Research Of Pulsed Fiber Laser Based On Acoustic-optic Q-switching

Q-switched pulsed fiber laser can get Q-switched pulse with the characteristics of the pulse width in the order of ns and the peak power in the order of KW by releaseing intracavity energy in a very short period of time.Combined with the main oscillator power amplifier scheme,the average power of the Q-switched pulsed fiber laser can be increased to several hundred watts and makes it widely used in laser processing,laser radar,optical time domain reflectometer,nonlinear frequency conversion and so on.As a kind of realization way of Q-switched pulsed fiber laser,acousto-optic Q-switching has the advantages of stable and controllable output Q-switched pulse,and has been widely concerned.In this paper,two kinds of Q-switched pulsed fiber laser experiment system are set up which are with asymmetric cavity structure and symmetric cavity structure,the characteristics of the output Q-switched pulse such as repetition frequency,smoothness,output power,pulse width and so on are studied.And the influence of the pump power,the acousto-optic Q-switch repetition frequency on the output Q-switched pulse repetition frequency is analyzed.Multipeak phenomenon in the output Q-switched pulse is also optimized,and finally smooth pulse is obtained.The specific work is as follows:Firstly,the principle and the commonly realization method of Q-switching technology are introduced,the influence of the pump power,the duration when cavity in the low Q value and the cavity length on the output characteristics of Q-switched pulsed fiber laser is analyzed theoretically.The working principle of acousto-optic Q-switched pulsed fiber laser is introduced in detail.Secondly,two kinds of Q-switched pulsed fiber laser experiment system are set up which are with asymmetric cavity structure and symmetric cavity structure,the characteristics of the output Q-swithed pulse are studied when the opening time of the acousto-optic Q-switch is 5 ?s,the repetition frequency is in the range of10KHz-80 KHz.In the asymmetric cavity,the maximum output power of 1.61 W and the narrowest pulse width of 61 ns is obtained by using the backward pump mode.In the symmetric cavity,three kinds of pump modes are adopted,namely,semiconductor laser pumping only,semiconductor module pumping only,the semiconductor laser and the semiconductor module pumping symmetrically.And the maximum outputpower of 0.59 W and the narrowest pulse width of 58 ns is obtained by using the symmetrical pump mode.Then,the repetition frequency and smoothness of the output Q-switched pulse in two kinds of cavity structures which are asymmetric cavity and symmetric cavity are focused on.Whether it is in the asymmetric cavity or in the symmetric cavity,only in a certain range of the pump power and the repetition frequency of the acousto-optic Q-switch,the repetition frequency of the output Q-switched pulse can be equal to the repetition frequency of the acousto-optic Q-switch.And when the pump power is fixed,with the increase of the acousto-optic Q-switch repetition frequency,the output Q-switched pulse appears at the first,second,third sub-harmonics of the acousto-optic Q-switch repetition frequency in order.When the repetition frequency of the acousto-optic Q-switch is fixed,with the decrease of the pump power,the output Q-switched pulse appears at the first,second,third sub-harmonics of the acousto-optic Q-switch repetition frequency in order.In the asymmetric cavity,by increasing the pump power,reducing the repetition frequency of the acousto-optic Q-switch,and reducing the opening time of the acousto-optic Q-switch,the number of multiple peaks in the output Q-switched pulse is reduced and the pulse waveform is optimized.And smooth Q-switched pulse with the pulse width of 38 ns is obtained when the pump power is 8W,the acousto-optic Q-switch repetition frequency is 10 KHz and the opening time is 230 ns by using this optimization method.In the symmetric cavity,smooth Q-switched pulse can be easily obtained at the frequency range of10KHz-80 KHz by the symmetrical pump mode.In this paper,the output characteristics of the asymmetric cavity structured and the symmetric cavity structured acousto-optic Q-switched pulsed fiber laser is studied,and the characteristics of the repetition frequency and smoothness of the output Q-switched pulse is focused on,finally smooth Q-switched pulse is obtained at the frequency range of 10KHz-80 KHz.