Study On Amplification Of Broadband Chirped Pulse

Chirped-pulse-amplification (CPA) is the basic technique to obtain an ultra-short and ultrahigh- intensity laser. However, in chirp pulse amplification system, the chirped pulse is influenced by the effects of gain narrowing, self-phase modulation and gain saturation, leading to the distortion of the temporal profile and spectrum distribution of the output pulse, resulting in the influence on the amplification, compression and beam quality of the pulse. It is necessary to study the propagation and amplification properties of the chirped pulse in the chirped pulse amplification system, so as to provide theoretical reference for optimal design of the ultra-short pulse amplification system.The model of Frantz-Nodvik which is described by transport equation and population inversion equation is valid only when the amplifier gain bandwidth is significantly larger than the input spectral bandwidth. That isn't significantly different when narrowband pulse is amplified in homogeneously broadening medium and inhomogenously broadening medium, but the efficiency of energy extraction is lower. Therefore, when input pulse is stretched by introducing linearity chirp, causing the input pulse width and the gain medium bandwidth compared, we can use broadband pulse amplification model to analysis, and the efficiency of energy extract is enhanced. But the influence of gain-narrowing effect to pulse is more obvious. Moreover, the gain coefficient is related with amplifier gain bandwidth and broadening type. The present research is considered only in homogenously broadening medium, and the correlation research in inhomogenously broadening medium is relative lag.The extended model in inhomogeneously broadening medium is the basis to build the model of the amplification in homogeneously broadening medium and the broadening type is considered. Using the relation between time and frequency of the linearly chirped pulse, the input chirped pulse is considered to consist of many narrowband pulses. In each narrowband pulse, thus using the nonlinear Schr(o|¨)dinger equation and the split-step Fourier method, and the Frantz-Nodvik model, the amplification is calculated. Numerical simulations indicate the different influences of gain narrowing, self-phase modulation and gain saturation between homogeneously and inhomogeneously broadening medium. In order to get perfect amplified pulse, the corresponding method is presented to avoid the effects through the numerical results.The compress of the pulse is also important in the chirped pulse amplification system. The basic structure and theory of compressor is been studied, and the instances of the dispersive is analyzed at different grating distance and input degree. In addition, the effects of the gain narrowing, self-phase modulation and gain saturation to compressed pulse are discussed.