Transient absorption spectroscopy pump-probe measurement

Fig. 15, were initially obtained from the DMN fluorescence lifetime data,92,102 but they have recently been measured using subpicosecond time-resolved transient absorption spectroscopy (pump-probe).105... 

The experimental configuration of the pump-probe experiment is similar to Ref. [5]. A home built non-collinear optical parametric amplifier (nc-OPA) was used as a pump, providing Fourier-transform-limited 30 fs pulses, which could be spectrally tuned between 480-560 nm. In all experiments white-light generated in a sapphire crystal using part of the fundamental laser (800 nm), was used as probe light. In the pump-probe experiments the pump was tuned to the S2 0-0 band for carotenoids with n>l 1. In the case of M9, it was not possible to tune the nc-OPA to its 0-0 transition, and hence another nc-OPA tuned to 900 nm was frequency doubled and used for excitation. In addition to conventional transient absorption pump-probe measurements, we introduce pump-deplete-probe spectroscopy, which is sensitive to the function of an absorbing state within the deactivation network. In this technique, we... 

Transient absorption spectroscopy has been a conventional technique for studying the configurational (conformational) changes that are reflected in the Tn <— T, optical transition. Picosecond to microsecond time-resolved, pump and probe measurement has been widely used to examine the triplet-state isomerizations as far as each ris-T, and the all-trans-Tj species are selectively observed. Even when their wavelengths are very similar to one another, the SVD and global-fitting analysis can successfully identify a set of triplet species appearing in different time-scales, when a correct kinetic model is built. 

The mechanism and dynamics of photoinduced charge separation and charge recombination have been investigated in synthetic DNA hairpins possessing donor and acceptor stilbenes (stilbene-4,4 -dicarboxylic acid, bis(3-hydroxypropyl)amide of stilbene-4,4 -dicarboxylic acid, bis(2-hydroxyethyl)stilbene 4,4 -diether) (Figure 11.1) using femtosecond broadband pump-probe spectroscopy, nanosecond transient absorption spectroscopy, and picosecond fluorescence decay measurements [11]. Nanosecond time-resolved spectra of stilbenes attached to DNA are shown in Figure 11.4. 

Abstract The concepts at the basis of transient absorption measurements were illustrated with particular reference to nanosecond kinetic spectrophotometry and femtosecond pump and probe methods. The main features of the typical experimental setups for both techniques were illustrated as regards optical parts, geometrical layout of components and light detection systems. Examples of application of transient absorption spectroscopy were illustrated for the elucidation of photoinduced processes in supramolecular systems like a fullerenepyrrolidine-oligophenyleneethynylene hybrid derivative, a drug-protein complex and a tri-chromophoric system consisting of two porphyrins and one perylene bisimide. 

While DFWM and other NLO measurement techniques yield information on response and decay times as well, as some of the data cited above indicate, additional data are obtainable from such techniques as pump-and-probe ps or fs transient absorption spectroscopy. Some of the first such data were collected by the Shank group at the erstwhile Bell Labs [524]. Fig. 12-31 shows their data for a 2.0 eV pump for cis-and trans-P(Ac), whilst Fig. 12-32 shows photoinduced absorption, at 1.4 eV, of P(cis-Ac) on a ps time scale. In the latter case, the rise time is less than 150 fs, the... 

Fig. 3. Pump-deplete-probe spectroscopy on lycopene in hexane, a) Experimental setup After excitation and depletion of Car S2 with a delay of r=50fs, a white-light probe pulse at delay tprob<.=2ps measures the transient absorption spectrum, b) Spectra without (solid curve) and with depletion pulse (dotted) and their difference (shaded area). Only the Car Si state is depleted the ground state bleach (S0-S2) and positive absorption feature on its low energy side (hotSo-S2) are unaffected.

Transient terahertz spectroscopy Time-resolved terahertz (THz) spectroscopy (TRTS) has been used to measure the transient photoconductivity of injected electrons in dye-sensitised titanium oxide with subpicosecond time resolution (Beard et al, 2002 Turner et al, 2002). Terahertz probes cover the far-infrared (10-600 cm or 0.3-20 THz) region of the spectrum and measure frequency-dependent photoconductivity. The sample is excited by an ultrafast optical pulse to initiate electron injection and subsequently probed with a THz pulse. In many THz detection schemes, the time-dependent electric field 6 f) of the THz probe pulse is measured by free-space electro-optic sampling (Beard et al, 2002). Both the amplitude and the phase of the electric field can be determined, from which the complex conductivity of the injected electrons can be obtained. Fitting the complex conductivity allows the determination of carrier concentration and mobility. The time evolution of these quantities can be determined by varying the delay time between the optical pump and THz probe pulses. The advantage of this technique is that it provides detailed information on the dynamics of the injected electrons in the semiconductor and complements the time-resolved fluorescence and transient absorption techniques, which often focus on the dynamics of the adsorbates. A similar technique, time-resolved microwave conductivity, has been used to study injection kinetics in dye-sensitised nanocrystalline thin films (Fessenden and Kamat, 1995). However, its time resolution is limited to longer than 1 ns. 

Transient absorption (TA) spectroscopy has greatly improved our understanding of solar-powered devices, particularly in the areas of photocatalysis and photovoltaics using Ti02- In the technique, a pump pulse, typically from a laser, places the sample in an excited state with new electronic and/or chemical properties. A time-delayed probe pulse measures the absorption spectrum of the sample after it is altered by the first pulse. Measuring the change in absorption compared to the initial value as a function of the delay between the pulses gives the dynamics of the system (Fig. 2). 

Abstract Far-ultraviolet (FUV) absorption spectroscopy provides molecular information about valence electronic transitions a, n, and Jt electron excitation and charge transfer (CT). FUV spectral measurements of liquid water and aqueous solutions had been limited, because the absorptivity of liquid water is very intense (absorptivity 10 cm at 150 nm). We have developed an attenuated total reflection (ATR)-type FUV spectrophotometer in order to measure FUV spectra of liquid water and aqueous solutions. The ATR-FUV spectroscopy reveals the features of the valence electronic transition of liquid water. This chapter introduces a brief overview of the first electronic transition (A. Y) of liquid water (Sect. 4.1) and the FUV spectral analyses (140-300 nm) of various aqueous solutions including how the hydrogen bonding interaction of liquid water affects the A <— X transition of water molecules (Sect. 4.1) how the A Y bands of water molecules in Groups 1, 11, xm, and lanthanoid (Ln +) electrolyte solutions are associated with the hydration states of the metal cations (Sects. 4.2 and 4.3) how the protonation states of amino acids in aqueous solutions affect the electronic transition of the amino acids (Sect. 4.4) and the analysis of O3 pulse-photolytic reaction in aqueous solution using a nanosecond pump-probe transient FUV spectrophotometer (Sect. 4.5). 

More recently, Gao et al reported transient absorption microscopy and spectroscopy measurements on chirality-assigned individual SWCNTs. Transient absorption spectra of individual SWCNTs shown in Figure 7.10 were obtained by recording transient pump probe images at different probe wavelengths and reveal different origins of photo-induced absorption. Population... 

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