Thermal properties of the nonlinear optical crystal zinc tris (thiourea) sulphate

The heat capacity of crystalline zinc tris (thiourea) sulphate, has been measured in the range from 220 to 500 K by differential scanning calorimetry, and was found to obey the relationship Cp(T)=2.76×10−3 T+0.366 J g−1 K−1. Thermal expansion data have been measured in the range from 150 to 473 K. From these data, the principal thermal expansion coefficients were found to be α1=6.41×10−5 K−1, α2=4.52×10−5 K−1, and α3=−4.32×10−6 K−1. The thermal conductivity tensor of this orthorhombic crystal was calculated from values of the thermal diffusivity in the directions normal to the (100), (010), and (001) crystal planes by the laser flash method. The thermal conductivity coefficients at 295 K are k=0.27 W m−1 K−1, k2=0.34 W m−1 K−1, and k=0.54 W m−1 K−1. REFERENCE

Preparation and structural evaluation of the conformational polymorphs of alpha-[(4-methoxyphenyl)methylene]-4-nitrobenzeneacetonitrile

Crystals of -[(4-methoxyphenyl)methylene]-4-nitrobenzeneacetonitrile (C16H12O3N2) are shown by X-ray crystallography to exist in three polymorphic trans forms (I-III) and one cis configuration (IV). Calorimetric studies show that at low temperature form I is thermodynamically the most stable phase, followed by form III and form II. On heating, form III undergoes a phase transformation to form II. There is no direct thermal transformation between forms II and I. Form I melts at 164.5 C. Mechanical damage of form II initiates a phase transformation into form III, and structural studies confirm that forms II and III, both of which show attractive second-order nonlinear optical behavior, are closely related. Though clearly conformational polymorphs, they also exhibit the essence of orientational polymorphism. Although form I is the most stable of the three trans isomers, nevertheless forms II and III are indefinitely stable and may be useful for development for NLO purposes. Crystal growth studies show that growth from the melt and vapor phases could be the only routes for the preparation of specimens for optical examination. The results show well the difficulties involved in the preparation and isolation of the different polymorphic forms of such materials

Quadratic Parametric Interactions in Organic Waveguides

This chapter addresses issues related to quadratic parametric interactions in organic waveguides. It attempts to give an overview of the field, especially emphasizing the initial experimental milestones together with the most recent results. This field of research is very challenging in terms of the technology required to turn a good candidate material into a useful optical device demonstration. The keys to this problem are the phase-matching conditions that must be fulfilled by the different interacting waves. These points are illustrated by the bibliography that, still to this day, contains mainly demonstration of the potential of various materials with very few subsequent demonstrations of efficient optical device operation. Nevertheless, this is still a relatively young field of research and there is no doubt that, given time, effort and investment, it will grow and mature along the lines of its successful electro-optic counterpart. © Springer-Verlag Berlin Heidelberg 2002