Subpicosecond Intensity Decays

As the intensity decays become shorter, the measurements become more complex than TCSPC This may be illustrated by the intensity decays of Nile Blue in aniline. 

Dimethylaniline (DMA) quenches Nile Blue by an elec-tron-transftf process, which in neat DMA occurs on a picosecond timescale.  

Intensity decays were recorded by the upamvoaon method (Hgure 4.47). The excitation source was a special R6G dye laser which xx Wded 70-fs pulses near 600 nm. The width of the instrument re tmse function was less than 1 ps. Emission was detected by mixing the emission with a longer-wavelength dye laser poise and detecting the harmonics. The intensity decay was obtained by scanning the time dday of tiie probe pulse. The inten ty decay contained components from 0-47 to 5.2 ps. Such time resolution on the subpicosecond timescale is not available from TCSPC. 

Rgure4.47. Inlensay decay of Nik Blue In aniline measured streak cainen. The dec has components of 470 ft. 1.8 ps, and 5.2 ps. Revised from Ref. 188. 

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The dynamics of the SHL intensity after subpicosecond UV laser excitation of RuC18B LB films is shown in Figure 32[115,116]. The SHL intensity decreased to 70 % of its initial value upon excitation and returned to almost the initial value within several hundred picoseconds as shown by a bold line. The fluorescence decay of RuC18B LB films measured by the single photon-counting... 

The nature of the excitation has a profound influence on the subsequent relaxation of molecular Uquid systems, as the molecular dynamics simulations show. This influence can be exerted at field-on equiUbrium and in decay transients (the deexdtation effect). GrigoUni has shown that the effect of high-intensity excitation is to slow the time decay of the envelope of such oscillatory functions as the angular velocity autocorrelation function. The effect of high-intensity pulses is the same as that of ultrafast (subpicosecond laser) pulses. The computer simulation by Abbot and Oxtoby shows that... 

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