Study and applications of THz and Lasers pulses for accelerator physics

The aim of my work during my PhD course (2016-2019) was to study and develop new applications in the field of accelerator physics using ultrashort lasers and high energy TeraHertz (THz) pulses. Most of my focus was aimed at the generation and control of high energy THz pulses using the Optical Rectification (OR) process. Those pulses are needed both as accelerating source and as diagnostic tool for charged particles. I had characterized in a broadband spectrum (50 to 36000 cm−1) the optical properties of two organic crystals HMQ-TMS and DSTMS, used for the high energy THz generation in OR. Trough an analytical study of the OR process. I had developed a simulation code that reconstructs the THz radiation generated in OR, given a pump laser pulse, and shows how is possible to shape the THz pulse by changing the nonlinear phase of the pump laser. Also inverting the previous technique it is possible to retrieve the laser parameters, resulting in a promising diagnostic tool for ultrafast lasers. I had worked on a new proposal, to use an high energy THz pulse as driver in the Laser WakeField Acceleration (LWFA), using Particle In a Cell (PIC) simulations. The results show how an intense THz pulse can be more efficient than a standard Ti:Sa laser pulse in the excitation of intense wakefield in the quasi-linear regime. The interaction of high energy THz pulses with the plasmas, used for LWFA, shows the possibility to develop a diagnostic tool for the plasma density and temperature along the plasma channel. I will present the model for this diagnostic technique and my work in its experimental application using the THz radiation generated by two color plasma with a plasma filament in air as target. I also developed a start-to-end simulation code to correctly model the THz propagation and interaction with the plasma filament. About the use of high energy ultrafast lasers in particle accelerators, I had studied a laser COMB technique aiming to obtain a good quality flat-top UltraViolet (UV) pulse for the use in a photocathode. The model takes into account the effect of the laser propagation, inside the nonlinear crystal − BBO up to the second order phase, aiming to better characterize the effect of the interference obtaining the best experimental condition for the final flat-top pulse. I carried out a study for different setups and a sensitivity test over the initial parameters for the laser and crystals length. Finally I will show the best setup needed to achieve a flat-top pulse with ripple below the 5% in the flat region. I will present the work done during my stay at CERN in the CLEAR collaboration. During this period, I have worked on the generation and detection of THz radiation, generated by electron bunches at the end of the CLEAR LINAC. THz pulses, generated by Coherent Transition Radiation (CTR), can be used as bunch length diagnostic. Also the radiation generated by different target will be presented along with transverse radial profile of the THz radiation took by a bolometric camera.