| For the past few years,with the rapid development of terahertz(THz)technology,the demand for THz wave radiation sources has also greatly increased.THz waves have important scientific research value and broad application prospects in many fields such as biological diagnosis and treatment,astronomical imaging,environmental monitoring and safety protection.In the electromagnetic spectrum,since the THz band radiation is between the millimeter wave and the infrared,there are relatively few studies on this band.In the field of microwave photonics,The heterodyne beat frequency of the dual-wavelength laser signal obtained by the ultra-large frequency difference dual-wavelength laser is an effective method for acquiring THz wave signals.In this thesis,a dual-wavelength laser based on Nd:YVO4/Nd:YLF combined crystal is designed.The power equalization mechanism and the time-synchronized dual-wavelength laser pulse are generated by passive Q-switched self-trigger mechanism of dual-wavelength laser are studied.Finally,the dual?wavelength laser signal output with THz frequency difference power equalization and the time-synchronized laser pulse output are obtained respectively.The details are as follows:(1)The background and significance of dual-frequency/dual-wavelength lasers are described in a general way,and the current research status of dual-frequency/dual-wavelength lasers at home and abroad is briefly introduced.(2)Firstly,the structure of the dual-frequency/dual-wavelength laser is introduced.Then,the operating conditions(the rate equation of four-level system)and output characteristics of the combined crystal dual-wavelength laser are analyzed.Finally,the power equalization principle and Q-switching pulse mechanism of the dual-frequency/dual-wavelength lasers are analyzed.(3)The dual-wavelength(1047 nm and 1064 nm)laser based on the Nd:YVO4/Nd:YLF combined crystal has been designed.The rate equation of the dual-wavelength laser with the combined crystal was analyzed theoretically,and the temperature characteristics of the dual-wavelength laser with fixed pumping power condition were investigated experimentally.During the experiments,setting the pumping power at 600 mW,and rising the heat sink temperature of the combined crystal from 7.0? to 22.0? by 1.0? step,the dual-wavelength laser signals with frequency separation from 4.58 THz to 4.63 THz and tunable power balance level were achieved.In the range of the heat sink temperature rise,the maximum frequency separation happened at 8.0?,which was measured as 4.63 THz;and the minimum frequency separation happened at 21.0?,which was measured as 4.58 THz.The experimental results show that the variation of frequency separation with heat sink temperature was stable around 4.60 THz.When the heat sink temperature was kept at 17.8?,the power balanced dual-wavelength laser signal was realized with frequency separation at 4.58 THz and output power at 18.48 mW.(4)Based on the Nd:YVO4/Nd:YLF combined crystal dual-wavelength laser,the time-synchronized dual-wavelength laser pulse is generated by the passive Q-switching mechanism.Firstly,through the numerical simulation of the passive Q-switched model of Nd:YVO4/Nd:YLF dual-wavelength laser,the combined crystal laser pulse diagram is obtained.It can be found that at the same pumping rate,the pulse width of the 1064 nm wavelength is larger than the pulse width of the wavelength of 1047 nm.Then through specific experiments,in the case of continuous pumping,the temperature of heat sink is controlled at 35?,and the pump power is gradually increased from 5.6 W to 6.6 W.It is found that the time synchronization characteristics of the dual-wavelength pulse have not been affected.As the pumping power increases,the peak power of the dual-wavelength laser pulse increases.And when the pumping power are 5.66 W,5.92 W,6.18 W and 6.40 W,the pulse repetition frequency are 70 kHz,100 kHz,64 kHz and 61 kHz,respectively. |
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