| In this dissertation, we have obtained lasers at 1064 nm, using LD pumped Nd: GdVO4 crystal. By using saturable output coupler(SOC) as the mode-locking device, passively Q-switched and mode-locked(QML) lasers have been obtained. To improve the stability of QML pulses, we have applied the actively modulation device to the passively mode-locked cavity. By combining electro-optic(EO) Q-switch with Kerr lens mode-locking(KLM) mechanism and SOC mode-locking respectively, two kinds of actively Q-switched passively mode-locked lasers have been demonstrated, with same structure of the cavity. The main contents of this dissertation are generalized as follows:ⅠA five-mirrors folded cavity(W-type cavity) has been designed and the variation of spot radius in the cavity has been numerical simulated, by calculating the ABCD matrix equation. Using a SOC as the mode-locking device and the output coupler, a passively QML Nd: Gd VO4 laser has been demonstrated and the characteristics of output pulses have been analysed. We have selected three SOCs with different parameters to demonstrate passively QML lasers respectively. By comparing their output characteristics, we have analysed the influence of several key parameters of the SOC to the mode-locked pulses.Ⅱ Using a four-mirrors folded cavity(Z-type cavity), we have obtained two kinds of actively Q-switched passively mode-locked lasers. Without any extra passively mode-locked devices in the cavity, we have obtained an actively Q-switched self-mode-locked Nd: GdVO4 laser, and the influence of the Q-switch to the self-mode-locked pulses has been analysed. Changing the output coupler to a SOC, an actively Q-switched SOC mode-locked Nd: GdVO4 laser has been demonstrated. Comparing the characteristics of the QML pulses when EO on and off, we have analysed the effect of pulse compression and peak power enhancement brought by the actively modulation.Ⅲ We have measured pulse duration, repetition frequency, and average output power of the actively Q-switched self-mode-locked laser as well as the actively Q-switched SOC mode-locked laser. Comparing the output characteristics, the further modulation caused by the SOC has been discussed. We have found that compared with the actively Q-switched self-mode-locked pulses, the envelope pulse duration of the actively Q-switched SOC mode-locked pulses has been compressed by 75% and the expanded mode-locking pulse duration has been compressed nearly a half. In this case, the actively Q-switched SOC mode-locked pulses are regarded as established on the operation of self-mode-locking, and the pulses are under modulation of both self-mode-locking and SOC mode-locking.Ⅳ The nonlinear losses induced by self-mode-locking and SOC mode-locking have been analysed, and the mathematical expression of the loss have been presented respectively. Using the the fluctuation mechanism, considering the space distribution, the temporal shape of the photon intensity, the upper state population density of the active medium and the ground/excited-state population density of the saturable absorber, using the hyperbolic secant square function as a model of the mode-locked pulse, a rate equation model for actively Q-switched passively mode-locked lasers has been presented. In the condition of actively Q-switched SOC mode-locked operation, we have explained the correlation of self-mode-locking and SOC mode-locking in the form of mathematical, considering the superposition of self-mode-locking and SOC mode-locking mechanisms. |
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