Single bunch X-ray pulses on demand from a multi-bunch synchrotron radiation source

Synchrotron radiation facilities routinely operate in a multi-bunch regime, but applications relying on time-of-flight schemes require single bunch operation. Here we show that pulse picking by resonant excitation in a storage ring creates in addition to the multi-bunch operation a distinct and separable single bunch soft X-ray source. It has variable polarization, a photon flux of up to 10 7 –10 9 ph s −1 /0.1%BW at purity values of 10 4 –10 2 and a repetition rate of 1.25 MHz. The quasi-resonant excitation of incoherent betatron oscillations of electrons allows horizontal pulse separation at variable (also circular) polarization accessible for both, regular 30 ps pulses and ultrashort pulses of 2–3 ps duration. Combined with a new generation of angularly resolving electron spectrometers this creates unique opportunities for time-resolved photoemission studies as confirmed by time-of-flight spectra. Our pulse picking scheme is particularly suited for surface physics at diffraction-limited light sources promising ultimate spectral resolution. Although synchrotron facilities routinely operate in a multi-bunch regime for maximum average brilliance, studies relying on time-of-flight schemes require single-bunch operation. Here, Holldack et al. isolate and apply single bunch X-ray pulses from multibunch radiation using pulse picking by resonant excitation.