| With the development of pulse laser technology,the demands for output pulses with shorter pulse width and higher peak power is also increasing.By using an active Q-switcher and a passive Q-switching saturable absorber simultaneously,active-passive doubly Q-switching techniques have gained more and more concentrations and studies in the fields of military,medicine,mechanical processing and remote sensing,due to the output pulses with better characteristics and controllable repetition.Meanwhile,the appearance of the new types of two-dimensional(2-D)saturable absorption materials,such as graphene,black phosphorous and transition metal dichalcogenides(TMDs),boosts the progresses of pulse laser techniques.In this thesis,based on the active-passive doubly Q-switched laser with an acousto-optic modulator(AOM)and a saturable absorber,the pulse characteristics and the depending characteristics of repetition rate of the output pulses,which from lasers of 1.34μm and 1.064μm by using various laser gain medium and saturable absorber have been studied.The improvement of the characteristics of output pulses have been discussed by comparison between singly passive Q-switched laser and doubly Q-switched laser.The main aspects of this thesis are as follows:I.A diode-end-pumped doubly Q-switched Nd:Gd0.63Y0.37VO4 laser emitting 1.34μm wavelength with an acousto-optic modulator and V3+:YAG saturable absorber was fabricated,and the pulse characteristics was measured by varying the pump power and modulation frequency of the AOM.The periodical ramping behavior versus modulation frequency of AOM was analysed.The coupled rate equations of the diode-end-pumped doubly Q-switched Nd:Gd0.63Y0.37VO4 laser emitting 1.34μm wavelength with an acousto-optic modulator and V3+:YAG saturable absorber was established with plane wave approximation,and the numerical simulated results are basically consistent with the experimental results.Ⅱ.A diode-end-pumped doubly Q-switched Nd:GGG laser emitting 1064nm wavelength with an acousto-optic modulator and monolayer graphene saturable absorber was fabricated,and the pulse characteristics,including repetition rate,pulse width,peak power,et al.,was measured by varying the pump power and modulation frequency of the AOM.The periodical ramping behavior versus modulation frequency of AOM was analysed.The output pulses with shorter pulse width and higher peak power can be achieved from doubly Q-switched laser,comparing with the singly passive Q-switched laser with monolayer graphene saturable absorber.Ⅲ.The few-layer MoS2 was fabricated by liquid-phase exfoliation method,and was characterized.A diode-end-pumped doubly Q-switched Nd:GGG laser emitting 1064nm wavelength with an acousto-optic modulator and few-layer MoS2 saturable absorber was fabricated.Characteristics of the output pulses versus pump power and modulation frequency of AOM was measured,the shortest pulse width of 150.1ns and maximum peak power of 33.7W was obtained.Comparing with singly passive Q-switch laser,doubly Q-switched laser can generate pulses with higher peak power and shorter pulse width,a maximum pulse width compression ratio 5.3 and a maximum peak power enhancement factor 21.3 can be obtained.The periodical ramping behavior versus modulation frequency of AOM and the phenomenon that pulse width decrease firstly and then increase,was discussed.The main innovations of this thesis are as follow:Ⅰ.A diode-end-pumped doubly Q-switched Nd:Gd0.63Y0.37VO4 laser emitting 1.34μm wavelength with an acousto-optic modulator and a V3+:YAG saturable absorber was fabricated for the first time.The periodical ramping behavior of pulse characteristics versus modulation frequency of AOM was analysed,and the numerical simulations verified the experimental results.Ⅱ.A diode-end-pumped doubly Q-switched Nd:GGG laser emitting 1064nm wavelength with an acousto-optic modulator and a monolayer graphene saturable absorber was fabricated for the first time.The pulse characteristics was measured by varying the pump power and modulation frequency of the AOM.The depending characteristics of repetition rate of the output pulses generated by doubly Q-switched laser was analysed.Ⅳ.A diode-end-pumped doubly Q-switched Nd:GGG laser emitting 1064nm wavelength with an acousto-optic modulator and a monolayer graphene saturable absorber was fabricated for the first time.The pulse characteristics versus various pump power and modulation frequency of the AOM was studied.The periodical ramping behavior versus modulation frequency of AOM and the phenomenon that pulse width decrease firstly and then increase,was discussed. |
