Free-electron Laser Amplifier Numerical Simulation Of Chirped Pulse

The free-electron laser (FEL) is a classical device that uses beam of electrons passing through a transverse periodic magnetic field to amplify electromagnetic radiation. Chirped pulse amplification (CPA) technology is one of the major ways to get high power and ultra short FEL pulse. A study of linear chirped pulse amplification at single pass FEL amplifier has been performed by means of the modified 1D time-dependent FEL code. The main progresses are:1. The basic theories of linear chirped pulse generating and compressing are introduced.2. In order to analyze the relationship between the power gain of FEL amplifier and the frequency detuning, the usual cubic characteristic equation of 1D FEL theory is solved when the frequency detuning is far from zero.3. The power gain will be reducing when FEL amplifies the chirped pulse, and the reasons of which are analyzed. The parts with large frequency detuning in the chirped pulse can't be amplified efficiently, which is the main reason of the gain decline as the chirped pulse is amplified by normal FEL amplifier. When the chirped pulse is amplified by the energy-chirped beam through the undulator, the main causation of the gain decline is the frequency detuning which is produced by slippage effect.4. The processes of chirped pulses with different chirped parameters being amplified by normal FEL amplifier and the FEL amplifier with energy-chirped beam are studied through numerical simulations. The peak power and width of the final compressed pulse with different chirped parameters have been computed. The results show that, the normal FEL amplifier can amplify the chirped pulse, the peak power of the final compressed pulse can reach 10s GW and the width of the pulse can be 10s fs. The means of using the energy-chirped beam to amplify chirped pulse can make the bandwidth of the FEL amplifier wider and make the output pulse be compressed more efficiently. Peak power of the final compressed pulse can even reach hundreds GW and the width of the pulse can be several fs if using the energy-chirped beam to amplify chirped pulse.