Time-delayed, two-color pulse laser

Time-Delayed, Two-Color Pulse Laser Photolysis... 

When cyclobutene 5 is irradiated with an XeCl excimer laser (308 nm), compounds 6 and 7 are formed (Scheme 3). It was revealed that 6 is formed by the excitation of the triplet state of 5 whereas 7 was formed from higher singlet states. The transient spectrum of 5 shows a triplet absorption maximum at 440 nm with its maximum intensity appearing 3.9 ps after the laser pulse. The time-delayed, two-color pulse laser photolysis technique using an XeCl and 440-nm laser pulses showed the increase in the ratio of the yields 6 7. 

The reaction shown in Scheme 12 was studied using the time-delayed, two-color pulse laser photolysis technique. An unstable o-quinodimethane derivative 42 is photochemicaUy generated from substituted indanone 41. The o-quinodimethane derivative 42 is further photolyzed to 43 and 44. In the case of simple 308-nm laser photolysis, the ratio of the yields 44 43 is 2.54, whereas the ratio changes to 3.93 when the time-delayed, two-color photolysis technique is used. In the two-color photolysis, the first laser used is a 308-nm laser pulse and the second is a 480-nm laser pulse that is irradiated 2 is after the first laser pulse. The wavelength of the second laser is adjusted to the absorption maximum of 42. 

Scheme 13 is another example of a time-delayed, two-color pulse laser photolysis. The unstable ketene 46 was generated by the first KrF laser pulse irradiation, which gave 47 by the addition of H2O. However, with successive 337-nm laser pulse irradiations, 50, 51, 53, and 54 are formed through the sequence of reactions shown in the scheme. The yields of 47, 50, 51, 53, and 54 were very dependent on the delay time of the two laser pulses. 

Time-delayed, two-color pulse laser photolysis is applied to the reaction of 55 (Scheme 14). An XeCl (308 nm) (first laser pulse) and an XeF (351 nm) (second laser pulse) excimer laser pulse are irradiated successively to 55 (X = Cl) with varying delay times.The result is shown in Figure 111.3. The horizontal... 

Figure 2.26. Three-color three-laser photolysis of l,8-(BPO-CH2)2Np (a, spectra b, time profiles detected at 345 nm) in Ar-saturated acetonitrile. The transient spectra observed during the irradiation of the 308-nm laser (at 500 ns after the laser pulse) (a), successive irradiation with the 308- and 430-nm lasers (at 300 ns after the second laser pulse delay time between the two lasers 200 ns) (b), successive irradiation of the 308- and 355-nm lasers (at 100 ns after the second laser pulse delay time between the two lasers 400 ns) (c), successive irradiation of the 308-, 430-, and 355-nm lasers (at 100 ns after the third laser pulse delay time between the lasers 200 and 200 ns) (d), and irradiation of the 355-nm laser (at 100 ns after the laser pulse) (e). The inset in (a) shows the spectra b — a (f) and d — c (g). In panel (b), 1, 2, and 3 refer to the irradiation sequence order of the 308-, 430-, and 355-nm lasers, respectively.

In the two-color experiments the pulses of the Tiisapphire laser (1.47 eV) were frequency-doubled by a 1 mm BBO crystal with a conversion efficiency of 15%. A dichroic mirror separated the fundamental from the second harmonic (2.94 eV). For convenience, a positive delay here means the pump beam is the second harmonic at 2.94 eV and the probe beam is the fundamental at 1.47 eV. For negative delay times the energies of the pump and probe pulses are interchanged. 

Upon absorption of an intense laser pulse by a solid sample, temperature is known to rise [112] however, the cooling time should be a microsecond-order event. In the present study, the authors eliminated the possibility of thermal effects contributing to the photo-coloration by simply splitting the laser pulse and delaying the two pulses by up to a few nanoseconds. In this case, the overall two-... 

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