Steady-State Far-Infrared Coherent Synchrotron Radiation detected at BESSY II

At BESSY II it is demonstrated that far-infrared coherent synchrotron radiation (CSR) can be generated by a controlled, steady-state process at storage rings. As an indication for coherent emission, the radiated power grows with the square of the beam current. The spectrum was analyzed by an interferometer in the 1-mm to 0.3-mm wavelength range. The CSR was enhanced more than 3000 times above background; the incoherent radiation remained below the background level. Steady-state and bursting CSR were discriminated by time resolved analysis from $\mu$ seconds to seconds.