High Power THz Generation from Sub-ps Bunches of Relativistic Electrons
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High Power THz Generation from Sub-ps Bunches of Relativistic Electrons S. Benson, D. R. Douglas, H. F. Dylla, J. Gubeli, K. Jordan, G. R. Neil, M. Shinn, S. Zhang and G.P. Williams FEL Facility, Jefferson Lab, 12000 Jefferson Avenue, Newport News, VA 23606 ABSTRACT We describe a > 100 Watt broadband THz source that takes advantage of the relativistic enhancement of the radiation from accelerating electrons according to the formula assigned the name of Sir Joseph Larmor[1,2]. This is in contrast to the typical 1 milliwatt sources available in a laboratory. Specifically, for relativistic electrons the emission is enhanced by the fourth power of the increase in mass. Thus for 100 MeV electrons, for which the mass increases by a factor of ~ 200, the enhancement is > 109. The experiments use a new generation of light source called an energy recovery linac (ERL) [3], in which bunches of electrons circulate once, but in which their energy is recovered. In such a machine the electron bunches can be very much shorter than those, say, in storage rings or synchrotrons. The Jefferson Lab facility operates in new limits of emission from relativistic particles involving both multiparticle coherence and near-field emission in which the velocity (Coulomb) term in the classical electrodynamical theory becomes as important as the acceleration term (synchrotron radiation). The sub-picosecond pulses of light offer unique capabilities in 2 specific areas, namely timeresolved dynamics, and imaging. High resolution THz spectroscopy has recently revealed sharp vibrational modes for many materials including malignant tissue, proteins, DNA, pharmaceuticals and explosive materials. Energetically the THz range embraces superconducting bandgaps, and regions of intense interest in the understanding of systems in which correlated motions of electrons are important, such as colossal magneto-resistive and high-Tc materials. The very high power levels of the new source will allow non-linear effects to be observed as well as the creation of novel states of materials, including electric-field driven localization[4]. We will give examples of existing work in these areas and present opportunities afforded by the new source. INTRODUCTION In this paper we compare and contrast a new high power THz source with conventional Auston switch[5] sources, and synchrotron radiation sources. We also discuss in detail the design of our user facility, and in particular the beam transport system that feeds it. We point out that this facility can probe materials at frontiers of ultra-fast and ultra-high electric and magnetic fields, and in addition can provide multiple photon beams for 2 or 3 photon pump-probe experiments such as those described above.
Mater. Res. Soc. Symp. Proc. Vol. 850 © 2005 Materials Research Society
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PHYSICS OF LIGHT PRODUCTION FROM ACCELERATED ELECTRONS – COMPARISON WITH STANDARD SOURCES Propagating fields of light can be generated from Maxwell’s equation:
∇× H = J free + ε
∂E ∂P + ∂t ∂t
(1)
which shows how a free curren
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