The Study Of Miniaturized Dualwavelength Nd:YVO₄ Laser For THz Radiation Source

THz wave with its unique transient,broadband,coherence,low energy,water absorption,fingerprint spectrum characteristics of electromagnetic waves,different from the traditional therefore,it has important applications in astrophysics,plasma physics and engineering,biomedical engineering,environmental science and engineering,materials science and engineering and technology,spectroscopy and imaging of information science and technology etc..At the beginning of the 1980s,due to the lack of effective means and methods for the generation of terahertz,the electromagnetic radiation properties of the band were very limited.In recent years,with the rapid development of THz technology,THz technology has attracted wide attention in basic research and practical application field.In the THz technology,the research of radiation source is the key factor to restrict the development of THz technology.At present,there are two methods to generate THz source:electronic method and optical method.Among them,the optical methods mainly include photoconductivity,optical rectification,parametric oscillation,optical stimulated scattering,optical difference frequency?DFG?and other methods.Optical method,dual wavelength laser frequency process by nonlinear differential?DFG?single band THz wave,with high peak power,no threshold,the program flexible and other advantages,has the advantages of simple structure,easy operation,and can realize miniaturization.Therefore,the use of dual wavelength laser is the premise of the realization of the difference frequency THz.Usually,dual wavelength laser output is mainly a nonlinear frequency conversion?such as frequency doubling,difference frequency,and frequency of Raman frequency shift,etc.?and the level of active ions?including different split Stark transitions and the same transition split?two methods.Through the analysis of Nd:YVO₄ crystal,it is found that the crystal Nd³⁺has a rich structure of energy levels and sub levels,which provides the possibility to realize the operation of the dual wavelength laser.In this paper,Using Nd:YVO₄ crystal as the foundation,by a single wavelength operation of the crystal angle tuning,the stimulated emission cross sections of the dual wavelength laser were balanced,and the dual wavelength laser at steady operation which laid the foundation for the THz source was successfully obtained.Specific work as follows:1.On the basis of the rate equation of single wavelength laser,the conditions of simultaneous operation of double wavelength laser are derived.The thermal effect of the crystal is analyzed,and the simulation results are given to guide the design of the experimental system.2.In this paper,the crystal temperature control system and the crystal heat sink are designed,and the crystal temperature can be accurately and quickly adjusted with the design of the heat sink and the temperature control system.The optimal design and stability analysis of the pump coupling system and the laser resonator are carried out by using the ABCD matrix analysis method.3.Through the design of the experimental system,from the view of the single wavelength laser operation,the stable operation of the dual wavelength laser is realized by adjusting the angle of the crystal,which provides an effective THz source.