Theoretical Research Of The Key Techniques Of Entangled Two-photon Correlated Terahertz Imaging

Terahertz(THz)imaging technology is an important imaging technology beside X-ray imaging and ultrasonic imaging.It has important scientific research value and wide application prospect.At present,the commonly used terahertz imaging technology mainly has time domain spectroscopy and continuous wave imaging.In this paper,a technology of terahertz correlation imaging based on quantum two-photon entanglement is proposed and is designed and a dual-wavelength,narrow-bandwidth terahertz wave parametric oscillator(TPO)is designed.Firstly,the Terahertz wave parameter generator(TPG)is used as the entangled two-photon source.Based on the principle of two-photon entanglement correlation imaging,THz correlation imaging based on two-photon entanglement is proposed,and the two schemes of its imaging are studied theoretically.The results show that when the imaging lens is placed on the THz optical path,a magnified image is achieved when the focal length f and the distance d1 which between the lens and the crystal satisfy d1>2f,and a reduced image is achieved satisfy f<d1<2f.The magnification increases with increasing d1,while decreases with increasing f.The angular resolution is only related to the lens radius R and decreases with increasing R.When the imaging lens is placed on the Stokes optical path,a magnified image can be acquired when the distance d1 between the crystal and the imaging lens and the lens focal length f satisfies d1/2<f<d1,a reduced image can be realized when f<d1/2.is related to the d2 which is the distance the sample and the crystal.The magnification is inversely proportional to d2 and is proportional to f.The angular resolution increases with d2 and decreases with d1.When d2 take a smaller value,the angular resolution can reach the order of microns.Secondly,a dual-wavelength,narrow-bandwidth TPO is designed based on the diffraction characteristics of the blazed grating.The resonator is composed of a double-blazed grating system and a right-angled prism.The two-wavelength and narrow-line Stokes light can be realized by approximating the-1-order and-2-order diffraction efficiencies,which corresponding to the two blinking angles of the double-blazed grating with the intersecting period.Thereby,the dual-wavelength and narrow linewidth THz wave Coherent output is realized,and dual wavelengths do not interfere with each other,this tuning method is flexible and diverse,and the TPO anti-detuning performance is improved.