| Millimeter wave/terahertz wave has gradually shown great application potential in various fields.Since the output signal phase of the dual-frequency/dual-wavelength lasers(DFLs/DWLs)are highly correlated and the frequency separation is more stable,a high-purity and stable millimeter-wave/terahertz band beat signal can be obtained.The power balance ratio of the output signal and the synchronization of the output pulse directly affect the frequency-beating efficiency,and the tunable high-frequency separation can realize the high-frequency output signal after the frequency-beating.In this paper,the DFL/DWL based on neodymium-doped crystal are proposed.The power balance tuning,frequency separation tuning and pulse synchronization are studied.Finally,the DFL/DWL output signal with large frequency separation and power balance is obtained,and a synchronized laser pulse with tunable frequency separation can be obtained.The basic structure of the DFL/DWL and the conditions for the oscillation of the mode are analyzed.Based on the transition characteristics of the four-level particle,the four-level state rate equation of the neodymium-doped medium DFL/DWL is derived.The properties of the output parameters of the DFL/DWL are further analyzed,which provides a theoretical reference for optimizing the output beam quality.By changing the pumping power and adjusting the heat sink temperature(Tc),the relationship between the parameters in the power balance state of the microchip DFL with different gain medium is explored.The results show that when the pumping power increases,Tc is negatively correlated with it,and the DFL power product is positively correlated with it.The results show that for neodymium-doped crystal microchip DFL with different parameters,the tunable power-balanced DFL signal can be realized by changing the pumping power and adjusting Tc.Then,by controlling Tc,the power balance mechanism of the Nd:YVO4/Nd:Gd VO4 combined crystal DWL is experimentally studied.When Tc is 32.3 °C,a power balanced dual-wavelength signal with an output power of 435 m W is obtained with a frequency separation of 324.29 GHz and a bimodal center wavelength of 1063.10 nm and 1064.33 nm,respectively.At the same time,in the case of tunable power balance,frequency separation tuning in a small range is also achieved.Based on the Nd:YVO4/Nd:Gd VO4 combined crystal DWL,the synchronized DWL pulse is generated by the passive Q-switched self-trigger mechanism,and a tunable and orderly controllable repetitive frequency laser pulse output using a continuous pumping and pulse pumping gain switching mechanism is realized.The pulse duty cycle is effectively reduced to 0.8%,the pulse width is 200 ns,and the stability is greatly increased.In this output case,the frequency separation tuning can be achieved by changing Tc,which is above 300 GHz.The frequency separation is negatively linearly related to Tc with a slope of-0.95 GHz/°C.A synchronous pulsed DWL with tunable frequency separation is finally obtained.The thermal-induced drift characteristics of the combined crystal emission cross-section(ECS)spectrum are studied.It can be found that the peak value decreased with the increase of Tc,and the central wavelength is linearly red-shifted with the shift rates of 2.31 pm/°C(Nd:Gd VO4)and 2.34 pm/°C(Nd:YVO4),respectively.By finite element analyzing,the temperature field of the combined crystal is modeled.From the simulation results,it can be found that the temperature difference between the center temperature of each crystal and Tc is constant.Based on the thermal-induced drift characteristics and thermal effect simulation results,the frequency-tuning characteristic of the DWL are further explored,which shows that the shift of the ECS spectra with Tc varying lead to the shift of the central wavelengths of the DWL spectra and the different shifting rates of ECS spectral of different crystals lead to the change in the frequency separation. |
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