NON-INTERFEROMETRIC SPECTRAL ANALYSIS OF SYNCHROTRON RADIATION IN THE THz REGIME AT ANKA

Interferometry is the quasi-standard for spectral measurements in the THzand IR-range. The frequency resolution, however, is limited by the travel range of the interferometer mirrors. Therefore, a resolution in the low megahertz range would require interferometer arms of about 100m. As an alternative, heterodyne measurements provide a resolution in the Hertz range, an improvement of 6 orders of magnitude. Here we present measurements done at ANKA with a VDI WR3.4SAX, a mixer that can be tuned to frequencies from 220GHz to 330GHz and we show how the bunch filling pattern influences the amplitude of specific frequencies. INTRODUCTION The single particle synchrotron spectrum emitted by an electron in a bending magnet is broad-band and also continuous. In a storage ring where an electron bunch emits synchrotron radiation on every turn, the emitted electric field consists of equally spaced (T0) series of short pulses. As an approximation we assume a Dirac delta function (δ(t)) as bunch signal which leads to an infinite pulse train, known as Dirac comb or Shah distribution, that can be represented as a Fourier series [1]: