David A. G. Deacon

Free electron laser experiment at Orsay: A review

In this paper we review the results obtained in the last two years with the Orsay free electron laser.

Reducing the sensitivity of a free‐electron laser to electron energy

A technique is described which allows a free‐electron laser to utilize an electron beam with a wide energy spread. A laser using this technique can be powered by a greater variety of electron sources than would otherwise be possible. In addition, the techniques ease some of the problems encountered when designing a laser to operate in conjunction with a storage ring.

Theoretical study of FEL active guiding in the small signal regime

Abstract We use a self-consistent small signal FEL field equation to study active guiding. We show that self-similar mode propagation is possible only in the exponential regime. These modes must be either growing or decaying; the purely oscillatory self-similar mode is not confined. By a Gaussian approximation, we investigate the eigenvalue structure of the fundamental mode analytically, and derive a cubic equation for the complex growth rate, the laser mode size, and the radius of the phase front curvature.

Gain measurements versus theory for the ACO storage ring laser

Abstract We discuss the gain measurements made on the Orsay storage ring free electron laser, and show that the peak measured gain is identical to that predicted by a modified theory which takes into account the electron trajectory distortions. This is the first free electron laser experiment in which the quality of the data is sufficiently good to permit a detailed verification of the Madey theorem.

Optical coating damage and performance requirements in free electron lasers

Abstract The new generation of free electron lasers will place demands on optics which are likely to stress the state of the art in both substrates and coatings. The major challenges are to reduce the causes for energy deposition into the optics, and to deal effectively with the resulting thermal effects. In this paper we review the scaling and possible mechanisms of single photon damage, and discuss the thermal phenomena expected in FEL optics.

Basic theory of the isochronous storage ring laser

Abstract The use of an isochronous storage ring as the electron source for a higher power, high efficiency free electron laser is proposed. Electrons can be trapped in the optical potential wells in such a system, where they couple energy directly from the radio frequency accelerating cavity into the optical frequency laser beam with negligible losses. The conditions for the existence of such traps are derived, as well as the dependence of their size and shape on the laser parameters and the deviations from isochronism in the arc of the storage ring. The results of a numerical stimulation extend the analytic results to the general case of large phase advance. The optimization of the laser parameters is discussed with the aid of a numerical example of the performance assuming a design which can be realized in practice.

Free Electron Lasers

Lasers based on the stimulated emission of radiation by free electrons in a spatially periodic magnetic field offer a unique potential for tunable operation at high power and high efficiency. Substantial advances have been made recently in the theoretical analysis of this class of device and in the operation in our laboratory of a 10 μ free electron laser amplifier. These results and the implications for the design of a practical device will be reviewed.

Performance of an XUV FEL oscillator on the Stanford storage ring

Abstract Operation of and XUV free electron laser (FEL) oscillator in the 27 m straight section of the 1 GeV Stanford X-Ray Center (SXRC) storage ring is examined. Based on high gain calculations made with the help of the FEL amplifier simulation code FRED, oscillation below 1000 A is found to be readily achievable. FEL longitudinal and transverse acceptances in the high gain regime for a constant parameter wiggler are investigated. Estimates are made of peak and average output powers for 960 A and 285 A oscillators operating in the storage ring cw mode. The case of a 960 A oscillator operating in the pulsed mode is also investigated. Time structures for both modes are calculated for single and multi-bunch ring operation.

Optical guiding simulations for high gain-short wavelength FELs

Abstract Optical guiding in the linear growth regime of an FEL amplifier has been reported in simulations by Scharlemann et al., using the LLNL 2D code FRED. We present the results of a parameter space investigation of optical guiding in an FEL using the FRED code with a realistic range of input parameters: optical wavelength, mode size and focus, current density, emittance, and wiggler period. We find that optical guiding has a profound impact on gain, and that within existing mirror technology and for the operating characteristics expected of the Stanford storage ring FEL now in construction, oscillation is achievable from the visible through 300 A. We also describe the relative importance of guiding in different regimes. In support of these predictions we present “FRED” benchmarking results.

Laser induced bunch lengthening on the ACO storage ring FEL

Laser induced bunch lengthening has been measured on the ACO storage ring FEL. The experimental data at low current generally confirm the existing theoretical models, while the high-current data is dominated by anomalous effects.