Shifted excitation

There is no easy understanding of the spectral properties of these compounds in general, which may or may not have a built-in chromophoric system responsible for a long-wavelength absorption like 7,8-dihydropteridin-4-one or a blue-shifted excitation like its 5,6-dihydro isomer. More important than the simple dihydropteridine model substances are the dihydropterins and dihydrolumazines, which are naturally occurring pteridine derivatives and reactive intermediates in redox reactions. 

Delagrave S, Flawtin RE, Silva CM, Yang MM, Youvan DC (1995) Red-shifted excitation mutants of the green fluorescent protein. Biotechnology (NY) 13 151-154... 

Cyan fluorescent proteins (CFPs) have blue-shifted excitation and emission spectra, because of the mutation Tyr66Trp inside the chromophore (Fig. 5.3C) [34], CFP fluorescence (Ex 435 nm/Em 474 nm) is less blue-shifted than for EBFP and CFP excitation is intermediate to the excitation of the neutral and anionic chromo-phores of avGFP [4], CFPs are widely used for dual-color imaging and FRET applications together with yellow fluorescent proteins (YFP, Section 3.6). 

Mitra, R. D., Silva, C. M. and Youvan, D. C. (1996). Fluorescence resonance energy transfer between blue-emitting and red-shifted excitation derivatives of the green fluorescent protein. Gene 173, 13-7. 

In spite of the frequency-shifted excitation, the quantized PIP inevitably excites multiple sidebands located at n/At ( = 1, 2,...) from the centre band. An attempt was made16 to calculate the excitation profile of multiple bands created by a PIP of a constant RF field strength, using an approximate method based on the Fourier analysis. The accuracy of the method relies partly on the linear response of the spin system, which is, unfortunately, not true in most cases except for a small angle excitation. In addition, the spins inside a magnet consitute a quantum system, which is sensitive not only to the strengths but also to the phases of the RF fields. Any classical description is doomed to failure if the quantum nature of the spin system emerges. 

The idea of using the linear phase increments to achieve frequency-shifted excitation can be adopted almost to any pulses, such as hard (amplitude fixed) pulses, shaped pulses, and even adiabatic inversion pulses. Unlike any other pulses, the adiabatic pulses have already used non-linear phase increments for tilting the effective RF field slowly compared with the Larmor frequency of the spins in the rotating frame in order to fulfill the adiabatic condition. 

The centre band RF field of a PIP is usually used to achieve a frequency-shifted excitation while preserving the phase coherence among the RF pulses applied before and after the PIP. The phase coherence in RF pulses is crucial in some of the multidimensional NMR experiments, especially in the 13C dimension where the 13CO and 13C need to be excited separately. Unpredictable results may occur if the phase coherence in RF pulses fails in some NMR experiments. 

The idea of using phase increment to achieve frequency-shifted excitation can be extended virtually to any sort of RF pulses, including the most complicated adiabatic inversion pulses where a non-linear phase increment has already been applied. Using the phase increment, double or multiple pulses can be constructed with only a single waveform generator in order to excite different regions of a NMR spectrum or to compensate the BSFS, BSPS, as well as BSOS. 

Of the five probes evaluated only Probes 1, 3, and 5 were worth evaluating in detail, as the others had small Stokes shift (excitation wavelength, /v, minus emission wavelength, /Vln) or no detectable emission. Fluorescence behavior was measured using a Zeiss LSM 510 Laser Scanning Confocal Microscope (LSCM) and an Ocean Optics USB2000 spectrometer. 

Shifted excitation Raman difference spectroscopy (SERDS) One way to remove the fluorescent background in traditional Raman Spectroscopy is to take advantage of the shift response of the Raman Effect to excitation wavelength shifts. In SERDS, two spectra of a sample are acquired with slightly different excitation wavelengths, and are then subtracted to estimate the Raman spectrum of a sample. This difference will impact the Raman spectra where the entire spectrum will shift in energy by the amount of excitation shift [16]. 

Fluorescence is commonly regarded as a major problem in the use of Raman spectroscopy and indeed fluorescence of species in the samples of interest can mask the Raman signal of the analyte molecules. However it is often possible to choose a laser wavelength that avoids the problem or to use techniques such as shifted excitation Raman difference spectroscopy [24] or subtracted shifted Raman spectroscopy [25]. 

Optical gain 1-2, 4 in porous silicon 4 in silicone nanocrystals 2 Photoluminescence of porous silicon 3 Shifted-excitation-spot (SES) measurement 3 Stimulated emission 1-2 in silicon nanocrystals 2 Variable stripe length (VSL) technique 3... 

C. G. Xie and Y. Q. Li, "Cohfocal micro-Raman spectroscopy of single biological cells using optical trapping and shifted excitation difference techniques," Journal of Applied Ply sics, vol. 93, pp. 2982-2986, 2003. 

Maiwald, M., Schmidt, H., Sumpf, B., Erbert, G., Kronfeldt, H.-D., and Traenkle, G. (2009) Microsystem 671 nm light source for shifted excitation Raman difference spectroscopy. Appl. Opt., 48, 27R9-n92. 

Launikonis, B. S. Zhou, J. Royer, L. Shannon, T. R. Brum, G. Rios, E. Confocal imaging of [Ca ] in cellular organelles by SEER, shifted excitation and emission ratioing of fluorescence. J. Physiol. 2005, 567, 523-543. 

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