Bichromatic

Separate sample blanking requires an additional analytical channel, and is therefore wasteflil of both reagents and hardware. An alternative approach that is used on several automated systems, eg, Du Pont ACA, BM-Hitachi 704, Technicon RA-1000, is that of bichromatic analysis (5) where absorbance measurements are taken at two, rather than one, wavelength. When the spectral curves for the interference material and the chromogen of the species measured differ sufficiently, this can be an effective technique for reducing blank contributions to assay error. Bichromatic analysis is effective for blanks of both the first and second type. 

Dichlorophenoxyacetic acid (2,4-D) is a selective effect herbicide of widely applied for annihilation of bichromatic weeds in sowings of gramineous cultures. 

Waren in der Losung aber auch Cer(IV), Permanganat oder Bichromat anwesend, so bleibt der diesen entsprechende Betrag an freiem Jod erhalten und kann mit Thiosulfat wie iiblich titriert werden. 

The profiles shown in Figure 9.18b correspond to pulses given by slightly modifying Eq. (9.69). More specifically, the pulses (E) and (E-bichromatic) are given by... 

D. A. Hutchinson, K. J. Woloschuk, and C. Mavroyannis, Physica 123C, 319 (1984). Third-Order Nonlinear Spectra of a Strong Bichromatic Field Interacting with a Three-Level Atom in a V Configuration. 

Since the classical treatment has its restrictions and the applicability of the quantum OCT is limited to low-dimensional systems due to its formidable computational cost, it would be very desirable to incorporate the semiclassical method of wavepacket propagation like the Herman-Kluk method [20,21] into the OCT. Recently, semiclassical bichromatic coherent control has been demonstrated for a large molecule [22] by directly calculating the percent reactant as a function of laser parameters. This approach, however, is not an optimal control. 

The role of the laser phase in controlling molecular dynamics was clear in the examples shown in Chapter 3, For example, in the one- vs. three-photon scenario the relative laser phase (3 — 3c/>,) enters directly into the interference term [see, e.g., Eq. (3.53)], as does the relative phase ((frl — (j>2) in the bichromatic control scenario [Eq. (3.19)]. These residts embody two useful general rules about the contribution of the laser phase to coherent control scenarios. The first is that the interference term contains the difference between the laser phase imparted to the molecule by one route, and that imparted to the molecule by an alternate route. Second, the phase imparted to the state Em) by a light field of the form ... 

The first panel of Figure 5.12 shows the bichromatic control scenario. The sec panel shows the simplest path to the continuum, consisting of one-photon absorpt of CO]. The subsequent panels show the three-photon process to the contir (absorption of a> followed by stimulated emission and reabsorption of coj, ctc ... 

Figure 5.12 Interfering pathways from Et) to the continuum associated with the scenario in Figure 5.11. The frequency and phase of the lasers are co, and (a) Bichromatic control, (b) One-photon absorption, (c) Three-photon process in which initially unpopulated state Ej) is coupled to the continuum at energy E and interferes with one-photon absorption from state ] ,). (d) Same as in (c) but for a five-photon process. Notice that in processes depicted in (c) and (d) the phase

Photodissociation is but one of many processes that are amenable to control. A host of other processes that have been studied are discussed later in this book, such as > asymmetric synthesis, control of bimolecular reactions, strong-field effects, and so forth. Also of interest is control of nonlinear optical properties of materials [203],i particularly for device applications. In this section we describe an application of thfrj bichromatic control scenario discussed in Section 3.1.1) to the control of refractive indices. riff... 

Here we show that an application of bichromatic control (Section 3.1.1) allows us to control both the real and imaginary parts of the refractive index. In doing so we consider isolated molecules [213, 214], or molecules in a very dilute gas, where collisional effects can be ignored and time scales over which radiative decay occurs can be ignored. 

Consider then the case of bichromatic control where a system prepared in a. superposition of bound Hamiltonian eigenstates IE,),... 

Examination of Eq. (6.21) shows that y(a>) is comprised of two terms that are proportional to c, 2 and that are associated with the traditional contribution to the susceptibility from state 11 ) and E2) independently, plus two field-dependent terms, proportional to a -j = c cje co /eia), which results front the coherent excitation of both II ) and E2) to the same total energy E = Ex + to) = E2+ to2. As a consequence, changing au alters the interference between excitation routes and allows for coherent control over the susceptibility. As in all bichromatic control scenarios, this control is achieved by altering the parameters in the state preparation in order to affect c1,c2 and/or by varying the relative intensities of the two laser fields. Note that control over y(ciy) is expected to be substantial if e(a>j)/e(cOj) is large. However, under these circumstances control over yfro,) is minimal since the corresponding interference term is proportional to e(a>t)/e(cQj). Hence, effective control over the refractive index is possible only at one of co( or >2. 

For zero detuning, however, the two frequencies thus emitted cannot be reab jl sorbed. That is, contrary to the emission process, the reabsorption process would lead to the same final state [ )), and there would be no way we can tell which pathway was chosen by the system (see Fig. 9.9). Thus, the resultant can cell atiprfj of reabsorption of the two emitted frequencies in the LWI case is seen to be a specia case of the bichromatic control scenario (Section 3.1.1). 

Thus, we obtain a form, which is correct (within the range of validity of the SVC A) for strong fields, that resembles the weak-field bichromatic control result of Eq. (3.12). The only difference is that instead of the Fourier transform of the electric field of the pulse, Eq. (10.19) depends on the Fourier transform of the product of the pulse electric field and the decaying factor exp[—(n/fyA Ei) J,oo /(OI2 dt ], which describes the depletion of the initial state(s) due to the action of the pulse. 

In essence, bichromatic control can be used to change the sign of a [Pg.286]

Istead of using the single-field Eq. (12.58), we pass the molecules in this super-isition state through a bichromatic standing-wave field of the form ... 

The bichromatic off-resonance LIP obeys the same general relation to the field as does the monochromatic LIP, namely, AW(y) = —dind E(y, f). All that one need do is calculate the dipole induced in the material superposition state by the bichro- matic field. Following our discussion of the control of refractive indices in Section, 6.2, the induced dipole is given by... 

The graph that can be marked in two colours is called bipartite, or bichromatic. Hereafter we shall designate the vertices of a topological molecular graph marked in one colour by an asterisk, and in another colour by a small circle, i.e. we shall keep to the designations adopted in Chapter 1. Figure 15 gives examples of bipartite (a) and... 

The three switches defined above rest on the mechanism of interspersed resonances, which was first suggested theoretically by Howard (1991). In the following we demonstrate the action of such a switch in the case of bichromatically driven hydrogen Rydberg atoms. It results in the prediction of a new kind of ionization peak in the microwave ionization of hydrogen Rydberg atoms. Recently performed experiments indicate that the effect actually exists. 

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