Photodynamic inactivation is a method widely used to eliminate pathogen micro-organisms. This involves the application of different wavelengths and sources. The ai m of this work is to evaluate the inactivation effect of red light on Escherichia coli applying continuous and partial exposures, and compare with the effect produced by a less used radiation: UVA. We measured survival curves by spectrophotometry and obtained cell cultures. Our results show that red light applied together with methylene blue in continuous and interrupted exposures has not inactivation effect on E. coli. However, UVA radiation applied without photosintetizer exhibits a delay in the first phase of replication process with similar consequences on exponential and stationary phases. It is interesting to explore in the future the use of different compounds which could enhance the effect of UVA radiation.
In this paper we analyze the influence of a spatial migration of the excited states on suppression of the population
gratings recorded in erbium-doped optical fibers (EDF). Such dynamic Bragg gratings are formed via saturation of the
optical transition between the fundamental and the meta-stable states of the active ions and are observed experimentally
via transient two wave mixing (TWM) of the phase-modulated counter-propagating recording waves. The reported
experiments were performed in the spectral range 1492-1568nm, which covers the absorption region of the fundamental
transition 4I15/2→4I13/2 of Er3+ ions. Significantly stronger grating suppression is observed at the central/long-wavelength
regions of the above-mentioned spectral region. A set of similar fibers with essentially different Er3+ ions concentrations
with maximum attenuation of 4, 9, 17 and 35 ± 1 dB/m at 1531 nm was investigated and a clear concentration
dependence of the grating suppression was observed. The TWM measurements are supported by the original
experimental data on the fluorescence depolarization. The observed spectral dependence of the grating reduction factor is
explained using the model of the vacant states limited spatial migration of the excitation among the Er3+ ions.
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