| Electromagnetic waves with frequencies in the 0.1 THz?10 THz frequency band are called terahertz waves,and it has shown great application potential in many aspects.There are many ways to generate terahertz waves.Because of its simple device,stable output,and relatively small propagation loss in the fiber,the photogenerated terahertz wave method has become a commonly used method to generate terahertz.It is a simple and easy way to beat frequency by using a frequency separation tunable dual-wavelength signal with a balanced output power of a solid-state laser.Due to its advantages in adjusting the pump power and heat sink temperature corresponding to different gain media,the Y-cavity dual-wavelength laser is avaiable to realize the frequency separation tuning and power balance of the dual-wavelength laser.The dual-wavelength laser generated by the Y-cavity is an ideal signal source for generating terahertz waves.The frequency separation of the dual-wavelength laser signal is the frequency of the terahertz wave.Firstly,this article analyzes the working principle of the Y-cavity neodymium-doped dual-wavelength laser from the perspective of gain medium,pumping source and laser resonator.Combining the energy level structure of neodymium element and the characteristics of the Y-shaped laser structure,it is derived based on the Y-cavity four-level rate equation of this laser.The frequency separation tuning and power equalization mechanism of continuous laser are explored,and the coupling rate equation of passive Q-switching based on Y-cavity is derived by combining Y-cavity structure and chromium-doped energy level structure.Subsequently,a Y-cavity neodymium-doped dual-wavelength laser based on Nd:YVO4 and Nd:Gd VO4 crystals was designed and built.By independently adjusting the temperature of the Nd:YVO4and Nd:Gd VO4crystal heat sinks,the center wavelength of the laser is shifted,so as to achieve a wide range of frequency separation tuning of the dual-wavelength laser signal.When the pumping power remains constant,the experiment found that as the temperature of the crystal heat sink increases,the center wavelength of the laser is red-shifted,and the output power reduces.Then adjust the corresponding pumping power to achieve a dual-wavelength laser signal power balance,and find that when the pumping power is adjusted,the center wavelength of the two lasers drift again.In the experiment,by independently adjusting the heat sink temperature of the two crystals of the laser,and controlling the heat sink temperature difference?T from-50°C to 30°C,the measured dual-wavelength frequency separation increased from 270.13 GHz to 379.75 GHz;adjusting the two crystals to correspond the pumping power of the power further realizes dual-wavelength power balance,and finally obtains a dual-wavelength laser signal with a frequency separation tuning range of 266.05 GHz?379.75 GHz and an output power of 230 m W under the power balance state.Finally,based on the passive Q-switched coupling rate equation based on the Y-shaped cavity,the mechanism of double-pulse time synchronization is explored through numerical simulation.The pulse peak power of the double-pulse laser is larger than and smaller than the bleaching threshold of the saturable absorber respectively,and the pulse triggering of the high-power laser to the low-power laser can be realized.On the basis of time-synchronized pulses,the influence of pumping rate and stimulated emission cross section on the power balance between double pulses is continuously explored.The two-pulse power balance increases with the decrease of the trigger optical pumping rate.When the triggering optical pump power increases from 4.8 W to 19.25 W,the dual-pulse power balance decreases from 0.564 to 0.485.When the pumping rate of the two crystals remains constant,the stimulated emission cross section can be changed by adjusting the temperature of the triggered crystal.The simulation results show that the power balance of the two pulses increases with the increased stimulated emission cross section of the triggered light.When the stimulated emission cross section of the triggered light increases from 4.6×10-19 cm-2 increases to 5.2×10-19 cm-2,power balance increased from 0.360 to 0.396,and power balance was greatly improved.The simulation results have certain reference value for the experiment. |
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