U. Ganiel

Amplified spontaneous emission and signal amplification in dye-laser systems

Transversely pumped dye-laser systems are investigated theoretically and experimentally. A set of coupled rate equations for the excited-state population densities and for the photon fluxes in both directions, at all wavelengths, is presented. Both the temporal and spatial dependence of these quantities are accounted for. The equations are solved numerically for a variety of practical situations, and analytical approximations for some limiting cases are discussed. The results describe the dependence of the amplified-spontaneous-emission (ASE) output flux on pumping rate, the spectral narrowing process, and the effects of gain saturation. It is found that under practical laboratory conditions the gain of such dye systems saturates rapidly. Consequently, at high pumping rates the output varies linearly with pump intensity, and the conversion efficiency from pump to ASE photons approaches unity. The performance of dyedaser amplifiers is described by the same set of equations, and the gain characteristics of such systems are analyzed as a function of input signal intensity and pumping rate. The theoretical calculations are compared with the results of a set of experiments, and good agreement is found. The operation characteristics of a dye-laser amplifier are evaluated and utilized in the design of a narrow-band oscillator-amplifier system.

Analysis of injection locking in pulsed dye laser systems

A pulsed dye laser system with a narrow-band signal injected into the cavity is considered. The injection starts prior to the excitation pulse. It is shown that during a transient period, injection locking can be achieved for a much wider range of parameters than under conventional CW conditions. The analysis is based on a set of coupled rate equations for the population densities and photon fluxes at all wavelengths. These are solved numerically with appropriate initial and boundary conditions. Analytical approximations, which are helpful for understanding the behavior of such systems, are presented. Both straight, two-mirror cavities, and ring laser cavities are discussed. The temporal evolution of the spectral components at all wavelengths is described. The range of tunability in this mode of operation and its dependence on various parameters, such as pulse length, cavity dimensions, and injection intensity are discussed.

A tunable, single mode, injection-locked flashlamp pumped dye laser

A tunable, very narrow bandwidth, flashpumped dye laser is described. Publse energies up to 50 mJ at a bandwidth of less than 30 MHz, and with a divergence of 0.4 mrad, are obtained. Spectral narrowing and tuning is achieved by injection locking of the pulsed laser to the radiation, of a tunable cw dye laser. The cavity is designed for single longitudinal and transverse mode operation, with a mode diameter large enough to fill the active medium.

Eigenmodes of optical resonators with mirrors having Gaussian reflectivity profiles.

A general procedure for calculating all the eigenmodes of optical resonators with mirrors having Gaussian reflectivity profiles is described. The eigenmodes are expanded in terms of the freely propagating Her-mite-Gaussian beams. The expansion enables one to apply well known matrix techniques to this kind of systems. The eigenvalues found determine the eigenfrequencies and the mode discrimination properties of such resonators.

Simultaneous multiple‐wavelength operation of a tunable dye laser

A new technique for simultaneous operation of a dye laser at a number of independently tunable wavelengths is described. The system utilizes holographic wavelength selectors in succession, each aligned to choose one particular wavelength, and the output beam contains these wavelengths collinearly. Strong competition effects due to the homogeneous broadening of the amplifying medium reduce the multiple‐wavelength tuning range. By proper adjustment of the components in the device, this range can be increased to cover most of the single‐wavelength tuning region. The operational characteristics and the experimental results obtained at two‐wavelength operation are presented and discussed.

Stability of Optical Resonators with an Active Medium

The problem of the stability of the Gaussian modes of an optical resonator of large mirror apertures filled with a medium having a gain and index profile is considered. Recent results by other investigators are carefully examined in an attempt to clarify a discrepancy between them. It is found that the modes of the resonator are stable if the gain is highest on the resonator axis. When the gain increases with distance from the resonator axis, one can calculate a Gaussian eigenmode,:but this mode is unstable in the sense that any deviation from the exact physical parameters defining the mode will cause its divergence to an infinite spot size.

Early termination of flashlamp pumped dye laser pulses by shock wave formation.

The problem of early termination of laser action in flashlamp pumped dye lasers is investigated. It is found that in high power, short pulse duration systems shock waves are created in the dye solution. Index inhomogeneities in the laser medium are created, and these lead to the termination of laser action. The velocity of propagation of the disturbance is measured. Some possibilities concerning the origin of these shock waves are examined. A design scheme that overcomes the effect of the disturbance in short pulse (</=5 microsec) systems is described.

Stability of optical laser resonators with mirrors of gaussian reflectivity profiles, which contain an active medium

Abstract The stability of laser resonators which contain a medium with a gain profile is investigated. Such resonators are unstable when the resonator mirrors are large (infinite aperture approximation), and the gain is lowest on the optical axis and increases with radial distance. It is shown that such resonators have well-defined regions of stability if the mirrors have gaussian reflectivity tapers.

Narrow-band tunable, subnanosecond pulse generation in injection locked dye laser systems

Abstract A simple method for generating tunable, subnanosecond pulses of very narrow bandwidth is proposed. The technique is based on the phenomenon of relaxation oscillations, combined with injection locking to the wavelength of an injected narrow-band signal. A detailed numerical simulation was performed, and the results for a realistic system are presented.

A tunable dye laser with a composite holographic wavelengths selector

Abstract Composite holographic diffraction gratings, each recorded with a different wavelength, are utilized to achieve simultaneous multiple wavelengths operation of a tunable dye laser. By properly selecting the recording wavelengths and adjusting the efficiency of the holographic gratings, the tuning range and output powers at the various wavelengths can be controlled.