Title: Monochromaticity of coherent Smith-Purcell radiation from finite size grating,
Abstract: Investigation of coherent Smith-Purcell Radiation (SPR) spectral
characteristics was performed both experimentally and by numerical simulation.
The measurement of SPR spectral line shapes of different diffraction orders was
carried out at KEK LUCX facility. A pair of room-temperature Schottky barrier
diode (SBD) detectors with sensitivity bands of $60-90$~GHz and $320-460$~GHz
was used in the measurements. Reasonable agreement of experimental results and
simulations performed with CST Studio Suite justifies the use of different
narrow-band SBD detectors to investigate different SPR diffraction orders. It
was shown that monochromaticity of the SPR spectral lines increases with
diffraction order. The comparison of coherent transition radiation and coherent
SPR intensities in sub-THz frequency range showed that the brightnesses of both
radiation mechanisms were comparable. A fine tuning feasibility of the SPR
spectral lines is discussed.