Showing papers on "Laser published in 1972"

Laser interferometer for measuring high velocities of any reflecting surface

Abstract: A laser velocity interferometer instrumentation system has been developed which can measure the velocity history of either spectrally or diffusely reflecting surfaces. The system provides two interferometer fringe signals in quadrature to improve resolution and to distinguish between acceleration and deceleration. Accuracies of 2% or better are attainable for peak surface velocities of 0.2 mm/μsec or more. The system has been applied to the measurement of free surface motion in plate‐impact experiments, and to the measurement of the velocity history of a projectile during its acceleration down a long gun barrel.

Laser Compression of Matter to Super-High Densities: Thermonuclear (CTR) Applications

Abstract: Hydrogen may be compressed to more than 10,000 times liquid density by an implosion system energized by a high energy laser. This scheme makes possible efficient thermonuclear burn of small pellets of heavy hydrogen isotopes, and makes feasible fusion power reactors using practical lasers.

Fluorescence Activated Cell Sorting

Abstract: An instrument has been developed for sorting biological cells. The cells are rendered differentially fluorescent and incorporated into a small liquid stream illuminated by a laser beam. The cells pass sequentially through the beam, and fluorescent light from the cells gives rise to electrical signals. The stream is broken into a series of uniform size drops downstream of the laser. The cell signals are used to give appropriate electrostatic charges to drops containing the cells. The drops then pass between two charged plates and are deflected to appropriate containers. The system has proved capable of providing fractions containing large numbers of viable cells highly enriched in a particular functional type.

Astigmatically compensated cavities for CW dye lasers

Abstract: An analysis is given of folded 3-mirror laser resonators with an internal cell set at Brewster's angle. A method is described to compensate the astigmatic distortions introduced by both the internal mirror and the cell. This compensation is achieved for a specific relation between cell thickness and folding angle. It allows the formation of a tight intracavity focus as required in applications such as CW dye lasers. A discussion is given of the mode characteristics of compensated cavities and of the limitation on beam concentration set by the thickness of the Brewster cell.

Reflectivity of mode at facet and oscillation mode in double-heterostructure injection lasers

Abstract: Reflectivity of a cleaved facet forming a laser cavity in a double heterostructure injection laser is analyzed on the basis of a dielectric waveguide model and the reflectivity of modes is numerically provided for a GaAs-AlGaAs double-heterostructure injection laser. The modes that distinguish field distributions perpendicular to a junction plane are considered up to the sixth order with TE and TM modes. The dependence of threshold conditions on the mode, the relations between the lowest threshold mode and the structures of the injection laser are studied. Provided mode reflectivity is solely responsible for modal selection, the single-mode operation is theoretically shown to be possible by choosing a suitable length of the cavity even though the thickness of the active layer is large.

Resonant absorption of laser light by plasma targets.

Abstract: It is proposed that a resonant mechanism should cause significant absorption of energy from intense laser pulses in plasma targets, and that the energy should be deposited in such a way as to form a very non-Maxwellian high-temperature tail on the electron velocity distribution

Passive mode locking of the cw dye laser

Abstract: Passive mode locking of a cw Rhodamine 6G laser is reported. A stable continuous output of picosecond pulses has been achieved. Correlation measurements using second‐harmonic generation (SHG) have determined the pulses to be as short as 1.5 psec. The pulses are transform limited and are wavelength tunable over the range 5900–6100 A.

Measurement of Particle Size, Number Density, and Velocity Using a Laser Interferometer

Abstract: A method for determining particle size, number density, and velocity utilizing a laser interferometer is analyzed. The results show that when the fringe spacing is comparable to a particle diameter, size can be estimated; and when the fringe spacing is much greater than the average particle diameter, number density can be measured. Since the optical arrangment for the interferometer is identical to that for a number of laser velocimeters, the effects of particle size on the velocimeter signal are discussed.

Coupling losses in hollow waveguide laser resonators

Abstract: Hollow waveguide gas lasers of the type described by Smith have some inherent loss in coupling radiation from the guide into free space and back into the guide. This paper calculates that loss for the EH 11 lowest order waveguide mode as a function of mirror position and mirror radius. It is shown that some mirror positions and radii are optimum, in that they provide low coupling loss and are relatively insensitive to mirror position.

Lased Enamel: Ultrastructural Observations of Pulsed Carbon Dioxide Laser Effects

Abstract: Scanning electron microscopic observations of the pulsed carbon dioxide laser effect on human enamel support microradiographic findings and indicate that this laser is significantly more efficient than the ruby laser within the limits of this investigation. Surface changes which were suggestive of fusion occurred between energy densities of 13 to 50 joules per square centimeter.

Speed of Light from Direct Frequency and Wavelength Measurements of the Methane-Stabilized Laser

Abstract: The frequency and wavelength of the methane-stabilized laser at 3.39 \ensuremath{\mu}m were directly measured against the respective primary standards. With infrared frequency synthesis techniques, we obtain $\ensuremath{ u}=88.376181627(50)$ THz. With frequency-controlled interferometry, we find $\ensuremath{\lambda}=3.392231376(12)$ \ensuremath{\mu}m. Multiplication yields the speed of light $c=299792456.2(1.1)$ m/sec, in agreement with and 100 times less uncertain than the previously accepted value. The main limitation is asymmetry in the krypton 6057-\AA{} line defining the meter.

Introduction to Classical and Modern Optics

Abstract: Preface. 1. Reflection and Refraction. 2. Thin Lenses. 3. Thick Lenses and Combinations of Lenses. 4. Mirrors. 5. Aberrations. 6. Stops and Pupils. 7. Gradient-Index, Fiber, and Integrated Optics. 8. Lens Design. 9. Optical Systems. 10. Systems Evaluation. 11. Interference. 12. Thin Films. 13. Coherence. 14. Diffraction. 15. Diffraction Gratings. 16. Light Scattering. 17. Polarization of Light. 18. Optical Data Processing. 19. Holography. 20. Light Sources and Detectors. 21. Radiometry/Photometry. 22. Absorption. 23. Lasers. 24. Relativistic Optics. Answers to Odd-Numbered Problems. Index.

Selective Two-Step (STS) Photoionization of Atoms and Photodissociation of Molecules by Laser Radiation.

Abstract: The general considerations for two-step photoionization of atoms and photodissociation of molecules using tunable laser sources are discussed. Experimental results are given for the (1) photoionization of rubidium vapor using a ruby-laser-pumped dye laser and a doubled ruby laser radiation, and (2) photodissociation of HCl using the Raman-shifted output and the fourth harmonic output of a tunable Nd-glass laser. The possibilities for other laser systems are also discussed.

Mode selection in lasers

Abstract: This is a tutorial review on the subject of mode selection in lasers. We begin with a historical review. After an introduction to the subject of modes in laser resonators and a brief review of the theory of laser gain saturation, the main body of the paper is devoted to a discussion of various mode-selection techniques, many which can be used to produce single-frequency laser operation. We discuss some systems for frequency stabilization of single-frequency lasers, and conclude with examples of laser applications where mode-selection techniques are required.

Instrument for performing laser micro-surgery and diagnostic transillumination of living human tissue

Abstract: An instrument for performing delicate surgery on man is provided with a continuous wave laser source specially associated with a binocular surgical microscope. The laser source emits electromagnetic radiation at wavelengths, preferably in the visible light range but also in the near visible infrared and ultraviolet ranges, which are absorbed selectively by different types of human tissue or tissue substructures. The source is mounted on a portable base remote from the operating area, and the radiation from the laser is communicated through a flexible fiber optic conductor to the binocular surgical operating microscope which is mounted on an articulating arm extending from the base so that the microscope may be freely positioned adjacent to the patient at the operating area. The laser beam is directed onto the tissue of the patient in a path coaxial with the viewing axis of the microscope to a point in the microscope''s field of view. Controls on the microscope give the surgeon complete control of the laser beam. These include a focusing telescope for control of the laser spot size and angle of convergence of the beam, a joy stick control for moving the fiber optic tip to cause a corresponding movement in the focused laser beam on the tissue within the field of view of the microscope to allow the surgeon to precisely prescribe an incision or effect localized irradiation on that area of the patient. Transillumination of the tissues in the area of interest on the patient is possible by the direct laser beam emitted at a low-nonhazardous power level or by a second laser system which may be operated independently of the main high power surgical laser and is delivered by a hand-held sterile probe.

Ultrasensitive response of a CW dye laser to selective extinction

Abstract: The sensitivity of a broad-band dye laser to selective intracavity absorption is proportional to the number of oscillating modes. This result is obtained from a rate equation model, taking into account the spectral homogeneity, but spatial inhomogeneity of the laser saturation. An increase of absorption sensitivity by a factor of 105, compared to a single-pass measurement, is observed in an experiment with an iodine vapor absorption cell inside the cavity of a CW dye laser. The fluorescence of an external iodine vapor cell provides a convenient selective absorption monitor.

Fluorescence in neodymium ultraphosphate

Abstract: The properties of the Nd-ultraphosphate NdP 5 O 14 (NdUP), a crystalline material that appears to be a promising candidate for an efficient Nd laser, are described. The Nd concentration of 4.1021/cm3is ∼60 times higher than the upper limit useful for doped laser crystals ( \simI percent) like Nd:YAG. Despite the much higher Nd concentration the linewidths and cross sections of the major transitions are shown to be very similar to those of Nd:YAG. Therefore, it is expected that the gain per unit length in NdUP is also ∼60 times higher than in Nd:YAG. The crystal structure, the absorption and fluorescence spectra, level assignments, and various other features of NdUP are reported. Other rare earths form similar insoluble stable compounds. Most of them are transparent from the UV to the near IR except for the absorption bands of the metal ions.

Switching and modulation of light in magneto‐optic waveguides of garnet films

Abstract: We report for the first time switching and modulation of light in a magneto‐optic waveguide that is a single‐crystal epitaxially grown iron‐garnet film. These experiments involve the Faraday rotation of the magnetic film and the motion of magnetization in the plane of the film. We have modulated light from a 1.152‐μm laser up to 80 MHz. We were also able to switch light between two waveguide modes by applying a magnetic field as small as 0.2 Oe.

Proton-bombardment formation of stripe-geometry heterostructure lasers for 300 K CW operation

Abstract: A method of defining the active region of stripe-geometry junction lasers by proton-bombardment-induced high-resistivity layers is described. The method yields more reproducible mode patterns and lower threshold currents than the previously used oxide insulation. The improved lasers operated continuously at heat-sink temperatures up to 110°C.

Frequency stabilization of the helium-neon laser by saturated absorption in iodine vapour

Abstract: Improvements in the frequency stability of the visible helium-neon laser are possible using saturated absorption in iodine vapour. Recent improvements in the design of these lasers are discussed, and the importance of third derivative locking methods in realizing the possible high reproducibility of the iodine reference frequencies is emphasized. Allan Variance measurements of the beat frequency between two stabilized lasers indicate a long term stability of better than 1 part in 1010.

Theoretical Study of Ionization of Air by Intense Laser Pulses

Abstract: A detailed theoretical study of cascade ionization of air by rf fields and by laser beams is given. Experimental rate constants for energy loss, ionization, and attachment are used. The Boltzmann equation for the electrons is solved in both classical and quantum form. Provision is made for both single-photon and multiphoton ionization and detachment processes. The latter processes have been incorporated parametrically in our calculations owing to the lack of a quantitative description of multiphoton absorption. Possible anomalies in comparison with available experiments are noted for photons in the 1-2-eV range when the illuminated volume is large.

Frequency stabilization of internal-mirror helium-neon lasers.

Abstract: A simple and inexpensive frequency stabilization system of a helium-neon two-mode laser with an internal mirror plasma tube is described. The stabilization depends on the comparison of the light intensities of the two operating longitudinal modes. The corresponding frequencies of the modes are symmetrized about the emission line of neon at the transition 3s(2)-2p(4). Experimental results are given. The relative uncertainty of the frequency stabilization is less than 1 part in 10(7).

Electron‐Beam‐Controlled Electrical Discharge as a Method of Pumping Large Volumes of CO2 Laser Media at High Pressure

Abstract: An electron‐beam‐controlled discharge has been used to pump a variety of CO2 laser gas mixtures at atmospheric pressure in substantial volumes. Electrical and laser properties of the pumped medium have been measured. Small‐signal‐gain coefficients up to 0.045 cm−1 were achieved at field strengths of 3 kV/cm.

High‐repetition‐rate optical pulse generator using a Fabry‐Perot electro‐optic modulator

Abstract: A high‐repetition‐rate optical pulse generator which employs a Fabry‐Perot electro‐optic modulator as the output coupler of a laser resonator was constructed. Using this generator with a He–Ne 6328‐A laser tube, 21‐psec optical pulses at a repetition rate of 2.7 × 109 pps were experimentally obtained with an average power level of 0.5 mW. In addition, it is demonstrated that the width of the pulses obtained from this generator can be narrowed without regard to the gain‐linewidth limitation. This kind of pulse generator may be particularly useful for obtaining short optical pulses from low‐gain gas lasers, and it is possible to obtain 1010‐pps picosecond pulses from a He–Ne 6328‐A laser.

Phase‐matched submillimeter wave generation by difference‐frequency mixing in ZnGeP2

Abstract: Using two step‐tunable CO2 lasers, we have observed phase‐matched generation of frequencies 70 <ν<110 cm−1 by nonlinear mixing in a birefringent ternary semiconductor, ZnGeP2. An observed power of ∼1.7 μW at 83.37 cm−1 gave a signal‐to‐noise ratio of ∼1000 with a Ge:Ga detector. In combination with tunable optical lasers, this technique should yield a tunable source of submillimeter wave radiation for high‐resolution spectroscopy.

High‐speed holography of laser‐induced breakdown in liquids

Abstract: The phenomenon of ruby laser‐induced breakdown in liquids is investigated by high‐speed holography. The advantage of using holography instead of ordinary photography lies in the possibility to easily suppress the bright white light emitted during the breakdown process. This light constitutes an incoherent background on the holographic plate and does not reproduce upon reconstruction of the recorded scene.

Laser Inhibition of Dental Caries Suggested by First Tests in Vivo

Abstract: Intact tooth enamel from humans was exposed extraorally to a superpulsed, carbon-dioxide laser at energy densities of 10 to 15 joules/cm 2 . When it was tested in the mouth of one of the investigators, the lased enamel proved much more resistant than unlased control enamel to the oral environmental influences generally conducive to dental caries.