Charles Kirkham Rhodes

Observations of stimulated emission from high‐pressure krypton and argon/xenon mixtures

Experimental data demonstrating coherent oscillation in high‐pressure krypton at 1457 ± 1 A with an 8‐A linewidth are reported. Observations of stimulated emission from argon/xenon mixtures arising from the operation of efficient energy transfer processes and resulting in a twofold enhancement of the xenon laser output at ∼ 1720 A are also given. The influence of collisional‐induced absorption on the oscillator output is indicated by the measurement of a blue shift in the spectrum of the stimulated output for argon/xenon mixtures relative to the case of pure xenon.

Radiative and kinetic mechanisms in bound-free excimer lasers

An interactive kinetic model for bound-free excimer lasers is described, with particular emphasis on the electron beam pumped rare gas systems. Important kinetic processes and the interaction of the photon field with excited states are examined in detail. Application of the model to the xenon and krypton oscillators yields results which are in good agreement with experimentally observed quantities. It is found that the collisional coupling of the excimer singlet and triplet manifolds in combination with the losses arising from photoionization play an important role in determining the performance. Numerical values of the parameters used in the computational model are given.

Laser oscillation on the green bands of XeO and KrO

Laser oscillation has been observed on the green bands of the XeO and KrO excimers using direct electron beam excitation of high‐pressure Xe or Kr containing small concentrations of O2. These bands are transitions between molecular levels correlating to the 1S0 and 1D2 metastable levels of atomic oxygen plus ground‐state Xe or Kr. The XeO laser emission is at a number of wavelengths between 5300 and 5550 A, while the KrO emission is at a single wavelength near the free atom line at 5577 A. Laser pulse energies of 10 mJ and peak powers of 100 kW are seen for both excimers.

Nonlinear optical processes in atoms and molecules using rare-gas halide lasers

The use of nonlinear optical processes expands the flexibility of excimer systems in the study of a wide range of atomic and molecular phenomena and materials. These mechanisms have already allowed for the selective excitation of states in the 10 to 20 eV range involving bound state excitation, ionization, and molecular dissociation. Specific examples involving the electronic excitation of H 2 , Kr, and Xe, the production of Xe+for the analysis of the molecular properties of XeF*, and nonlinear photodissociation of N 2 O and OCS are discussed.

Review of ultraviolet laser physics

A review of the status and properties of coherent sources of ultraviolet radiation is presented. This includes a wide range of developments concerning atomic and molecular systems useful for generating wavelengths below 4000 A, as well as progress in alternative methods of ultraviolet production. Particular emphasis is placed on recent advances in molecular bound-free systems whose operation is enhanced at high densities. It is believed that some of these systems may be scalable to sufficiently high-energy outputs to be useful in controlled fusion applications. A brief prognosis and discussion of future developments tending to the X-ray region are given.

Dynamic model of high‐pressure rare‐gas excimer lasers

The dynamic behavior of the high‐pressure rare‐gas VUV excimer systems is examined. It is found that the collisional coupling of the excited singlet and triplet manifolds in combination with the losses arising from photoionization play a vital role in determining the over‐all performance. The proposed mechanisms provide a unified description of both the pressure dependence of the stimulated output and the observed pressure shift of the stimulated spectrum in xenon. Numerical values of the relevant parameters are given.

Kinetic model of ultraviolet inversions in high‐pressure rare‐gas plasmas

It is shown theoretically that stimulated vacuum ultraviolet emission at [inverted lazy s] 1700 A is possible in the afterglow of a suitably prepared ionized xenon plasma. Our model involves the dissociative recombination of Xe2+ as a key step in the kinetic scheme leading to the production of excited Xe2* dimers. It is found that the maximum value of the dimer population occurs for a plasma that is initially [inverted lazy s] 1% ionized with cold gas atoms. Both plasma heating and higher levels of ionization inhibit dimer formation. Excited state‐excited state loss channels are also seen to play an important role in limiting the peak dimer density. Comparison of this theory with recent experimental results involving relativistic electron‐beam‐excited plasmas is good.

Demonstration of temporal coherence, spatial coherence, and threshold effects in the molecular xenon laser☆

Abstract Stimulated emission has been observed at 1722 ± 1 A in high-pressure xenon gas originating from the bound-free continuum of the Xe∗2 molecule. This emission exhibits strong line narrowing, spatial coherence corresponding to a few times the diffraction limit, a sharp oscillation threshold, and an output time dependence radically different from the spontaneous emission observed without an optical cavity or below threshold. The confluence of all these observations is an explicit and unequivocal demonstration of a coherent stimulated emission process. Specific data detailing the pressure dependence of the stimulated output and results with rare-gas mixtures are given.

Model of the Self-Q-Switching Instability of Passively Phased Fiber Laser Arrays

We present a simple model for self-pulsation instability in passively phased high power optical fiber amplifier arrays with external feedback. Its key features are, first, the feedback levels sensitivity, and thus that of the cavity Q-value, to small phase changes of the array fields, and, second, the effect of refractive index nonlinearity in the amplifiers. The models prediction of an instability threshold for arrays of at least two amplifiers is confirmed by a linearized stability analysis of a system in ring-cavity geometry, and the magnitudes of predicted power levels are well within the domain of recent experiments.

Simple model to explain instabilities in passively-phased high-power fiber laser arrays

We propose a simple physical mechanism to explain observed instabilities in the dynamics of passively phased fiber amplifier arrays that arises from two properties: First that a weak phase disturbance of the output field of the array is converted into a strong intensity disturbance through the mode-selective feedback mechanism. Second, that this intensity fluctuation regenerates a phase fluctuation due to the nonlinear properties of the amplifying media. At sufficiently high operating power levels this cyclic disturbance continues to grow upon each cavity round trip, creating instability. This simple picture is supported by the results of a linear stability analysis of the set of propagation and population rate equations, which are in good agreement with observed critical power levels. A third level of quantitative confirmation was obtained by comparison to the results of numerical integration of the original set of nonlinear equations. This predicted instability is entirely a property of passively phased arrays of more than one element.