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Báo cáo nghiên cứu khoa học: "Tán xạ raman cưỡng bức trong gần đúng ba chiều"

Tham khảo luận văn - đề án 'báo cáo nghiên cứu khoa học: "tán xạ raman cưỡng bức trong gần đúng ba chiều"', luận văn - báo cáo phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | TRƯỜNG ĐẠI HỌC VINH TẠP CHÍ KHQA HỌC TẬP XXXVII số 2A-2008 RAMAN STIMULATED SCATTERING IN THREE-DIMENSIONAL APPROACH CHU VAN LANH a DINH XUAN KHQA a HQ QUANG QUY b PHAM THI THUY VAN c Abstract. In this paper we present a theory of Raman stimulated scattering in three-dimensional approach. The intensity of Stokes waves is introduced and discussed in two limit conditions there are transient limit and steady-state limit. I. THREE-DIMENSIONAL MAXWELL-BLOCK EQUATIONS We consider a collection of indentical atoms or molecules initially in ground states contained in a pensil-shaped volume with length L and cross-sectional area A. The atomic positions are random but fixed and the average number density is N atoms cm-3 . A laser with electric field SL p t . El p t ei ot-kLZ E p t e i Lt kLZ propagates through the volume in the z direction which is parallel to the pencil axis. As shown in Fig.1 an atom may absorb a laser photon at frequency OL and scatters a photon at Stokes frequency 0S 0L 031 ending up in the final state 13. We will treat the laser field mode as a classical electromagnetic wave and assume that it does not undergo depletion or any other back reaction from the medium. On the other hand the remaining modes of radiation field will be treated quantum mechanically to allow for the spontaneous initiation of Raman scattering. As well as shown in previous works 1 2 3 we introduce a set of MaxwellBlock equations describing Raman stimulated scattering in three-dimensional space V2 1 E p. t e i st ksz 2k2 E p. t Q p t e i st ksz V 2 -X 2 s r 1 e _ . L t L Q r 1 e c dt J cos dt Q p. t rQ p. t ik E p. t E p t F p. t Q i i Q f I ik1 El r t Es r I F r I dt 1 E l r t is the intensity operator of laser field with slowly-varying envelope where approximation E p t is the intensity operator of Stokes field with slowly-varying envelope approximation dependent on frequency C0S Q p t is the atomic-transition operator which describes the relation between two states 11 and 13 see .