Showing papers on "Ruby laser published in 1991"

Lasers in periodontics.

Abstract: Clinical lasers are of two types. Soft lasers are essentially an aid to healing, with relatively few rigorous studies available to support their use. Surgical hard lasers, however, can cut both hard and soft tissues, replacing the scalpel and drill in many areas. After initial experiments with the ruby laser, most clinicians have been using argon, carbon dioxide, and now Nd:YAG systems. The first dental laser based on a Nd:YAG engine provides handpieces of similar size to conventional instrumentation, and being fed by a fibre-optic "cable," has the flexibility for intra-oral use that the carbon dioxide lasers, widely used in oral surgery, lack. Furthermore, extensive clinical investigation has demonstrated their safety in clinical practice, and the fact that procedures can usually be performed without a local anaesthetic is obviously seen as an advantage by patients. Sterilizing as it cuts, the Nd:YAG laser promises to find uses not only in caries removal and soft tissue surgery but also in periodontics and endodontics.

Composition and structure of Si–Ge layers produced by ion implantation and laser melting

Abstract: Si samples (001) oriented have been implanted with 10 17 74 Ge/cm 2 (17.7 at. % maximum Ge concentration) and then pulse annealed with either ruby or excimer (XeCl) lasers in the energy density range from 0.1 to 1.5 J/cm 2 . Compositional and structural characterization has been performed showing that for both laser wavelengths the final product of the annealing process is a single crystal characterized by a surface layer about 150 nm thick whose composition is Si 0.9 Ge 0.1 . While after ruby laser irradiations defects are present even in the fully recrystallized samples, after XeCl irradiations good strained layers in epitaxy to the underlying silicon crystals and free from misfit dislocations are produced. Structural characterization of the regrown films indicates that the governing factor for the recovery of the crystalline quality and for the “building up of strain” is the state of the implantation “end-of-range defect” layer. When this defected layer is not melted, textured columnar grains are formed. Upon melting of the end-of-range defect layer, a single crystal epitaxial layer under compressive strain is formed.

Pulsed laser processing of Ge/Se thin film structures

Abstract: The comparison between results of a systematic experimental study on Q-switched ruby laser processing of supported thin Ge/Se bilayer structures and model calculations permits us to unfold the rather complicated events into elementary steps. Depending on the sequence of the elemental layers and the absorbed fluence, compound synthesis, total or partial ablation of one of the constituents or the compound formed, and simultaneous transfer of the ablated material onto a separate substrate in close proximity is possible with a single laser pulse. The striking agreement between experimental findings and model calculations indicates the validity of the simple thermal model applied. The results establish a novel, inherently simple, single-step technique for local deposition of compound films from stacked elemental layers as a source onto any substrate.

Localized Corrosion Studies on Laser Surface Melted Type 316 Austenitic Stainless Steel

Abstract: An attempt was made to modify the surface of an austenitic stainless steel using laser surface melting (LSM) technique to improve the localized corrosion resistance. AISI type 316 stainless steel (SS) specimens in solution annealed, cold worked (5, 10, 15 and 20%) and sensitized (923 K, 20 h) conditions were laser surface melted using a pulsed ruby laser at the energy of 6 J per pulse. The melted layers were characterized by small angle X-ray diffraction (XRD), optical microscopy and scanning electron microscopy (SEM)

Melting and solidification in laser-irradiated HgCdTe

Abstract: The results of the numerical analysis of the effects induced by pulsed Nd:YAG and ruby laser on Hg0.8Cd0.2Te are presented. The proposed model facilitates the planning of HgCdTe laser processing and the choice of the processing parameters such as: melt depth, melt duration of the surface layer and melt front velocity, as well as the irradiation parameters. The influence of the optical parameters and the temperature dependence of the HgCdTe thermal parameters on the results of laser irradiation are specially analyzed.

Ruby laser‐induced linear dichroism of FA(II) centers in KCl:Li crystals

Abstract: The FA(II) color centers of KCl:Li crystals were observed to reorientate at room temperature under the exposure of a ruby laser. The linear dichroism of the centers, induced by ruby laser light, is presented here.

Nonresonant third‐order optical response of polyphenyl acetylene

Abstract: Optical phase conjugation by degenerate four‐wave mixing in samples of pristine and iodine‐doped polyphenylacetylene at ruby laser wavelength (694.3 nm) is reported here. The nonresonant values of the third‐order optical susceptibility χ(3) are determined from the measurements of reflectivity of phase conjugate signals.

Practical system for time-resolved holographic interferometry

Abstract: An easily implemented and easily manageable system for timeresolved holographic interferometry is presented. The system consists of a multiple-pulsed Q -switched ruby laser and a rotating disk having radial slits with a constant angular separation. The disk is used to scan the reference beam along a holographic plate, thereby achieving spatial multiplexing. Since the influence on the beam is negligible and a single slit is illuminated by every laser pulse, there is no need for synchronization. The interferometric pattern is achieved by removing the disk and exposing a reference image on the holographic plate. The system may serve as an excellent tool for full-field dynamic measurements. A simple experiment has been performed showing a sequence of momentary interference patterns on a vibrating plate.

Development of chemical oxygen-iodine laser for industrial application

Abstract: Since the first oscillation of a ruby laser obtained in 1960, an enormus amount of efforts have been concentrated on laser researches. Fundametal researches were almost finished in 1960's, then aims of investigations were turned to find out new applications.

Refractive fringe diagnostic of spherical shocks

Abstract: The refractive fringe diagnostic was applied to a spherical shock wave in air generated by an arc discharge. A pulsed ruby laser, synchronized with the shock generation, was used as the probe beam. Both fine and coarse fringes were observed and were modelled computationally. Agreement with the broad features of the density profile predicted by theory was obtained, but the gradient of the theoretical shock rear was found to be too shallow. The shock tail was seento be stationary over a duration of hundreds of microseconds.

High-speed laser speckle photography

Abstract: A rotating mirror camera and pulsed ruby laser have been combined to record laser speckle photographs at framing rates in the range 105 - 106 frames s"1 The laser is repetitively Q-switched by means of a Pockels cell, which is controlled by photodetectors inside the camera This allows well-correlated double exposure speckle photographs to be recorded on two separate runs of the camera The photographs are analysed by an automated image processing system to give whole-field displacement data with submicron accuracy The paper is illustrated with results showing the dynamic displacement field in polymethyl methacrylate due to solid particle impact

Picosecond pulse generation in a benzene raman generator amplifier system

Abstract: Picosecond ruby laser pulses generate simultaneously Stokes pulses of the 992 cm−1 ring breathing mode and of the 3063 cm−1 CH-stretching mode of benzene in a Raman generator cell by stimulated Raman scattering under self-focusing conditions. The Raman generator light is spectrally filtered, collimated, and amplified in three Raman amplifier cells pumped by ruby laser pulses. Both first Stokes lines have been selectively amplified to short, low divergence, intense light pulses.

Effect of laser irradiation on the superconducting properties of high- T c SmBa 2 Cu 3 O x

Abstract: Studies of the effect of high power laser (Q-switched Ruby laser, 694 nm, 30 ns) irradiation on the critical current density (J c ) and magnetic hysteresis at 77K and temperature variation of microwave induced d.c. voltage on SmBa2Cu3O x ceramic samples have been performed. Irradiation did not substantially changeT c but caused a strong increase inJ c and magnetic hysteresis at 77K. The microwave-induced d.c. voltage at 77K showed appreciable decrease after irradiation. SEM studies showed grain growth due to sintering which improves the interconnectivity among the superconducting grains. These are attributed to physical densification and consequent reduction in the number of weak links. The increase of magnetic hysteresis after laser irradiation is presumably connected with the creation of defects which act as pinning centres. Thermal modelling suggests that on irradiation the surface melts up to a depth of 1µ and laser-induced evaporation occurs at energy density of 2·5 J/cm2.

Durability investigation of a KCl:Li FA-center optical memory at room temperature

Abstract: The reorientation of F(A)(II) centers in electrolytically colored KCl:Li crystals under ruby laser exposure was studied at room temperature. A prolonged series of laser pulses was applied over a period of three days to check the durability and possible fatiguing of the crystals.

What is eye safe

Abstract: Manufacturers have referred to lasers with operating wavelengths longer than 1400 nm (mid to far infrared) as eyesafe. Wavelengths in this region are absorbed in anterior portions of the eye (mainly cornea) and therefore never reach the retina. This is in contrast to the eye- hazardous portion of the optical spectrum of 400 - 1400 nm (visible and near infrared) where the anterior portions of the eye have high transmittance and refractive power. Irradiance levels are typically 5 orders of magnitude greater at the retina than at the cornea for visible and NIR wavelengths. Although wavelengths longer than 1400 nm do not interact with the retina, they can interact with the skin or cornea and cause a thermal injury. Specifiers of laser equipment have required that systems be eyesafe at a particular distance with or without optics. By this they mean that exposure at that distance for the naked eye or optically aided viewing through a specified power of optics should not exceed exposure limits. Some wavelengths in the visible and near IR are more 'eyesafe' than others because the safety factor between the level that would actually produce an injury (ED-50 value) and the exposure limit is greater. For example, the ED-50 value for a single Q-switched laser pulse for the ruby laser wavelength of 694.3 nm is 11.2 (mu) J into the eye and the Accessible Emission Limit (AEL) is 0.19 (mu) J, a factor of 59 between ED-50 and the AEL. The ratio for 1064 nm for a single Q- switched pulse is 99 (mu) J/1.9 (mu) J or 52. So, in a sense, exposure to 694 laser radiation at the AEL, is slightly more 'eyesafe' than exposure to 1064 nm radiation at the AEL. To the laser safety specialist, however, eyesafe, means only one thing, Class 1. Class 1 is a laser hazard classification that means the laser does not exceed specified limits for a reasonable, worst-case combination of distance, exposure duration, and collecting aperture diameter during its intended use. Determining whether a laser is Class 1 is usually a two-step process. The first step is determination of the AEL and the second is determining whether or not the laser in question exceeds this AEL. Exceeding the AEL is determined by calculation or measurement. If the AEL is exceeded under prescribed parameters then the laser is not Class 1. Differences in laser safety standards in both of these classification steps have caused confusion. Differences in exposure limits chosen by laser safety specialists based upon the same criteria have also caused confusion.

Are Einstein’s transition probabilities for spontaneous emission constant in plasmas?

Abstract: The quenching of spontaneous emission coefficients, presumably by electron collisions, which was recently inferred at Princeton from measured intensity ratios of visible and extreme‐ultraviolet lines from a common upper level in laser blow‐off plasmas, was investigated using a ruby laser. The line intensity ratios of the Civ 3s‐3p and 2s‐3p transitions, for similar laser targets, show a similar dependence on separation from the target as the previous experiments. Both of these results can, however, be interpreted in terms of density gradients and Stark broadening without invalidating Einstein A values. This interpretation also applies to Ciii and Nv line intensity ratios, which are further compromised by blends with other lines. The quenching of Arii lines by photon collisions, which had been reported by the same Princeton group, can finally be shown to have been mimicked by other effects, in this case by the Rabi oscillations and associated power broadening in the argon ion laser cavity.

Feasibility of constructing a picosecond terawatt neodymium laser with a contrast ratio ~?1013

Abstract: A proposal is made and calculations are reported for a neodymium glass laser system capable of generating picosecond terawatt-power pulses with a leading edge of ~ 1 ps duration at the 10−13 level. Formation of a pulse at λ = 1.056 μm would involve a two-stage stimulated Raman scattering process of frequency conversion of ruby laser radiation in SF6 and H2.

Length of Laser-Produced Dense Plasma in High Pressure Argon Gases

Abstract: When a high pressure gas was irradiated by a focused ruby laser light, a hot and dense plasma was produced, and moved towards the lens under the action of the laser radiation. The length of the laser-produced plasma was calculated on the basis of a breakdown wave and a radiation supported shock wave processes. The plasma length is experimentally observed in high pressure argon gas up to 200 atm, which agrees with the calculated one. At high pressure, the breakdown wave is dominant, while the radiation supported shock wave is predominant at low pressure.

Multiframe interferometric study of a laser irradiated plasma in the presence of the two plasmon decay instability

Abstract: The temporal development of the electron density distribution in a CO2‐laser produced plasma is studied interferometrically at 10.5 GHz framing rates with 50 psec resolution. The plasma is produced in a helium gas jet target and has a maximum density of 5×1018 cm−3. Thomson scattering of probe ruby laser radiation in a second experiment shows that the two plasmon decay instability is excited in this plasma and appears in multiple bursts. Excellent correlation between the temporal variations of the density scale length just below quarter critical density and that of the two plasmon decay wave intensity demonstrates the instability quenching property of ponderomotive profile steepening.

Lasers as a Test Bench for Theories of Non-Equilibrium Structures

Abstract: The appearance of intensity pulsations at the output of a laser was noted immediately after the first successful operation of the ruby laser. At first this phenomenon was thought to be the consequence of external noise, optical inhomogeneities in the active medium or mechanical instabilities; later it became apparent that, while the stability of the output intensity was surely conditioned by instrumental imperfections, self-pulsing could also be the consequence of the nonlinear interaction between the electromagnetic radiation and the active atoms [1]. In 1975 H. Haken [2a] showed that the single mode equations of the laser are isomorphic to the Lorenz equations [2b]. Because the latter at that time were already known to include chaotic oscillations among its possible solutions, Haken’s proof endowed the laser with a complex temporal phenomenology of its own. In the early 1980’s the first experimental observations of period doubling, bifurcations and chaos began to appear in the literature [3 4]. Maybe, the main reason for the delay was the fact that during two decades laser physicists were worried more on the design of new and more stable lasers than in the study of laser physics. Since 1982 a a considerably body of evidence has been uncovered leading to the observation of period doubling, quasi-periodicity, intermittency, crises, Shil’nikov instabilities and many other phenomena in optical systems [5 6].

Laser-produced continua for studies in the XUV

Abstract: The spectrum of a laser-produced plasma in the XUV-VUV region consists typically of many strong emission lines together with varying degrees of continuum, the latter being due primarily to recombination. In plasmas produced by a Q-switched ruby laser (approximately 1 J output in approximately 25 ns) on a range of high Z targets, in particular the rare earth metals, it was found that the spectrum, over a wide wavelength region, consisted of smooth continuum with apparently no individual lines. The spectrum of samarium, for example, consisted of continuum from approximately 200 to 4 nm with no evidence of lines (except occasional impurity lines, due usually to oxygen). For ytterbium a similar clean continuum extended from 60 to 4 nm (the limit of the authors observations). The dominant stages of ionization in the plasmas are A10+ to A15+, and the observed absence of lines can be explained by a consideration of the electron configurations in these stages. The continua are very useful for experiments such as absorption spectroscopy and other applications in the XUV-VUV region and offer an alternative to the synchrotron when polarized radiation is not required. The sources are simple to mount and operate, are reproducible, intense, and insensitive to ambient pressure. Because of their pulsed mode of operation they are particularly suitable for time-resolved studies. Several applications of the sources are described and some possible future developments are suggested, including the use of excimer lasers.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Laser‐Induced Defect Formation in ZnxCd1−xSe Solid Solutions and Its Influence on Electrophysical Properties

Abstract: The influence of irradiation with ruby laser emission pulses of 2 × 10−8 s in duration on electrical, photoelectrical, and luminescent properties of single crystals of ZnxCd1−xSe solid solutions (SS) is investigated. An increase of the conductivity and photosensitivity in irradiated samples is observed, which is explained by the formation of r-centres, which are metal vacancies counterbalanced by shallow donor centres. Also, a layer with a wider forbidden gap forms in the subsurface region of ZnxCd1−xSe SS crystals after irradiation. The composition changes by 3 to 5% towards an increase of x. [Russian text Ignored.]

How to get an exact impact on the object in double-pulsed ruby laser holographic interferometry-new instrumentation

Abstract: A new instrumentation for non-destructive testing of metals is described. In the course of the test an external impact is given to the object and simultaneously a double-pulsed ruby laser interferogram is taken of the object. The difficulty with these kinds of NDT method is to get a good, well controlled impact. The problem is solved by using a CO2 pistol and a timer based on a fast hardware multiplier. The apparatus designed for working outside the laboratory, and some results, are described.

Laser medical treatment device

Abstract: PURPOSE:To execute a safe and exact medical treatment by providing a guide light radiating means for radiating a guide light oscillated in a visible area, and a film plate which is placed in protective spectacles and reduces a laser light, and also, has a light reduction characteristic for allowing the guide light to pass through. CONSTITUTION:An operator wears protective spectacles G10 and holds a case of a laser radiating part 14, and radiates a guide light to the body surface Of of a living body. Subsequently, the laser radiating part 14 is moved and positioned so that the affected part to be brought to medical treatment is positioned between two pieces of irradiation patterns P1G. Next, the operator emits a ruby laser light from a laser control part 12 in a state he wears the protective spectacles G10. This laser light is guided in an optical fiber 13a and transmitted to the laser radiating part 14, and a laser light is condensed strongly by a laser light radiating light guide 18, and radiated to the affected part. Since a medical treatment by a laser light can be executed in a state of wearing the protective spectacles G10, an irradiation object part, an irradiation field, etc., of a laser light can be confirmed easily, the operability is satisfactory, and the medical treatment is executed safely and exactly.

Design requirements of a pulsed ruby laser for an underwater holographic camera

Abstract: The practical implementation of wavelength compensation in a portable underwater holographic camera is primarily intended to provide a facility for the inspection and metrology of subsea installations within the offshore oil and gas industries. Stability requirements dictate that the camera should incorporate a pulsed laser source. The choice of a suitable source is considerably limited by the requirement that the recording and replay wavelengths comply with the condition for wavelength compensation. The authors consider the design aspects of a pulsed ruby laser that is used in the development of the camera. >

Ion flows from laser-irradiated microcylinders

Abstract: Hollow aluminium microcylinders were irradiated internally through a circular aperture located in one wall using a pulsed ruby laser beam. Plasma formation and ion flows were monitored using a Nomarski interferometer and an array of Faraday cups. A collimation of ion energy along the cylinder axis was observed.

Generation of single-frequency high-power microsecond pulses by a ruby laser

Abstract: It was established that mode competition has a decisive influence on the kinetics of the intensity and the emission spectrum of a ruby laser with slow resonator-Q switching. Smooth pulses having a duration of 1–10 μs, a spectral width of ~ 10 − 4 cm − 1, and a power of up to 10 kW were obtained. It was demonstrated that, under free-running conditions, quasi-cw emission of a single mode (single-frequency lasing) with a duration of up to 300 μs and a radiation power higher than 100 W could be achieved. These results are of interest for high-speed interferometry.