Electronic Pulse Processing Units

Transformation of the data into a pulse height distribution is shown on the right. The FWHM measurement is shown for the higher peak. (From Heisen, L.A. and Kuczumow, A., in Van Griekin, R.E. Markowicz, A.A. (eds.), Handbook of X-Ray Spectrometry, 2nd edn., Marcei Dekker, inc., 

Pulse processing also incorporates dead time correction. Dead time results from the inability of the detector electronics to process the pulses fast enough to match the volume of input signals. Therefore, the greater the incident intensity, the greater the losses would be during measurement. Dead time is typically 300-400 ns for modern spectrometers. 

---

For compound (Scheme 1 and Table 1) the oxidation pattern is quite different the differential pulse voltammetry exhibits two peaks of equal height, both corresponding to a two-electron oxidation process (Figure 11). The first oxidation occurs at nearly the same potential as the four-electron process of compound 6F. This shows that, as expected, the two Os(bpy)2( i-2,3-dpp) units are the first to be oxidised (Table 2). The second process concerns the oxidation of the two Ru(bpy)2(p-2,5-dpp) units. Since such units lie far away from the previously oxidized Os-containing units, their oxidation occurs at a potential (Table 2) close to that of the equivalent peripheral units of 6D. As in the case of the compounds 6A-F the oxidation of the two inner units are displaced outside the accessible potential window. 

In ultrafast laser science the emergence of attosecond laser pulses raises the prospect of studying electronic wavepacket motion on the natural timescales of this motion in nature, namely the atomic unit of time (1 a.u. = 24 attosec-onds = 0.024 femtoseconds) [1,2]. Attosecond science may have a profound impact on the way we understand photo-induced physical and chemical processes. 

The major limitation of photoelectric recording is what can be thought of as the nanosecond barrier. This limitation arises because of the intrinsic time response of the electronic devices that must be used to acquire and process the photongenerated cathode current of the PMT or photodiode. All such devices have impedance, and even the best-designed circuitry has stray capacitance of typically 20 pF which, when combined with the 50-Q industry/standard of electronic amplifiers, yields a RC time constant of 1 ns. Hence, instruments that are built up from conventional electronic units will have minimum rise times in the ns region and therefore chemical changes that have lifetimes less than 5 ns, say, will be severely deformed. Of course, other reasons may intervene (e.g. 10-ns-wide laser pulses) that make the instrument response even poorer than implied by the nanosecond barrier. 

The emergence in the late 1980s of chirped pulse amplification techniques [1] meant that it was now possible to produce focused laser intensities well in excess of 10 W/cm. This is equivalent to a laser electric field approaching one atomic unit and it is perhaps not surprising, therefore, that conventional perturbation theory cannot be applied to the dynamics of atoms and molecules in such intense laser fields. In fact these fields dress the electrons and nuclei on a timescale that is short compared to those of conventional atomic or molecular processes and new non-linear phenomena are observed. 

---