| THz?Terahertz?wave,also known as far-infrared wave or sub-millimeter wave,located at the boundary between the microwave and optical bands.It has many pretty properties,and is now regarded as a popular subject which can be applied in imaging,nondestructive testing,communications,national defense and security,environment monitoring.As one of the optical methods for the generation of terahertz waves,terahertz parametric oscillators based on the stimulated polariton scattering in nonlinear crystal have many advantages,such as room temperature operation,compactness,high peak power,good temporal and spatial coherence,continuous tunability,and the scholars around the world have done a lot of works in recent years.However,the main problem of existed terahertz oscillators is the low output power and conversion efficiency.In this paper,a surface-emitted ring cavity terahertz parametric oscillator is designed for the high-energy and fast-tuned terahertz output.At the same time,the output characteristics of this new structure are analyzed and it is compared with the results of the traditional cavity terahertz parametric oscillator.Due to the accurate tuning and the high energy output characteristics of the ring cavity terahertz parametric oscillator,the accurate output characteristics of the KTiOPO4?KTP?crystal in the terahertz parametric oscillator are obtained,and the tunable range of terahertz parametric oscillator based on the KTP crystal is widened.The reason for the discontinuous tuning range and dual-wavelengths output characteristics in KTP crystal is explained theoretically.The main work of this paper is as follows:1.A terahertz-wave parametric oscillator based on the surface-emitted ring-cavity configuration was designed to realize the high-energy?12.9?J/pulse?and fast tuning?600?s/THz?THz wave output.The output energy is 1000 times larger than the results of the similar ring-cavity configuration reported in Japan,we get the high beam quality and high pulse energy THz wave output.At the same time,the parameters of the new structure are analyzed.By comparing the output energy of the THz oscillators with the same crystal structure of the same pump source,the ring cavity structure has higher energy THz energy output and lower pump energy loss,which means that the ring The cavity structure has a higher photon conversion efficiency.2.In order to broaden the tunable range of the terahertz parametric oscillator,we design a ring-cavity terahertz wave parametric oscillator with a KTP crystal,and a wide tuning range of 0.96-7.01THz was obtained.The tuning range was observed intermittently from 0.96-1.87 THz,from 3.04-3.33 THz,from 4.17-4.48 THz,from4.78-4.97 THz,from 5.125-5.168 THz,from 5.44-5.97 THz and from 6.74-7.01 THz.The dual-Stokes wavelengths resonance phenomena were observed in some certain tuning angle ranges.Through the theoretical analysis of the dispersion curve in KTP crystal,the intermittent THz wave tuning range and dual-wavelength Stokes waves operation during angle tuning process were explained.And the theoretical analysis was in good agreement with the experiment results.The maximum terahertz output energy was 5.47?J at 5.7 THz under the pump energy of 210 mJ,corresponding to the maximum THz wave conversion efficiency of 2.61×10-5. |
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