We report and discuss high-flux generation of circularly polarized γ-rays by means of Compton scattering. The γ-ray beam results from the collision of an external-cavity-enhanced infrared laser beam ...and a low emittance relativistic electron beam. By operating a non-planar bow-tie high-finesse optical Fabry-Perot cavity coupled to a storage ring, we have recorded a flux of up to (3.5 ± 0.3) × 10
photons per second with a mean measured energy of 24 MeV. The γ-ray flux has been sustained for several hours. In particular, we were able to measure a record value of up to 400 γ-rays per collision in a full bandwidth. Moreover, the impact of Compton scattering on the electron beam dynamics could be observed resulting in a reduction of the electron beam lifetime correlated to the laser power stored in the Fabry-Perot cavity. We demonstrate that the electron beam lifetime provides an independent and consistent determination of the γ-ray flux. Furthermore, a reduction of the γ-ray flux due to intrabeam scattering has clearly been identified. These results, obtained on an accelerator test facility, warrant potential scaling and revealed both expected and yet unobserved effects. They set the baseline for further scaling of the future Compton sources under development around the world.
In the Advanced Virgo+ interferometric gravitational-wave detector, the length control of the Fabry-Pérot cavities in the arms and of the detuned filter cavity, used for generating ...frequency-dependent squeezing, uses an auxiliary green beam at half of the operation laser wavelength (1064 nm). While operating the filter cavity with such a bichromatic control scheme for tens of hours, we observed that the mirror reflection phase shift of the fields at the two wavelengths responds differently to temperature changes in the mirrors, causing a change in the relative resonance condition of the two beams. In this paper we show that this thermal detuning effect can be explained by considering the thermomechanical properties of the mirror coating. Our experimental measurements are in good agreement with the theoretical predictions and allow us to drive requirements on the bicolor coating design and mirror temperature stability for long-term stable cavity control.
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