Super-radiant THz sources: Challenges and opportunities

The past fifteen years have seen a rapid development of novel techniques to generate and detect ultra-short and high power THz pulses. The availability of these pulses with electric field strength in the few 10 to
100 MV/m regime has led to a number of exciting experiments in particular in the field of non - linear THz spectroscopy and THz control experiments.
One class of these THz generation techniques utilizes highly charged, ultra short electron bunches accelerated to relativistic speed in linear particle accelerators [1]. A variety of different source concepts allows to shape the THz pulses from single cycle/broad band pulses to multicycle/narrow - bandwidth pulses with polarizations ranging from radial to linear. One main attraction of accelerator- based THz originates from the fact that the THz generation process does not take place in a medium but in the ultra - high vacuum of the accelerator, so that the THz pulse energy can hence theoretically much easier up scaled than in any of the table top sources available today. Additionally it could recently be shown that coherent THz radiation can be generated residually and in parallel to the femtosecond X - ray pulses in 4th generation X-ray light sources such as FLASH [2,3,and 4] and LCLS [5]. This opens up the exciting opportunity to perform naturally synchronized THz pump X-ray probe experiments on few femtosecond time scales [2,3,and 5]. An overview over different THz facility projects will be presented and experimental opportunities and challenges ranging from atomic physics, condensed matter to biophysics will be discussed.

[1]G.L. Carr et. al., High power terahertz radiation from relativistic electrons,Nature420(2002), 153.
[2] M. Gensch et. al., New infrared undulator beamline at FLASH, Infrared Phys. Technol.51(2008), 423.
[3]U. Fruehling et.al., Single-Shot THz-field-driven X-ray streak camera,Nat. Photon.3(2009), 523.
[4] F. Tavella, N. Stojanovic, G. Geloni, M. Gensch, Few-Femtosecond timing at Fourth-Generation X-ray Lightsources,Nat. Photon.5(2011), 162.
[5]D. Daranciang et. al.,Single cycle terahertz pulses with > 0.2 V/angstrom field amplitudes via coherent transition radiation, Appl. Phys.
Lett.(2011), 141117.