Nanosecond measurements

For times less than the transit time of the wave, the current is proportional to the stress at the input electrode in a linear approximation. For times greater than the wave transit time, the current is proportional to the stress difference between the electrodes. Thus, the thin-film nature of PVDF provides a means to measure stress differences, and, given mechanical tolerances that limit loading times to a few nanoseconds, measurements are difficult to... 

The superscripts, 1 and c, in Table I identify linear and circular polarised light respectively. Since the nanosecond measurements were dominated by molecular rotation in the dithiolene complexes, degenerate four wave mixing measurement were carried out using 100 ps pulses to measure the electronic contribution directly. 

The experimental set-up for femtosecond hyper-Rayleigh scattering is in essence identical to the one for the nanosecond experiments.9 Only the gated integrators for the nanosecond measurements are replaced by a chopper and a phase-sensitive detector in the high-frequency femtosecond experiment. 

Recombination rates range from 10 to 10 M s, with similar values obtained by nanosecond measurements, whereas photodissociation yields are low and range from 0.03 -0.08. These low yields have been interpreted in terms of rapid relaxation of the photoexcited six-coordinate complex competing with ligand release. Other five-coordinate complexes are also formed on picosecond photolysis for example, a protoheme dimethyl ester bis(t-butyl isocyanide) in pure t-butyl isocyanide or in toluene. This photolysis results in the loss of one isocyanide ligand to produce an electronically excited five-coordinate complex, which decays to the ground state within 40 ps. The recombination rate for the formation... 

Figure 3.45. Experimental and theoretical TP induced fluorescence excitation spectra (without (e) from the original Ref. [474]) for (a) compound 58b, (b) compound 78a, (c) compound 58c, (d) compound 78b, and (f) compound 78c. Experimental results (a) femtosecond measurements using fluorescein as standard ( ) nanosecond measurements using fluorescein as standard (o) nanosecond measurements using bis(methylstyryl)ben-zene as standard. Theoretical results solid line. (From Ref. [474] with permission of the American Chemical Society.)...

Figure C3.1.4(d) illustrates use of a pulsed xenon flashlamp probe source with a typical pulse width of several microseconds. This has the advantage of providing very high peak power for nanosecond measurements with high S/N, but low integrated intensity so that samples need not be exposed to excessive light from the probe source. For single-wavelength kinetic measurements, however, flashlamps have the disadvantage of being able to probe transient absorptions only for the duration of the flash, i.e., for microseconds or less.

The other coimnon way of measuring nanosecond lifetimes is the time-correlated single-photon counting... 

Typical singlet lifetimes are measured in nanoseconds while triplet lifetimes of organic molecules in rigid solutions are usually measured in milliseconds or even seconds. In liquid media where drfifiision is rapid the triplet states are usually quenched, often by tire nearly iibiqitoiis molecular oxygen. Because of that, phosphorescence is seldom observed in liquid solutions. In the spectroscopy of molecules the tenn fluorescence is now usually used to refer to emission from an excited singlet state and phosphorescence to emission from a triplet state, regardless of the actual lifetimes. 

Kummer S, Mais S and Basche T 1995 Measurement of optical dephasing of a single terrylene molecule with nanosecond time resolution J. Chem. Phys. 99 17 078-81... 

Figure C3.1.13. Experimentai configuration for far-UV nanosecond CD measurements using a frequency-upconverted Ti sapphire iaser as a probe source. Pj and P2 are Mgp2 Rochon poiarizers at cross orientations. SP is a strained transparent piate with about i ° of iinear birefringence for quasi-nuii eiiipsometric CD detection. Prism PMj and the iris Ij seiect the far-UV fourth hannonic of the argon iaser-pumped Ti-sapphire iaser s near-IR fundamentai output to probe the eiiipticity of the sampie. A second iaser beam at 532 nm is used to pump CD...

Lewis J W, Yee G G and Kliger D S 1987 Implementation of an optical multichannel analyzer controller for nanosecond flash photolysis measurements Rev. Sol. Instrum. 58 939-44... 

Lewis J W, Tilton R F, Einterz C M, Milder S J, Kuntz I D and Kliger D S 1985 New technique for measuring circular dichroism changes on a nanosecond time scale. Application to (carbonmonoxy)myoglobin and (carbonmonoxy)hemoglobin J. Rhys. Chem. 89 289-94... 

There are two common occasions when rapid measurement is preferable. The first is with ionization sources using laser desorption or radionuclides. A pulse of ions is produced in a very short interval of time, often of the order of a few nanoseconds. If the mass spectrometer takes 1 sec to attempt to scan the range of ions produced, then clearly there will be no ions left by the time the scan has completed more than a few nanoseconds (ion traps excluded). If a point ion detector were to be used for this type of pulsed ionization, then after the beginning of the scan no more ions would reach the collector because there would not be any left The array collector overcomes this difficulty by detecting the ions produced all at the same instant. 

Very Fast Kinetics. One nanosecond is by no means the limit for kinetic measurements. The state-of-the-art for direct, time-domain measurements Hes close to s (10 fs). At times shorter than a few nanoseconds, however, there is usually not a weU-stinred solution. Even usiag a... 

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