Incoherent interference control

One example is the two-photon plus two-photon scheme discussed in Section 6.1. J An alternative, which we sketch here and discuss in further detail in relation to strong-field scenarios (Section 11.2) is called incoherent interference control. 

11 Sample scenario for the incoherent interference control of the photodissociation (Taken from Fig. 1, Ref. [200].) 

An experimental realization with the pulsed laser version of this approach [201] if discussed in detail in Section 11.2 where control over both relative populations info different channels, as well as over the photodissociation yield into both channels is- computed and demonstrated. V  

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Having suggested that the STIRAP process can be thought of as a special case of an assisted adiabatic process, we now examine another special case of an assisted adiabatic process, namely the composite STIRAP protocol proposed by Torosov and Vitanov [77]. This protocol uses a sequence of an odd number of pairs of delayed pulses (Figure 3.24) with carefully selected phases (listed in Table 3.4) to cancel by destructive interference the nonadiabatic transitions that reduce the efficiency of STIRAP-generated population transfer. We note that this protocol resembles the pulsed incoherent interference control protocol proposed by Shapiro et al. [78]. Torosov and Vitanov show that, for the triad of states illustrated in Figure 3.24, the efficiency of population transfer can be driven arbitrarily close to unity, for example, a deviation from unity of order 10 for the case of resonant excitation with three pairs of pulses. 

M. Shapiro, Z. Chen, and P. Brumer. Simultaneous control of selectivity and yield of molecular dissociation pulsed incoherent interference control. Chem. Phys., 217(2) 325—340(1997). 

Control over the product branching ratio in the photodissociation of Na2 into Na(3s) + Na(3p), and Na(3s) + Na(3d) is demonstrated using a two-photon incoherent interference control scenario. Ordinary pulsed nanosecond lasers are used and the Na2 is at thermal equilibrium in a heat pipe. Results show a depletion in the Na(3d) product of at least 25% and a concomitant increase in the Na(3p) yield as the relative frequency of the two lasers is scanned. 

Figure 1. Incoherent Interference Control (IIC) scheme and potential energy curves for Na2- This scheme is composed of a 2 wi photon process proceeding from an initial state, assigned here as (v = 5, J = 37), via the u = 35, J = 36, 38 levels, belonging to the interacting A1 Xu /3nu electronic states, and a one 2 photon dresses the continuum with the (initially unpopulated) v = 93, J = 36 and v = 93, J = 38 levels of the A1 Xu /3H electronic states.

To confirm that the observed Na(3d) dip and Na(3p) peak structures are indeed due to incoherent interference control, i.e., the interference between the co i and the C02 induced optical processes, we ran the following checks ... 

M. Shapiro The method of incoherent interference control used in our experiment is completely general and allows us to use Fano type interferences to control final states even if such lines do not naturally exist. Of course if the molecule accommodates you (as FNO) you do not need this but this is a rare situation. 

Figure 11.3 Incoherent interference control (IIC) scheme and potential energy curves fori, Na2 - Na + Na(3d), Na(4s), Na(3p). In this scheme an (on + a), photon excitation to the continuum interferes with an co2 photon from an initially unpopulated state. Two-photons absorption proceeds from an initial state, 0) (in Na2 it is taken to be the v = 5, 7 = 37 state), via the ]is1) (u = 35, 7 = 36,38) intermediate resonance belonging to the interacting, S /3n electronic states. The oj2 photon couples the continuum to the (initially unpopusf lated) E2) (v = 93, J — 36 or u = 93, 7 = 38) level of the lSll/3ril, electronic state j (Taken from Fig. 1, Ref. [201].). feg...

Z. Chen, M. Shapiro, P. Brumer, Incoherent interference control of two-photon dissociation, Phys. Rev. A 52 (1995) 2225. 

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