Indirect laser-induced change

The time range of the electrochemical measurements has been decreased considerably by using more powerful -> potentiostats, circuitry, -> microelectrodes, etc. by pulse techniques, fast -> cyclic voltammetry, -> scanning electrochemical microscopy the 10-6-10-1° s range has become available [iv,v]. The electrochemical techniques have been combined with spectroscopic ones (see -> spectroelectrochemistry) which have successfully been applied for relaxation studies [vi]. For the study of the rate of heterogeneous -> electron transfer processes the ILIT (Indirect Laser Induced Temperature) method has been developed [vi]. It applies a small temperature perturbation, e.g., of 5 K, and the change of the open-circuit potential is followed during the relaxation period. By this method a response function of the order of 1-10 ns has been achieved. 

An adaptation of the temperature-jump method, named indirect laser-induced temperature jump [29], was used in studies of distance dependence of electron transfer at electrodes. A pulsed Nd YAG laser was used to cause a sudden (<5 ns) change in temperature (<5 K) at an electrode/electrolyte interface. The increase in temperature causes a change in the open-circuit potential. The relaxation step is a function of the dissipation of thermal energy and the rate of electron transfer between the electrode and its redox partners. 

All techniques of saturation spectroscopy discussed so far monitor directly some change in the probe beam. For this reason, they work best with samples of non-negligible absorption. For very weakly absorbing samples, it is often advantageous to detect the absorption of light in the sample indirectly, for instance by observing the laser-induced fluorescence. 

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