Research On Output Frequency Characteristics Of Thz Wave Parametric Oscillator

The terahertz wave(l THz = 1012 Hz)is an electromagnetic wave located between the infrared wave and the microwave.Because of its special position in the electromagnetic spectrum,it has important applications in material detection,medical imaging,and spectrum analysis.A terahertz parametric oscillator(TPO)based on stimulated EM scattering can output a narrow pulse width,high power,continuously tunable THz wave with good directivity at room temperature,which is the main output of terahertz output today.method.In this paper,the effects of Stokes light and pump light shape on the output THz light in TPO and the effects of various parameters in TPO on the oscillation threshold are studied.In terms of theory,the basic theory of TPO to generate THz light is analyzed.According to the lattice parameters of Mg O:Li Nb O3 crystal,the gain expressions of signal and idler light in the TPO process are calculated,and the signal light and the The power of idler light obtains the conclusion that the idler optical power produced is proportional to the loss when the loss is relatively high.The dispersive equation of the terahertz band is calculated and the dispersion distribution and absorption characteristic curve of the A1 symmetrical mode in the Li Nb O3 crystal are simulated.The phase matching relationship at the pump wavelength of 1064 nm is obtained.In experiments,the dispersion characteristics and gain coefficient of Stokes light in the stimulated electromagnetic scattering(SPS)process were experimentally studied through a terahertz parameter generation(TPG)experiment;the crystal was replaced at a pump light energy of 10 m J.The length and the relative intensity of the Stokes light were measured separately,and the Stokes light gain coefficient was 1.32 cm-1 during the SPS process.By setting up a silicon prism array coupled output TPO experimental platform,it was verified that the transmission of the THz light in the pump light will not have energy attenuation.When the Stokes light is not cut,the output THz frequency range is 1.22 to 2.54 THz,and after the Stokes light cut,the output THz frequency range is 0.86 to 2.54 THz,which indicates that the method of cutting the pump light can ensure the THz light output energy.Achieve a larger tuning range.The influence of TPO parameters on the oscillation threshold was studied.When the cavity length was increased from 170 mm to 260 mm,the threshold power density increased from 52 MW/cm2 to 70 MW/cm2,an increase of 35%.When the output mirror reflectivity R decreased from 0.9 to 0.5,the TPO threshold increased from 51 MW/cm2 to 53 MW/cm2,an increase of 5.3%.When the crystal length was reduced from 70 mm to 30 mm,the TPO threshold increased from 58 MW/cm2 to 128 MW/cm2,an increase of 2.2 times.Finally,a TPO experiment platform with a shallow surface vertical coupling output is built to shape the pump spot into an elliptical spot,which improves the quality of the output THz beam and extends the output tuning range.