Light time-resolved

E. Soini, Pulsed light, time-resolved fluorometric immunoassay, in Monocolonal Antibodies and New Trends in Immunoassays (Ch. A. Bixollon, ed.) pp. 197-208, Elsevier Science Publishers, Amsterdam (1984). 

R. P Ekins and S. Dakubu, The development of high-sensitivity pulsed-light, time-resolved fluoroimmunoassays. Pure Ap. Chem., 57 473-482 (1985). 

Morita N and Yajima T 1984 Ultrafast-time-resolved coherent transient spectroscopy with incoherent light Rhys. Rev. A 30 2525-36... 

Ulness D J and Albrecht A C 1997 A theory of time resolved coherent Raman scattering with spectrally tailored noisy light J. Raman Spectrosc. 28 571-8... 

An interferometric method was first used by Porter and Topp [1, 92] to perfonn a time-resolved absorption experiment with a -switched ruby laser in the 1960s. The nonlinear crystal in the autocorrelation apparatus shown in figure B2.T2 is replaced by an absorbing sample, and then tlie transmission of the variably delayed pulse of light is measured as a fiinction of the delay This approach is known today as a pump-probe experiment the first pulse to arrive at the sample transfers (pumps) molecules to an excited energy level and the delayed pulse probes the population (and, possibly, the coherence) so prepared as a fiinction of time. 

So far we have exclusively discussed time-resolved absorption spectroscopy with visible femtosecond pulses. It has become recently feasible to perfomi time-resolved spectroscopy with femtosecond IR pulses. Flochstrasser and co-workers [M, 150. 151. 152. 153. 154. 155. 156 and 157] have worked out methods to employ IR pulses to monitor chemical reactions following electronic excitation by visible pump pulses these methods were applied in work on the light-initiated charge-transfer reactions that occur in the photosynthetic reaction centre [156. 157] and on the excited-state isomerization of tlie retinal pigment in bacteriorhodopsin [155]. Walker and co-workers [158] have recently used femtosecond IR spectroscopy to study vibrational dynamics associated with intramolecular charge transfer these studies are complementary to those perfomied by Barbara and co-workers [159. 160], in which ground-state RISRS wavepackets were monitored using a dynamic-absorption technique with visible pulses. 

In time-resolved fluorescence, rare earths are frequently used as fluorescent labels. The fluorophores have large Stokes shifts, ie, shifts of the emitted light to a higher wavelength relative to the absorption wavelength, and comparatively long decay times, approximately 0.5 ms. This simplifies the optical... 

In many respects the time-resolved pump-probe technique is similar to the CW counterpart. The use of pulsed laser light permits direct probing of both the magnitude of the PA and its dynamics. The experimental arrangement is practically the same as for the CW version, i.e., both pump and probe beams are focused and overlapped onto same spot on a sample. In addition, the pump and probe pulses are synchronized so that the lime interval t between them is constant and confined to a certain time range (in our case up to 3 ns). 

With this expression, kjkn can be obtained by the measurement of one set of [RI ], [R2 ] values, at full light intensity only. As to kii itself, which is needed to evaluate kc, one must either do a separate experiment by time-resolved EPR spectroscopy (see Chapter 11) or, with less accuracy and reliability, one can assign it the value for the diffusion-controlled rate constant in that solvent. 

BURNS c s, HEYERICK A, KEUKELEiRE D D and FOBES M D E (2001) Mechanism for formation of the light struck flavour in beer revealed by time-resolved electron paramagnetic resonance, Chem Eur J, 7, 4554-61. 

Nagahara, T., Imura, K. and Okamoto, H. (2004) Time-resolved scanning near-field optical microscopy with supercontinuum light pulses generated in microstructure fiber. Rev. Sci. Instrum., 75, 4528-4533. 

In addition to the fourth-order response field Tfourth, the probe light generates two SH fields of the same frequency 211, the pump-free SH field Eq(2 Q), and the pump-induced non-modulated SH field non(td> 211). The ground-state population is reduced by the pump irradiation and the SH field is thereby weakened. The latter term non(td, 211) is a virtual electric field to represent the weakened SH field. Time-resolved second harmonic generation (TRSHG) has been applied to observe E on (td, 211) with a picosecond time resolution [20-25]. The fourth-order field interferes with the two SH fields to be detected in a heterodyned form. 

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