Showing papers on "Laser published in 1978"

Photosensitivity in optical fiber waveguides: Application to reflection filter fabrication

Abstract: The observation of photosensitivity in Ge‐doped core optical fibers is reported. The photosensitivity is manifested by light‐induced refractive‐index changes in the core of the waveguide. Narrowband reflectors in a guide structure have been fabricated using this photosensitivity and the resulting DFB reflectors employed as laser mirrors in a cw gas laser in the visible.

Spectrally narrow pulsed dye laser without beam expander.

Abstract: We have developed a simplified version of the side-pumped pulsed dye laser which has a spectral halfwidth of 1.25 GHz and a peak power of 10 kW at 600 nm. The basic laser consists of only four components (output mirror, dye cell, diffraction grating, and tuning mirror) and is exceptionally easy to align. Since the beam expander has been eliminated, the laser cavity can be made quite compact. Under the condition of reduced gain, the laser has been operated in a single mode.

Coherent trapping of atomic populations.

Abstract: It is often desirable in laser spectroscopy and isotope separation to extract as much as possible of an atomic or molecular population that is distributed among a number of ground-state sublevels and low-lying metastable levels. We describe a form of coherent trapping that occurs when multiple resonant laser beams are used to couple the various ground states to a common upper level. This effect prevents the extraction of the entire population. We then study the effect with two dye lasers and an atomic beam and suggest possible ways to maximize the pumping efficiency.

"Optical-sideband Cooling of Visible Atom Cloud Confined in Parabolic Well"

Abstract: An assemblage of 50 ${\mathrm{Ba}}^{+}$ ions, contained in a parabolic well, has been visually observed and cooled by means of near-resonant laser irradiation.

Laser beam propagation in the atmosphere

Abstract: The classical theory of wave propagation in a turbulent medium- Modern theories in the propagation of optical waves in a turbulent medium- Similarity relations and their experimental verification for strong intensity fluctuations of laser radiation- The beam wave case and remote sensing- Imaging and optical communication through atmospheric turbulence- Thermal blooming in the atmosphere

An electronic transition chemical laser

Abstract: cw laser action was achieved on the 2P1/2→2P3/2 transition of the iodine atom by energy transfer from the 1Δ metastable state of O2. The excited oxygen was generated chemically by flowing chlorine gas through a basic solution of 90% H2O2. The effluent from the oxygen generator was mixed with molecular iodine at the entrance of a longitudinal flow laser cavity where the I2 was dissociated by a small amount of O2(1Σ) that was present in the flow due to energy pooling processes. The measured output power was greater than 4 mW.

Industrial Applications of Lasers

Abstract: Preface. Acknowledgments. Historical Prologue: Fundamentals of Lasers. Electromagnetic Radiation. Elementary Optical Principles. Energy Levels. Interaction of Radiation and Matter. Laser Materials. Population Inversion. Resonant Cavity. Selected References.Properties of Laser Light: Linewidth. Beam Divergence Angle. Spatial Profiles of Laser Beams. Temporal Behavior of Laser Output. Coherence. Radiance. Focusing Properties of Laser Radiation. Power. References. Selected Additional References. Practical Lasers: Gas Lasers. Solid State Lasers. Semiconductor Lasers. Organic Dye Lasers. References. Selected Additional References. Trends in Laser Development: Semiconductor Lasers. Diode-Pumped Solid State Tunable Lasers. Chemical Lasers. Free Electron Lasers. X-Ray Lasers. References. Selected Additional References. Laser Components and Accessories: Mirrors. Optics. Polarizers. Infrared Materials. Detectors. Modulators. Light Beam Deflectors. Q-Switches. Nonlinear Optical Elements. Optical Isolators. Raman Shifters. Injection Seeders. Beam Profilers. Optical Tables. Spatial Light Modulators. Beam Homogenizers. Selected References. Care and Maintenance of Lasers: Damage and Deterioration of Lasers.Care and Maintenance. References. Selected Additional References. Laser Safety: Physiological Effects. Laser Safety Practices and Standards. References. Selected Additional References. Alignment, Tooling and Angle Tracking: Position-SensitiveDetectors. Laser Tooling. Angle Tracking. Lasers in Construction. References. Selected Additional References. Principles Used in Measurement: The Michelson Interferometer. Beat Production (Heterodyne). The Doppler Effect. Coherence Requirements. Selected References.Distance Measurement and Dimensional Control: Interferometric Distance Measurement. Laser Doppler Displacement. Beam Modulation Telemetry. Pulsed Laser Range Finders. A Laser Interferometer Application in Mask Production: A Specific Example of Distance Measurement and Dimensional Control. References. Selected Additional References. Laser Instrumentation and Measurement: Velocity Measurement. Angular Rotation Rate. Diffractive Measurement of Small Dimension: Wire Diameter. Profile and Surface Position Measurement. Measurement of Product Dimension. Measurement of Surface Finish. Particle Diameter Measurement. Strain Measurement. Vibration. Cylindrical Form Measurement. Defect Detection. Surface Flaw Inspection Monitor-A Specific Example. Summary. References. Selected Additional References. Interaction of High-Power Laser Radiation with Materials: References. Selected Additional References. Laser Applications in Material Professing: Selected References. Applications of Laser Welding: Seam Welding-Subkilowatt Levels. Welding with Multikilowatt Lasers Spot Welding. Specific Examples of Laser Welding Capability. Summary. References. Selected Additional References. Applications for Surface Treatment: Hardening. Glazing. Laser Alloying. Laser Cladding. Specific Examples of Laser Heat Treating Capability. References. Selected Additional References. Applications for Material Removal: Drilling, Cutting, Marking: Laser-Induced Material Removal. Hole Drilling. Cutting. Scribing. Marking. Balancing. Paint Stripping. Laser Deposition of Thin Films. Specific Examples of Material Removal. References. Selected Additional References. Lasers in Electronic Fabrication: Established Applications in Electronics.Applications in Integrated Circuit Fabrication. Summary. A Specific Example-Laser-Based Photomask Repair. References. Selected Additional References. Principles of Holography: Formation of Holograms. The Holographic Process. Hologram Types and Efficiency. Practical Aspects of Holography. References. Selected Additional References. Applications of Holography: Holographic Interferometry. A Miscellany of Applications. Holographic Optical Elements. An Example of Holographic Application. References. Selected Additional References. Laser Applications in Spectroscopy: Lasers for Spectroscopic Applications. Types of Laser Spectroscopy. Applications of Laser Spectroscopy. References. Selected Additional References. Chemical Applications: Laser-Initiated Reactions. Laser-Altered Reactions. Laser Monitoring of Chemical Dynamics. Isotope Separation. References. Selected Additional References. Fiber Optics:References. Selected Additional References. Integrated Optics: Optical Waveguides. Components for Integrated Optics. Integrated Optic Circuits. Applications. References. Selected Additional References. Information Related Applications of Lasers: Lightwave Communications. Optical Data Storage. Optical Data Processing. Laser Graphics. Consumer Products. References. Selected Additional References. Epilogue--A Look at the Future. References. Selected Additional References.

Time‐resolved reflectivity of ion‐implanted silicon during laser annealing

Abstract: The time‐resolved reflectivity at 0.63 μm from arsenic‐implanted silicon crystals has been measured during annealing by a 1.06‐μm laser pulse of 50‐ns duration. The reflectivity was observed to change abruptly to the value consistent with liquid silicon and to remain at that value for a period of time which ranged from a few tens of nanoseconds to several hundreds of nanoseconds, depending on the annealing pulse intensity. Concurrently, the transmission of the primary annealing beam dropped abruptly. These observations confirm the formation of a metallic liquid phase at the crystal surface during the annealing process.

Heterostructure lasers. Part A. Fundamental principles

Abstract: The book consists of two parts. Part A contains chapters entitled: Introduction; Optical Fields and Wave Propagation; Stimulated Emission in Semiconductors; and Heterojunctions. (TFD)

Single-mode operation of grazing-incidence pulsed dye laser.

Abstract: A variation of the grazing-incidence pulsed dye laser is presented. This laser has been operated in a single longitudinal cavity mode with a single-shot linewidth of less than 300 MHz and a time-averaged linewidth of 750 MHz. The single-mode conversion efficiency of the laser is 2% using Rhodamine 6G dye.

Time dependent propagation of high-energy laser beams through the atmosphere, 4

Abstract: Various factors that can effect thermal blooming in stagnation zone situations are examined, including stagnation-zone motion, longitudinal air motion in the neighborhood of the stagnation zone, and the effects of scenario noncoplanarity. Of these effects, only the last offers reasonable hope of reducing the strong thermal blooming that normally accompanies stagnation zones; in particular, noncoplanarity should benefit multipulse more than cw beams. The methods of treating nonhorizontal winds hydrodynamically for cw and multipulse steady-state sources are discussed. Aspects of pulse “self-blooming” are also considered.

Heavily doped semiconductors and devices.

Abstract: High carrier concentrations and the fluctuations in random potential resulting from ionized impurities alter the density of states and electron wavefunctions in heavily doped semiconductors. The theoretical and experimental work on these effects is reviewed, special attention being paid to the consequences for the optical and transport properties. Semiconductor devices are often heavily doped and the influence of heavy doping is illustrated in the injection laser and bipolar transistor, which also serve as investigative tools.

Picosecond pulse generation with a cw GaAlAs laser diode

Abstract: We report the generation of 20‐ps optical pulses at microwave repetition rate from a GaAlAs double‐heterostructure diode operating cw at room temperature The diode is operated in an external optical resonator and is actively modulated at 3 GHz The pulses are measured by autocorrelation using SHG in LiIO3 They are the shortest pulses ever reported for a cw laser diode

An Instrument to Measure Cutaneous Blood Flow Using the Doppler Shift of Laser Light

Abstract: A system utilizing the Doppler shift of monochromatic laser light has been developed to measure blood flow in skin. Light from a low power (S mW) He-Ne laser is coupled into a quartz fiber and transmitted to the skin. This light is reflected from both the nonmoving tissues (reference beam) and moving red blood cells (Doppler shifted beam), received by a plastic fiber, and transmitted back to a photodiode where optical heterodyning occurs. The heterodyned output signal, which is proportional to the Doppler shift frequency, is amplified and both RMS and dc values obtained. The RMS value is weighted against the backscattered light intensity using the measured dc value as an index of total received power. This is used as the output flow velocity value.

Detection of Optical and Infrared Radiation

Abstract: 1. Thermal Radiation and Electromagnetic Modes.- 2. The Ideal Photon Detector.- 3. Coherent or Heterodyne Detection.- 4. Amplifier Noise and Its Effect on Detector Performance.- 5. Vacuum Photodetectors.- 6. Noise and Efficiency of Semiconductor Devices.- 7. Thermal Detection.- 8. Laser Preamplification.- 9. The Effects of Atmospheric Turbulence.- 10. Detection Statistics.- 11. Selected Applications.- References.

Infrared‐laser‐induced unimolecular reactions

Abstract: Photochemistry, which deals with the way in which chemical reactions are induced or altered by the presence of photons, has been a very active branch of science for many years. Although visible and ultraviolet photons, by giving rise to excited electronic states, have the most pronounced effects, much attention in recent years has gone to infrared photochemistry. Molecules irradiated with a powerful electromagnetic wave in the infrared remain in the electronic ground state (in the Born–Oppenheimer sense), but their vibrational modes may become highly excited. As a result, infrared‐laser radiation often profoundly affects chemical reaction rates.

cw laser anneal of polycrystalline silicon: Crystalline structure, electrical properties

Abstract: 0.4‐μm‐thick polycrystalline silicon deposited in a low‐pressure CVD reactor was implanted with B to a dose of 5×1014/cm2 and then irradiated in a cw laser scanning apparatus. The laser annealing produced an increase in grain size from ∼500 A to long narrow crystals of the order of ∼25×2 μ, as observed by TEM. Each grain was found to be defect free and extended all the way to the underlying Si3N4. Electrical measurements show 100% doping activity with a Hall mobility of about 45 cm2/V sec, which is close to single‐crystal mobility at the same carrier concentration. Thermal annealing produces material with an average grain size of 1000 A and a resistivity higher by a factor of 2.2 than that obtained with the laser anneal. Laser annealing performed after a thermal anneal reduces the resistivity to approximately the same value obtained by laser annealing only.

Collision Experiments with Laser Excited Atoms in Crossed Beams

Abstract: Publisher Summary This chapter discusses collision experiments using laser excited atoms in crossed beams. With the advent of tunable narrow-band lasers, especially cw dye lasers, the situation has changed and it has become clear that it should be possible to excite atoms optically within the scattering region of an otherwise conventional crossed-beam experiment. In this way a steady-state upper-state population could be reached that may be comparable to the ground-state population. When an atomic beam is excited, it is free of internal collisions and, for right angle intersection with the laser, free of Doppler broadening. Then the laser properties allow selecting the state into which the atom is excited. Specific fine- and hyperfine-structure states may be chosen as well as a particular combination of sub-states. The novel techniques allow preparing states with an angular momentum different from zero and to vary systematically the alignment and orientation of the resulting non-spherical interaction potentials. Frequency doubling of dye lasers can also widen the scale of possible applications. Very high powers are needed and one probably would have to use a pulsed laser. An alternative to frequency doubling is the direct two-photon excitation of atoms.

Is complete spatial coherence necessary for the generation of highly directional light beams

Abstract: An equivalence theorem is formulated that provides conditions under which planar sources of different states of spatial coherence will generate optical fields that have identical far-zone intensity distributions. As an example, a partially coherent source whose linear dimensions are large compared with the correlation length of the light across the source is described that will generate a field whose far-zone intensity distribution is identical with that of a Gaussian laser beam.

Laser annealing of boron-implanted silicon

Abstract: The properties of boron‐implanted silicon annealed by high‐power Q‐switched ruby laser radiation are compared with results obtained by conventional thermal annealing. Laser annealing of the implanted layer results in significantly increased electrical activity, as compared to thermally annealed implanted silicon. This correlates well with transmission electron microscopy and ion‐channeling measurements which show a dramatic removal of displacement damage as a result of laser annealing. A substantial redistribution of the implanted boron concentration profile occurs after laser annealing which cannot be explained by thermal diffusion in the solid.

Laser‐generated stress waves in liquids

Abstract: The generation of laser‐induced stress waves in liquids by the vaporization process and the thermoelastic effect was studied experimentally. A high‐speed camera and special high‐sensitivity stress transducers with a response time of a few nanoseconds have been used for these investigations. The experimental results obtained for water, n‐heptane, and carbon tetrachloride are discussed. For the first time, the individual contributions of vaporization and the thermoelastic effect on stress generation are separated. In addition, tunable high‐frequency acoustic waves, with frequencies up to 60 MHz, have been generated in water by the impact of a laser pulse exhibiting longitudinal mode beating. Since existing theories on the thermoelastic generation of acoustic waves do not yield satisfactory agreement with our experimental data, a new spherical model is proposed, where the transient heating caused by the laser impact, is represented by the three‐dimensional heat pole. This solution of the equation of heat conduction corresponds to a Gaussian distribution of the excessive temperature in space, and thus to the TEM00 mode of the incident laser beam. An analytical solution of the thermoelastic pressure wave is derived for this case of temperature distribution. Its good agreement with the experiment is discussed for various liquids and for two different laser characteristics.

Laser photo-CIDNP as a surface probe for proteins in solution

Abstract: APPLICATIONS of chemically induced dynamic nuclear polarisation (CIDNP) have been limited so far to reactions of small organic molecules1,2. We report here the observation of CIDNP in the 360-MHz NMR spectrum of a protein. The effect is generated by a cyclic reaction of a photo-excited dye with certain amino acid residues that are accessible to the dye. Of the common amino acids polarisation has been observed in tyrosine, histidine and tryptophan. The method distinguishes between exposed and buried groups and thus yields valuable information on the solution structure of proteins. Here we discuss the CIDNP observed in tyrosine residues of bovine pancreatic trypsin inhibitor (BPTI). The three-dimensional structure of BPTI (molecular weight 6,500) has been studied extensively by X-ray crystallography3,4 and by NMR5,6.

Computer modeling of gas lasers

Abstract: The book offers an extensive in-depth examination of gas kinetics, excitation processes, hydrodynamics, and other important aspects of gas lasers with specialization to CO2. Almost every area of modeling discussed includes a standard description of an appropriate computer program. Most of the theory discussed is readily applicable to other gas systems. The discussion covers relaxation phenomena in gases, vibrational kinetics, electron excitation rates, rotational kinetics, a general plasma model, plasma chemistry models of gas lasers, stability analysis of laser plasmas, the Haas approximation to the general model, devices (unstable optical resonators, waveguide lasers, FIR gas lasers), and injection locking.

Measurement of excited‐state‐absorption loss for Ce3+ in Y3Al5O12 and implications for tunable 5d→4f rare‐earth lasers

Abstract: Broad bandwidth 5d→4f transitions in Ce3+ have been considered for tunable laser action. In this letter, optical probe measurements of excited Ce3+ ions in Y3Al5O12 show that stimulated emission in the 550–610‐nm region is not possible at 295 K because of excited‐state absorption. Transient measurements demonstrate that part of this loss has ≈75‐ns lifetime and is associated with absorption from the lowest 5d level; a longer‐lifetime loss is also observed. The excited‐state‐absorption loss is reduced at lower temperatures.

Linear, annular, and radial focusing with axicons and applications to laser machining

Abstract: New optical combinations of axicons and axicons with spherical mirrors and lenses suitable for laser machining are presented. Linear and annular focusing, coaxially and radially to the laser beam, are possible. Most combinations allow continuous adjustment of exit beam parameters, focal line length, focal ring diameter, and magnification, by varying the relative position of one of the axicons. Potential new laser applications are also discussed in relation to these optical devices.

Multiphoton dissociation of molecules with low power continuous wave infrared laser radiation

Abstract: Recent studies have suggested the possibility of effecting dissociation processes with relatively low power CW lasers (several watts) provided that a molecule can be irradiated under nearly collision-free conditions for times approaching 1 sec. The establishment of such conditions and the observation of multiphoton dissociation processes are reported. The methodology applies techniques involving trapped ion cyclotron resonance spectroscopy and a CW CO/sub 2/ laser. Typical experimental conditions and results are described for the irradiation of diethyl ether at long trapping times and low pressures. The processes occurring during the photoionization were determined. The dissociation rate has a linear relationship with irradiation time and no dependence on wavelength over the 925 to 1090 cm/sup -1/ tuning region of the laser. (JSR)

Laser tunnelling device

Abstract: A device for use primarily in medical applications to locate, analyze, illuminate and destroy obstructions in a tube. The device includes a fiberoptics bundle for insertion to the tube in a flexible conduit. The conduit includes a connection to a suction source at one of its ends, a valved means of controlling the application of suction, which functions also to control the injection of locating material, and a connection to the fiberoptics bundle. The fiberoptics bundle is divided into an illuminating source bundle portion, a viewing bundle portion and a laser bundle portion. The device functions to remove obstructions in tube structures, both biological and non-biological, by insertion of the conduit sheathed device into the tube structure, distal to the obstruction. A dye, or the like, is injected and the site of the obstruction thereby determined under the guidance of image-intensified fluoroscopy. The conduit is moved toward the obstruction until resistance is felt, and the negative pressure source or suction applied to attach the conduit to the obstruction. The physical contact between the device and the obstruction, as well as the physical appearance of the obstruction, are determined by direct viewing. The obstruction is then vaporized by the laser beam with vaporized debris being constantly removed by the suction, and at the same time, the conduit is advanced by the suction, so that it is in continuous contact with the obstruction. A transparent reservoir is connected to the conduit so that upon complete tunnelling an indication thereof may be observed in the transparent reservoir.