Multibeam irradiation

PHOTOCHEMISTRY OF SHORT-LIVED SPECIES USING MULTIBEAM IRRADIATION... 

By combination of these pulse techniques (multibeam irradiation), multistep excitation of intermediates can be achieved. For example, laser excitation of an intermediate generated during pulse radiolysis can be realized. For years, chemistry based on multibeam irradiation methods has been investigated [3], There are several advantages for the multibeam irradiation method. 

Second, it should be pointed out that yield and selectivity of these photoin-duced processes caused by the multibeam irradiation depend largely on the delay time of the second beam irradiation with respect to the first beam. Because an intermediate generated by the first beam excitation has a finite lifetime, concentration of the targeted intermediate depends on the delay time of the second laser irradiation after the first beam excitation. That is, chemical reaction induced by the multibeam irradiation is a time-selective process (Fig. 2.3). This feature is... 

Third, since a chemical reaction induced by multibeam irradiation only proceeds at the position where both beams overlap, a chemical process induced by multibeam irradiation is a site-selective process. This third advantage is important in photodynamic therapy, in which damage to healthy cells must be avoided. One of the most advanced techniques is to perform selective damage of cancer tissues deep beneath the skin surface (Fig. 2.4). Molecular memory is also possible when taking this feature into account. Because various reactive... 

In this chapter, we summarize recent progress in the photochemistry of shortlived species by use of multibeam excitation, including our recent achievements in this field. Our research group has employed various multibeam irradiation methods to reveal reaction processes of various excited intermediates, including basic molecules and biomolecules. We also achieved direct observation of shortlived species utilizing ultrashort pulse lasers. These results are interesting recent examples of reactions induced by multibeam irradiation. Based on the excitation method, this chapter is divided into the following sections Pulse Radiolysis-Laser Flash Photolysis (Section II), Two-Color Two-Laser Flash Photolysis (Section III), and Three-Color Three-Laser Flash Photolysis (Section IV). Each section is further divided into subsections based on the topics. 

Combination of pulse lasers can be achieved rather easily by using delay circuits as indicated earlier. We have already reported the studies using three-color three-laser photolysis. In this section we briefly introduce the results to show the availability of the multibeam irradiation method. 

In this chapter, several examples of photochemistry of short-lived species by multibeam irradiation are introduced. In many cases, the properties of excited intermediates have been investigated by using nanosecond lasers. Since the lifetime of excited intermediates is usually quite short, investigations employing ultrashort laser pulses are intrinsically important. Various properties estimated by the direct manner will appear in the near future. Recent progress of ultrashort pulse lasers and detection systems will make this possible. On the other hand, utilization of multiple excitations is not limited to the basic study of excited intermediates. These are applicable to biological and environmental fields. Further fruitful results are expected for these explorations. 

Photochemistry of Short-Lived Species Using Multibeam Irradiation... 

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