Stark shifts

There are three main EA spectral features in the energy range of band I a derivative-like feature with zero-crossing at 2.29 eV, followed by vibrational features, and an induced absorption band between 2.9 and 3.2 eV. The features below 2.5 eV are the results of a redshifted 1 Bu exciton energy, and its phonon sidebands (Stark shift). These features are more easily observed in EA than in absorp-... 

Kuhn B, Fromherz P, Denk W (2004) High sensitivity of stark-shift voltage-sensing dyes by one- or two-photon excitation near the red spectral edge. Biophys J 87(1 ) 631—639... 

In Equation 12.6 p, is the permanent dipole moment, h is Planck s constant, I the moment of inertia, j the angular momentum quantum number, and M and K the projection of the angular momentum on the electric field vector or axis of symmetry of the molecule, respectively. Obviously if the electric field strength is known, and the j state is reliably identified (this can be done using the Stark shift itself) it is possible to determine the dipole moment precisely. The high sensitivity of the method enables one to measure differences in dipole moments between isotopes and/or between ground and excited vibrational states (and in favorable cases dipole differences between rotational states). Dipole measurements precise to 0.001 D, or better, for moments in the range 0.5-2D are typical (Table 12.1). 

Figure 4.5 Schematic drawing of system and bath, (a) Amplitude noise (AN) (red) combatted by AC-Stark shift modulation (green), (b) Phase noise (PN) (red) combatted by resonant-field modulation (green). (See color plate section for the color representation of this figure.)...

We first consider the AN regime of a two-level system coupled to a thermal bath. We will use off-resonant dynamic modulations, resulting in AC-Stark shifts (Figure 4.5(a)). The Hamiltonians then assume the following form ... 

This would accomplish the goal of DD [39,41 7, 79], Conversely, the increase of R due to a shift can be much greater than that achievable by repeated measurements, that is, the anti-Zeno effect [9,13-15]. In practice, however, AC Stark shifts are usually small for (cw) monochromatic perturbations, whence pulsed perturbations should often be used, resulting in multiple shifts as per Eq. (4.132). 

While the formalism of DD is quite different from the formalism presented here, it can be easily incorporated into the general framework of universal dynamical decoherence control by introducing impulsive PM. Let the phase of the modulation function periodically jump by an amount 4> at times r, 2t,. .. Such modulation can be achieved by a train of identical, equidistant, narrow pulses of nonres-onant radiation, which produce pulsed AC-Stark shifts of co. When (/> = tt, this modulation corresponds to DD pulses. 

For a molecule in a given electronic and vibrational state, it is convenient to define the permanent dipole operator d = (i/r // i/r), where v/) is a product of the electronic and vibrational states. This vector operator depends on the angles that specify the orientation of the molecule with respect to the external field axis. For diatomic molecules, d is directed along the intermolecular axis. The Stark shifts of the molecule in a DC electric field can (almost always) be found by treating the molecule as a rigid rotor and diagonalizing the matrix of the operator... 

Several reasons have been put forward to explain the change in the angular intensity pattern of the photoelectrons. One explanation is that intermediate neutral energy levels are ac-Stark shifted into resonance and contribute new selection rules to the photoionization process [53,54], Another possibility is that the electrons of the Kr or D2 are driven into the core Kr+ or D2 in a scattering-like process that creates interference fringes in the photoelectron angular distribution due to interference between multiple scattering channels [55],... 

As the laser intensity is increased and the vibrational energy levels of the ion are ac-Stark shifted to higher energy, they bring with them the Rydberg states of the neutral D2. As the laser intensity moves a particular vibrational level of the D2 into and through resonance with the laser light at the... 

In fast beams optical excitation has proven to be most useful. Since the fast beams are low in intensity, but continuous, cw lasers have been used. Usually, fixed frequency lasers have been used since fine tuning can be done using the Stark shift or the Doppler shift of the fast beam. The Doppler shift can be used either by changing the angle at which the laser beam and fast beam cross, or by altering the velocity of the fast beam. An early example was the use of the uv line of an Ar laser to drive transitions from the metastable H 2s state to the 40 < n < 55 np states.27 In this particular case the velocity of the beam was changed to tune different np states into resonance. 

That part of the black body spectrum coincident with the atomic transition frequencies leads to the transitions which redistribute the population. In contrast, all the energy of the black body radiation contributes to the shift of the energy levels. The energy shift is a second order ac Stark shift, and for state n the shift AWb is given by10... 

While the black body radiation energy is mostly at frequencies high compared to the Rydberg state frequencies, it is low compared to the frequencies of transitions of low lying states. Explicitly, a>n-v n( Stark shift is equal to that produced by a static field and can be expressed as... 

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