Investigation Of Continuous-wave Dual-wavelength Laser Performance With Neodymium-doped Vanadate Crystal

Dual-wavelength lasers(DWLs)are light sources that radiate two-frequency coherent signals and are currently widely used in the fields of next-generation communications,precision metrology,differential analysis,pumping detection,and spectroscopy research.The coherent terahertz(THz)wave signals generated by optical heterodyne of the DWLs with 0.1-10 THz frequency separations are becoming important tools in military and scientific research fields due to their unique optical characteristics.Frequency separation tuning and output power balanced are two important functions of the DWLs.Based on the a-cut neodymium-doped vanadate crystals,this paper explores the methods of obtaining stable frequency separation tuning and output power balanced dual-wavelength difference frequency sources.The main content of this paper consists of the three parts as follows:Firstly,the domestic and foreign research status and development trend of the DWL based on different types of laser medium to achieve frequency separation tuning and output power balanced technologies are briefly introduced.The system composition and operating principles of the DWL based on a-cut neodymium-doped vanadate crystals are analyzed in detail.Though to the four-level rate equations,the operating characteristics of the neodymium-doped gain medium and the output characteristics of the DWL are theoretically analyzed.Secondly,the Y-type cavity tunable DWL based on the a-cut Nd:GdVO₄ and Nd:YVO₄ crystals is demonstrated.The DWL consists of two end-pumped structures being joined by a polarizer and sharing one same output coupler.The two end-pumped structures generate the DWL beams at 1063nm and 1064 nm with orthogonal polarizations.Utilizing neodymium-doped vanadate crystals thermally induced emission cross section spectra shift characteristics,by independently adjusting the incident pump powers,the DWL signal with frequency separation tuning is achieved.The experimental results show that the center wavelength differences of Nd:GdVO₄ and Nd:YVO₄crystals are adjusted from 0.98 nm to 1.41 nm when the incident pump powers are adjusted from 2W to 7 W,the frequency separation of the DWL is tuned from 0.26 to 0.37 THz with the output power ratio from 0.08 to 13.77;the output powers of 1063 nm and 1064 nm laser linearly increase with the incident pump powers increasing,reach 598.73 mW and 601.04 mW with the corresponding slope efficiencies at 18.9%and 13.1%.In addition,the long-term stability of output powers is measured less than 2.0%in 2 h.Thirdly,a power balanced DWL based on the Nd:GdVO₄ crystal is presented.The orthogonally polarized gain spectral evolution of the Nd:GdVO₄ crystal versus the temperature is studied,and the power balancing conditions of the DWLs are theoretically analyzed firstly.In the experiment,by using two output couplers and a temperature controller,the power balanced Nd:GdVO₄ DWL signals of wavelengths at 1063 nm(?)and 1065 nm(?)are obtained with the heat sink temperature(T_c)in the range from 20°C to 40°C.The experimental results show,by employing the pump power at 9.3 W and T_c at 25°C,the DWL signal with the balanced power at0.78 W for each wavelength and the frequency separation at 0.62 THz is realized.The beam quality M²of the?-and?-polarized DWL signals are measured between 2.1 to 2.4.The maximum total output power is 1.75 W with the pump power of 11.1 W and T_cof 25?,the total output power optical-to-optical slope efficiency is up to 15.2%.