Tickle frequency

FIGURE 11.14 Fluorescence at 397 nm as a function of the applied tickle frequency. The graph shows part of the frequency spectrum of a small Ca+ -ion cloud for different values of V and with U=0. Once the ions are in resonance with the excitation frequency, the energy absorption leads to a sudden decrease of the fluorescence. 

Several methods for ion isolation exploit relatively straightforward combinations of DC voltages, RF ramps and tickle frequencies to eject unwanted ions. An example is the so-called DC isolation method , which is based upon an earlier method used for selective ion storage (Bonner 1977 FuRord 1978). This isolation method uses... 

Fig. 5.—Diagrammatic Representation of the Relationship of the Observe and Irradiate" Fields Used for Performing Various Double-resonance Experiments in the Frequency-sweep Mode. [A, For spin-decoupling, the irradiation field is positioned at the mid-point of the X-resonance B, for spin-tickling, the irradiation field is set on transition X-2 (for both of these experiments, the effect of the perturbation is monitored by scanning the observing field) and C, for an INDOR experiment, the observing field is held positioned on the transition X-2, and now it is the irradiating field that is scanned.]...

Consider first the spin-decoupling experiment (see Fig. 5A) provided that the decoupling field is positioned at the correct frequency and its power is suificiently high, the A-doublet will be detected by the observing radio-frequency as a spin-decoupled singlet. In the case of the spin-tickling" experiment (see Fig. 5B), a much weaker... 

Three important conclusions emerge from this analysis. First of all, all INDOR responses induced by this particular mechanism will be in the negative direction, as they eifectively correspond to the trace of the valley between a pair of spin-tickled transitions. The second, and more important, conclusion is that INDOR responses will only be induced at frequencies corresponding to transitions that are spin-coupled to the transition that is being monitored no other transitions can induce INDOR responses. Thus, as the third conclusion, the INDOR experiment can be used to detect transitions that are entirely obscured by other overlapping transitions. ... 

The frequency spectrum gives information on the dynamic properties of the ion motion and the storage capability of this home-made trap. The amplitude of the tickle was chosen to be sufficiently large to reveal the main couplings that existed without losing any ions. 

SFM involves modest variations in the amplitude Vg of the RF drive potential applied to the ring electrode, such that ions move into and out of resonance with the applied single frequency tickle waveform such slight modulation of Vg changes and so as to produce a sweep of the axial secular frequency g over a narrow range of some 1-2 kHz. Thus the resonance condition for ion activation is guaranteed to be met for some fraction of the time over which the resonant excitation voltage is applied. 

Double resonance experiments include a group of techniques in which a sample is simultaneously irradiated with two or more signals of different radio frequencies. Among these methods are spin decoupling, the nuclear Overhauser effect, spin tickling, and inter-nuclear double resonance. These procedures aid in the interpretation of complex NMR spectra and enhance the information that can be obtained fromjhem. Only the first of these techniques, spin decoupling, will be described here. The nuclear Overhauser effect is discussed briefly in Section 19E-1. 

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