Pulse parameters

Fig. 5, also an A-scan, shows the possibility of the echo-technique for concrete. The interface and backwall-echo of a 20 cm thick concrete specimen are displayed (RF-display). A HILL-SCAN 3041NF board and a broadband transducer (40mm element 0) are used which enable optimal pulse parameters in a range of 50 to 150 kHz. Remarkable for concrete inspections is the high signal-to-noise ratio of about 18 dB. 

In this framework, we have developed an analytical model based on a self-consistent solution of the Poisson equation using an adiabatic approximation for laser generated fast electrons [75], This model, briefly outlined in the following, allows the determination of the optimal target thickness to optimize the maximum proton (and ion) energies, as well as the particle number as a function of given UHC laser pulse parameters. 

The realization of SPODS via PL, that is, impulsive excitation and discrete temporal phase variations, benefits from high peak intensities inherent to short laser pulses. In view of multistate excitation scenarios, this enables highly efficient population transfer to the target states (see Section 6.3.3). Furthermore, PL can be implemented on very short timescales, which is desirable in order to outperform rapid intramolecular energy redistribution or decoherence processes. On the other hand, since PL is an impulsive scenario, it is sensitive to pulse parameters such as detuning and intensity [44]. A robust realization of SPODS is achieved by the use of adiabatic techniques. The underlying physical mechanism will be discussed next. 

Small changes in the modulated pump parameters Q,f0 and in the pulse parameters 7), T2-f0 induce dramatic changes the output fields. Therefore... 

The wavepacket calculation for the femtosecond pump-probe experiment presented in Fig. 16 (bottom) is the result of the first consistent ab initio treatment for three coupled potential-energy surfaces in the complete three-dimensional vibrational space of the Naa molecule. In order to simulate the experimental femtosecond ion signal, the experimental pulse parameters were used duration A/fWhm = 120 fs, intensity I - 520 MW/cm2, and central... 

An approximate method, described in detail in Ref. (15), was applied to simulate a complementary pump-probe experiment performed with picosecond laser pulses. In this method the interaction with the probe laser pulse is approximated. A complete three-dimensional ab initio simulation, as carried out for the femtosecond experiment, is hardly possible for the picosecond experiment with the computers available today. The free laser pulse parameters were taken from the picosecond experiment duration AffWhm = 1.5 ps, intensity I = 300 MW/cm2, and central wavenumber v = O.QTiEh/h = 16021 cm 1. The dynamics induced by such a laser pulse are illustrated by... 

Common to all narrow-bandwidth excitation schemes is sequential scanning of an experimental parameter in order to adjust the Raman shift in CRS detection. In order to obtain an entire CRS spectrum, this is not only time consuming but also prone to sources of noise induced by fluctuations in laser pulse parameters. As a consequence, dynamical changes in a CRS spectrum are difficult to follow. This problem can be circumvented by use of multiplex CRS spectroscopies [48, 49], which will be discussed in combination with CARS and SRS microscopy in Sects. 6.3 and 6.4, respectively. 

The electrodeposition of metals from ionic liquids is a novel method for the production of nanocrystalline metals and alloys, because the grain size can be adjusted by varying the electrochemical parameters such as over-potential, current density, pulse parameters, bath composition and temperature and the liquids themselves. Recently, for the first time, nanocrystalline electrodeposition of Al, Fe and Al-Mn alloy has been demonstrated. 

The remainder of this paper is organized as follows In Sect. 5.2, we present the basic theory of the present control scheme. The validity of the theoretical method and the choice of optimal pulse parameters are discussed in Sect. 5.3. In Sect. 5.4 we provide several numerical examples i) complete electronic excitation of the wavepacket from a nonequilibrium displaced position, taking LiH and NaK as examples ii) pump-dump and creation of localized target wavepackets on the ground electronic state potential, using NaK as an example, and iii) bond-selective photodissociation in the two-dimensional model of H2O. A localized wavepacket is made to jump to the excited-state potential in a desirable force-selective region so that it can be dissociated into the desirable channel. Future perspectives from the author s point of view are summarized in Sect. 5.5. 

In this sense, the control of electronic transitions of wavepackets using short quadratically chirped laser pulses of moderate intensity is a very promising method, for two reasons. First, only information about the local properties of the potential energy surface and the dipole moment is required to calculate the laser pulse parameters. Second, this method has been demonstrated to be quite stable against variations in pulse parameters and wavepacket broadening. However, controlling of some types of excitation processes, such as bond-selective photodissociation and chemical reaction, requires the control of wavepacket motion on adiabatic potential surfaces before and/or after the localized wavepacket is made to jump between the two adiabatic potential energy surfaces. 

There is a range of pulse parameters (such as the pulse area, maximizes the association yield for a fixed initial wave packet. For both the intuitu) and the counterintuitive schemes there is a clear maximum at a specific puke ar< merely increasing the pulse intensity does not lead to an improved association yieht We can attribute this to the fact that the association rate of Eq, (1 increases linearly with increasing pulse intensity, whereas the dissociaiion... 

Iplgure 11.8 Rates of association (Prec), back-dissociatioin (Pdiss), and total molecule Bti tion (P) vs. t in the counterintuitive scheme. Dashed lines are pulse intensity profile, spitted lines denote effective Rabi frequency d2(t)/% where is peak pulse intensity and (a) Initial wave packet width of SE = 10 3 cm-1 and other pulse parameters as fi Fig. 11.7. (b) Dynamics scaled by s— 10 [Eq. (19.81)] Initial wave packet width of 10 4 cm-1 both pulses lasting 85 ns pump pulse peaking at / =200 ns and dump... 

Oscilloscope to control voltage and electric pulse parameters. 

Although the signal positions will spread out (when measured in hertz), the chemical shifts (8) should remain unaffected. Relative intensities might vary a little because of different pulse parameters. But, by and large, the spectra should not change significantly, since there are no accidental equivalencies to resolve. 

Fig. lla-d. Transient absorption spectra of reaction intermediates (a-c) and final product (d) observed upon photopolymerization of a TS-6 crystal with a 308 nm laser pulse. Parameters are the temperatures and the delay times (At) between the laser pulse and spectra recording. In b and c the time window of the detection circuit was 100 ps. AOD is the difference of the optical densities after and before the UV-flash (from Ref. 

Based on a model on the features of the double-pulse technique, various structures of silver nanoparticles grown onto a thin ITO film covered glass plate were generated and characterized [30]. With this method, the conflict between both optimal conditions for nucleation and growth is partially defused. This is due to the amount of small seed additionally nucleated at the higher polarization and resolved as soon as the potential is switched over to the lower polarization of the growth pulse. The interaction of the pulse parameters was modeled, thus forming the basis for how the electrodeposition process of noble metal clusters can be variably controlled. 

Recent investigations on the electrodeposition of silver demonstrated that the double-pulse method is a suitable technique for controlling the nanoparticle preparation, if the pulse parameters are carefully chosen and adjusted to the desired particle structure [29, 30]. Whereas particle density can be controlled via the overpotential and duration time ti of the nucleation pulse 1, the particle size can be enlarged by the growth time 2 (Fig. 8.5, [30]). 

Based on the model on the features of the double pulse parameters [29, 30], samples with isolated clusters and low particle density were electrochemically prepared from cyanide solution, as explained in Sect. 4.1. The particles, having a diameter of about 200 nm, were partially aggregated (Fig. 8.8a, b, c). 

Figure 3. Typical signal decay for a partially crystallized fat, following a 90° r.f. electromagnetic pulse. Parameters required for measurements of solid fat content (SFC) are shown.

Figure 6.7 Influence of pulse parameters on deposit morphology for copper deposition from a copper sulfete/sulfuric acid electrolyte [6.102]. p pulse current density ipj limiting pulse current density i average current density jj limiting current density under dc conditions.

The fundamental basis of the sonoelectrochemical technique to form nanoparticles is massive nucleation using a high current density electrodeposition pulse (ca. 150-300 mA cm ), followed by removal of the deposit from the sonoelectrode by the sonic pulse. Removal of the particles from the electrode before the next current pulse prevents crystal growth. Overall there are many experimental variables involved in sonoelectrochemical deposition electrolyte composition and temperature, electrodeposition conditions including current density (le), pulse-on time (te(on)) and ratio between pulse-on time and pulse-off time (te(off)) (the duty cyde) sonic probe conditions sonic power (Is), sonic pulse parameters, fs(on) and ts(off). 

The scale factors and tilt angles were evaluated assuming the pulse parameters given in Section 7.3. 

Under these conditions, in order to obtain a high degree of accuracy of electrochemical reproduction, the pulse parameters (pulse-on time, the amplitude) should be chosen such that, on the area with the minimum gap (the minimum voltage drop in the solution and, correspondingly, the maximum current), a sufficient charge will be consumed by metal dissolution, that is,... 

In order to work with mammalian cells, pulse parameters need to be much better controlled, and this is efficiently done with a square wave electroporator [3]. Here, the pulse amplitude and duration may be individually controlled, allowing a much better adaptability to the target cells or tissues as well as to the molecule that is to be transferred. Another important stage of the development has been the availabihty of square wave pulse generators designed and approved for chnical use. 

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