Sarin, a well-known chemical warfare agent, is toxic for concentrations as low as 0.03 ppm in the air (Immediately Dangerous to Life or Health value). A technology providing “on the field” detection could be fluorescence spectroscopy. This presentation shows a sensitive method for the detection of Diethyl Chlorophosphate (DCP), a Sarin surrogate, which provides in a few seconds a turn-off fluorescence response of the sensor for ppb levels of DCP. For instance, a I/I0 = 0.68 (fluorescence quenching) was obtained when the sensor was exposed to 16 ppb of DCP.
For 50 years, it was assumed that unlike liquid scintillators or organic crystals, plastic scintillators were not able to discriminate fast neutrons from gamma. In this work, we will demonstrate that triplet-triplet annihilations (which are responsible of n/γ discrimination) can occur even in plastic scintillators, following certain conditions. Thus, the presentation will deal with the chemical preparation, the characterization and the comparison of n/γ pulse shape discrimination of various plastic scintillators. To this aim, scale-up of the process allowed us to prepare a Ø 100 mm × ≈ 110 mm thick.
Azo-polymers have been the subject of a growing interest since the first demonstration of reversible birefringence and
dichroism effects induced optically at room temperature in such materials. It is well established that the mechanisms
involved are related to a molecular reorientation following photo induced trans-cis-trans isomerization of the
chromophores.
The interest for such materials has been strengthened with the more recent demonstration that the photo-isomerization
mechanisms can be employed to induce controlled topographic modifications. A simple example is the induction of a
sinusoidal modulation of the film surface by the irradiation with an interference pattern between two laser beams. Such a
simple step technique appears thus as a simple tool towards realisation of photonic devices.
However, if the realisation of gratings with periods in the visible wavelength scale is widely investigated, a strong
decrease of the patterning efficiency is observed in the case of periods below 400nm, limiting then the potential of the
technique.
In order to circumvent this problem we have developed a new azo-polymer presenting an absorption band shifted to the
Ultra Violet (UV) region of the spectrum. The possibility to induce gratings with periods down to 200nm with UV
irradiation is evidenced. Optical geometries of excitation have been implemented to optimise the modulation efficiencies.
As a potential application of the material investigated, the realisation of a polymer micro laser based on a distributed
feedback scheme is demonstrated.
We have investigated properties of poly(9-vinylcarbazole) (PVK) doped with 30% wt 4-dibutylamino-4'-nitrostilbene
(DBANS), depending on orientation of the polar DBANS molecules. Appearance of the orientation-induced built-in
electric field was proven optically by the solid electric field induced second harmonic generation and electrically by the
current-voltage characterization. Modification of optical properties was evidenced by the spectral dependencies of the
absorption coefficient. The thermally stimulated current spectra had demonstrated that carrier transport and trapping are
affected, too.
In a classical multilayer organic light emitting diode (OLED) structure, almost 80% of the light emitted happens to be lost following guiding through the different layers. Patterning of the OLEDs structure was already proposed and reported as an interesting solution towards the optimization of an OLED external efficiency. As an alternative to classical lithographic patterning methods which appear to be quite complex, we propose here the implementation of a quite direct and easy-to-set light-induced patterning method using azo-dye polymers. When a polymer film containing azobenzene dyes is irradiated by an interference pattern between polarized laser beams at a wavelength near the chromophore absorption band, the film surface undergoes a direct, reversible and controlled topographic modification. More surprisingly, we have recently experimentally evidenced that uniform irradiation of an azo-dye polymer using a single laser beam with normal incidence onto the polymer film surface could lead to a self structuration process resulting in the formation of a quasi hexagonal surface-relief grating. After a description of the main features related to light-induced surface relief gratings, we show here that this original patterning process offers an interesting solution for control and optimisation of optoelectronic devices such as OLEDs. The guiding properties of both 1D and 2D structures have been studied and their effects on the light emission properties of a patterned electroluminescent polymer have been characterized and compared after angle dependent measurement of the photoluminescence spectrum. Quite efficient decoupling is evidenced.
It is now well established that, in azo-dye polymers repeated trans-cis-trans isomerization cycles induces molecular reorientation leading to quasi-permanent birefringence and dichroism. More recently, it has been shown that irradiation of an azo-polymer thin film with an interference pattern between polarized laser beams can lead to a direct and reversible topographic modification of the polymer film surface resulting in the induction of surface relief gratings in conjunction with the light interference pattern. Here, we provide experimental evidence of an original spontaneous light-assisted submicrometer patterning process. We show that uniform irradiation of an azo-dye polymer using a single collimated laser beam with normal incidence leads to the formation of organized hexagonal patterns. These structures geometry depends on the laser beam polarization : their period is about the irradiation wavelength and their modulation amplitude can reach one hundred nanometers. Possible origin of such process is discussed. Although showing similar features with models or experiments already described in the literature, the origin of light-assisted spontaneous patterning in azo-polymers is still unclear and further complementary investigations are needed. Indeed, accurate determination of the relevant parameters at the origin of such process should enable a full control of the process together with further possible generation of more complex structures.
We present a study of Distributed Feedback laser emission in various polymer materials. This laser scheme permits efficient control of the stimulated emission in dye doped polymer materials. Optical feedback is provided by distributed Bragg gratings formed in the film by interference patterns from the pump beam. We demonstrate broad tunability of laser emission in polymeric waveguides doped with stilbenoid, phenylene vinylene and oligomers of phenyl ethynylene used for OLEDs. Laser action was also obtained with Rhodamine 6G in PMMA deposited on surface relief grating and excited in a transverse single beam pumping geometry.
We present a study of Distributed Feedback laser emission in various polymer materials. This permits efficient control of the stimulated emission in dye doped polymer materials. Confinement and waveguiding effects are evidenced. We also propose a dynamical study of the effect using 4 wave mixing in the saturable absorption regime with stimulated emission.
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