Entangled Photon Radiation Field Of The Compression And Shaping

Spontaneous parametric down-conversion(SPDC) is at present the most mature and the most widely-used way of generating highly correlated photon pairs. Because of its highly correlation features in time,space, frequency and polarization, it is widely applied in the technical fields of quantum information, optical communication, laser technology and optics metrology. But it must satisfy the phase-matching requirement among the pump laser, the output signal and idler wave.So in normal conditions, the conversion efficiency is much lower. The traditional method to solve this problem is using birefringence phase-matching technology(BPM). But this method is limited by the direction of wave and polarization, it only can achieve the phase-matching on fixed wavelengths and certain crystal, so it is badly limited in application. And another method to promote the conversion efficiency is quasi-phase-matching technology(QPM).Its basic idea is the periodic or aperiodic modulation on polarizability in the nonlinear optical crystal.In this way, we can greatly promote the nonlinear optical frequency conversion efficiency. But in many researching fields,we need higher radiation intensity and regulable entangled photon radiation, such as:In the research of quantum positioning, we need good entanglement and higher intensity photon radiation, and in quantum measurement, quantum coherence tomography, we need regulable and narrow frequency linewidth entangled photon radiation. Researchers do lots of good work to improve the characteristics of entangled photons radiation, but there all exist certain disadvantages when solving certain problems. To sum up, so far, people still haven't an effective method to narrow bandwidth and regulate entangled photons radiation or plastic shape output. In this article, according to that entangled photons radiation likes wide slot diffraction behavior when chirp pump laser working in thin crystal or a bunch of pump laser working in chirp polarization crystal, and using the idea of Fresnel zone plate that multi-slit interfere cause coherent superposition, we try to discover new mechanism and method to realize more practical value and regulable entangled photons radiation.The paper is mainly divided into three partsIn the first part, based on Yaron Silberberg group's method of researching the physical process of Two-photon Absorption and parametric down-conversion,in which they used pulse shaping technology to achieve the phase modulation and optical field cropping, and refer to the Fresnel diffraction half wave band method,we in theory introduce a new way of compressing wide frequency entangled photons in frequency domain and frequency selective output on the condition of chirp short pulse broad-spectral-bandwidth optical field working in the thin crystal. And in detail we study the effect of pump optical field phase on the parameters process. According to this method, the intensity of output entangled photons can increase more than an order of magnitude, meanwhile it maintains good coherence between the entangled photons.In the second part, according to that the evolution laws of entangled photons radiation gained by SPDC in the chirp polarization crystals likes a wide slot diffraction process of optical fields in frequency domain.We put forward a new idea of coherent superposition by phase- regulable multi-slit interfere. By changing the optical field phase relationship, we can realize compression on entangled photons radiation, improve the radiation intensity of entangled photons, and also can obtain plastic output of arbitrary waveform.In the third part, We study the interaction between a chirped laser pulse and a two-level atomic system under the first order perturbation theory, obtain the approximate solutions for the density matrix equation and the propagation equation, get the relationship of density matrix element and time, and analyze the propagation of the signal field produced by polarization of the atomic medium. It is shown that the interference between the input field and the signal field occurs. By using this principle, we can realize the modulation and plastic optical field.