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Two methods of producing the long pulse lengths that promote efficient extraction of energy from low-gain, quasi-four-level lasers are analyzed. A long pulse length output can mitigate laser-induced damage effects and can be generated in quasi-four-level lasers by two disparate methods. One method utilizes Q-switching techniques in resonators designed to extend the pulse length and another utilizes the first pulse in a relaxation oscillation pulse train. Models for quasi-four-level lasers are derived here taking into account the nonnegligible thermal population of the lower laser level. Closed-form expressions are derived for both modes of operation of quasi-four-level laser systems so the parametric dependencies of both forms of operation become obvious, allowing facile comparison. In addition, a combined absorption and quantum efficiency, germane for flash-lamp pumping, is calculated for both Cr and Er sensitizers. Although the former has the advantage of broad absorption bands, the latter has the advantage of a quantum efficiency approaching 3.

We demonstrate and analyze an upconversion blue fiber laser pumped by two wavelengths. Lasing at 0.48 [[micro]meter] with very low pump threshold power is obtained from a Tm-doped fluorozirconate fiber that is counterpropagating pumped by 1.21- and 0.649-[[micro]meter] light. We employed a rate-equation analysis using parameters obtained by fitting to the experimental data to predict the 0.48-[[micro]meter] output characteristics as a function of fiber length and output reflectivity.

The amplified spontaneous emission (ASE) of a strained quantum-well distributed feedback (DFB) laser biased below laser threshold was employed to extract the gain and refractive index spectra systematically. A modified Hakki-Paoli method was employed to determine the gain and differential gain spectra. The refractive index change because of carrier injection was determined from the shift of the Fabry-Perot peaks in the ASE spectrum. The measured ASE spectrum, gain, refractive index change and linewidth enhancement factor were then compared with the theoretical model for strained quantum-well lasers.

A combined experimental and computational approach utilizing tunable C[O.sub.2] lasers and chemometric analysis was employed to detect chemicals and their concentrations in the field under controlled release conditions. We collected absorption spectra for four organic gases in the laboratory by lasing 40 lines of the laser in the 9.3-10.8-[[micro]meter] range. The ability to predict properly the chemicals and their respective concentrations depends on the nature of the target, the atmospheric conditions, and the round-trip distance. In 39 of the 45 field experiments, the identities of the released chemicals were identified correctly without predictions of false positives or false negatives. Key words: Lidar, C[O.sub.2] lasers, infrared spectroscopy, plume absorption, remote sensing, partial least squares, differential absorption lidar, chemometrics, optical spectroscopy.

Systems of coherent optics with cheaper spatial light modulators are discussed. The aim is toward the behavior differences of the color components of a color liquid-crystal television (CLCTV) screen illuminated by a He-Ne laser (633 nm) and white light. Several conclusions have been derived about (1) the summary effects of numerous components, (2) the response of single components, (3) the comparison of conversion from color to gray between laser and white light, and (4) the approach of encoding and addressing a CLCTV. Key words: Spatial light modulator, liquid-crystal television, color.

The diameter dependence of laser performance and discharge features of a segmented hollow cathode Cu-II 780.8 nanometer laser transition were analysed by laser tubes with internal diameter of 2,3,4 and 5 nanometer. It was observed that decrease of diameter raised the gain for a given current, while the highest output came from large-diameter tubes: 20 mW from a 5-centimeter-long, 5-millimeter-diameter tube at 2-Amps current.

A study of modeling and characterization of serpentine superlattice nanowire-array lasers shows that lateral quantum confinement is more potent than vertical quantum confinement. The net gain spectra at 1.4 K reveals strong optical gain anisotropy. Suitable polarization-dependent gain spectra is obtained with aluminium segregation of 8% and homogeneous line broadening of 7 meV. The laser used was an aluminum-gallium-arsenide semiconductor device which was built for the research.

Two types of channel waveguides exhibit the same electrooptic (EO) coefficient r(sub 33) under the same poling condition, where the photobleached waveguides shows a lower half-wave voltage, in 1.32 micrometer laser light. The fabrication of traveling-wave channel-waveguide modulators, by using diazo-dye-substituted poled polymers and the measurement of the EO modulation of laser light in Mach-Zehnder channel waveguides, showed that. The maximum r(sub 33) value of the poled diazo-dye-substituted polymer was 26 pm V.

A study of partially gain-coupled 1.55 micrometer distributed feedback (DFB) lasers shows dynamic aspects such as lasing mode behaviors, modulation bandwidths and chirp associated direct modulation characteristics. The differential gain, the damping rate and the damping factor were determined by analyzing data from RIN measurement. The high band width is associated with high differential gain produced by the combination of longitudinal gain- and index-coupling mechanisms. These devices have small wavelength chirp and clear eye openings below 10 Gbit/s pseudorandom NRZ modulation thereby making them useful for high bit-rate and long haul applications.

Theoretical analysis of the GaInP-AlGaInP strained quantum well laser, considering spin-orbit split-off bands at 85 angstroms, shows that spin-orbit split-off subbands reduce the threshold current of the unstrained quantum-well structure. The differential gain is improved by the spin-orbit split-off bands in the tensile-strained quantum well because the split-off bands enhance the density of states at the valence band-edge. The unstrained quantum well has more threshold current as compared to strained quantum well.

Experimental studies reveal the ability of femtosecond ultraviolet laser pulse to ionize gases and the resultant ionization channel induces lightning discharges in gases. Measurement of voltages between two planar electrodes helps follow the discharging process triggered by the laser. The evolution of the plasma of electron-ion in the applied field and the electron seeding are simulated by a theoretical model, which also helps predict the parameters of a laser system for lightning protection.

Characterization of InGaAsP lasers by a near-field scanning optical microscope reveals irregularities and defects in the waveguide. The local and overheating of the laser assessed through shear force and near-field images enable better understanding of inhomogeneities in growth. This technique helps overcome carrier leakage and decrease in threshold current and does not require any particular kind of surrounding. All these facts make this method a favored one.

Spectroscopic and diffraction studies confirm that ion-assisted pulsed laser deposition generates sp3-bonded cubic boron nitride (c-BN) films. Irradiation of the hexagonal boron nitride layer present on Si(100) surfaces with ions from a broad beam ion source causes the deposition of c-BN at a temperature range of 50 to 800 degrees C. The c-BN amount on Si surfaces depends on growth time and deposition temperature. The compressive stress under which c-BN grows decreases with growth time.

A 4.25 cm by 4.25 cm clear-aperture KrF laser uses an X-ray preionization process to spatially modify preionization flux and to reduce gain nonuniformity that occurs due to electrostatic-field nonuniformity and discharge plasma skin depth. Partially transmitting and opaque attenuators placed between discharge point and preionization source help modulate flux. The capacity of the method to generate square, uniform output profiles enables its use in amplification of unity aspect ratio beams.

Wavelength mismatch between pump and the pump line can be compensated with the adjustment of laser plasma parameters to suit the particular situation. Short-wavelength pump lasers are ideal for generating Si pump line in Si-Mg photoresonant scheme. In Mg yielding Mg self pumping, the lines originating from higher levels show intensive Stark broadening than the one from low resonance level. The main parameters that need modulation are electron density and wavelength of pump laser.

Capping of a multichip module thin film's copper features through a laser technique prevents the corrosion and diffusion of copper to the other layers of the thin film. Undercapping and capping metal's thickness variations, which are problems faced in the electroless plating capping and photolithography methods, are overcome by the use of lasers. The variables associated with the capping process are independent of the nature of the capping metal.

Theoretical analysis of surface relief stability during laser melting of semiconductors and metals with high absorption coefficient or thermal diffusivity, reveals the presence of irradiation regimes that lack the nonresonant surface wavy relief for pulsed and CW irradiation. These results enhance laser material processing such as laser modification of surfaces, and in microelectronics.

The quantum well laser differential gain varied nonlinearly with the quantum well structure's thickness, as determined by parabolic band model and valence-band-mixing model. A smaller differential gain was observed when the band-mixing model was used. The gain profile was determined both from the density matrix formalism and the multiband effective mass theory.

The output of a modulation instability laser functioning at 514.5 nm contains downshifted and upshifted orthogonally polarized sideband pulses. Feedback to the laser decreases pump power and produces terahertz regulated light pulses. Integration of sideband pulses generates 4-THz oscillations with a duration of 10 to 15 ps.

The Pound-Drever stabilization method involves the use of the Fabry-Perot cavity and the RF phase modulator to generate a high speed discrimination signal that detects frequency disturbances in quantum lasers. The signal also helps identify the effects of quantum noise on the laser frequency spectrum. Cavity bandwidth and output coupling cause the frequency disturbances.

An experimental analysis of soliton resonance sideband production femtosecond fiber lasers reveals that sideband wavelengths depend on pulse length and third-order dispersion. Cavity dispersion defines the minimum pulse length resulting in sideband loss. Sideband spectrum can be used to study ultrashort laser pulses and fiber parameters.

Solutions of time-dependent coupled wave equations in the time domain help generate an algorithm for the computation of large-signal response of distributed feedback lasers. A traveling wave model representing the solutions indicates that radiations in the laser affects the side-mode suppression ratio. The model considers photon densities, carrier densities and spontaneous emission noise effects.

I INTRODUCTION One of Cartwright's arguments in defense of entity realism focuses on the difference between theoretical and causal explanations. On her view, explanation using theoretical laws fails to provide [...]

Emission spectra of highly ionized elements having medium atomic numbers are recorded using a grazing incidence spectrometer fitted with microchannel plate detector. The absolute photon intensities are established by measuring the emission from a carbon plasma with an accurately calibrated CCD and the microchannel plate detector. The ionized elements exhibit intense spectral bands, which shift toward laser wavelengths and weaken with progressive increase in atomic number.

Effects of changing the write parameters in Co/Pt multilayer films are determined. Modified differential phase contrast mode of Lorentz electron microscopy images the domains yielded thermomagnetically by laser modulation. The investigation of the effects of different laser powers indicates that the laser power increases the domain size and the domain regularity is increased by the bias field.

Irradiation with a 30 nanoseconds XeCl excimer laser aids in analyzing laser-incited melting mechanism which is followed by solidification of silicon films produced on a quartz substrate. The amorphization of silicon films on a substrate is not dependent on the rate of cooling. The temperature gradient in liquid silicon influences the quick and uniform solidification of silicon films.

Pulsed laser ablation in hydrogen atmosphere from surfaces of oxide facilitate deposition of metal films with enhanced quality. An analysis of alpha-Fe2O3 and CuO ablation reveals that film quality is enhanced particularly in Cu films which demonstrate high resistivity. Spectroscopic analysis reveal that YBaCuO surface ablation results in a plasma of neutral excited atomic/ionized and molecular complexes.

A technique for the comprehensive analysis of distributed feedback (DFB) lasers is discussed. The technique, which is based on a recursive Green's function method, allows exact calculationof the resonance wavelengths and threshold gains of arbitrary DFB laser diode structures. It can be easily implemented on a computer. A comparative analysis reveals that the proposed technique has a faster computational time compared tothe conventional coupled-mode theory.

Abstract Fractional resurfacing may be an effective treatment for burn scars because of its unique healing properties and depth of penetration. This case report shows the successful use of fractional [...]