Pulse width definition

Experimentally, it has become possible to follow chemical reactions on a femtosecond time scale with excellent time resolution— with precise definitions of f = 0, time separations between pulses, and with very narrow pulse widths. 

If delayed extraction increases the mass resolution without degradation of sensitivity compared with continuous extraction, it also has limitations. Indeed, delayed extraction complicates the mass calibration procedure. It can only be optimized for part of the mass range at a time and is less effective at high mass. Delayed extraction partially decouples ion production from the flight time analysis, thus improving the pulsed beam definition. However, calibration, resolution and mass accuracy are still affected by conditions in the source. For instance, in the usual axial MALDI-TOF experiments, optimum focusing conditions depend on laser pulse width and fluence, the type of sample matrix, the sample preparation method, and even the location of the laser spot on the sample. 

The sinc fiinction describes the best possible case, with often a much stronger frequency dependence of power output delivered at the probe-head. (It should be noted here that other excitation schemes are possible such as adiabatic passage [9] and stochastic excitation [fO] but these are only infrequently applied.) The excitation/recording of the NMR signal is further complicated as the pulse is then fed into the probe circuit which itself has a frequency response. As a result, a broad line will not only experience non-unifonn irradiation but also the intensity detected per spin at different frequency offsets will depend on this probe response, which depends on the quality factor (0. The quality factor is a measure of the sharpness of the resonance of the probe circuit and one definition is the resonance frequency/haltwidth of the resonance response of the circuit (also = a L/R where L is the inductance and R is the probe resistance). Flence, the width of the frequency response decreases as Q increases so that, typically, for a 2 of 100, the haltwidth of the frequency response at 100 MFIz is about 1 MFIz. Flence, direct FT-piilse observation of broad spectral lines becomes impractical with pulse teclmiques for linewidths greater than 200 kFIz. For a great majority of... 

We recall that in the simulation (dots in Fig. 6) C and B were, respectively, 25 and 38 Hz. The applied field was assumed to be perfectly homogeneous and C originated entirely from the finite width of the pulses. The fact that the experimental value of B is smaller than that derived from the simulations is not surprising because the simulations were carried out for the crystal orientation where the dipolar coupling of the methylene protons has its absolute maximum, whereas the experiment was done for a different, alas unknown, orientation. For this orientation the dipolar coupling was definitely even smaller than the maximum accessible with our arbitrarily fixed sample crystal, which itself is smaller than the absolute maximum, as can be inferred from a comparison of the t = 1.5-/1S spectrum in Fig. 23 with the MREV spectrum in Fig. 22a. In any event the result B p < B - is pleasing and gives credit to our spectrometer (the indices exp and sim mean experimental and simulated). From B < B it also follows that the finite-pulsewidth contribution to is smaller... 

Combination of a pulsed bias and noncontact AFM has been found to improve the control of the writing process [78]. This method reduces the tip-substrate interaction time and thus improves the reliability and lithographic resolution. The frequency of oscillation and the field pulsing frequencies need to be adjusted to create a definite phase relation between the two and it was found that the minimum line width is obtained when the applied field is on during the time the cantilever tip is furthest from the substrate. The process also needs adjustment of the duty cycle. 

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