Dual pulse excitation

Control of the Energy Transfer Pathway by Dual Pulse Excitation. 94... 

Fiickel B, Hinze G, Nolde F, Miillen K, Basche T (2009) Control of the electronic excitation energy transfer pathway between two single fluorophores by dual pulse excitation. Phys Rev Lett 103 103003... 

Figure 2 Transient curve of thermai iens signal (A) singlebeam system using CW iaser (B) duai-beam system using CW exciting laser (C) dual-beam system using pulsed exciting laser.

Hydrogen transfer in excited electronic states is being intensively studied with time-resolved spectroscopy. A typical scheme of electronic terms is shown in fig. 46. A vertical optical transition, induced by a picosecond laser pulse, populates the initial well of the excited Si state. The reverse optical transition, observed as the fluorescence band Fj, is accompanied by proton transfer to the second well with lower energy. This transfer is registered as the appearance of another fluorescence band, F2, with a large anti-Stokes shift. The rate constant is inferred from the time dependence of the relative intensities of these bands in dual fluorescence. The experimental data obtained by this method have been reviewed by Barbara et al. [1989]. We only quote the example of hydrogen transfer in the excited state of... 

The imaging of conversion within the fixed bed was achieved by using a distortionless enhancement by polarization transfer (DEPT) spectroscopy pulse sequence integrated into an imaging sequence, as shown in Fig. 44. In theory, a signal enhancement of up to a factor of 4 (/hZ/c 7i is the gyromagnetic ratio of nucleus i) can be achieved with DEPT. In this dual resonance experiment, initial excitation is on the H channel. Consequently, the repetition time for the DEPT experiment is constrained by Tih (< T lc) where Tn is the Ty relaxation time of... 

SM-FRET experiments are typically performed by using a dual-channel detection scheme. More specifically, one photo-excites the donor with CW radiation or a train of pulses, while simultaneously detecting the fluorescence photons from the donor and acceptor in a selective manner. The fraction of photons detected in the acceptor channel, over a given time averaging window of length Tw, provides a direct measure of the time-averaged FRET efficiency, which we will denote by E(Tw)- One may then define a time-averaged and TV-dependent donor-acceptor distance, which will be denoted by R)tw, such that... 

The deconvolution procedure has been validated for triple exponential fits using synthetic test data. Confidence in the procedure is also enhanced by the high signal to noise ratio obtainable with pulsed laser excitation. It should be noted that dual exponential decay would be anticipated on the basis of Scheme 1. 

Transmit-receive surface coils are generally used for MR spectroscopic studies in organs other than the brain. If dual-frequency techniques such as NOE, polarization transfer, or decoupling are to be utilized with surface coil excitation, or if relaxation time measurements are to be performed, RF pulses that are insensitive to spatial and amplitude... 

Two studies have examined the role of detection methods in the reliability of detection of brain metabolites in humans. A study has been carried out on the reproducibility of H NMR data obtained using spectroscopic imaging in the human brain. A PRESS-based pulse sequence with dual-band RF pulses was used to excite the resonances of Cho, creatine plus phosphocreatine (tCr) and NAA while simultaneously suppressing water and lipids. Spiral k-space trajectories were used for fast spectral and spatial encoding of 1 cm voxels throughout the brain. Automated quantification of the spectrum of each... 

Another most exciting new tool for the analysis of complex polyolefins is the direct coupling of high-temperature liquid chromatography and H-NMR. Such equipment became available only recently when a high-temperature flow-through NMR probe was introduced by Bruker. The construction and experimental setup of the LC-NMR coupling is described in detail by Hiller et al. [130]. In brief, the NMR flow probe can operate at temperatures up to 150°C. The probe has an active flow cell with a volume of 120 pL. It is a dual inverse H/ C probe with pulse field... 

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