Frequency domain photon

Frequency domain photon migration (FDPM) has been investigated as an optical technique with potential application to particle size analysis,67 albeit in a laboratory environment. The approach could be readily implemented in situ, with appropriate... 

Sun, Z. Torrance, S. McNeil-Watson, F.K. etal., Application of frequency domain photon migration to particle size analysis and monitoring of pharmaceutical powders Anal. Chem. 2003, 75, 1720-1725. 

Pan, T. 8t Sevick-Muraca, E.M., Volume of pharmaceutical powders probed by frequency-domain photon migration measurements of multiply scattered light Anal. Chem. 2002, 74, 4228M234. 

Sun, Z. Huang, Y. Sevick-Muraca, E.M., Precise analysis of frequency domain photon migration measurement for characterization of concentrated colloidal suspensions Rev. Sci. Instrum. 2002, 73, 383-393. 

A method for on-line monitoring of particle size distribution and volume fraction in real time using frequency domain photon migration measurements (FDPM) has been described. In FDPM the time dependence of the propagation of multiply scattered light provides measurement of particle size distribution and volume fraction. The technique has been applied to a polystyrene latex and a titanium dioxide sluny at volume concentrations in the range 0.3 to 1% [341]. 

NIR is not the only technology available for blend monitoring, Ught-induced fluorescence (LIF) [11] has also been used as has frequency domain photon migration (FDPM) [12, 13]. A second type of formulation process is wet granulation. In wet granulation a dry excipient blend is dosed with API and wetted under shear to form particles of known size, each of which contain the... 

The separation of absorption and scattering often requires specific types of instrumentation, based on the theoretical approach that is used. In this section, four main designs will be discussed integrating sphere-based reflectance and transmittance, spatially resolved spectroscopy, time-resolved spectroscopy, and frequency domain photon migration. 

Richter, S. M., Shinde, R. R., Balgi, G. V., Sevick-Muraca, E. M., Particle Sizing Using Frequency Domain Photon Migration, Part. Part. Sy r. Charact, 1998, 15,9-15. 

Photon noise is stochastic phenomena and has a white spectrum over the electronic frequency domain. 

Gratton, E., Breusegem, S., Sutin, J., Ruan, Q. and Barry, N. (2003). Fluorescence lifetime imaging for the two-photon microscope time-domain and frequency-domain methods. J. Biomed. Opt. 8, 381-90. 

Esposito, A., Gerritsen, H. C. and Wouters, F. S. (2007a). Optimizing frequency-domain fluorescence lifetime sensing for high-throughput applications photon economy and acquisition speed. J. Opt. Soc. Am. 24, 3261-73. 

As shown in Section 11.2.1.1, more details can be obtained by confocal fluorescence microscopy than by conventional fluorescence microscopy. In principle, the extension of conventional FLIM to confocal FLIM using either time- or frequency-domain methods is possible. However, the time-domain method based on singlephoton timing requires expensive lasers with high repetition rates to acquire an image in a reasonable time, because each pixel requires many photon events to generate a decay curve. In contrast, the frequency-domain method using an inexpensive CW laser coupled with an acoustooptic modulator is well suited to confocal FLIM. 

From the standpoint of time domain (e.g., time-correlated single photon counting) experiments the method of modelocking is not too crucial as long as the pulse jitter is modest (some picoseconds), and the pulse intensity doesn t vary too much if the time-to-amplitude converter is being started instead of stopped by the excitation pulse, it may be immaterial. From the standpoint of the frequency domain, however, the... 

At the present time, two methods are in common use for the determination of time-resolved anisotropy parameters—the single-photon counting or pulse method 55-56 and the frequency-domain or phase fluorometric methods. 57 59) These are described elsewhere in this series. Recently, both of these techniques have undergone considerable development, and there are a number of commercially available instruments which include analysis software. The question of which technique would be better for the study of membranes is therefore difficult to answer. Certainly, however, the multifrequency phase instruments are now fully comparable with the time-domain instruments, a situation which was not the case only a few years ago. Time-resolved measurements are generally rather more difficult to perform and may take considerably longer than the steady-state anisotropy measurements, and this should be borne in mind when samples are unstable or if information of kinetics is required. It is therefore important to evaluate the need to take such measurements in studies of membranes. Steady-state instruments are of course much less expensive, and considerable information can be extracted, although polarization optics are not usually supplied as standard. 

From a frequency domain point of view, a femtosecond pump-probe experiment, shown schematically in Fig. 1, is a sum of coherent two-photon transition amplitudes constrained by the pump and probe laser bandwidths. The measured signal is proportional to the population in the final state Tf) at the end of the two-pulse sequence. As these two-photon transitions are coherent, we must therefore add the transition amplitudes and then square in order to obtain the probability. As discussed below, the signal contains interferences between all degenerate two-photon transitions. When the time delay between the two laser fields is varied, the... 

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