Inverse Free Electron Laser Research Articles

Experimental observation and investigation of energy exchange between an electron beam and counterpropagating laser beams in a Compton-scattering free-electron-laser scheme.

We report the observation and investigation of synchronous energy exchange between nonrelativistic electrons and the ponderomotive (beat) force of two counterpropagating intense pulsed ${\mathrm{CO}}_{2}$ laser beams, operating at different frequencies in a stimulated Compton-scattering scheme. The interaction occurred in the nonlinear (trapping) regime, the physics of which is the same as that which occurs in laser accelerators and efficiency-enhanced free-electron lasers (FEL's) with long wigglers. The experiment is a first demonstration of the principle of inverse FEL acceleration and electromagnetic pump FEL operation in the nonlinear (trapping) regime. It can also be described as a demonstration of a ``traveling beat-wave'' Kapitza-Dirac effect in the nonlinear regime. Two different mechanisms of enhanced energy transfer were observed---electron trapping and phase-area displacement. Experimental results and computer simulations of both mechanisms are presented.

Limiting factors in an inverse free electron laser

The main problems connected with the optimum design of an inverse free electron laser are discussed. Particular attention has been paid to the diffraction and pump depletion effects.

The quest for ultrahigh energies

A categorization is given of all the methods for accelerating particles. It is shown that in principle one can employ the large fields of a laser for this purpose as well as the wake fields of intense low-energy particle beams. Discussion is given of four acceleration schemes which offer the possibility of attaining very high-energy particles; namely, the inverse free-electron laser accelerator, the beat-wave accelerator, the wake-field accelerator, and the two-beam accelerator.

Free-electron laser and laser electron acceleration based on the megagauss magnetic fields in laser-produced plasmas.

It is suggested that the megagauss magnetic fields generated in laser-produced plasmas be applied for (a) the construction of a wiggler for an x-ray free-electron laser and (b) charged-particle acceleration to high energies using the inverse free-electron laser and the autoresonance laser acceleration schemes. Coherent amplification of 10-\AA{} radiation with a 150-MeV electron beam seems feasible and gigaelectronvolt electron beams may induce a $\ensuremath{\gamma}$-ray laser. An acceleration gradient of about [100 MV/cm] ${[\frac{z}{(10cm)}]}^{\frac{\ensuremath{-}1}{3}}$ can be achieved at a distance $z$ along a 1-MG axial magnetic field in the autoresonance laser acceleration scheme, using a Nd:glass laser of ${10}^{18}$ W/${\mathrm{cm}}^{2}$.

High-energy inverse free-electron-laser accelerator.

We study the inverse free-electron-laser (IFEL) accelerator and show that it can accelerate electrons to the few hundred GeV region with average acceleration rates of the order of 200 MeV/m. Several possible accelerating structures are analyzed, and the effect of synchrotron-radiation losses is studied. The longitudinal phase stability of accelerated particles is also analyzed. A Hamiltonian description, which takes into account the dissipative features of the IFEL accelerator, is introduced to study perturbations from the resonant acceleration. Adiabatic invariants are obtained and used to estimate the change of the electron phase-space density during the acceleration process.

A Modified Two Beam Accelerator Driven by a D. C. Pelletron Free Electron Laser

Assembling the next generation of linear particle accelerators requires progress in three areas. Sources must be developed to provide the coherent electromagnetic radiation used to power the device. Physical structures must be designed which efficiently transfer the power to the high energy beam. Cooling techniques must be developed in order to enhance beam transport and to provide sufficient luminosity. This paper will describe a method of obtaining a highly efficient coherent radiation source by using a continuous wave Free Electron Laser (FEL). Several possibilities exist for an accelerating structure which could use this radiation as a power source. These include scaling down the size of traditional R-F cavities, inverse free electron lasers, and surface grating schemes. Inverse free electron lasers have the possibility of intrinsic cooling of the high energy beam.

Increasing the acceleration gradient of the transverse-field accelerator using a dielectric medium

A gas-loaded undulator is proposed as a method for the coupling of intense optical radiation and charged particles to achieve high-gradient acceleration of 100 MeV/m or more. The theory of the gas-loaded inverse free electron laser (IFEL) is the same as that of the vacuum IFEL, with the exceptions that the phase-matching condition between the optical field and the charged particle is changed, and that multiple scattering of the electrons by the gas molecules has been introduced. The new phase matching condition allows reasonable undulator magnetic fields while still maintaining good acceleration gradients for extremely relativistic beams. Synchrotron radiation losses can then be kept to acceptable values. A Monte Carlo simulation of the interaction has been done which includes elastic scattering, radiation losses, laser and electron beam characteristics, and gas and helix parameters. As with the conventional IFEL, tapering the undulator with an increasing magnetic field is found to affect both the maximum energy and population of the accelerated particles.

Small-signal gain analysis for IR tapered inverse free-electron lasers

A detailed analysis of the small-signal regime for an IR inverse free-electron laser has been performed. Both configurations based on tapered undulators and on optical klystrons have been analyzed.

Laser Accelerators

The use of lasers to accelerate particles to ultra-high energies is motivated by the very high electric fields associated with focused laser beams. A number of such schemes have been proposed: for example, microstructures driven by lasers operating in the optical-near infrared frequency range, laser-driven space charge plasma waves, inverse free-electron laser accelerator and the two-beam accelerator. Current status of these schemes is reviewed. Lasers may also find an application in improving the power sources and in focusing very high energy particle beams.

A parametric analysis of inverse free electron laser accelerators based on tapered undulators and optical klystrons

The acceleration gradient and the energy spread of an inverse free electron laser accelerator are examined for different parameters of a non uniform undulator and an optical klystron.

Transverse Particle Acceleration Techniques Using Lasers and Masers

The concept discussed herein uses an intense traveling electromagnetic wave, produced by a laser or maser source, to accelerate electrons in the Rayleigh region of a focused beam. Although the possibility of non-synchronous acceleration has been considered, very little analysis of potential device configurations has been reported. Computer simulations of the acceleration process indicate practical figure of merit values in the range of 100 MeV/m for achievable electric field strengths with current technology. The development of compact, high energy electron accelerators will provide an essential component for many new technologies. Such as high power free electron lasers, X-ray and VUV sources, and high power millimeter and microwave devices. Considerable effort has been directed toward studies of new concepts for electron acceleration, including inverse free electron lasers, GYRACS, and modified betatrons.

Laser Driven Electron Accelerators

The following possibilities are discussed: inverse free electron laser (wiggler accelerator); inverse Cerenkov effect; plasma accelerator; dielectric tube; and grating linac. Of these, the grating acceleraton is considered the most attractive alternative. (GHT)