Space-Resolved Measurements

As with alternating electrical currents, phase-sensitive measurements are also possible with microwave radiation. The easiest method consists of measuring phase-shifted microwave signals via a lock-in technique by modulating the electrode potential. Such a technique, which measures the phase shift between the potential and the microwave signal, will give specific (e.g., kinetic) information on the system (see later discussion). However, it should not be taken as the equivalent of impedance measurements with microwaves. As in electrochemical impedance measurements, 

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Matsui, Y., Kamimoto, T., and Matsuoka, S., A Study on the Time and Space Resolved Measurement of Flame Temperature and Soot Concentration in a D.I. Diesel Engine by the Two-Color Method, SAE, 790491,1974. 

Figure 6. Scheme of microwave-electrochemical setup showing time-resolved, space-resolved and potential-dependent measurement techniques, as well as combinations of these. 

Figure 7 shows an example of a space-resolved microwave conductivity measurement of the semiconducting surface of a natural pyrite (FeS2) sample (from Murgul, Turkey). The overflow of the PMC signal (white color) was adjusted to a level that shows the patterns of distribution of low photoeffects (dark areas). Figure 8 shows a similar image in which,... 

Preliminary measurements with space-resolved PMC techniques have shown that PMC images can be obtained from nanostructured dye sensitization cells. They showed a chaotic distribution of PMC intensities that indicate that local inhomogeneities in the preparation of the nanostructured layer affect photoinduced electron injection. A comparison of photocurrent maps taken at different electrode potentials with corresponding PMC maps promises new insight into the function of this unconventional solar cell type. 

Figure 1.17 An experimental set-up for electron spectrometry with synchrotron radiation which is well suited to angle-resolved measurements. A double-sector analyser and a monitor analyser are placed in a plane perpendicular to the direction of the photon beam and view the source volume Q. The double-sector analyser can be rotated around the direction of the photon beam thus changing the angle between the setting of the analyser and the electric field vector of linearly polarized incident photons. In this way an angle-dependent intensity as described by equ. (1.55a) can be recorded. The monitor analyser is at a fixed position in space and is used to provide a reference signal against which the signals from the rotatable analyser can be normalized. For all three analysers the trajectories of accepted electrons are indicated by the black areas which go from the source volume Q to the respective channeltron detectors. Reprinted from Nucl. Instr. Meth., A260, Derenbach et al, 258 (1987) with kind permission of Elsevier Science—NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands.

Table II Space- and Time-Resolved Measurements from Inelastic Light Scattering. All methods are suitable for nonequilibrium conditions. Here, RS refers to Raman scattering, CARS to coherent anti-Stokes Raman spectroscopy, and RIKES to Raman-induced Kerr effect.

The interaction of an ultrahigh-intensity laser with a dense plasma is of wide interest, as these lasers open up new horizons for research, such as fs X-ray radiation probing [1,2], energetic particle acceleration [3], and inertial confinement fusion [4,5]. A new spectroscopic method that provides the kind of time- and space-resolved information required to obtain a more quantitative understanding of energy deposition than that provided by particle measurements has been under development [5-8]. Because of the relatively low temperatures that can be accessed with current lasers, conventional K-shell line spectroscopy using near-fully ionized plasma is not suitable. 

Figure 12.13 illustrates a versatile experimental set-up for microwave conductivity measurements with the microwave source (8 0 GHz), a circulator and a detector, which monitors the microwave energy reflected from the electrochemical or photovoltaic cell. The cell and electrode geometries are designed in such a way that the microwave power can reach the energy-converting interface (losses in metal contacts or aqueous electrolyte should be minimised). Depending on the experimental conditions, time-resolved, space-resolved or potential-dependent measurements are possible as well as combinations (for further details, see Schlichthbrl and Tributsch, 1992 Wiinsch et al., 1996 Chaparro and Tributsch, 1997 Tributsch, 1999). 

The manner in which protons diffuse is a reflection of the physical properties of the environment, the geometry of the diffusion space, and the chemical composition of the surface that defines the reaction space. The biomembrane, with heterogeneous surface composition and dielectric discontinuity normal to the surface, markedly alters the dynamics of proton transfer reactions that proceed close to its surface. Time-resolved measurements of fast, diffusion-controlled reactions of protons with chromophores and fluorophores allow us to gauge the physical, chemical, and geometric characteristics of thin water layers enclosed between phospholipid membranes. Combination of the experimental methodology and the mathematical formalism for analysis renders this procedure an accurate tool for evaluating the properties of the special environment of the water-membrane interface, where the proton-coupled energy transformation takes place. 

Current investigations are directed toward full-field measurement techniques and direct numerical simulation (DNS). The numerical approaches are limited by the need for much bigger and better computers. Previously, visual observations were used for qualitative assessment. Hot-wire/film and LDA measurements were used to provide the hard numbers for a few points in space in the time domain. Today, the visual-based techniques are being extended to allow full-field, time-resolved velocity vector information to be obtained. However, the need for full-field and time-resolved measurements put vast restrictions on what can be accomplished. To get time-resolved results, often today, we must sacrifice resolution. To get resolution, we must sacrifice the dynamics. Ultimately we want both. 

There are numerous additional reasons for measuring tune-resolved fluorescence. In the presence of eneigy transfer, the intensity decays reveal how acc tors are distributed in space around the donors. Time>resolved measurements reveal whether quenching is due to diffusion or to complex formatioD with the ground-state fluoro-phores. In Huorescence, much of the molecular informaticMi content is availaHe only from time-resolved measurements. 

Figure 10.1 Layout of the experimental procedure used for measuring time- and space-resolved Raman spectra on bisected AI2O3 catalyst bodies after impregnation with an aqueous ammonium...

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