SECTION I

Physical and mathematical sciences

Unit 1

Grammar: The Adjective and the Participle as an Attribute

Word List:

1. guest-host	«гость-хозяин» – один из эффектов в жидких кристаллах
2. to be doped with	достраиваться
3. elevated temperatures	повышение температуры
4. molecular ordering	упорядоченное расположение молекул
5. to be bonded together, to be crosslinked	соединяться, цепляться
6. crosslinking	образование поперечных межмоле­куляр­ных связей; структурирование, сшивание полимеров
7. to be aligned	выравниваться, устанавливаться в ряд/линию
8. straight-forward	прямой, простой
9. with respect to	по отношению
10. second-order nonlinear optical effects	нелинейные оптические эффекты второго порядка
11. submicrometer	нанометровый диапазон волн, 10–9 м
12. optical coefficients	коэффициент отражения и коэффициент преломления
13. non-centrosymmetrical arrangement	расположение, не симметричное относительно центральной оси
14. gradual relaxation	постепенный отход/уход
15. orientation = arrangement	расположение
16. reactive site	месторасположение в результате химической реакции

“Guest-Host” Systems

The move toward small-scale, submicrometer, integrated optical circuits has revealed fundamental disadvantages in the use of traditional inorganic materials for the required nonlinear optical devices. Organic chemistry has promised materials with not only large nonlinear optical coefficients but also the structural properties required for the production of these small-scale devices. The simplicity of the so-called guest-host system, in which a polymeric matrix is doped with molecules possessing high nonlinear optical coefficients, has made such materials a popular choice in the production of many prototype systems. An external electric field, applied at elevated temperatures, induces the non-centrosymmetrical arrangement of nonlinear molecules required for second-order nonlinear optical effects. However, this molecular ordering has been shown to be unstable resulting in a gradual relaxation in the induced orientation.

Possibly the most promising alternative to the straight-forward guest-host system is to chemically functionalize the guest molecule by generating several reactive sites within its structure. The idea behind such a development is that once aligned, the nonlinear molecules can be chemically bonded together (crosslinked) to form a long-ranged network. Such a network will dramatically reduce the mobility of the nonlinear molecules and thereby preserve the non-centrosymmetrical arrangement.

The stability of the induced orientation of these materials has already been demonstrated with respect to electro-optic modulation devices. The subject of the work being done is a study of the optically nonlinear guest molecule with respect to its nonlinear optical properties and its crosslinking process.