials. In all of these operations , coherent light has been used for both writing and reading the information. In an effort to increase the S/N ratio, we have studied an experimental arrangement in which a white light source of limited dimensions has been used for both recording and reading. The signals to be treated are in the form of realamplitude transparencies. With our technique we have obtained the sum and difference of two signals. Contrast enhancement can also be achieved . The two sianals are suitably modulated and are recorded once for all and the different operations are carried out by different manipulations at the reading stage. A further advantage of our system is that the output information can be displayed in color. The writing and reading processes are explained in the following paragraphs.
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An experimental technique of in-plane strain measurement on large rotating structures in service, requiring only minor surface preparation and little or no interruption to or shut-down of costly production-line plant is extremely attractive. The development of ESP1 (electronic speckle pattern interferometry), which displays this potential, using a pulsed laser is described. Some preliminary results for component tangential velocities up to 3.4 ms-1 are presented.
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Holographic interferometry and speckle application are powerful techniques for deformation, displacement and vibration analysis especially when they can be applied in real time. Bismuth Silicon Oxide crystals Bi12 Si 020 (BSO) were used for real-time deformation displacement and vibration analysis using holography and "speckle photography". After a short introduction of holographic interferometry for deformation measurement using BSO crystals, speckle applications for deformation, displacement and vibration analysis in real time will be discussed.
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Printed circuits on plates of epoxy resin reinforced by glass fibres or on glass or ceramics are deformed by electrical loads applied to them. These deformations can be made visible by real-time holography. This testing method reveals concealed defects such as hairline cracks, circuits peeling off the plates or air cavities in multi-layer plates.
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A process is described in the following, with which it is possible to simply produce intensely colored rainbow holograms by using only one laser wavelength. An observer who is in a suitable position in front of the hologram, sees a three-dimen-sional black and white or multi-colored reconstruction of a subject in natural or other colors.
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A system for video recording of holograms using phase modulation of the reference wave and heterodyne detection of only the cross-interference terms is described. The system permits nearly complete use of the limited spatial resolution capability of an image dissector camera for recording object wave information. The method has been used to record holograms of simple objects. Results are presented and system reauirements for extension to complex objects and to quasi-real-time display are discussed.
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In-plane as well as out-of-plane displacements and vibrations of objects with diffusely scattering surfaces are measured in real-time. Micro-vibrations with amplitudes down to 1 nm and frequencies up to 10 MHz were analysed at a spatial resolution of 30 μm.
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A compound microscope is described which consists of a combination of a holographic interference microscope and a conventional microscope. Both systems can be optimized independently for fringe and image contrast, respectively. Both these systems proved to be indispensable for the description of complex phenomena, such as etch pit formation. On their own, they presented incomplete and even highly misleading information. The complete system combines i) the highly corrected image and long free working range of microscopy, with ii) the large vertical resolution and overall spatial information of interferometry and with iii) the increased depth of imaged volume and potentialities for time sequential observations of holography. The coherence of the light enables interference microscopy during crystal growth from a bulk solution. With the compound microscope the development of high index (or vicinal) faces, step bunches and etch pits were recorded during crystal growth and/or dissolution. Simultaneously also both concentration gradients and equiconcentration profiles surrounding the growing (or dissolving) crystal were made visible. Microinterferograms were obtained from i) interference of the reconstructed image (crystal, solution or free space) of a single exposure hologram with a real object beam; from ii) the superposed reconstructions of two such holograms; and from iii) the reconstruction of double exposure holograms (time sequential). The applicability of the various techniques is discussed with respect to the study of crystal growth processes.
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Two-dimensional mapping of a solution's temperature and concentration profiles is possible in principle by pointwise combination of data from simultaneous absorption and interferometric images. Preliminary feasibility analysis and experiments indicate that adequate precision is attainable for selected solution crystallization systems.
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With optically generated component filters a binary recognition of 2-D objects is possible. The correlation signals of the filters are processed by a digital computer system to achieve a classification by signal intensity and shape. The computer also controlls the filtergeneration and carries out the recognition.
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For high precision (50 μm) surface measurements of a mm-wavelength radio reflector we have developed a modulated laser (He-Ne 632 nm, mod. freq. 1.7 GHz) distance ranger and an angular measuring system of 0.4" accuracy. We give test results of the system.
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A simple low cost image derotation system has been devised and used to render optically stationary the infra red images of high speed rotating hot components. The derotator has been specially designed to utilise to the maximum reflective surfaces and not transmissive optics, in order to pass the maximum range of infra red-wavelengths (or the range of component temperatures being measured). The derotated or non-rotating image of the hot rotating component is focussed on to a small sheet of encapsulated chloresteric liquid crystals, the invisible infra red image being rendered visible in colour by the liquid crystal sheet. It is concluded from the results obtained from the preliminary experiments presented in this paper that the image derotator-liquid crystal unit so described should prove to be a useful tool for the engineer. Real time whole field maps of thermal patterns are of vital importance to the engineer, providing knowledge of the effect of those thermal patterns on the component material properties, which in turn affect the vibration and centrifugal stress patterns associated with rotating components.
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The digital image analysis system (DIAS) is a software-oriented, computer-based approach to automatic image analysis. In this paper, some aspects of DIAS are discussed that can be performed with commercially available image pickup equipment attached to an optical microscope and linked to a sensor-based small computer (such as a System/7 or a Series/1). Through the application of an optical edge detection program, the system is adapted to precision measurement of linewidths and other parameters on semiconductor and garnet wafer patterns.
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A microprocessor controlled photo-thermoplastic device has been developed for the real-time recording of holographic filters in a hybrid digital-optical data processing system. It is possible to position the filters with an accuracy of 0,2 µm.
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A review is given of recent developments in the use of CO2 lasers, direct and heterodyne detection, and modern signal processing techniques for the measurement of the range and velocity of both solid and atmospheric targets.
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A novel type of laser rangefinder,based on a CW CO2 laser and a specially-designed acousto-optic modulator,applies microwave signal processing concepts in the 10 micron spectral region. We used )4 microsecond duration, 14 MHz bandwidth chirp pulses and surface-acoustic-wave (SAW) expander and compressor devices. Compact optical design with a range capability of several kilometres is obtained by digitally integrating many returns processed at the rate of 30,000 returns per second. In chirp systems,moving targets produce, via the Doppler effect, a range error (8m per ms-1 our case), but, by using up-chirp and down-chirp waveforms, which produce opposite-sign errors, we determined both the range and radial velocity of moving targets.
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The dispersion of artificial aerosol plumes over sea surfaces was measured using a portable lidar system. The momentary distribution of aerosol concentrations could be derived from short-time measurements. Some effects of the aerosols and the sea surface on the plume dispersion were estimated.
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A helicopter-borne fluorescence LIDAR system is described, and the detection of tracer dyes in ocean waters is reported. Computer simulations concerning the influence of the surface structure of the sea have been performed.
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The mass concentration in a pollutant cloud can be estimated from the normalized range-corrected LIDAR signal S(R) if the clear-air mass concentration and the parameter Ω defined as the ratio of some weighted (by the product of the size distribution function and the square of the radius) average of the total scattering efficiency to the volume to surface average radius, are known. The ratio Ω can be calculated by numerically solving the LIDAR equation for three different wavelengths in terms of the observed quantities S(R,λ), the known values of the λ's and an assumed value of the refractive index m. In the present analyses, S-functions are simulated for log-normal size distributions with different values of the standard deviation. For simplicity spatially uniform number density is assumed so that only two-wavelength calculations are needed. Assumed mass concentrations (for different widths of the size distribution) are compared with those calculated using the modified LIDAR equation. The results show that the validity of the method is limited by the width of the size distribution and the product (R-Ro)N where (R-Ro) is the probed range inside the cloud and N is the number density.
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Applications of lasers in photobiology and photomedicine will be reviewed; for example, genetic processes, photosynthesis, vision, spectroscopy of skin, phototherapy and photochemotherapy of dermatosis and tumors are considered. New results and future possibilities are discussed.
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As most hemangiomas and tattoos require many sessions to be cured completely by argon-laser or conventional therapy I developed a new combined surgical and laser-therapy method for large hemangiomas and tattoos. This is a three step method. First: The skin lesion is treated by argon-laser with the point by point method, developed by ourself. Second: Under local or general anaesthesia a) the hemangioma is partially excised and undermined letting only the skin which is already treated by argon-laser-beams. Than the hemangioma is exstirpated in toto, the wound closed by running intradermal sutures and a pressure bandage applied, b) the tattoo is abraded as deep as possible, draped by lyofoam. Then a pressure bandage is applied. Third: The hemangioma as well as the tattoo are treated by argon-laser-beams after the operation. This method is safe and effective, gives good results, minimal scars in the case of hemangiomas and tattoos. In this paper the method is described and some cases are illustrated by pre- and postoperational photographs.
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The carbon dioxide laser has been used for cutting and cauterizing tissue in a variety of surgical procedures by means of a dry-field air/tissue interface approach. Recently, a new wet-field CO2 laser technique has been developed and is being used successfully in humans to seal intraocular fibrovascular fronds and retinal tears at the time of vitrectomy, to close rubeotic vessels in the iris, and to excise fibrovascular fronds and epiretinal membranes in cases of severe diabetic retinopathy. Specialized wet-field CO2 photosurgical probes for use in gynecologic microsurgery have been developed and are being studied experimentally. Other potential applications include otolaryngologic micro-surgery, neurosurgery, and gastrointestinal and urologic wet-field surgery.
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The mechanism of laser coagulation of skin abnormalities is discussed. A simple model, including absorption and scattering coefficients derived from literature data predicts an optimal coagulation wavelength of 420 nm, and a 1 mm Ar-ion-laser coagulation depth for port-wine stains.
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When a deep-sea diver returns to the surface, he may suffer decompression sickness (commonly known as the bends). The disease occurs when the excess inert gas that dissolves in tissues during the dive (N2 or He) forms bubbles. The standard treatment is rapid recompression in order to redissolve the bubbles. The diver is placed in a hyperbaric chamber, which is then pressurized to a point where symptoms are relieved; this pressure is maintained for an arbitrary period presumed adequate to fully dissolve all bubbles. The pressure is then reduced gradually until atomospheric pressure is reached. If all has gone well, the diver experiences no residual effects.
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The optical diffractometric method for the measurement of cellular deformability is described. It permits working in real time and enables measuring of an internal viscoelasticity of cells. Deformability of human erythrocytes as a function of applied fluid shear stress is analyzed. It is shown that some limit of proportionality exists below which the deformation of cells is proportional to the fluid shear stress value. But the cells deformability is nearly independent on the stress beyond this limit. Both blood of healthy adults and newborn infants was studied and obtained results are described. Drawbacks of the method are discussed and an improved measuring system is proposed.
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We report on experiences gained in healing clinical cases treated with He-Ne and Argon-laser grouped according to etiology. In order to elucidate the action mechanism of the bioregulatory process, the following experiments were carried out: 1. Serial electron-microscopic and radioactivity studies of samples obtained from human ulcers; 2. Chemical transfer of stimulating substrate on human leukocyte population; 3. Enzyme histochemical studies in experiments on rats; 4. Study of vascularization with the "ear chamber" technique carried out on rabbit's ear; 5. The increase of tensile strength in rats; 6. Biochemical demonstration of the RNA, DNA, albumin synthesis on human fibrocyte-cultures; 7.a, 7.b, Immunological studies; 8. Prostaglandin producing effect. The discovery of laser opened up new prospects in the field of the biological research and medical use.
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Low-power laser irradiation has been employed in the attempt to accelerate the wound-healing of ischemic cutaneous ulcerations with threatening or manifest gangrene due to arteriosclerosis obliterans of the lower limbs. Irradiation was performed by using a low-power He-Ne gas laser of 6328 Å wavelength and was concentrated at the peripheral zone of the lesions. The preliminary results of the study indicate that laser stimulation might be new approach in the conservative menagement of the ischemic ulcers in patients with severe peripheral obstructive arteriopaties not suited for arterial reconstruction.
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The effect of low power laser radiation from a He-Ne CW laser on middle ear inflammatory otitis is discussed.
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Artificial acetabular cups loose their original shape and undergo deformations during implantation, caused by the polymerization shrinkage of the bone cement. In laboratory experiments, two acetabula of different material - both common in clinical use - were studied by holographic real-time interferometry during cement hardening. This method picks up characteristic features in the transient behaviour of the form changes. It is shown, that temperature, porosity and shrinkage of the cement has a large influence on the form of a polyethylene acetabulum, whereas there is only little effect on an acetabulum, made of alumina ceramic.
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During demineralization and remineralization of dental enamel its structure changes resulting in a change of the absorption and scattering coefficients of the enamel. By measuring these coefficients during demineralization and remineralization these processes can be monitored in a non-destructive way. For this purpose an experimental arrangement was made: a fibre illuminates a spot on the sample with monochromatic light with a wave-length between 400 nm and 700 nm; a photomultiplier measures the luminance of the light back-scattered by the sample as a function of the distance from the measuring snot to the spot of illumination. In a Monte Carlo-model this luminance is simulated using the same geometry given the scattering and absorption coefficients in a sample. Then the scattering and absorption coefficients in the sample are determined by selecting the theoretical curve fitting the experimental one. Scattering coefficients below 10 mm-1 and absorption coefficients obtained with this method on calibration samples correspond well with those obtained with another method. Scattering coefficients above 10 mm-1 (paper samples) were measured ton low. This perhaps is caused by the anisotropic structure of paper sheets. The method is very suitable to measure the scattering and absorption coefficients of bulk materials.
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Three flow measurement techniques make use of fast digital correlators. (1) Most widely spread is photon correlation velocimetry using crossed laser beams and detecting Doppler shifted light scattered by small particles in the flow. Depending on the processing of the photon correlogram, this technique yields mean velocity, turbulence level, or even the detailed probability distribution of one velocity component. An improved data processing scheme is demonstrated on laminar vortex flow in a curved channel. (2) Rate correlation based upon threshold crossings of a high pass filtered laser Doppler signal can he used to obtain velocity correlation functions. The most powerful setup developed in our laboratory uses a phase locked loop type tracker and a multibit correlator to analyse time-dependent Taylor vortex flow. With two optical systems and trackers, crosscorrelation functions reveal phase relations between different vortices. (3) Making use of refractive index fluctuations (e. g. in two phase flows) instead of scattering particles, interferometry with bidirectional fringe counting and digital correlation and probability analysis constitute a new quantitative technique related to classical Schlieren methods. Measurements on a mixing flow of heated and cold air contribute new ideas to the theory of turbulent random phase screens.
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A laser microanemometer has been developed for contactless measurement of flow velocity distributions in the immediate vicinity of vessel walls. This new anemometer is basically a microscope using incident coherent light and spatial frequency plane filtering for noise suppression. Velocities of submicroscopic particles suspended in the fluid and backscattering the laser light are measured using a modulating prism grating, a differential photodetection system and a digital correlator. With this system a flow velocity distribution can be analysed with a spatial resolution approaching the theoretical resolution limit given by the numerical aperture of the objective lens. Flow velocity profiles in glass capillaries could be measured down to wall distances on the order of 1 micron (μm) for water as well as human blood plasma.
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A system for simultaneous measurement of particle size and velocity in two phase flows is developed. It uses the doppler frequency shift for particle velocity. Particle size is determined by using the amplitude dependence of the signal. As the doppler frequency shift has already been used since a long time for velocity measurements, this study is in a great extent dedicated to this new second aspect.
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Theoretical beam propagation studies in a high powered laser system are described. The basis of the model is a diffraction propagation code which includes a wide range of non-linear optical effects and optical components. Parameters of interest to the laser designer, such as beam quality at the output of the laser, focussable power through a given lens placed downstream and peak to average intensities in optical components such as turning mirrors are all discussed in the context of the laser layout.
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Recent progress in development of injection lasers has resulted in high lifetime with fundamental transverse mode operation. Now the interest is focused on properties like noise, spectral behavior, sensitivity to optical feedback etc.. In this respect, laser diodes show remarkable differences depending on whether gain-guiding or index-guiding is the predominant mechanism for transversal confinement of the optical wave.
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The technique of image derotated holographic interferometry provides unique information about the fluttering, vibratory behaviour of rotating components. A theoretical treatment of holographic bias fringe formation, due to the rigid body motions of the rotating axis, is presented and oractical methods of ameliorating their effects are discussed.
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A cavity-dumped, YAG oscillator-amplifier system has been built which offers significant advantages over conventional Q-switched and modelocked systems. Pulse risetime of one nanosecond and pulsewidth of two nanoseconds has been achieved with greater than two hundred millijoule output at 532 nm. The system design is simple and straightforward, as opposed to the complex and difficult to operate mode-locked systems. It is provided in a fieldable configuration, making it quite attractive for ranging, tracking, remote sensing and non-linear studies.
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The optical design and the structure of an infrared emitting diode is described, where the spatial intensity distribution of the radiation is adjusted to a light scattering smoke detector. This is not achievable with conventional elements. Only the introduction of novel manufacturing methods enables the designer to build up systems with increased optical efficiency and high reliability characteristics.
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In the present paper a general model of plasma instabilities in high-power e-beam sustained CO2 laser amplifiers is illustrated. This model improves the Haas-Nighan one by allowing explicitly for the various degrees of vibrational freedom and taking into account the stabilizing effect of the laser field intensity. The model has been used to test the degree of thermal and ionic instability of an EDCL device using four-component gas mixture(CO2:N2:He: CO).
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Efficient upconversion of infrared to visible has been observed in impurity doped GaP. Device applications are discussed.
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We report the generation of 180mW of FIR power at i53μm (15NH3 pumped by the isotopic 13C16O2 u laser) from a commercially available laser system. The fine tuning characteristics of the FIR laser are also discussed.
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The N2 laser requires the uniform glow discharge for the high power- and stable-operation. This paper describes a novel stabilization technique for the glow discharge of N2 laser in an open-air operation. The laser of 12-cm active length is excited transversely by the Blumlein pulser, and uses the simple distributed-capacitor. This distributed-capacitor leads to the pilot-discharge to suffer the high density glow discharge between the main electrodes. The suitable conditions of the glow discharge formation in an atmospheric air were found experimentally, and glow discharge in TEA operation was achieved by applying the pre-ionization technique, and nano-second UV N2 laser pulses were obtained.
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The photoionization cross section of excited atomic selenium, Se(1S0), obtained by photodissociation of 0CSe, has been measured in the wavelength region 170 - 175 nm using a tunable xenon laser. A minimum value, at 172 nm, was found to be 1.2 x 10-20cm2, approximately ten times less than a recently calculated value. The photodissociation cross section for OCSe, at the same wavelength, was found to be 0.8 x 10-16 cm2, in good agreement with published work. The effect of an electron cooling buffer gas upon the electron production from excited selenium was also investigated.
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More than 350 mW quasi cw laser output for transitions between 248 - 270 nm and 1 W for 740 - 730 nm have been obtained with hollow cathode CuII-lasers. The laser characteristics are discussed for three different tube designs.
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An actively mode-locked and Q-controlled Nd:YAG laser system has been developed to produce single 200 ps pulses with 20 mJ energy and repetition rate up to 10 Hz. The output pulses are synchronizable to an external event with high precision. New scheme for pulse duration measurement using noncollinear second harmonic generation has been employed.
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Results of the analysis of radiation spatial and energetic characteristics influence upon the pulse evolution in the amplifier as well as in the focus region of focussing systems are being presented.
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The two techniques of backward-wave Raman pulse compression and pulse stacking are reviewed in the context of using KrF lasers as drivers in inertial confinement fusion. Experimental and theoretical results on Raman pulse compression in methane are presented including data on 70-75% pump energy extraction by the counterpropagating Stokes wave. Results from on-going pulse stacker/Raman compressor experiments are also described, along with future investigations in this general area.
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The operation of CO2 waveguide lasers has been studied in an extensive programme of life testing and quantitative analysis. This work has led to the development of a sealed-off long life device.
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A new dye-liquid crystals laser pumped with UV radiation is presented. The possibility to change the polarization direction of the output by acting on the matrix orientation is shown.
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A passively mode-locked TEM-00 Nd:YAG laser is investigated theoretically and experimentally in detail. The numerical calculations base on the refined Letokhov model, taking into account the spontaneous emission and the time dependent pumping light. The statistical noise pulses of the spontaneous emission are approximated by an average noise power and two single pulses which develop into the mode locking pulse and its satellite. By starting at t = 0 with all atoms in the ground state, the temporal behaviour of the following quantities is pursued: main pulse energy and width, energy of the satellite pulse, average noise power, and their dependence on absorber transmission, pumping rate, and resonator losses. Special importance is attached to a realistic model of the nonlinear absorber which compresses the mode-locking pulse and determines the resulting pulse width in conjunction with the amplifier. The gaussian structure of the pulse in time and space is taken into account. The numerical results were checked experimentally. Pulse width measurements were carried out with two photon fluorescence and a fast streak-camera. The results confirm the theory and demonstrate that the refined Letokhov-model is suitable to describe mode-locking quantitatively.
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this paper deals with the super fluorescence observed from the 3Σu - 3Σg transition in S2 molecules pumped by a N2 laser. Laser intensifies are scaled for various experimental conditions and an anaysis of results is proposed. From this, laser cross-section was estimated about 10-12cm2.
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An optical fibre current measurement device has been used to monitor currents up to about 14 kA from a 500 MW set at Fawley Generating Station. The device performance has been satisfactory and been unaffected by vibration and local temperature variations. The output of the device has remained within 2% of the output of the conventional current measurement equipment for long periods and for periods of one hour agreement to within 0.6% is typical.
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Consideration is given to a new optical-fibre technique for the measurement of the spatial distribution of physical fields (e.g. magnetic field, electric field, temperature, mechanical stress, etc.). The technique relies upon the time-resolution of light backscattered from a pulse propagating in a monomode optical fibre to measure the spatial distribution of the fibre's polarization properties. These properties are modified by the field under investigation.
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A 30 cm long waveguide made of two specularly reflecting water-cooled brass plates was built for use with a 3 kw CO2 laser beam focused with telescopes having numerical apertures ranging between f/7 and f/150. In order to improve the collection efficiency a V-shaped throat was used as input section. The coupling coefficients of a Gaussian beam were calculated for different illuminations by using simple expressions derived from the uniform asymptotic theory (UAT) of diffraction . Essential to this approach it was to simulate the beam as a wave radiated by a source located at a complex point.
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A waveform monitoring for a picoseconds-width, single-shot optical pulse is possible with optical circuit of optical fibers and LiTaO3 Pockel's cell. This method is based on having cross correlation integral between delayed signals and a single step function. The inquired waveform is reproduced by a deconvolution. The principle can be implemented by four fundamental functions, branching to make replicas of a source signal, delay, optical gate, and time integration. Optical fibers were employed as delay lines whose delay time is controlled by their length. A small cylindrical lens was used for the branching from a single optical fiber to a bundle of fibers as delay lines. The optical gate is composed of a LiTaO3 Pockel's cell which is driven by a specifically manufactured optoelectronic switch. The time integration is achieved by photodiodes whose electric charge output is proportional to the energy, a time integral of temporal power,of the incident optical pulse. Experiments were made for a 2ns FWHM optical pulse of a dye laser, which demonstrates the expected ability. Very fast A/D conversion for a picosecond optical pulse waveform is basically possible, which is more profittable than a pure electronic metnod.
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Sinde the beginning of integrated optics many progresses have been made in the domain of optical switches. This includes switches realized with semiconductor materials and switches based on the use of crystals like LiNbO3 . In this paper, we shall describe different switching devices which have been realized with channel waveguides by Ti in diffusion in LiNb03 crystals . After having briefly described some configurations which can be used to achieve switching in integrated optic, some recent applications and proposals based on these devices will be discussed.
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In this communication we report a new method for deflecting a laser beam with liquid crystals cells. In order to improve previous response times of these cells, we use a wedge structure with twisted orientation.
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The Microchannel Spatial Light Modulator (MSLM) is a versatile, highly-sensitive and optically-addressed modulator that is well suited for low-light-level, real time, optical information processing. It consists of a photocathode, a microchannel plate, a planar acceleration grid, and an electro-optic plate in proximity focus. The image processing operations that can be achieved with the MSLM include contrast reversal, contrast enhancement, edge enhancement, image addition and subtraction, analog and digital intensity level thresholding, and binary-level logic operations such as AND, OR, EXCLUSIVE OR and NOR. Recent prototype MSLMs have exhibited a half-wave exposure sensitivity of 2.2nJ/cm2, an optical information storage time of more than two months, and a framing rate of 20 Hz with full modulation depth (100 Hz with 20% modulation depth). The materials and device parameters that limit the ultimate performance of the modulator are discussed.
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Polarization modulators are investigated in which optical anisotrpy is induced by acoustical waves in isotropic materials. The theory of operation is presented for the case when according to various polarization conditions the modulation appears on the first or on an even harmonic of the generation. The dependence of modulation parameters on the driving voltage and on the geometrical position is discussed. The modulator developed gives a modulated signal of high quality which on the first harmonic attained 80 % on the second harmonic 45 % of the incident light intensity with practically total extinction in the minimum points. According to their resonance frequency the modulators of this type can over the 40-1000 kHz frequency range. The possibility of a quarz stability chopper relaised on this principle is indicated.
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Acoustic transient phenomena induced piezoelectrically by high voltage switching pulses can greatly affect the shutter operation. The sensitivity and the spatial resolution of a photographic method developed for visualisation of acoustic transients in electrooptic light modulators is improved by applying a linear array of 256 photodiodes. The spatial distribution of the strain and the time dependence of the acoustic pulse shape is investigated.
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An home made electronic spectrophotometer using a self-scanned photodiode array detector, designed for short luminous pulses and a CAMAC fast data acquisition system (20 MHz) are interfaced to a microcomputer (D.E.C. PDP 11V03). System characteristics are improved by a pertinent software for efficient information processing. This system is used to diagnose and to study supersonic flow, low temperature, UV and visible pulsed high power lasers.
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A new scheme for a NxM electrooptical switching network in a planar LiNb03 optical wave-guide for computer communications has been demonstrated and will be reported here. Experimental data and analysis will be presented to show its performance characteristics, such as the maximum number of communications channels, the "on/off" difference (i.e. signal-to-noise ratio) and the switching voltage, as affected by the inplane scattering noise in the waveguide, the lens performance, switching electrode design, and detectors.
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Laser radiation induced Faraday rotations of over 100 degrees per cm are reported in InSb for low incident powers (<< 1 W) in the largely transmitting region below the frequency for direct interband transitions. The effect has been systematically studied as a function of pump radiation frequency and power in addition to applied magnetic field. The inter-related effects of saturation and blocking are discussed as potential mechanisms responsible for the observed effects. Results of preliminary two-beam pump and probe experiments are also reported.
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We report the realisation of optically bistable switching and memory elements, and the transphasor Can all-optical transistor) in simple one element nonlinear Fabry-Perot interferometers made from the semiconductor InSb. These devices, which operate at 5 K and 77 K with mW powers from a cw CO laser between 5 and 6 μm rely on a strongly intensity-dependent refractive index discovered near the bandgap region of InSb and explained by bandgap resonant saturation. Switching speeds are shown to be < 500 ns in these first devices and operation to much shorter timescales is predicted. Operation at room temperature and in other semiconductors at other wavelengths remains a possibility and such devices offer considerable potential for all-optical switching in integrated optics and laser pulse control.
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The combination of color multiplexing techniques using a stripe filter with a CCD solid state image sensor forms the basis for a compact, low weight and low power color camera. With its potential for low cost fabrication it represents a likely candidate for the consumer camera of the future. The following description focusses on the optical aspects of the stripe filter approach which uses lenticular array relay optics.
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The frequency response of most bulk semiconductor junction solid-state detectors are limited by transit time delays due to diffusion and drift of carriers within the junction.
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First, the fundamental properties of optical heterodyne receivers are described in brief. A detailed description of an experimental arrangement to verify the main properties is given. Finally, are discussed the deviations in practice from theory.
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Efficient down conversion in GaSe crystals of the signal and idler output beam from a LiNbO3 optical parametric oscillator was obtained. With a 0.8 cm long GaSe crystal, the maximum peak power output was 1 kW and the maximum energy conversion efficiency was 2.5%. The wavelength can be continuously tuned over the 4-15 μm range.
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General aspects of laser annealing of semiconductors are discussed.
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An overview of the mastering process including the necessary equipment used for the generation of master disks for the Philips optical disk systems- Video Long Play, Audio Compact and Preformatted data disks is given.
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Lasers are widely used today for the most different kinds of processing operations of most practical materials. Heat treating, surface melting, welding, drilling, cutting and so on can be realized with a quality responding to industrial requirements. Particularly processing problems difficult or impossible to solve by conventional techniques, e.g. with respect to small size, hardness, brittleness, temperature sensitivity, processing of high volume production requiring extensive automatization are calling for the laser. An extensive process control to evaluate and solve practical problems has been developed. The laser parameters, to realize a desired processing of a given material, can be determined in a first approximation and the corresponding laser system can be specified. A first order economico/technical evaluation of the problem solution can be deduced. An experimental optimization considering all the boundary conditions has to be done only if the first evaluation is favourable. This procedure has been applied successfully to many industrial processing problems of variety of materials.
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Characteristics of a laser-generated acoustic source are discussed from measurements carried out using a Nd:YAG Q-switched laser incident on free metal surfaces. Longitudinal, shear and surface acoustic pulses have been generated. Laser energies as low as 3mJ are sufficient to generate such pulses that are readily detected by conventional piezoelectric transducers, without the need for laser focusing. Experimental data highlights several features of the acoustic source.
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Accurate measurements of the phase modulation induced by known dynamic deformations on a single-mode optical fiber are given in the mechanical vibrations frequency range 2 ÷ 7 KHz. The characteristic phase behaviour can be correlated with the modal frequencies of the structure supporting the optical fiber.
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