Research On Atomic Optical Filter Based On Laser Induced Dichroism And Birfringence

In recent years, optical information technology has got rapid development, andpeople pay more and more attention in laser communication, laser radar, remotesensing and spatial information technology. But as a result of laser transmission infree space not only suffer broadband background radiationfrom sunlight, but alsodispersion medium influence by air, sea water, so that the optical system signal tonoise ratio (SNR) is very poor,and that will reduce the sensitivity of the system.One of the important ways to improve the signal to noise ratio and sensitivity is theuse of utra narrow band optical filter before the receiving equipment. Previousstudies show that the atomic optical filter having high transmission and narrowbandwidth characteristic, thus it has obtained widespread application. In this paper,we first introduce the research progress of various atomic optical filter, and analysisthe current status of the research, and then inverstigate an atomic filter based onlaser induceed dichroicsm and birefringent by botg theoretically and experimentally.The main contents include the following aspects:Firstly, we analysed the dynamics process by using circlely polarized opticalpumping in two-level systems. Then, in order to explain the filter mechanism, weinvesgited the filter in Rb D2 line experimentaly, and three different transmissionpeaks which corrospoding to three hyperfine level transitions were observed.Secondly, we use the system of rubidium atoms excited 775.9 nm filtercharacteristics for example, and by analysising the priciple of the filter based onlaser induced dichroism and birefringence, we use emi-classical theory to deal withthe density matrix equation. By solving the equtions in steady state, we got thesusceptibility of the midium, and then stablished a complete filter model and thenumerical simulation. Through the analysis of the results, we proposal the use ofAutler-Townes splitting which is formed in atomic energy under strong pumping toachieve a wide range of tuning of the filter's transmission peak. In experiment, weboth investigated the filter characters when the pump is co-propagating andcounter-propagating with the probe. Experimental and theoretical results match wellto verify the correctness of the theoretical model.Again, we proposed a theoretical model of an incoherent pump assisted filterbased on laser induced dichroism and birefringence in atomic vapors, and go alongwith numerical simulation analysis. The presence of incoherent pumping canchange the medium's absorption and dispersion properties for the linely polarizedprobe. By selecting the appropriate parameters, it can increase the transmittance ofthe filter, even with amplification of the probe. Finally, we proposed a theoretical model of an atimoc filter based on laserindeced dichroism by double selective optical pumping. By the double selectivecircularly polarized optical pumping, the atoms only populated in special Zeemansub-level, and the population inversion only takes place in special transitions. Sothe gain was only for one circular component of the linearly polarized probe, andthe other suffers pure absorption. The resulting circular dichroism not only makesthe probe through the orthogonal Grand - Thomson prism, but also to obtain a hugegain.