{'fraction_non_alphanumeric': 0.025069637883008356, 'fraction_numerical': 0.016713091922005572, 'mean_word_length': 4.923076923076923, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Use Of Picosecond Lasers In Measuring Ultrafast Molecular Processes

Picosecond lasers can be used to observe the kinetics of two rapid processes in solution: relaxation of excited molecules prior to Stokes-shifted fluorescence and relaxation of oriented molecules. Experimentally, the measurements are similar. An ultrafast shutter driven by a picosecond pulse and an optical multichannel analyzer (OMA) enable the rise of fluorescence to be observed during a single, picosecond exciting pulse. For excitation at 355 nm risetimes are: 4.2 ± 2.2 psec for esculin, 1.0 ± 2.2 psec for dimethyl POPOP, and 5.3 ± 2.2 psec for tetraphenylbutadiene. The shutter is an optical Kerr cell in which an intense pulse induces birefringence by orienting the molecules in the liquid. As orientational relaxation occurs, birefringence decays. Using the OMA to observe a scattered picosecond pulse through the shutter enables the decay to be measured in a single shot. Rotational relaxation times for pure liquids and mixtures vary from 2 psec for carbon disulfide to 21 psec for nitrobenzene.