Influence And Control Of The Optical Parametric Amplifier Pump Laser Phase

The device of optical parametric amplifier mainly including optical parametric amplifiers (OPAs) and optical parametric chirped pulse amplifiers (OPCPAs) is one of the effective laser pulse amplification device, based onχ(2) nonlinearity. The spectracular developments in ultrafast laser technology and the appearance of new nonlinear optical crystals, have made optical parametric amplifier (OPA) as a routine technique to generate tunable femtosecond pulses from a fixed laser source. OPCPA technique has been well recognized to be an effective approach to generate high-power ultra-short pulses. Employing OPCPA, PW magnitude power pulse has been obtained.The beam and pulse quality of laser are of the key issues for laser amplification system. While, the pump pulse is always with certain degrees of phase noise due to unsuppressed longitudinal lasing modes and amplified stimulated emissison (ASE). In the case of high-energy pump pulse, particularly, the laser pulse is intentionally modulated in phase to suppress the effect of stimulated Brillouin scattering (SBS). As a result, the thesis mainly studies the impact and control of the pump phase-noise on signal in the device of optical parametric amplifier. By analyzing the phase transfer in the process of OPA, we employ the hybrid seeded optical parametric amplifier (HSOPA) to control the phase transfer caused by group-velocity mismatch (GVM) or spatial walk-off, and eliminate the detrimental influence of pump phase-noise on the signal. Further studying the spatial phase characteristic of OPAs or OPCPAs pumped by two phase-distorted laser beams (TBOPA), we employ a design of two crystals to control phase transfer and make TBOPA more similar to the conventional quantum laser amplifier. For the high-intensity OPCPA system, the temporal phase-noise of pump pulse causes the contrast degradation of the recompressed signal pulse. We reveal two physical mechanisms reducing the contrast in such a parametric process, and by HSOPA, to a degree, we reduce the impact of pump phase-noise on the contrast. The results presented in this paper are of particular importance for extremely intense OPCPA system requiring high contrast. This paper includes the following contents: 1. Summarizing the development of ultrafast optics and several key laser pulse amplification techniques and introducing the high intensity solide laser and its accompanying pulse-contrast problem.In the development process of ultrafast technology, Kerr lens mode-locking, the control of group-velocity dispersion (GVD) based on angle dispersion, frequency conversion technology, CPA, OPCPA and so on, all of them plays a prominent role. Now, laser systems have realized the output of 100as and pw magnitude perk-power. One of the major challenges limiting the development of high-intensity laser systems is the pulse-contrast. For the high contrast requirement, even the weak influence factors impacting pulse contrast must also be taken into account and analyzed, which has stimulated people to study the new mechanism impacting the contrast.2. The study on the phase transfer and control of pump-to-signal in OPAs.Based on the nonlinear couple-wave equations, Standard split-step method and Runge-Kutta algorithm are adopted to simulate the parametric process and study the phase transfer and its physical influence factor. HSOPA is employed to control pump-to-signal phse transfer, which make signal independent on the pump phase-noise and maintain the signal pulse and beam quality. HSOPA configuration may offer additional merits, which is also studied.3. The study on the phase characteristic of OPAs and OPCPAs pumped by two phase-distorted laser beams.Based on the advantages of two beam pumped OPAs (OPCPAs), and improvement the performance of OPAs, we study the phase characteristic of OPA or OPCPA pumped by two phase-distorted laser beams. The spatial walk-off induced a complicated interaction where both of the pump phase will be partly transferred to signal in a single crystal. An OPA configuration with walkoff-compensated crystal pair is demonstrated for reducing phase transfer, which make signal independent on any pump phase-noise, hence maintain the signal beam-quality. Such a TBOPA is similar to the conventional quantum laser amplifier by means of eliminating its sensitivity to the phase and number of the pump beams.4. Pulse-contrast degradation due to pump phase-modulation and its optimization in optical parametric chirped-pulse amplification system.Since the prospects in obtaining high-power few-cycle laser pulses, we theoretically study the pulse-contrast degradation of OPCPA system pumped with a temporally phase modulated laser. We reveal two physical mechanisms reducing the contrast in such a parametric process:the effect of phase transfer caused by GVM and the effect of pump phase modulation (frequency modulation)-to-intensity modulation (amplitude modulation) conversion (FM-to-AM conversion) caused by GVD. Emplying the HSOPA, we reduce the impact of pump phase-noise on the contrast.