STIRAP Technique

The acronym STIRAP stands for 5r/mulated Raman Adiabatic Passage [888]. Its principle is illustrated in Fig. 7.15. The molecules under investigation are irradi- 

The Stokes laser generates a coherent superposition of the wavefunctions of levels 2) and 3). The states 2) and 3) are, however, not occupied before the pump pulse arrives. The wavefunction oscillates between levels 2) and 3) with the Rabi frequency which depends on the intensity of the Stokes pulse and its detuning from resonance. Now the pump pulse comes with a time delay At with respect to the Stokes pulse, where At is smaller than the width of the Stokes pulse, which means that the two pulses still overlap (Fig. 7.15b). This places the molecule at a coherent superposition of levels 1) and 2) and 2) and 3). If the delay At, the detuning A v and the intensities of the two lasers are correctly chosen, the population in level 11) can be completely transferred into level 13) without creating a population in level 2) (Fig. 7.15c). The coherently excited levels 1) and 2) are described by the wavefunction 

Contrary to stimulated emission pumping with the time sequence pump pulse-Stokes pulse, where a maximum of 50 % of the population can be transferred to 3) (because a maximum population difference 2 - A i = 0 N2 = Ni(0)/2 and N3 - N2 = 0 N3 = N2 = Ni (0)/2 can be reached), a transfer efficiency of 100 % can be achieved with the SIRAP technique [889]. The population N3 can be monitored through the laser-induced fluorescence induced by a weak third laser (probe laser in Fig. 7.15e). 

The transfer efficiency was checked for several molecules [890], The technique is very useful for generating molecules in definite quantum states. If these molecules are reactants for reactive collisions, the initial conditions for the reaction are known. Changing the populated state then gives information on the dependence of the reaction probability on the initial states of the reactants (see Sect. 8.4). 

---

FIGURE 23 Illustration of the STIRAP technique used for coherent population transfer. Shown are the time evolution of (a) the Rabi frequencies of the pump and Stokes lasers, (b) the mixing angle, (c) the dressed-state eigenvalues, and (d) the populations of the initial and final levels. [Reproduced with permission from Bergmann, K., Theuer, H., and Shore, B. W. (1998) Rev. Mod. Phys. 70, 1003.]... 

The topics that mainly concern us in this review have to do with the connections between various coherent optical experiments and LICS. In the next section we discuss the relation between LICS and EIT, examples of which include experiments done in Rb [83,84] and Kr [85]. We then extend the discussion to EIT with structured continua [86, 87]. We proceed by reviewing the use of LICS in the control of population transfer processes [88] the control of PD [89] the production of photo-electrons [90-92] and as a means of steering population transfer processes [93]. We also discuss the connection between LICS and ultrafast methodologies [94] generalized STIRAP techniques [95-97] and coherent population trapping [69,93, 98-101]. 

The maximum transfer efficiency by STIRAP in systems involving con-tinua is far less than 100%, due to dynamic Stark shifts and incoherent losses from the target state induced by the pump laser, as theory predicts [202, 215, 219, 220]. However, since techniques based on incoherent excitation via resonant continuum couplings do not usually permit any transfer at all, the STIRAP technique offers an advantage in such environments, even though the efficiency of STIRAP in such cases is far less than in purely bound systems. 

FIGURE 5.11 A combination of the demonstrated formation of -Jf v" = 36) transla-tionally ultracold molecules [31] with the well-documented stimulated Raman adiabatic passage (STIRAP) technique [32] could produce small numbers of translationally ultracold... 

V. Engel Prof. Neusser, you mentioned the technique of Stimulated Raman Rapid Adiabatic Passage STIRAP, which allows for the coherent transfer of vibrational population selectively. Is the technique not another very efficient and experimentally verified scheme of coherent control ... 

In Figure 6.15 we present a representative example of phase control in this system. In the chosen parameter region the underlying classical dynamics of rota- tional excitation is strongly chaotic [231 ] and the excitation is far off-resonance, with many levels excited. We choose j = 1 and j2 =2 to create the initial superposition y state ( 1, 0) 2, 0))/V2, that is, a = 7t/4 and p = 0, % in Eq. (6.69). (Such states 1 can be prepared experimentally by, for example, STIRAP, a technique discussed in detail in Section 9.1.) The results, shown in Figure 6.15, display striking phase... 

Numerous novel techniques related to STIRAP have been further developed recently. Examples are the hyper-Raman STIRAP [196, 197, 221], Stark-chirped rapid adiabatic passage (SCRAP) [222, 223], adiabatic passage by light-induced potentials [224-227], and photo-associative STIRAP, as a source for cold molecules [228-231]. Some experimental implementations of fhese ideas, e.g., fo fhe formafion of dark states in the photo-association of an afomic Bose-Einsfein Condensafe (BEC) to form a molecular BEC, have already been reporfed [232, 233]. 

F-STIRAP is usually used to create maximal spin coherence. During the building of spin coherence by F-STIRAP, the medium memorizes the pulse information. The pulse information exists as spin coherence in the medium. So F-STIRAP is used as a technique of light storage. This technique is a different mechanism from the eonventional EIT-based processes [23,24]. In this section, we present our experimental researeh on light storage and release based on F-STIRAP in atomic vapor and Pr YSO crystal. 

---