Showing papers on "Ruby laser published in 1988"

The LIDAR Thomson scattering diagnostic on JET (invited)

Abstract: By combining the time‐of‐flight or LIDAR principle with a Thomson backscatter diagnostic, spatial profiles of the electron temperature and density are measured in a magnetically confined fusion plasma. This technique was realized for the first time on the JET tokamak. A ruby laser (3‐J pulse energy, 300‐ps pulse duration, 0.5‐Hz repetition rate) together with a 700‐MHz bandwidth detection and registration system yields a spatial resolution of about 12 cm. A spectrometer with six channels in the wavelength range 400–800 nm gives a dynamic range of the temperature measurements of 0.3–20 keV. The stray light problem in the backscatter geometry is overcome by spectral discrimination and gating of the photomultipliers. A ruby filter in the spectral channel containing the laser wavelength allows calibration of the vignetting along the line of sight by means of Raman scattering, enabling the measurement of density profiles. The low level of background signal due to the short integration time for a single spatial...

Experimental and theoretical investigation of tunable picosecond pulse generation in longitudinally pumped dye laser generators and amplifiers

Abstract: Picosecond pulse generation in longitudinally pumped dye laser generators and amplifiers is studied experimentally and theoretically. Frequency-tunable pulses between 720 and 940 nm are generated with a picosecond ruby laser pump source. The amplification of spontaneous emission and of seeding pulses in the generator and amplifier cells is investigated. Stimulated emission cross-sections and excited-state absorption cross-sections are determined by computer simulations. The coherence properties of the generated radiation are analysed. Resonance Raman contributions are resolved.

Density determination in the TEXTOR boundary layer by laser‐ablated fast lithium atoms

Abstract: A method is presented which allows a determination of electron density profiles in the plasma boundary of a fusion device up to some 1013 cm−3 within about 100 μs. For this purpose, the complete attenuation of an injected lithium beam is determined by measuring its optical emission profile. The beam is generated by a ruby laser, which ablates small portions of a LiF coating with a thickness of about 1000 A from the rear side of a glass substrate. The produced lithium atoms have velocities of 1×106 cm/s and can penetrate into the plasma until ne×l ≊1×1013 cm−2. For the measurement of the optical emission profile of the excited lithium atoms, a silicon photodiode array camera is used. The emission profile is then converted into an electron density profile with the help of the ionization rate for lithium atoms by electron impact.

Laser Ablation for Direct Elemental Analysis of Solid Samples by Inductively Coupled Plasma Mass Spectrometry

Abstract: The results of a preliminary study on direct analysis of solid metals and nonconductive samples by inductively coupled plasma mass spectrometry (ICP-MS) are described. The aerosols ablated from solid samples by a ruby laser are introduced into an inductively coupled plasma, with detection of the resulting ions by a mass spectrometer. With conventional solution introduction, polyatomic species from mineral acids and solvents prevent the accurate determination of some trace analytes. However, using laser ablation, these background peaks are greatly reduced. The relative sensitivity factors for the laser ablation method are seen to vary from unity, with volatile elements such as Pb and Bi being more sensitive. Detection limits of rare-earth elements, Th and U in silicate rocks are excellent (0.02-0.9ppm at the effective integrating time of 1.4s), being better than those of the examined elements in steel (1.7-29ppm at the effective integrating time of 0.6s).

Use of laser‐ablated fast particle beams for the measurement of ne and Te profiles in the TEXTOR boundary layer

Abstract: We have developed a source of suprathermal atoms consisting of a laser system, which ablates small portions of coating materials from the rear side of a glass substrate. The coating can be either a single species or a multilayer of several‐thousand‐angstrom thickness. Neutral particle beams produced by this method can have energies in the range of about 10 eV and penetrate into the plasma up to line densities of about nel=1×1013 cm−2. For the determination of the electron temperature we have chosen two elements, the ionization and excitation cross sections of which differ in the range up to 100 eV. For TEXTOR a two‐component target with a C‐LiF coating is used, which delivers a Li and C beam with about 5‐ and 15‐eV energy, respectively, ablated by a ruby laser with 1‐J energy. The beam attenuation is determined from the emitted light by using a camera with a Si‐diode array system for spatial recording. The different attenuations and emission characteristics then allow the determination of radial electron ...

Explosive crystallization in amorphous Si initiated by long pulse width laser irradiation

Abstract: Explosive crystallization of amorphous Si is studied in a new heat‐flow regime using long pulse (45 ns full width at half‐maximum) ruby laser irradiation. In this regime, previously unobserved phenomena are found. Nucleation of crystalline Si is observed while the amorphous phase is melting at high (m/s) velocity and epitaxy from the underlying crystalline substrate is observed even under conditions for which the amorphous Si is never at any instant fully melted. These measurements, combined with previous measurements using short pulse irradiation, lead to development of a more complete model of explosive crystallization.

Generation of Ultrashort Optical Pulses

Abstract: It has been two decades since the era of ultrashort optical pulse generation was ushered in with the report of passive model-locking of the ruby laser by Mocker and Collins [2.1]. Shortly, followed the generation of the first optical pulses in the picosecond range with Nd: glass laser by DeMaria [2.2]. Since that time we have witnessed dramatic advances in pulse generation. As is seen in Fig. 2.1 the shortest optical pulse width has fallen at an exponential rate, a reduction of more than three orders of magnitude since 1966. Optical pulse widths as short as 6 fs have been generated, approaching the fundamental limits of what is possible in the visible region of the spectrum. In addition, ultrashort optical pulse lasers have become more useful as advances have taken place in pulse energy, tunability, repetition rate, reliability and ease of operation. A bewildering array of techniques and lasers systems are currently available to meet a diverse set of needs.

High rejection ruby filter for laser light scattering experiments

Abstract: A rejection filter against stray ruby laser light in scattering experiments is described. It consists of an array of sixty-four ruby crystal cubes with a doping of up to 2.3 wt. % of chromium oxide. The filter is 15 mm thick. Suppression factors of more than 106 are achieved with individual cubes (5 × 5 × 15 mm3), the effective overall suppression of the assembled array being 104. The filter facilitates Raman calibration of the lidar Thomson scattering system of the JET tokamak.

Laser Generated Ultrasound

Abstract: This paper describes a laser-based ultrasonic system using high-energy, short-pulse trains for laser generation. Ongoing research includes the theoretical extension of laser-solid interactions related to laser generation of ultrasound in complex structures and advanced materials and the investigation of methods to achieve a high speed, high resolution laser excitation system for integration with a highly sensitive ultrasonic signal detector. Experiments are being conducted for the flaw inspection/characterization of rails using laser-based photoacoustic excitation techniques including ultrasonic detection by both piezoelectric and noncontacting laser interferometric means. This work was supported in part by the U.S. Department of Transportation under Contract No. DTRS-57-85-C-00132

Ge diffusion into GaAs by pulsed laser irradiation

Abstract: Ge diffusion into GaAs from thin evaporated layers as sources is reported. Irradiation with aQ-switched ruby laser gives rise ton-type diffused layers of a thickness from 240 to 710 A. A strong compensation of the diffused layers, that cannot be removed by thermal annealing, was observed. From the present experimental results it can be inferred that the diffusion coefficient increases at the melting point by 5 to 6 orders of magnitude.

Automatic laser beam alignment for a Thomson scattering system

Abstract: A system for the automatic alignment of a pulsed ruby laser beam is under development for the Thomson scattering diagnostics of RFX, a large reversed‐field pinch machine now under construction. In this experiment the laser will be 11 m from the machine and the beam alignment at the 750×4‐mm scattering volume will be actively maintained to within 0.5 mm. The beam direction in space is measured in two reference planes fixed to the collection optics frame by means of two 80‐mm2 fast quadrant photodiodes. A double‐channel preamplifier is used for each quadrant in order to measure both the 30‐ns FWHM ruby pulse and a low‐power cw He–Ne beam propagating through the same optical path. Every time the main laser is fired, the relative direction of the two beams is determined so that the position of the He–Ne beam can be used for feedback control of the steering optics between plasma shots.

Current Developments in Laser Surgery for Skin Cancer

Abstract: The acronym “LASER” connotes “Light Amplification by Stimulated Emission of Radiation:” and describes the emission process of an intense beam of electromagnetic energy. Einstein first discussed the concept in 1917. In 1953–1954, Townes in the United States and Basov and Prokhorov in Russia independently advanced the theoretic framework that led to the development of the laser-and their sharing of the Nobel Prize in Physics in 1964 (1). In 1960 Mairnan produced the first working laser, a ruby model (2). One of us (L.G.) began employing laser surgery in 1961 (3). There have been many advances in the laser and its use in the past 28 years.

Laser Pulse Stretching Via Enhanced Closed Loop Control With Slow Q-Switching

Abstract: In testing a holographic particle track recording system for the Fermilab 15 foot bubble chamber, it was shown that the peak power of Q-switched laser pulses (50ns duration) at the required energy gave rise to boiling during the chamber expansion. A pulse stretching technique is described which was developed to reduce the peak power. Applied to a ruby laser (oscillator and three amplifiers) with a maximum Q-switched output of 30J, pulses of up to 10-μs duration with coherence up to and exceeding 11 m at 2.5μs were produced. The considerably increased coherence length will find applications in many fields of pulsed holography, and its use with fiber optics is particularly promising.

Laser emission in Tm 3+ - and Er 3+ -doped fluorozirconate glass at 2.25, 1.88, and 2.70 µm

Abstract: Thulium cascade laser operation using resonant pumping was first reported1 in Tm3+:YLF using a ruby laser to pump the 3H4 → 3F3 transition. Recently Tm3+:YLF was pumped with alexandrite and laser diodes, and the 2.3-µm transition was observed.2,3 We report the first observation of Tm3+ laser action in fluorozirconate glass. The Er3+ transition near 3 µm was recently lased in Er3+:YLF using a GaAIAs laser diode pump source.4 The first Er3+ 2.70-μm laser in fluorozirconate glass is reported.

Segregation of impurities in pulsed‐laser‐melted carbon

Abstract: The segregation of 73Ge and 75As in pulsed‐laser‐melted carbon has been investigated. Both 73Ge and 75As were implanted into highly oriented pyrolytic graphite at a fluence of 1.0×1015 cm−2 at several energies. The implanted graphite was subsequently irradiated with a 30‐ns pulsed ruby laser with laser pulse energy densities above the melt threshold for graphite. The distribution of impurities was measured before and after laser irradiation using Rutherford backscattering spectrometry to determine the redistribution of impurities resulting from diffusion in liquid carbon and segregation at the liquid‐solid interface. Numerical calculations were then used to determine the diffusivity of the impurities in liquid carbon and the nonequilibrium segregation coefficient of Ge and As in carbon.

Data for Laser Biostimulation in Wound-Healing

Abstract: Since the first ruby laser was made in 1960, multiple applications of lasers have been identified. The special burning, coagulating, and vaporizing effects of high output lasers, together with their easy manipulation using optical systems, have resulted in extensive medical use. Additionally, there is much interest in the nonthermic effects of lasers in photodynamic tumor therapy and in biostimulation.

Experimental investigation of the sound field generated by a moving ruby‐laser thermoacoustic array

Abstract: A high‐power laser is used to produce via thermal expansion a long thermoacoustic broadside array in water by deflecting a ruby‐laser beam (optical wavelength 0.6943 μm) off a rotating mirror to a body of water. The rotation of the mirror results in a rectilinear motion of the source over the water surface. Such a source is commonly referred to as a moving thermoacoustic array (MTA) and its penetration depth into the water is inversely proportional to the coefficient of absorption of the laser intensity in water. The sound field radiated by the ruby MTA (long array) is analyzed experimentally for subsonic, sonic, and supersonic source velocities. The results obtained with the long ruby MTA are compared with those obtained with a much shorter glass–neodymium MTA (optical wavelength 1.06 μm). Results reported here include directivity patterns, both in a plane perpendicular to the water surface and in a plane parallel to the water surface, and sound‐pressure level (SPL) dependence on distance between the source and the receiver.

Multiphoton ionization of aluminum and copper planar target

Abstract: The total charge of the emitted ions from the planar metal targets irradiated by the mode‐locked ruby laser was measured. The dependence of the total emitted ions on the laser fluence is consistent with the theory of the multiphoton ionization in the low fluence region. However, it shows saturation phenomena at the higher fluence regions. These saturations could be explained by the depletion of the neutral atoms and the level shifting of the intermediate state due to the strong Stark effect.

Spatial and temporal distributions of liquid drops in an erosion jet formed as a result of interaction of laser radiation with a lead target

Abstract: A determination was made of the spatial and temporal distributions of the transmission, scattering, and absorption coefficients of ruby laser radiation used to probe an erosion jet created as a result of interaction of radiation from a free-running neodymium laser (output energy ~ 1 kJ and pulse duration ~ 1 ms) with a lead target. The experiments with a probe beam were supplemented by a spectroscopic study of the erosion jet. The probe results and the Love–Mie scattering theory were used to determine the spatial and temporal distribution of lead drops in an erosion jet formed as a result of volume vaporization.

Production of support base for planographic plate

Abstract: PURPOSE:To produce a support base for a printing plate which is free of thermal deformation, enbales fine graining, enhances resistance to contamination during printing, and ensures excellent plate wear characteristics, by graining a support base for a planographic plate by irradiating with laser in a liquid. CONSTITUTION:A base for a planographic plate is grained by irradiating with laser in a liquid. As a blank material for an aluminum plate, a material having a purity of aluminum of at least 99.0% is preferred. The thickness of the aluminum plate is practically selected appropriately from the range of 0.1-0.5 mm. The laser for irradiation may be CO laser, yttrium-aluminum-garnet (YAG) laser, ruby laser or the like, and is appropriately selected according to the kind of the support base, a grained shape desired, or the like. For example, in the case of an aluminum plate, a laser with a shorter wavelength such as YSG laser is preferable, and the energy of irradiation is appropriately selected according to the material of the support base, focal length, beam diameter, the kind of laser or the like.

A Brief History of the Nd:YAG Laser

Abstract: The successful operation of the first working laser by Theodore Maiman1 in 1960 was like the key to a locked chest full of other types of laser, just waiting to be discovered. Only six years later, working prototypes of gas, liquid, solid, and semiconductor lasers had been constructed by several groups of investigators, spurred on by Maiman’s achievement. By the end of that decade, hundreds of materials had been found capable of laser action.

Pulsed laser treatment at Fe/C 6 H 6 interface: a Mossbauer effect study

Abstract: The pulsed ruby laser induced reactive-quenching process at Fe/C6H6 Ibenzenel has been investigated using conversion electron Mossbauer spectroscopy [CEMS]. It is shown that iron carbide phases can be synthesized when an iron foil immersed in benzene is treated with ruby Laser pulses [λ=694 nm, pulse width ∼30 ns, energy density =15 J/cm2]. The results indicate the formation of e-carbide and Fe5C2 phases in the as-treated sample and its transformation to Fe3C upon thermal treatment. The result of the CEMS measurements are supported by small angle X-ray diffractometry.

A technique for long duration q-switching of a ruby pulse laser

Abstract: A technique is described for extended time flashlamp firing using a Q -switching ruby laser, which gives a fairly constant output energy when triggered at any time over 1 ms.

Explosive crystallization of dilute amorphous Si‐Ge alloys

Abstract: Structural characterization of pulsed laser irradiated amorphous alloys of Si(Ge) obtained with heavy dose (Ge) implantation in Si have been carried out using Rutherford backscattering spectrometry/channeling technique and transmission electron microscopy. Comparison of these alloys with self‐implanted amorphous Si after irradiation with a ruby laser showed significant reductions in the laser energy densities required for melt propagation, amorphous‐crystalline interface penetration, and laser‐induced damage formation. Explosive crystallization was found to occur in all samples. Large reductions in melting temperatures and latent heat of melting were found to be necessary to explain the results.

Bistable direction switching in an off-axis pumped continuous wave ruby laser

Abstract: A report is presented of the observation of hysteretic bistable direction switching in a single-mode CW ruby laser system. This effect is only observed when the pump beam which is focused into the ruby rod is misaligned with respect to the rod end faces. At low pump powers, the ruby lases in a mode nearly collinear with the pump axis. At a higher pump power the ruby switches to a mode that is collinear with the rod end faces and preserves the original polarization. The effect is large enough to switch the beam by an angle equal to twice the diffraction angle. The observations show that under steady-state pumping, a CW ruby laser can exhibit bistable operation in its output direction and power. A calculation using the heat equation with two concentric cylinders with one as a heat source (pump laser) and the outer wall of the other held at 77K, gives an increase in core temperature of about 0.01 K. Therefore, the increase in temperature is not large enough to change the index of refraction to account for such large macroscopic effects. >

The Contact Nd:YAG Laser in Neurosurgery

Abstract: It took 10 years to recognize the laser for its neurosurgical application since Rosomoff1 tried to use a ruby laser for surgery on a brain tumor. Today three lasers, CO2, argon and Nd:YAG, are widely used for neurosurgery. Among these lasers, the Nd:YAG has been evaluated to be inappropriate for neurosurgery, in spite of its excellent hemostatic capability, because of an unsatisfactory cutting-off effect. At the same time, this ability to achieve hemostasis has been highly successful in endoscopic procedures.

Role of thermal conductivity and optical absorption coefficient of amorphous silicon in pulsed laser melting

Abstract: An expression showing the temperature dependence characteristics of the thermal conductivity of amorphous silicon is examined using the heat flow model to calculate the melting threshold energy Eth for various laser conditions. The results agree well with the experimental data for excimer and Nd:YAG frequency-doubled laser irradiation but not with those for ruby laser irradiation. Various factors which might contribute to the discrepancy between experimental and calculated Eth values for ruby laser irradiation are discussed. We conclude that this discrepancy is probably due to the inaccuracy of the experimental value for the optical absorption coefficient of a ruby laser that we used in the calculations.

Laser Processing (Welding, Cutting and Drilling)

Abstract: Since the first demonstration of drilling with a ruby laser, laser processings, such as welding, cutting and drilling have been used in industrial manufacturing. In these applications, laser light is focused on a small spot on the surface where the laser energy is converted to thermal energy, instantly resulting phase changes, melting and vaporization. This paper reviews some fundamental studies and new techniques of laser processing. Fundamental studies include the interaction of laser beams with materials and the beam hole formation.