Phenanthrenequinone (PQ) doped poly(methyl methacrylate) (PMMA) photopolymer material has been studied
extensively due to the growing interest in application involving photopolymers. However, to progress the development
a more physical material model has become necessary. In this article, a kinetic model is developed, which includes: (i)
the time varying photon absorption, including the absorptivity of a second absorber, i.e., the singlet excited state of PQ,
(ii) the recovery/regeneration and the bleaching of the excited state PQ, (iii) the nonlocal effect, and (iv) the diffusion
effects of both the ground and excited state PQ molecules and of the methyl methacrylate (MMA). A set of rate
equations are derived, governing the temporal and spatial variations of each chemical component concentration. The
validity of the proposed model is examined by applying it to fit experimental data for PQ-PMMA layers containing three
different initial PQ concentrations, i.e., 1 mol.%, 2 mol.% and 3 mol.%. The effect of different exposure intensities is
also examined. Material parameters are extracted by numerically fitting experimentally measure normalized
transmission curves and the refractive index modulation growth curve using the theoretical models.
Phenanthreneauinone (<i>PQ</i>) doped poly(methyl methacrylate) (<i>PMMA</i>) photopoplymer material has been actively investigated in the literature. Based on the previously developed NPDD model and the analysis of the mechanisms, the behavior of the material is being further studied. The first harmonic refractive index modulation has been examined for both long time post-exposure and under thermal treatment. Twelve and four spatial concentration harmonics in the Fourier series expansions are applied respectively for comparison. Several effects, i.e., the non-local effect, the diffusion of both the ground state and excited states <i>PQ</i> molecules, which occur during and post-exposure in <i>PQ-PMMA</i> photopolymer materials, have been studied under thermal treatment. For long time post-exposure or when the heating treatment is applied, the formation of the photoproduct, <i>PQ/PMMA</i>, has become very important. The effects of nonlocality, diffusion and the different exposing intensities on the distribution of <i>PQ/PMMA</i> over space and higher harmonic <i>PQ/PMMA</i> concentration have been shown. The experimental results are presented, where no thermal treatment is applied.
The paper presents theoretical and experimental investigations of light beam self-trapping in a photorefractive
medium based on Plexiglas (polymethylmethacrylate, PMMA) with photosensitive phenanthrenequinone (PQ)-
molecules. It is shown that the self-trapping of a laser beam is generated due to the self-interaction of the propagating
light wave under the conditions of a well balanced concurrence of the effects of light diffraction and nonlinear focusing.
A new method for controlling the waveguide cross-section by changing the ratio of two competing mechanisms of the
nonlinear refractive-index variation (namely the formation of the photoproducts and the heating of the medium while
varying the power of the light beam) is proposed.
The recording of self-trapping structures implemented in PQ-PMMA layers has been realized with two laser sources
(405 nm and 514.5 nm) with an average power of several mW. It is shown that the photoattachment of the PQ-molecules
to the polymeric chains and the formation of the photoproduct play the decisive role for the light-induced increase of the
refractive index. Besides, the formation of the waveguide is strongly influenced by heating of the medium, which results
in an additional thermal defocusing of the light beam.
It has been established that the parameters of the waveguide (cross-section and length) are strongly dependent on the
wavelength and the power of the laser radiation, as well as on the concentration of the PQ-molecules. Waveguiding
structures with a diameter of 100 μm were recorded in samples with a high PQ-concentration (up to 4 mol.%) for the
wavelength of 514.5 nm. Reducing the dye-concentration by one order requires shorter (blue) wavelengths (405 nm).
The dependence of the waveguide parameters and the optimal laser wavelength on the concentration of PQ-molecules is
confirmed by the numerical calculation including a 3D-model of the light self-trapping.