Within the framework of laboratory research, conventional laser spectroscopic studies on the ultrafast time scale employ the concept of pump-probe spectroscopy. In this general setup, two separate femto- or picosecond optical pulses are required: one to excite (“pump”) the sample of interest, and another to interrogate (“probe”) the deexcitation of the sample, both of which are required to overlap both spatially and temporally. An optical delay line can effectively lengthen the path the probe pulse takes, thereby temporally delaying it with respect to the pump pulse. As the pump pulse excites the molecule, the increasingly delayed probe pulse monitors the decay of the excited electrons. From this, dynamic, time-resolved data for the sample of interest can be obtained and analyzed. Pump-probe spectroscopy is used, most typically, to monitor the recovery of saturable absorbers after photoinduced excitation, to measure the temporal signatures of chemical reactions, or the transfer of energy from one molecule to another. This information may then guide further design, synthesis, and implementation of studied materials for a wide variety of applications, including but not limited to: photocatalysis, photoelectrochemistry, and photovoltaics. The main industries utilizing pump-probe spectroscopic technology are academia, aerospace, metallurgical, biophotonics, microscopy and medicine. The efficiency of solar cell materials, as an example, may be determined by such pump-probe techniques through monitoring crucial excitation recombination dynamics, or the charge carrier recombination efficiency of water hydrolysis materials to generate clean-burning hydrogen fuel.
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