Research On Bandwidth And Signal - To - Noise Ratio Based On Quasi - Phase Matching Parameter

Optical parametric chirped pulse amplification (OPCPA) has a large bandwidth, high single-pass gain and low pre-pulse signal-noise ratio (SNR) better than10-8,which makes it an essential method for high-power ultrashort pulse lasers. Compared to conventional birefringent nonlinear crystals like BBO and LBO in OPA, quasi-phase-matching crystals have many advantages over traditional ones, like big nonlinear coefficient, large working wavelength range, more designable and avoid walking-off effect. In this paper, based on the quasi-phase-matched materials, bandwidth and SNR of ultrashort pulse parametric amplification are going to be discussed and theoretical studies. The main work of this paper includes the followings:1. QPM principles in OPA. Three-wave parametric coupled equations are derived and numerically simulated; QPM principles and polarization conditions are discussed to instruct the experiment. Physical properties of common periodically poled crystals, like LiNO3, KTP, LiTaO3, are introduced as a choose reference.2. Based on optical parametric amplification of QPM crystals, different poled structures that have influences on the bandwidth are discussed. Grating vector kg is discussed to control the spectra and bandwidth in OPA. OPA with broadband pump, especially a chirped pump, is considered to improve the bandwidth. Chirped poled crystals are simulated to explain its effects on parametric bandwidth and the principle to achieve broadband amplification.3. For "SG" upgrade PW system, SNR of OPCPA front-end are experimentally measured, and spectral shaping method is used to improve the SNR. And based on the QPM parametric amplification technology, a high SNR seed source scheme is designed. SNR of better than1010is expected. And the scheme is designed to replace the existing petawatt femtosecond mode-locked oscillator.