Interference Control

Ke S-H, Yang W, Baranger HU (2008) Quantum-interference-controlled molecular electronics. Nano Lett 8(10) 3257-3261... 

Figure 8.25 from Brown and Dymott, The use of platform atomisation and matrix modification as methods of interference control in graphite furnace analysis, by permission of Philips Scientific and Analytical Equipment. 

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). 

An example of one photon-three photon continuous-wave (CW) interference control of the product distribution in the branching photofragmentation and photoionization reactions... 

There are many different variants of the Brumer-Shapiro control scheme the reader is referred to the original publications for discussions of these variants. Brumer and Shapiro have also discussed the selection rules relevant to interference control of product selectivity and the influence of sources of incoherence on the quality of interference control achievable [26],... 

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. 

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. 

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

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...

Ordinary STIRAP is only sensitive to the energy levels and the magnitudes of transition-dipole coupling matrix elements between them. These quantities are identical for enantiomers. Its insensitivity to the phase of the transition-dipole matrix elements renders STIRAP incapable of selecting between enantiomers. Recently we have demonstrated [11] that precisely the lack of inversion center, which characterizes chiral molecules, allows us to combine the weak-field one-and two-photon interference control method [29,54,95,96] with, the strong-field STIRAP to render a phase-sensitive AP method. In this method, which we termed cyclic population transfer (CPT), one forms a STIRAP loop by supplementing the usual STIRAP 1) o 2) <=> 3) two-photon process by a one-photon process 1) <=> 3). The lack of inversion center is essentrat, because one-photon and two-photon processes cannot connect the same states in the presence of an inversion center, where all states have a well defined parity, because a one-photon absorption (or emission) between states 1) and 3) requires that these states have opposite parities, whereas a two-photon process requires that these states have the same parity. 

Z. Chen,M. Shapiro, P. Brumer, Interference control of photodissociation branching ratios. Two-color frequency tuning of intense laser fields, Chem. Phys. Lett. 228 (1994) 289. 

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

Sources of error in the sample preparation should be recognized and interferences controlled. However, each analysis involves random (statistical) errors, and the whole error is the sum of cumulative errors at each stage of an analytical procedure. A number of effects contribute to the uncertainty of the final signal displayed on the readout system. In the measurement stage various sources of interference are fluctuations in radiation source signal, photomultiplier shot noise , electronic noise , flame fluctuations, nebuliza-tion and atomization noise , inaccuracies in the read-out system, and interelement interferences. 

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