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Coupled-mode rate equations for coupled-cavity lasers are derived using a novel approach. The method, based on the Mittag-Leffler theorem, is exact. The coupling coefficients are compared to those derived by several different approximations.
Coupling of laser optical modes by intracavity time varying perturbation
A single Nd:YAG laser crystal was pumped by three 10-W fiber-coupled diode lasers. At 50 kHz pulse repetition frequency, average output powers exceeding 11 W of continuous-wase 1064 nm, and 3.5 W of 532-nm were achieved.
A fiber-coupled laser based on a whispering-gallery-mode resonator formed of a laser gain medium and an angle-polished fiber coupler.
A diode-pumped laser with over 11 W of continuous-wave 1064 nm, and 3.5 W of frequency-doubled average power at 50 kHz pulse repetition frequency, has been developed.
Coupling between oppositely directed traveling waves in He-Ne ring laser in form of mutual backscattering of energy from each beam into direction of other
The potential capabilities and limitations of single ball lenses for coupling laser diode radiation to single-mode optical fibers have been analyzed; parameters important to optical communications were specifically considered. These parameters included coupling efficiency, effective numerical apertures, lens radius, lens refractive index, wavelength, magnification in imaging the laser diode on the fiber, and defocus to counterbalance spherical aberration of the lens. Limiting numerical apertures in object and image space were determined under the constraint that the lens perform to the Rayleigh criterion of 0.25-wavelength (Strehl ratio = 0.80). The spherical aberration-defocus balance to provide an optical path difference of 0.25 wavelength units was shown to define a constant coupling efficiency (i.e., 0.56). The relative numerical aperture capabilities of the ball lens were determined for a set of wavelengths and associated fiber-core diameters of particular interest for single-mode fiber-optic communication. The results support general continuing efforts in the optical fiber communications industry to improve coupling links within such systems with emphasis on manufacturing simplicity, system packaging flexibility, relaxation of assembly alignment tolerances, cost reduction of opto-electronic components and long term reliability and stability.
Tapered transmission line couples energy from magnetic switch to excimer laser. Transmission line provides constant impedance for pulses from switch and distributes pulses across length of laser as nearly uniform wave fronts. Allows smaller, more efficient magnetic core to be used in switch. Losses and circuit capacitance are less than for full-laser-width line and core.
A module developed for the generation of a stable single wavelength to be used for a fiber optic multiplexing scheme is described. The laser is driven with RZ pulses, and the temperature is stabilized thermoelectrically. The unit is capable of maintaining a fixed wavelength within about 6 A as the pulse duty cycle is changed between 0 and 100 percent. This is considered the most severe case, and much tighter tolerances are obtainable for constant input power coding schemes. Using a constricted double heterostructure laser, a wavelength shift of 0.083 A mA is obtained due to laser self-heating by a dc driving current. The thermoelectric unit is capable of maintaining a constant laser heat-sink temperature within 0.02 C. In addition, miniature lenses and couplers are described which allow efficient coupling of single wavelength modes of junction lasers to thin film optical waveguides. The design of the miniature cylinder lenses and the prism coupling techniques allow 2 mW of single wavelength mode junction laser light to b coupled into thin film waveguides using compact assemblies. Selective grating couplers are also studied.
External cavity for monolithic array of three GaAs lasers phase-coherently couples individual outputs to produce single spatially coherent beam. Fourier transform properties of lens and spatial filter are used to select coherent mode.
Two techniques have been proposed to increase the efficiency of coupling of light from lasers to Cassegrain telescopes and, in general, telescopes with secondary or tertiary mirror obscuration. The need to increase the efficiency of coupling arises in laser transmitters of lidar and freespace optical communication systems that utilize Cassegrain telescopes. The vignetting caused by the secondary reflector and baffle in such a telescope reduces the transmitted power by a large fraction because (1) the obscured area is central and is a significant fraction of the telescope aperture and (2) the cross-sectional intensity profile of a typical laser beam is Gaussian, so that intensity is greatest in the obscured central area. In a technique proposed previously for increasing the efficiency of coupling, an optical assembly comprising an axicon device and a folding mirror that would render the solid laser beam annular - in effect, turning the laser beam inside out - so that the laser light would be concentrated into an annular cross section that would not be obscured by the secondary reflector and baffle. Hence, most or all of the light would be coupled into the output beam. Another prior efficiency-enhancing technique is denoted subaperture illumination. In this technique, the laser beam is displaced laterally with respect to the optical axis of the secondary reflector, such that the beam impinges on an off-axis subaperture of the primary reflector that is not obscured by the secondary reflector and baffle.
Design and experimental data for obtuse-angled wedges used in coupled configurations of diode lasers and multimode fibers are presented. An analytic definition of the connection between the wedge angle and the fiber acceptance half-angle is developed, along with a formula for the minimum half-angle. An inequality is defined for determining the bevel angle of the output end of the fiber to eliminate end reflections. The fiber parameters are accounted for in the bevel. The formulations were tested in comparison with the performance of a coupled CDH laser system and good agreement was found in the output spectrum.
The efficacy of laser saturated fluorescence (LSF) for OH concentration measurements in high pressure flames was studied theoretically and experimentally. Using a numerical model describing the interaction of hydroxyl with nonuniform laser excitation, the effect of pressure on the validity of the balanced cross-rate model was studied along with the sensitivity of the depopulation of the laser-coupled levels to the ratio of rate coefficients describing: (1) electronic quenching to (sup 2) Sigma (+) (v double prime greater than 0), and (2) vibrational relaxation from v double prime greater than 0 to v double prime = 0. At sufficiently high pressures and near-saturated conditions, the total population of the laser-coupled levels reaches an asymptotic value, which is insensitive to the degree of saturation. When the ratio of electronic quenching to vibrational relaxation is small and the rate of coefficients for rotational transfer in the ground and excited electronic states are nearly the same, the balanced cross-rate model remains a good approximation for all pressures. When the above ratio is large, depopulation of the laser-coupled levels becomes significant at high pressures, and thus the balanced cross-rate model no longer holds. Under these conditions, however, knowledge of the depletion of the laser-coupled levels can be used to correct the model. A combustion facility for operation up to 20 atm was developed to allow LSF measurements of OH in high pressure flames. Using this facility, partial saturation in laminar high pressure (less than or equal to 12.3 atm) C2H6/O2/N2 flames was achieved. To evaluate the limits of the balanced cross-rate model, absorption and calibrated LSF measurements at 3.1 and 6.1 atm were compared. The fluorescence voltages were calibrated with absorption measurements in an atmospheric flame and corrected for their finite sensitivity to quenching with: (1) estimated quenching rate coefficients, and (2) an in situ measurement from a technique employing two fluorescence detection geometries.
Achieving a high conversion efficiency into relativistic electrons is central to short-pulse laser application and fundamentally relies on creating interaction regions with intensities $\ll$ 10 18 W / cm 2 . Small focal length optics are typically employed to achieve this goal; however, this solution is impractical for large kJ-class systems that are constrained by facility geometry, debris concerns, and component costs. We fielded target-mounted compound parabolic concentrators to overcome these limitations and achieved nearly an order-of-magnitude increase to the conversion efficiency and more than tripled electron temperature compared to flat targets. Particle-in-cell simulations show that plasma confinement within the cone and formation of turbulent laser fields that develop from cone wall reflections are responsible for the improved laser-to-target coupling. These passive target components can be used to improve the coupling efficiency for all high-intensity short-pulse laser applications, particularly at large facilities with long focal length optics.
Semiconductor-laser arrays more reliable, more powerful, and easier to make. Improved design intended to eliminate undesired electromagnetic modes and mode shifts sometimes occuring in gain-guided variety. Reflected from mirror/window at end of common resonator section of laser, energy refracted from each laser enters adjacent laser. Mutual coupling establishes phase relationships among lasers. Monolithic laser array made by standard epitaxial techniques. Made in part with polymeric materials to mitigate some deleterious effects of all-expitaxial processing. Potential applications include optical communications, ranging, printing, and recording.
Laser propagation experiments using four beams of the National Ignition Facility to deliver up to 35 kJ of laser energy at 351 nm laser wavelength to heat magnetized liner inertial fusion-scale (1 cm-long), hydrocarbon-filled gas pipe targets to ~keV electron temperatures have demonstrated energy coupling >20 kJ with essentially no backscatter in 15% critical electron density gas fills with 0–19 T applied axial magnetic fields. The energy coupling is also investigated for an electron density of 11.5% critical and for applied field strengths up to 24 T at both densities. This spans a range of Hall parameters 0 < ω ce τ ei ≲ 2, where a Hall parameter of 0.5 is expected to reduce electron thermal conduction across the field lines by a factor of 4–5 for the conditions of these experiments. At sufficiently high applied field strength (and therefore Hall parameter), the measured laser propagation speed through the targets increases in the measurements, consistent with reduced perpendicular electron thermal transport; this reduces the coupled energy to the target once the laser burns through the gas pipe. In conclusion, the results compare well with a 1D analytic propagation model for inverse Bremsstrahlung absorption.
This paper develops an analytical, algebraic formalism that predicts effects induced in ring lasers by phase modulation, corresponding both to mode-decoupling mechanisms deliberately incorporated in the ring laser and to naturally occurring periodic or random angular or linear accelerations. The analysis is based on an approach that seems potentially convenient in the analysis of other systems that are physically stable but mathematically nonlinear.
Monolithic two-dimensional arrays of GaAs/AlGaAs diode lasers with light emission normal to the surface have been obtained by fabricating edge-emitting quantum-well lasers coupled with external mirrors that deflect the radiation from the laser facets by 90 degrees. Linear arrays of GaAs/AlGaAs devices in which one of the laser facets was cleaved while the other facet and an adjacent 45 degree deflector were formed by ion-beam-assisted etching (IBAE) have been reported. For the arrays reported in this section, IBAE was used to form all of the laser facets and the deflecting mirrors. A mass transport process of the type employed to fabricate two-dimensional arrays of GaInAsP/InP lasers coupled with deflecting mirrors is not known for AlGaAs.