We report generation of third to ninth order harmonics in argon gas by narrow band Q-switched Nd:YAG laser. Saturation of the third harmonics was observed. Further the seventh and ninth harmonics intensities are about the same. This is the first step for our high harmonics generation experiment. In our laser system, we can generate sub-single cycle and sub-femtosecond pulses by synthesizing the first five harmonics of the same high-power Nd:YAG laser. According to the theory of “three-step model”, the generation of high harmonics depends critically on the
incident driving laser field. Base on the premise of the same fluence (total power) per period, the sawtooth waveform close to the optimum. In addition, the theoretical impact of third harmonic generation by modulating the relative phase of fundamental and second harmonic of the driving laser will also be discussed.

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