Near Stark shift

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... 

Fabre et a/.28 used a projection operator technique to describe the Stark shifts at fields below where low states of large quantum defects join the manifold. A less formal explanation is as follows. If, for example, the s and p states are excluded, as in Fig. 6.13 below 800 V/cm, effectively only the nearly degenerate (22 states are coupled by the electric field. The only differences among the m = 0,1, and 2 manifolds occur in the angular parts of the matrix element, i.e.1... 

Fig. 10.19 The microwave frequency dependence of the n changing signals at low microwave power, where n changes up or down only by 1. Resonant multiphoton transitions are observed near the expected static field Stark shifted frequencies indicated. These resonances involve the absorption of four or five microwave photons. The down n changing atom production curve was obtained with the state analyzer field EA set at 50.0 V/cm, while up n changing was studied as n = 60 atom loss with EA = 45.5 V/cm. The locations of resonances for larger direct (not stepwise) changes in n are indicated along with...

As shown by Fig. 14.15, the resonances occur near zero field, and it is easy to calculate the small Stark shifts with an accuracy greater than the linewidths of the collisional resonances. As a result it is straightforward to use the locations of the collisional resonances to determine the zero field energies of the p states relative to the energies of the s and d states. Since the energies of the ns and nd states have been measured by Doppler free, two photon spectroscopy,22 these resonant collision measurements for n = 27, 28, and 29 allow the same precision to be transferred to the np states. If we write the quantum defect dp of the K np states as... 

We have calculated exactly the Zeeman effect for the levels IS, 3S and 3P. Indeed it is necessary to know the shift for all the hyperfine levels very well. These calculations are very classical and we just present the results in a Zeeman diagram (see Fig. 5). The most important part in the diagram is the crossing between the 38 2 (F=l, mp=-l) and 3P1/2(F=1, mj =0) levels, because the quadratic Stark effect is proportional to the square of the induced electric field and inversely proportional to the difference of energy between the two considered levels. Moreover the selection rules for the quadratic Stark effect in our case (E perpendicular to B) impose Am.F= l. So it is near this crossing that the motional Stark shift is large enough to be measured. In our calculations the Stark effect is introduced by the formalism of the density matrix [4] where the width of the levels are taken into account. The result of the calculation presented on... 

In our picture of microwave ionization the n dependence of the ionization fields comes from the rate limiting step between the bluest n and reddest + 1 Stark states. It would be most desirable to study this two level system in detail, but in Na this pair of Stark levels is almost hopelessly enmeshed in all the other levels. In K, however, there is an analogous pair of levels which is experimentally much more attractive [17,18]. The K energy levels are shown in Fig. 6. All are m = 0 levels, and we are interested in the 18s level and the Stark level labelled (16,3). We label the Stark states as (n, k) where n is the principal quantum number and k is the zero field state to which the Stark state is adiabatically connected. As shown in Fig. 6, the (16, k) Stark states have very nearly linear Stark shifts and the 18s state has only a very small second order Stark shift, which is barely visible on the scale of Fig. 6. The 18s and (16,3) states have an avoided crossing at a field of 753 V/cm due to the coupling produced by the finite size of the K-" core [19]. 

The other probabilities of photon emissions or absorptions are negligible. During the process, we remark that small transient 001 and 002 photon absorption probabilities arise. An early 002 photon absorption is observed, coinciding exactly with the (negative) shift of the transfer eigenvector. The first effects of the ( 2 pulse are indeed to (i) split the unpopulated dressed states connected to 2) and 3) and (ii) produce a Stark shift of the dressed state connected to 1) (the early part of the transfer state), which is equivalent to a partial absorption of a 002 photon. Symmetrically, a late 001 photon absorption occurs. It is due to a (positive) Stark shift of the dressed state connected to 3) (the late part of the transfer state). Arising near the end of the process, for which one 001 photon has already been absorbed, it leads to a partial absorption of a second 001 photon. At the end of the process the complete population transfer from state 1) to state 3) is accompanied by the loss of a 001 photon and the gain of a 002 photon. Thus the final result is not different from the semiclassical result. 

We now address the question how much atomic physics needs to be included in order to account for ATI In fig. 9.6, we show experimental data for ATI from [493], obtained at several laser intensities. One of the important properties of ATI peaks, referred to as peak suppression, is that the relative intensity of the first ATI peaks above threshold does not increase uniformly with laser field strength, but actually begins to decrease in intensity relative to higher energy peaks as the laser field strength increases. Such behaviour cannot be explained in a perturbative scheme, in which interactions must decrease monotonically order by order as the number of photons involved increases, but can be accounted for in terms of the AC Stark shift of the ionisation potential in the presence of the laser field. In ATI experiments, the ionisation potential appears to shift by an average amount nearly equal to the ponderomotive potential, so that prominent, discrete ATI peaks are seen despite the many different intensities present during the laser pulse. However, ATI peaks closest to the ionisation limit become suppressed as the amplitude of the laser field oscillations increases and the ionisation threshold sweeps past them (a different effect which also suppresses ionisation near threshold is discussed in section 9.24.1). 

We studied photoluminescence (PL) properties of CdSe nanorods integrated in a thin film sandwiched between transparent electrodes to which an electric field applied. Nearly 20 % of PL quenching accompanied with the weak Stark shift have been observed. This effect is proposed to be used for PL modulation, in particular in the wavelength range beyond the range that traditional optoelectronic devices may cover. 

Rydberg states with a principle quantum number w> 100. These Rydberg states are formed by laser excitation and are located a few cm (or a fraction of meV) below the ionization threshold. Because the electrons ejected from these Rydberg states carry near zero electron kinetic energy, these states are known as ZEKE states and the ejected electrons are named as ZEKEs. The measured electron peak position is lower than that without the presence of the field by the Stark shift 6)... 

Sensitive and accurate measurements of atomic and molecular Rydberg levels have been performed [6.87-6.89] with thermionic diodes. With a special arrangement of the electrodes, a nearly field-free excitation zone can be realized that allows the measurement of Rydberg states up to the principal quantum numbers n = 300 [6.89] without noticeable Stark shifts. 

Another molecule of interest is HBr (and DBr). HBr has a large dipole moment, but due to its ground state configuration HBr has a very small first order Stark shift, which makes it hard to Stark decelerate and electrostatically trap. However, HBr is near mass degenerate with Kr and as is discussed in Sec. 8.4, DBr is nearly mass degenerate with Rubidium Rb. 

Second, the resolution achieved in a 2-D experiment, particularly in the carbon domain is nowhere near as good as that in a 1-D spectrum. You might remember that we recommended a typical data matrix size of 2 k (proton) x 256 (carbon). There are two persuasive reasons for limiting the size of the data matrix you acquire - the time taken to acquire it and the shear size of the thing when you have acquired it This data is generally artificially enhanced by linear prediction and zero-filling, but even so, this is at best equivalent to 2 k in the carbon domain. This is in stark contrast to the 32 or even 64 k of data points that a 1-D 13C would typically be acquired into. For this reason, it is quite possible to encounter molecules with carbons that have very close chemical shifts which do not resolve in the 2-D spectra but will resolve in the 1-D spectrum. So the 1-D experiment still has its place. 

CO adsorption on an nm-Pd/GC electrode in alkaline solution (Section 21.4.3) we know that the nm-Ru/GC exhibited also AIREs in alkaline solution. The enhancement factor Air of IR absorption of COad is 33, which is larger than the Air measured in acid solutions. We can see that both the COl and COr bands are shifted linearly to higher wavenumbers when the s is increased positively. The Stark effect of the COr band is 34 cm V It may be noteworthy that in an early study [50] of CO adsorption on a massive Ru electrode in alkaline solutions, only one COad band near 1970cm was observed and assigned incorrectly to IR absorption of bridge-bonded CO species. 

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