DEVELOPMENT OF A HIGH GAIN LASER SYSTEM FOR THE INVERSE COMPTON SCATTERING SOURCE BRIXSINO

BriXS is a project of the University of Milan and the Italian Institute of Nuclear Physics (INFN) aiming at the realization of an Inverse Compton Scattering (ICS) source. This source is based on electrons superconducting cavities with energy recirculation and on a high-power laser system at a repetition rate of 100 MHz and producing monochromatic X-Rays in the energy range of 20 keV to 180 keV, mainly devoted to medical applications. A demonstrator is currently under development at the Accelerators and Applied Superconductivity Laboratories of (INFN) and University of Milan, in Segrate, Milan, consisting in a smaller version of BriXS, called BriXSino, also finding the collaboration of Ospedale San Raffaele of Milan, which is interested in the medical applications of X-rays produced with BriXSino. The high optical power (>100 kW) necessary for the Compton interaction of both BriXS and BriXSino is supposed to be reached with a combined use of active and passive amplification, where, in particular, implementing both a fiber amplifier and an optical cavity. In this thesis work, we developed and realized the whole optical stages for BriXS/BriXSino up to an average power of 11 kW, consisting of a mode locking laser source, a first stage of fiber amplification up to 4 kW and, the most important part of my work, an optical cavity for passive pulses stacking up to 11 kW. Besides the realization of this complex system, during this thesis we have developed several new techniques with a general interest in optics. In particular, a new and very general technique for the measurement of the Finesse of an optical cavity is presented, also focusing on the effect of the Carrier Envelope Offset of the laser on this parameter, which determines the passive gain. As far as the Carrier Envelope Offset is concerned, we found that it can be exploited to dramatically reduce the power noise of the laser beam coupled in the optical cavity, allowing to reach the same passive gain but with a much lower noise. During this thesis work, we developed a new technique to shift the focus of our optical cavity while maintaining the high-power level stored in it. Since this approach allows a large movement >100 μm in a time of 50 ms, faster than biological dynamics of some hundreds of milliseconds, it enables for the first time the implementation of the dual color X-rays technique with an ICS source, by switching the interaction of the electron beam between two optical cavities with two different interaction angles, thus activating two different ICS spectral lines in sequence. Thanks to the similarities between the optical cavity used for BriXS/BriXSino and the Optical Parametric Oscillator (OPO) implemented in our laboratory for the generation of quantum optical squeezed states, in this work we present a study of a new technique to stabilize the relative phase between the seed and the pump involved in the squeezing process, greatly improving the stability of the system. This setup up also allowed to study a new method to counteract phase noise on quantum optical states, squeezing their phase diffusion.