Space Charge and Quantum Corrections in Free Electron Laser Evolution

Effects producing gain dilution in Free Electron Laser devices are well documented. We develop here a unified point of view allowing the introduction of space charge effects, along with the gain deterioration due to inhomogeneous broadening contributions and discuss the relevant interplay. We outline future developments and comment on the possibility of including in the formalism effects of quantum mechanical nature.Comment: 10 pages, 7 figure

Criterion of applicable models for planar type Cherenkov laser based on quantum mechanical treatments

A generalized theoretical analysis for amplification mechanism in the planar-type Cherenkov laser is given. An electron is represented to be a material wave having temporal and spatial varying phases with finite spreading length. Interaction between the electrons and the electromagnetic (EM) wave is analyzed by counting the quantum statistical properties. The interaction mechanism is classified into the Velocity and Density Modulation (VDM) model and the Energy Level Transition (ELT) model basing on the relation between the wavelength of the EM wave and the electron spreading length. The VDM model is applicable when the wavelength of the EM wave is longer than the electron spreading length as in the microwave region. The dynamic equation of the electron, which is popularly used in the classical Newtonian mechanics, has been derived from the quantum mechanical Schrödinger equation. The amplification of the EM wave can be explained basing on the bunching effect of the electron density in the electron beam. The amplification gain and whose dispersion relation with respect to the electron velocity is given in this paper. On the other hand, the ELT model is applicable for the case that the wavelength of the EM wave is shorter than the electron spreading length as in the optical region. The dynamics of the electron is explained to be caused by the electron transition between different energy levels. The amplification gain and whose dispersion relation with respect to the electron acceleration voltage was derived on the basis of the quantum mechanical density matrix. © 2013 Elsevier B.V

A quantum mechanical analysis of Smith-Purcell free-electron lasers

The paper presents a quantum mechanical treatment for analyzing the Smith-Purcell radiation generated by charged particles passing over a periodic conducting structure. In our theoretical model, the electrons interact with a surface harmonic wave excited near the diffraction grating when the electron velocity is almost equal to the phase velocity of the surface wave. Then, the surface harmonic wave is electromagnetically coupled to a radiation mode. The dynamics of electrons are analyzed quantum mechanically where the electron is represented as a traveling electron wave with a finite spreading length. The conversion of the surface wave into a propagating mode is analyzed using the classical Maxwell equations. In the small-signal gain regime, closed-form expressions for the contributions of the stimulated and spontaneous emissions to the evolution of the surface wave are derived. The inclusion of the spreading length of the electron wave to the emission spectral line is investigated. Finally, we compare our results based on the quantum mechanical description of electron and those based on the classical approach where a good agreement is confirmed

Quantum characteristics of stimulated Cherenkov radiation in dielectric-lined waveguide operating at optical wavelengths

In this paper, a quantum mechanical model is proposed to describe the basic features of stimulated Cherenkov radiation in the small-signal low-gain regime. In this model, the electron is described by a wavepacket with finite spreading length and the electron wave function is a solution of the Schrödinger equation. We show that the quantum effects are manifested when the spreading length of the electron wave is much longer than the electromagnetic (EM) wavelength such as in the optical wavelength range. The effect of electron relaxation due to Coulombs collisions with neighboring electrons is introduced to characterize the damping of the vibration of the electron wave with time. When the relaxation effect is neglected, we prove that our essential results match with other classical and quantum approaches based on different theoretical concepts. © 2011 Elsevier B.V. All rights reserved

Analysis of saturation phenomena in Cerenkov free-electron lasers with a planar waveguide

In this paper, the operation of the stimulated emission in Cerenkov free-electron laser (CFEL) is studied on the basis of the modulations of electron velocity and density by the electromagnetic (EM) field. The influence of the electron relaxation, due to mutual electrons collisions, on the electron dynamics is taken into account. We investigate the growth characteristics of Cerenkov laser operating in the small-signal and saturation regimes. In the saturation regime, the effect of velocity reduction of the electron beam on the gain dynamics is demonstrated. We also show that our results match with those of other well-known treatments in the small-signal gain limit. © 2011 American Institute of Physics

Design of sub-Angstrom compact free-electron laser source

In this paper, we propose for first time practical parameters to construct a compact sub-Angstrom Free Electron Laser (FEL) based on Compton backscattering. Our recipe is based on using picocoulomb electron bunch, enabling very low emittance and ultracold electron beam. We assume the FEL is operating in a quantum regime of Self Amplified Spontaneous Emission (SASE). The fundamental quantum feature is a significantly narrower spectrum of the emitted radiation relative to classical SASE. The quantum regime of the SASE FEL is reached when the momentum spread of the electron beam is smaller than the photon recoil momentum. Following the formulae describing SASE FEL operation, realistic designs for quantum FEL experiments are proposed. We discuss the practical constraints that influence the experimental parameters. Numerical simulations of power spectra and intensities are presented and attractive radiation characteristics such as high flux, narrow linewidth, and short pulse structure are demonstrated

Two models for electro-magnetic wave amplifier by utilizing traveling electron beam

金沢大学理工研究域電子情報学系Electro-magnetic (EM) wave amplifiers by utilizing traveling electron beam in vacuum come to have attention as devices covering over extremely wide frequency range from the microwave to the X-ray regions. We point out that two different amplification mechanisms should exist according to the relation between the EM wavelength and the electron size. The first model is named as Coherent Electron Wave (CEW) model. Another one is named as Localized Electron (LE) model. The boundary of these two models is locating in the THz region. © 2008 IEEE

Two models for electro-magnetic wave amplifier by utilizing traveling electron beam

金沢大学理工研究域電子情報学系For the electro-magnetic (EM) wave amplifier, we point out two amplification mechanisms should exist according to the relation beween the EM wavelength and the electron size. First model is named as Coherent Electron Wave (CEW) model. Another one is named as Localized Electron (LE) model. ©2008 IEEE