Study On Broadband Femtosecond Optical Parametric Amplification Based On Quasi-Phase Matching

Femtosecend optical parametric amplification (OPA) is an important tunable device for producing ultashort pulses for its large gain and broad gain bandwidth. Tranditionally, femtosecend OPA is based on BBO and LBO, however, for quasi-phase matching crystal, due to its different phase matching structure and different phase matching way, it has many advantages over BBO. Thus, we investigate theoretically femtosecend OPA based on PPLN in the present thesis.The main contents of this dissertation are listed below:1. The theory of femtosecend OPA is reviewed. The concepts, characteristics of quasi-phase matching (QPM) are presented. Meanwhile, its advantages over birefringent phase matching (BPM) are introduced. The principles of QPM are derived from Maxwell's equations. The characteristics of several periodically poled crystals are discussed, and the physical and optical characteristics of PPLN are introduced.2. The tuning properties of collinear and noncollinear QPM are discussed respectively. The parametric bandwidth of noncollinear QPM femtosecond OPA based on PPLN crystal with a 532nm pump pulse is theoretically investigated. The results demonstrate that the parametric bandwidth of noncollinear QPM is much wider than that of collinear QPM. Broad parametric bandwidth exists above 180nm at a signal beam continuously tunable from 774 nm to 881nm under the condition that GVM is satisfied with noncollinear QPM. And it also demonstrates the noncollinear angle which is a little deviation from group-velocity-matched noncollinear angle can improve parametric bandwidth further.3. The gain properties of noncollinear QPM femtosecond OPA based on PPLN crystal with a 532nm pump pulse are theoretically investigated. The dependence of gain intensity and gain bandwidth upon the noncollinear , grating period and crystal angle are calculated. The results show that there are many ways to obtain noncollinear QPM, and broad gain bandwidth exists 85nm at a signal wavelength of 800nm with every way. Meanwhile, it show that with lower intensity, a higher gain can be obtained using quasi-phase matching.4. In conclusion, the results show that not only a wide parametric bandwidth could be obtained in noncollinear QPM femtosecond OPA, but a high gain can be obtained.