Image excitation probability images

Visualization of the optical field is feasible by detecting the PL intensity while scanning the sample surface laterally. Optical images obtained in this way reflect the excitation probability at the tip position (we should note that the obsCTved image... 

Meanwhile, the excitation probability is proportional to the square of the laser flux, with virtually no excitation outside the laser focal volume. This enables precise spatial imaging in the biomedical field [67]. In this sense, silk scaffolds functionalized by two-photon materials will certainly have an unbeatable advantage in TPF bio-imaging. 

Room-temperature fluorescence (RTF) has been used to determine the emission characteristics of a wide variety of materials relative to the wavelengths of selected Fraunhofer lines in support of the Fraunhofer luminescence detector remote-sensing instrument. RTF techniques are now used in the compilation of excitation-emission-matrix (EEM) fluorescence "signatures" of materials. The spectral data are collected with a Perkin-Elraer MPF-44B Fluorescence Spectrometer interfaced to an Apple 11+ personal computer. EEM fluorescence data can be displayed as 3-D perspective plots, contour plots, or "color-contour" images. The integrated intensity for selected Fraunhofer lines can also be directly extracted from the EEM data rather than being collected with a separate procedure. Fluorescence, chemical, and mineralogical data will be statistically analyzed to determine the probable physical and/or chemical causes of the fluorescence. 

Values of the radiative rate constant fcr can be estimated from the transition probability. A suggested relationship14 57 is given in equation (25), where nt is the index of refraction of the medium, emission frequency, and gi/ga is the ratio of the degeneracies in the lower and upper states. It is assumed that the absorption and emission spectra are mirror-image-like and that excited state distortion is small. The basic theory is based on a field wave mechanical model whereby emission is stimulated by the dipole field of the molecule itself. Theory, however, has not so far been of much predictive or diagnostic value. 

Technically, the heterogeneity of skin and the presence of refractive index gradients likely impose some constraints to the accurate determination of imaging parameters. However, uncertainties in the determination of spatial resolution and axial location in transparent samples from which spectra are extracted, such as those described by Everall [21-23] and others [24, 25], are probably not important for highly opaque skin samples. We estimate the axial resolution to be 2-3 pm with the 785 nm excitation wavelength used in the current measurements. A study from this lab has suggested that errors in depth measurements are less than 15% which is probably adequate for most current purposes. 

The emission spectrum of a fluorophore is the image of its absorption spectrum when the probability of Si —> So transition is identical to that of So —> Si transition. If, however, excitation of the fluorophore leads to an So —> Sn transition, with n > 1, internal relaxation will occur so that molecules reach the first excited singlet state before emission. 

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