Pump - probe technique

B2.5.4.2 LASER FLASH PHOTOLYSIS AND PUMP-PROBE TECHNIQUES... 

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.

In many respects the time-resolved pump-probe technique is similar to the CW counterpart. The use of pulsed laser light permits direct probing of both the magnitude of the PA and its dynamics. The experimental arrangement is practically the same as for the CW version, i.e., both pump and probe beams are focused and overlapped onto same spot on a sample. In addition, the pump and probe pulses are synchronized so that the lime interval t between them is constant and confined to a certain time range (in our case up to 3 ns). 

In this section experimental results are described, which are obtained by applying the conventional pump-probe technique to m-LPPP films kept in vacuum at the temperature of liquid nitrogen [25], These results allow the identification of the primary excitations of m-LPPP and the main relaxation channels. In particular, the low and high excitation density regimes are investigated in order to get an insight into the physical processes associated with the emission line-narrowing phenomenon. 

Proton inventory technique. 21.9-220 Pseudo-first-order kinetics, 16 Pulse-accelerated-flow method. 255 Pulse radiolysis, 266-268 Pump-probe technique. 266... 

Absorption and Ensuing Ion-Molecule Reactions via Ultrafast Laser Pump-Probe Techniques.196... 

Through the use of pump-probe techniques pioneered by Zewail and coworkers,62 it is becoming possible to identify the detailed mechanisms of reactions at the molecular level and follow the actual course of a reaction. The study of ammonia clusters has provided an example of what can be accomplished using these techniques. 

The power of these techniques in elucidating the detailed mechanisms of ion-molecule reactions is well demonstrated by this example. Undoubtedly, we can expect to see increasing use of the ultrafast pump-probe technique in the field of ion-molecule reaction dynamics. 

As discussed in Sect. 1.2.3, it is usually not possible to distinguish ESA from 2PA with Z-scan experiments if they are performed with only one excitation pulsewidth. However, since ESA is not an instantaneous process as is 2PA, the pump-probe technique can be successfully used to verify the origin of the nonlinearity for the spectral regions close to the main absorption band. Figure 7 illustrates how the influence of the ESA can be distinguished from the 2PA with pump-probe experiments. The curve labeled (1) shows an instantaneous 2PA response without ESA and the long-lived components of the transmittance change seen in (2) and (3) are due to ESA. 

When metals have Raman active phonons, optical pump-probe techniques can be applied to study their coherent dynamics. Hase and coworkers observed a periodic oscillation in the reflectivity of Zn and Cd due to the coherent E2g phonons (Fig. 2.17) [56]. The amplitude of the coherent phonons of Zn decreased with raising temperature, in accordance with the photo-induced quasi-particle density n.p, which is proportional to the difference in the electronic temperature before and after the photoexcitation (Fig. 2.17). The result indicated the resonant nature of the ISRS generation of coherent phonons. Under intense (mJ/cm2) photoexcitation, the coherent Eg phonons of Zn exhibited a transient frequency shift similar to that of Bi (Fig. 2.9), which can be understood as the Fano interference [57], A transient frequency shift was aslo observed for the coherent transverse optical (TO) phonon in polycrystalline Zr film, in spite of much weaker photoexcitation [58],... 

Another very informative nonlinear experiment involves a typical pump-probe technique, but with varying laser polarization. These experiments, again for isolated chromophores, measure the rotational anisotropy TCF [122]... 

The outlook is good for applications of these picosecond methods to an increasing number of studies on reactive intermediates because of the limitations imposed by the time resolution of nanosecond methods and the generally greater challenges of the use of a femtosecond spectrometer. The pump-probe technique will be augmented in more widespread applications of the preparation-pump-probe method that permits the photophysics and photochemistry of reactive intermediates to be studied. 

Following another experimental approach, GWgoire et al [9] have tried to understand the influence of an increasing number of solvent molecules on the femtosecond dynamics of diatomic molecules, including the dimers Nal and Csl. Due to its relative simplicity, the isolated Nal molecule has been studied extensively with pump-probe techniques both experimentally [10], and theoretically [11,12], In this report, we investigate theoretically the femtosecond pump-probe ionization of Nal and Csl when aggregated with a molecule of acetonitrile CH3CN. 

Right Dependence of the dissociation rate constant kd on solvent composition. (A) data measured using the TCSPC technique, (o) data measured by the pump probe technique. 

Table 1. Parameters Used in Fitting the Signal Decay of 10-CPT in methanol-water using the pump-probe technique [4],...

The solutions were photolyzed by 266 nm quanta of a Nd YAG laser (FWHM < 3ns, energies up to 15 mJ) equipped with an optical absorption detection setup and by 253 nm quanta of a 10 Hz Ti Sapphire laser system generating 250 fs pulses up to 2 mJ at 253 nm. Absorption measurements were performed by the pump-probe technique. 

In my talk I surveyed recent advances in the methodology and selected 2D-IR spectra of secondary structures. The results promise to provide structurally based kinetic probes for conformational dynamics, sharp tests of anharmonic potential surfaces and novel information regarding the transient and equilibrium vibrational dynamics of peptides. The heterodyned 2D-IR approach has proven useful in determining structures of peptides in solution and the anharmonic nature of the potential surfaces of peptides and secondary structures [1-10], as have polarized photon echo [2,6,10-12] or pump-probe techniques [4,13-16]. 

Transient absorption and gain spectroscopy was performed by the pump-probe technique using a subpicosecond set-up described in detail elsewhere [10-12]. For the present experiments, the pump was set at 355 nm (pCA2- and pCM ) or 430 nm (pCT ) and the probe was a white-light continuum produced by focusing 570 nm pulses in a 1-cm water cell. The... 

We have employed this phase-sensitive pump-probe technique to further investigate the multiphoton ionization of Na2 with 618-nm femtosecond pulses as discussed in the previous paragraph and have observed the interference of the A E and 2 Tlg wavepackets created by the first pulse and those created by the second pulse in the Na2+ signal. The amplitude of the high-frequency oscillations in the Na2+ signal was obtained as a function of pump-probe delay by filtering the transient with the laser frequency. It is shown in Fig. 8 (top). Below the averaged Na2+ transient of Fig. 4 is... 

J. Mauritsson, T. Remetter, M. Swoboda, K. Kliinder, A. L HuiUier, K.J. Schafer, et al., Attosecond electron spectroscopy using a novel interferometric pump-probe technique, Phys. Rev. Lett. 105 (2010) 053001. 

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