Pulse splitting

Programmed temperature vaporisation Capillary Split Pulsed split Splitless Pulsed splitless Solvent vent High concentration High concentration Low concentration Low concentration Low concentration ... 

In the previous section, we described the situation that a single WP created by a pump pulse splits into two counter-propagating WPs due to potential anharmonic-ity. Similar interfering WPs can be generated by time-delayed double pump pulses. 

First, it is important to note that what is actually observed, in experiment and in simulation alike, is not a steady-state self-guided filament. Rather, we deal with a series of pulse splitting events akin to the scenario of spatial dynamical replenishment [7], In this case, however, the role of plasma as the arrestor of the self-focusing collapse is less pronounced compared to propagation in air. 

Fig. 13.5. Femtosecond pulse loosely focused into water creates a long filament with a nearly constant diameter that extends over many Rayleigh ranges (left), and generates a broad supercontinuum spectrum (right). This seemingly stationary filament is created by a series of very dynamic multiple pulse splittings illustrated in the following...

Fig. 13.6. Pulse splitting cycle Single central pulse undergoes splitting. The split-off-pulses act a scatterers , which concentrate most of the energy in the spatio-temporal spectrum around loci that support diffractionless wave-forms. This provides the energy for a new central pulse, and the cycle repeats. . . ...

J. K. Ranka, R. W. Schirmer, A. L. Gaeta, Observation of pulse splitting in nonlinear dispersive media, Physical Review Letters 77, 3783 (1996)... 

Figure 4 Crossing of ultrashort pulses, (a) The pancake effect is illustrated for two crossed 40 fs pulses with 200 pm spot sizes. These two pulses, which travel from left to right, would have been produced from a single pulse with a beamsplitter. The spatial extent of the overlap area is seen to be only a fraction of the incident beam s spatial extent, (b) Pulses split with diffractive optics and recombined with a two-lens telescope overlap over the entire spatial extent of the beam profile. (Adapted from Ref. 14.)...

For A = m 27T the pulse area A does not change because dA/dz = 0. It turns out, however, that for m > 1 the pulse splits into m 27T-pulses, which propagate as hyperbolic secant-pulses through the medium. The total pulse area A is still preserved. 

Of the four modulation formats discussed, NRZ and URZ assume zero memory between pulses, and differentially encoded and spHt phase have memory imposed between pulses. Split phase has zero power density at / = 0 with the result that its bandwidth is double that of nonreturn-to-zero. In a sense, the zero power density at / = 0 is obtained in the case of split phase by imposing a particular type of memory between pulses. More general memory structures are used between pulses for applications such as magnetic recording. These can be classified as line codes. It is beyond the scope of this chapter to go into this subject here. A simple example is provided by assuming a square pulse function of width Ty for each bit, but with successive pulse multipliers related by at = Ay — Ay-i where At = 1 represent the bit value in signaling interval k. Thus the multiplier for puke k can assume the values 2 Ay = 1 and Aj i = —1), 0 (Ak = 1 and A/t i = 1), or —2 (A = —1 and A -i = 1). The power spectral density of this pulse modulation format can be shown to be (Ziemer and Tranter, 2002)... 

Simulations of that kind result in a wide variety of A-scans and wavefront snapshots. The first screening of this material reveals, that the simulations in which the transducer is coupling partly to the V-butt weld and partly to the steel exhibit quite a number of pulses in the A-scans because the coupling at the interface of the weld results — due to the anisotropic behavior of the weld — in a complicated splitting of the transmitted wavefront. The different parts of the splitted wavefront are reflected and diffracted by the backwall, the interface, and — if present — by the notch and, therefore, many small signals are received by the transducer, which can only be separated and interpreted with great difficultie.s. 

Fig. 4 Testing configurations of the pump-probe system (a) pulse-echo configuration, (b) split...

The absolute measurement of areas is not usually usefiil, because tlie sensitivity of the spectrometer depends on factors such as temperature, pulse length, amplifier settings and the exact tuning of the coil used to detect resonance. Peak intensities are also less usefiil, because linewidths vary, and because the resonance from a given chemical type of atom will often be split into a pattern called a multiplet. However, the relative overall areas of the peaks or multiplets still obey the simple rule given above, if appropriate conditions are met. Most samples have several chemically distinct types of (for example) hydrogen atoms within the molecules under study, so that a simple inspection of the number of peaks/multiplets and of their relative areas can help to identify the molecules, even in cases where no usefid infonnation is available from shifts or couplings. 

Figure Bl.12.12. Pulse sequences used in multiple quantum MAS experiments and their coherence pathways for (a) two-pulse, (b) z-filter, (c) split-t with z-filter and (d) RIACT (II).

Figure B2.5.8. Schematic representation of laser-flash photolysis using the pump-probe technique. The beam splitter BS splits the pulse coming from the laser into a pump and a probe pulse. The pump pulse initiates a reaction in the sample, while the probe beam is diverted by several mirrors M tluough a variable delay line.

The following sources and instruments dominate studies in the area of liquids and amorphous materials. Although there are a number of sources available, each is optimized for a particular class of experiment. The sources can be split into two types pulsed neutron sources and reactor sources... 

There was thus the need for optical experiments showing the flaws of classical electrodynamics. An important difference between a wave and a particle is with respect to a beam splitter a wave can be split in two while a photon can not. An intensity correlation measurement between the two output ports of the beamsplitter is a good test as a wave would give a non zero correlation while a particle would show no correlation, the particle going either in one arm or the other. However, when one takes an attenuated source, such as the one used by Taylor, it contains single photon pulses but also a (small) fraction of two... 

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