Lensing effects in Q-switched unstable laser cavities with side-pumped Nd:YAG and ruby crystal rods

We present a comprehensive numerical model that accounts for non-uniform pumping and a related thermal and electronic lensing effects in Q-switched unstable laser cavities. We study the influence of these effects on the output beam profile in Nd:YAG and ruby laser systems with side-pumped crystal rods. We also constructed both lasers to experimentally validate the numerical results and found very good agreement. The results show that both types of lensing effects are particularly detrimental in ruby, while they are insignificant in Nd:YAG.     

Huge retardation of grating formation in holographic polymer-dispersed liquid crystals

Phototriggered kinetics is investigated in the dark for holographic polymer-dispersed liquid crystal gratings. Subsequently to holographic recording, the diffraction efficiency first slightly increases, then decreases, and afterwards starts to grow again. The remarkable growth continues for several days until the diffraction efficiency stabilizes at values several times larger than the initial ones. The initial increase is attributed to a dark polymerization reaction as confirmed by electron paramagnetic resonance spectroscopy. The slow process is associated with the kinetics of a phase-separation mechanism. The non-monotonic behaviour of the diffraction efficiency is explained by superposition of refractive-index and extinction modulations. PACS 42.40.Ht; 61.30.Pq; 42.70.Df; 64.70.Md     

Enhancement of second harmonic generation in helical Sc liquid crystals

In a ferroelectric liquid crystal, a special type of phase-matching for optical second harmonic generation (SHG) is possible, where two counter-propagating fundamental waves create second harmonic waves at the edge of the selective reflection band. We compute the SHG intensity in such a situation and show that, at slight detuning from exact phase-matching, useful resonance enhancement can be obtained. A considerable amount of SHG also appears when the second harmonic frequency is in the reflection band, where the SHG wave is non-propagating.     

Correlation between structural properties and iridescent colors of cellulose nanocrystalline films

We investigate the effect of shear flow applied during the drying of aqueous suspension of cellulose nanocrystals on optical reflective properties and structural characteristics of the resulting solidified films. Shear flow can significantly improve internal structural homogeneity of the films, while its effect on optical reflective properties is relatively minor. The measured width of the selective reflection peak is an order of magnitude larger than expected for an ideal helically modulated structure, which reflects a distribution of pitch values and possibly also of regimes of distorted helical modulation. We attribute these imperfections to the broad size distribution of the cellulose nanocrystals.     

Dynamic light scattering and <Superscript>31</Superscript>P NMR study of the self-assembly of deoxyguanosine 5’-monophosphate: the effect of added salt

Self-assembling and dynamical properties of deoxyguanosine 5-monophosphate in isotropic aqueous solutions were studied by ³¹P NMR spectroscopy and dynamic light scattering (DLS). All solutions had the same c = 4 wt% guanosine concentration, while the added KCl molarity ranged from 0 to 1.5 M. ³¹P NMR measurements show that potassium ions strongly enhance the stacking process of guanosine tetramers until a saturation is reached at 0.1 M KCl with more than 70% of the molecules aggregated. Polarized light scattering reveals the presence of a fast relaxation mode that arises from the translational dynamics of the self-assembled stacks. The diffusion coefficient of this mode shows a strong dependence on molarity of added salt, which can be described in terms of the coupled mode and counterion condensation theories for polyelectrolyte solutions. Depolarized light scattering reveals the rotational dynamics of the self-assembled stacks which exhibits a pronounced slowing down with increasing the added salt content.Received: 19 November 2003, Published online: 2 March 2004PACS: 81.16.Dn Self-assembly - 61.30.St Lyotropic phases - 82.35.Rs Polyelectrolytes