Electron Beams from Needle Photocathodes and a New Theory of the Smith-Purcell Free-Electron Laser
0
Citation
6
Reference
20
Related Paper
Abstract:
A promising source of radiation in the important terahertz (THz) region of the spectrum is the Smith-Purcell free-electron laser (SPFEL). This dissertation presents a new theory of the SPFEL, taking into account dispersion of evanescent surface waves on the grating. From the dispersion relation for these waves, it is found that the device can operate as an amplifier or as an oscillator. The gain length is calculated in the amplifier regime, as well as the growth rate and start current in the oscillator regime. The theory is supported by published computer simulations, but in conflict with previous experiment.
These devices require a high-quality electron beam, and this dissertation also presents developments in needle photocathodes designed to drive an SPFEL. Data on emission current are presented as a function of voltage for various drive laser wavelengths. A simplified model is used to interpret the data as variation in the emitting area with voltage for photon energies below the cathode workfunction. Data and a new scaling law for the divergence of the beam at high current are also presented.Keywords:
Free-electron laser
Free electron model
Dispersion relation
Cite
The radiation from a modulated electron beam, such as that produced in a radio-frequency accelerator, passing through a magnetic undulator is analyzed. The authors show that in a waveguide free electron laser (FEL), this may lead to an emission of a significant amount of coherent radiation in the far infrared to millimeter wave range. A simple and powerful method of calculating the spectral distribution of the radiated power is presented along with an analysis of the gain and the saturated power. The experimental results of spontaneous emission measurements on an RF driven FEL, are presented and compared to theoretical predictions.< >
Undulator
Free-electron laser
Extremely high frequency
Cite
Citations (124)
A theoretical study of the possibility of a free-electron laser in the XUV and soft X-ray region of the spectrum, using a counterpropagaing CO/sub 2/ laser beam as an undulator, is presented. A one-dimensional model is used to evaluate the single-pass power gain of such a device. The detrimental effects due to the energy speed, emittance of the electron beam, and the diffraction of the electromagnetic undulator are explicitly incorporated in the formalism. An oscillator experiment is also considered. The solutions of the optical pulse evolution equation in the weak field, low gain, and long-electron-pulse regimes are all derived.< >
Undulator
Free-electron laser
Free electron model
Cite
Citations (33)
A Smith-Purcell device can operate as a backward-wave oscillator for intense, narrow-bandwidth, continuous wave radiation at terahertz wavelengths. We determine the requirements on electron beam current and emittance for the system to oscillate based on a three-dimensional extension of our previous two-dimensional analysis. It is found that specially designed electron beams are required with a current that exceeds a certain threshold value and a flat transverse profile that allows the beam to travel very close to the grating surface. Two methods for producing electron beams with the required characteristics are discussed.
Backward-wave oscillator
Cite
Citations (37)
The high brightness electron beam required by a short wavelength self-amplified spontaneous emission free-electron laser (FEL) may be reached only with an accurate design of the beam dynamics from the generation in the rf injector up to the undulator. The beam dynamics is affected by strong self-consistent effects at injection, in the compression stage, and during the FEL process. The support of numerical simulations is extensively used in the predictions of the beam behavior in these nonlinear dynamical conditions. I present a review of available simulation techniques, currently exploited in the design of short wavelength free-electron lasers.
Undulator
Free-electron laser
Free electron model
Cite
Citations (20)
We study the Smith-Purcell (SP) radiation emission generated in terahertz (THz) frequency range by an electron beam passing close to the surface of a 3-D quasi-periodic array of metallic slots. When more than one electron beam is used in the SP-based periodic structures, the two or more colors can be generated. In this paper, two-color SP emission of radiation with variable frequency separations has been examined in a proposed quasi-periodic Fibonacci-class structure through 3-D-particle-in-cell (PIC) simulations. In spite of using an electron beam instead of implementing a double-electron beam streaming method, in this paper, a new method for successful two-color SP radiation generation in the THz frequency domain is reported in both quasi-spontaneous and quasi-super-radiant regimes. Finally, we show that quasi-superradiance simulations demonstrate the possibility of frequency separation controlling through repetition frequency of applied periodic bunches.
Purcell effect
Terahertz gap
Cite
Citations (3)
We present a study based on a parametric optimization of a Thomson Source operated in FEL mode. This deals with the proposed scheme to use a high intensity laser pulse colliding with a high brightness electron beam of low to medium energy (around 10 MeV). Electrons undulating in the incoming laser field may emit radiation in a FEL coherent mode as far as some conditions are satisfied. A set of simple analytical formulas taking into account 3D effects is derived, in order to express these conditions in terms of three free parameters, namely the wavelength of the colliding laser pulse, the FEL ρ parameter, and the peak current carried by the electron beam. A few examples of possible operating points are compared with results of 3D numerical simulations, showing the FEL coherent emission of X-rays by high brightness electron beams colliding with high intensity laser beams carrying pulse energies of about 10 J.
Scaling law
Free-electron laser
Cite
Citations (0)
The orotron [1], ledatron [2], and diffraction radiation generator [3] are electron-tube devices that generate millimeter and submillimeter wave radiation by means of the Smith-Purcell effect. We have shown [4] that these devices are special cases of a general class of Smith-Purcell free-electron lasers considered by Wachtel [5]. The essential difference between these Smith-Purcell lasers and other free-electron lasers [6] is that in the former the electrons are bunched by a longitudinal rf electric field but in the latter they are bunched by a transverse magnetic field.
Free electron model
Cite
Citations (0)
Abstract : The nonlinear physics of the free electron laser (FEL) involves waves set up in a nearly cold electron beam when it passes through the undulator. In addition to the pump field and the growing scattered EM wave moving parallel to the electrons, there is a disturbance in the beam space charge caused by the ponderomotive force. In this paper we discuss initial experimentation using a simple Raman oscillator and amplifier. The purpose of the oscillator and amplifier. The purpose of the oscillator is to define initially the regions of substantial gain by observing the emission wavelength. Following this, the gain is observed in and amplifier configuration, using a CO sub 2 laser pumping an NH sub 3 gaseous laser at 140 GHz (2.14mm).
Undulator
Free-electron laser
Cite
Citations (0)
We propose to generate a train of prebunched electron beams for producing coherently enhanced Smith-Purcell radiation [S. J. Smith and E. M. Purcell, Phys. Rev. 92, 1069 (1953)] in the terahertz wavelength range. In this scheme, a train of picosecond laser pulses is produced to drive a photoemission gun to generate a train of 50keV electron pulses. The parameters are chosen so that the space-charge effect does not destroy the pulse time structure. Smith-Purcell radiation from the electron pulse train is enhanced due both to the short length of the individual electron bunch and to the repetitive structure of the beam. Example systems producing coherent terahertz power at about 1mW are described.
Picosecond
Cite
Citations (43)
A new concept of the optical oscillator driven by low- voltage high current electron beam is discussed. The amplification effect is based on the dissipative instability of electron beam near the surface of resonant absorbing material.
Free-electron laser
Free electron model
Cite
Citations (0)