The Optical Parametric Chirped Pulse Amplification System Key Technology Research

Optical Parmetric Chirped Pulse Amplifier (OPCPA) is a kind of technique that was developed in recent years. OPCPA has advantages such as large gain band, high gain, short medium, low heat deposition and high contrast. OPCPA will be used in the system for shorter and more intense pulses. One important application of OPCPA is to replace Ti:sapphire high-gian system. To get stable and good-beam-quality output from OPCPA high-gain system, optimized design of nonlinear Amplifier system and stable and good-beam-quality pump are needed. Pump usually is the second harmonic of amplified laser. All the courses of generation, amplification and harmonic generation are important for pump. To compensate gain-narrowing effect in the followed amplifiers, spectra of signal out from OPCPA high-gain system should be shaped. So this thesis study on the key techniques for OPCPA such as design of Optical Parametric Amplifiers (OPA), generation and amplification of pump, second harmonic conversion of pump, spectra shaping by OPCPA. A lot of innovations are obtained.The major research work can be listed as follows:1. Design of the nonlinear amplifier system.After the three-wave coupling equations are deduced, three kinds of simplified models are set up. They are homochromatic-and-plane-wave model, plane-wave model and homochromatic wave model. These models can be used separately to solve different questions and can be used together to solve some other questions such as make certain the length for the nonolinear amplifier. All these models are theoretical basis for design of the nonlinear amplifier system. Using these models, two basic questions to design the nonlinear amplifier system are studied. These two questions are how to design a single nonlinear amplifier and how two nonlinear amplifiers coupling. The design method is established and lots of laws are obtained. Then the characteristics of amplified signal are studied. Ways to improve stability, intensity distribution and contrast of amplified signal are found out.2. Generation and amplification of the pump.After lots of innovations on key techniques, the system to gererate joules of pump is designed. The system can get stable and uniform pump pulses. These innovations are:1) The pump and the signal are synchronized with high resolution using phase-locking synchronization systems.2) Two sets of valuating specificatios are put foreward for laser diode (LD) array side-pumped rod amplifiers and LD array end-pumped disk amplifiers. These specifications will impove the design of these two kinds of amplifiers.3) The soft to model the pumping course of LD array side-pumped rod amplifiers is finished. The pumping structure and many other paramtrics are optimized using this soft. The manufactured Φ2mm,Φ3mm Nd:glass rod amplifiers based on the optimized design can get gain 40 and 10. These amplifiers also have unifiorm pumping intensity.4) A new kind of coupling method is put forward for LD array end-pumped amplifiers. In this new way, LD array is arranged on a sphetic face and a duct is followed. The soft to simulate this coupling way is finished. Characteristics of this new method are obtained and an ampilifer pumped by 25kW LD array is optimized using the soft. The soft to study ASE in LD array end-pumped Nd:glass amplifiers are finished and using this soft the parameters of the Nd:glas disk is optimized.5) The model is set up to simulated multi-pass amplifier. This model consists of simplest nonlinear Schn(o|¨)dinger equation and rate equations considering thermo effect and relaxing effect. Using this model changing of energy and waveform in the pump amplifying system is studied. The input waveform for sqrare output waveform can be obtained using this model and it can be to condition this arbitrary waveform generator which will be used to shape the waveform of input pump seed. As a result, square output pump waveform can be expected.6) The model is set up to simulate the amplifying course in systems such as three dimensional gain distribution and tilted incident laser pulse. The model is used to optimize the 12-pass Nd:glass amplifier.3. Stabilizing the second harmonic generation of pumpTheorectical analysis and numerical simulation are done on three ways to stabilize the second harmonic generation of pump. Study results show that these ways can improve the stability of the second harmonic generation of pump. It is also found that these ways can improve beam quality of the second harmonic generation of pump bying reduced spatial and time modulation. Base on the reduced time modulation of the pump, higher contrast from OPCPA system can be achieved.4. Spectral shaping in OPCPAThe idea is put forward that the amplifying course of OPCPA is used as a way of spectral shaping. In this way, there is no loss in it and the PW system can be simplified. Two methods such as supersaturating and phase mismatching are studied. Results show that both kinds of methods can work well and a lot of parameters can be tuned in OPCPA to get different spectral shaping results.