Research On All-solid-state Q-switched Pulsed Laser Based On Graphene Quantum Dots And Molybdenum Disulfide

All solid state,narrow pulse width,high repetition rate Q-switched laser has attracted much attention because of its wide application prospect in laser communication,laser medical treatment,information transmission,military remote sensing and other fields.The double loss modulation technique can further compress the pulse width and improve the symmetry of the pulse waveform.Compared with active and passively Q-switched laser,double passively Q-switched laser do not need to add active Q-switched elements such as electro-optic modulator or acousto-optic modulator,which can not only reduce the cost,but also help to shorten the cavity length of the laser,which is very beneficial for the development of solid-state lasers to the miniaturization market in the future.In this paper,graphene quantum dots(GQDs)and molybdenum disulfide(MoS₂)with nonlinear absorption characteristics are prepared as double saturable absorbers,and used as Q-switched devices of Nd:YVO₄ laser.The output characteristics of double passively Q-switched laser at 1064 nm and 532 nm are researched.The main contents of this paper are as follows:(1)Graphene quantum dot solution and molybdenum disulfide solution were obtained by hydrothermal method and lithium ion intercalation method,respectively,and the saturable absorbers were prepared.In order to verify whether GQDs-SA and MoS₂-SA can be used as Q-switched devices of Nd:YVO₄ laser,the surface structure and optical properties of GQDs and MoS₂ were studied firstly.Secondly,the films were analyzed by conventional characterization methods.Finally,the nonlinear transmission characteristics of GQDs-SA and MoS₂-SA were measured.The modulation depth was 7.1%and 8.4%,and the saturation intensity was 25.4MW/cm² and 2.5 MW/cm²,respectively.(2)An all solid state laser with a cavity length of 25 mm were designed and built.GQDs-SA and MoS₂-SA were placed in the cavity as passively Q-switched devices respectively.The threshold value of the pulse laser is 1.02 W.When the absorbed pump power is increased to7.74 W,the stable pulse laser output with pulse width of 226 ns and 262 ns,signal-to-noise ratio of 48 d B and 46 d B,and output power of 764 m W and 687 m W are obtained for the laser device based on GQDs-SA and MoS₂-SA respectively.(3)By inserting GQDs-SA and MoS₂-SA into the Nd:YVO₄ laser at the same time,double passively Q-switched operation is realized.The experimental results shown that the maximum output power of the laser is 595 m W,the maximum repetition rate is 1085 k Hz,and the signal-to-noise ratio is up to 44 d B,which shows that the laser has good stability.In addition,the shortest pulse width of the laser is 180 ns,compared with the single passively Q-switched laser,the compression of pulse width and the optimization of pulse waveform symmetry are realized.A 532 nm double passively Q-switched pulsed green laser based on GQDs-SA and MoS₂-SA is realized by inserting PPLN frequency doubling crystal into the resonator.