Abstract
In recent year, the coherent control technology is widely used in high-order harmonic generation for many researchers. By controlling two- or three- color waveform synthesis, it will enhance the efficiency of high harmonic generation and cut of frequency. Compared with the high-order harmonic in XUV, the coherent light source in UV and VUV are very important to spectroscopy、photochemistry and laser processing…etc. In this thesis, we study harmonic generation by three color waveform synthesis in inert gas system. The three-color coherent light are emitted from Nd:YAG laser with fundamental light of 1064 nm (ω1), second harmonic of 532 nm (ω2) and third harmonic of 355 nm (ω3). In order to control the synthesized waveform, we manipulated relative phase and amplitude among these three-color via the amplitude and phase modulator. In the third-order nonlinear process, the interaction between three-color beam and inert gases can be used to fourth to ninth harmonics of the laser fundamental output. For fourth harmonic generation, there are three kinds of four-wave mixing processes (ωn=ωi+ωj+ωk、ωn=ωi+ωj-ωk). For fifth harmonic generation, there are three possible processes: ω5=ω1+ω2+ω2、ω5=ω1+ω1+ω3、ω5=ω3+ω3-ω1. For sixth and seventh harmonic, there are two kinds of four-wave mixing processes. For eighth and ninth harmonic generation, there is one four-wave mixing process possible. We also assume to simulated Fifth harmonic generation by three-color tightly-focused Gaussian beam. By manipulating the relative phase and amplitude of three-color laser field, we can observe the enhancement of conversion efficiency of fifth harmonic generation in Argon gas. Initial experimental results are in good agreement with theoretical predictions. We successfully demonstrated coherent control of fifth harmonic generation by controlling three-color laser field. Thus, those results shows the feasibility of high-order harmonic generation by using multi-color coherently waveform controlled.