Nonlinear optical polymer electrets current practice

Abstract

Amorphous polymers with strong second-order optical nonlinearities contain molecular chromophore dipoles as guest molecules, as side groups, or as main-chain segments. In order to break the inherent centrosymmetry of the initially isotropic dipole orientation in these materials and to render them nonlinear optically active (as well as piezo- and pyroelectric), preferential dipole alignment by means of electrical poling is necessary. After poling the nonlinear optical polymer films are molecular dipole electrets so that the full range of techniques for the preparation and investigation of polar electrets may be employed, together with nonlinear optical techniques, originally developed for the investigation of ferroelectric polymers, such as poly(vinylidene fluoride). The field of nonlinear optical polymers developed from very enthusiastic beginnings in the early eighties to the present and more realistic approach, with real applications just about to appear

Temperature-domain analysis of primary and secondary dielectric relaxation phenomena in a nonlinear optical side-chain polymer

“…Finally, well below T g the fictive temperature reaches a final limiting value and the Adam-Gibbs expression ͑4͒ reduces to an Arrhenius relation, which has been found to be a reasonable approximation below T g . 12,14,15,21 The temperature-dependent mean relaxation times ␤,␥ (T) of the secondary relaxations below T g often follow Arrhenius laws 28…”

“…18 However, the dielectric characterization of NLO polymers above the glass-transition temperature T g is by no means trivial as the dipoles can degrade at high temperature. [19][20][21] Usually, broadband dielectric spectroscopy over a very wide range of frequencies is applied for the investigation of the ␣ relaxation in NLO polymers. 9,[12][13][14][15] If experiments are performed at several, densely spaced temperatures above T g , the time-consuming measurement procedure cannot rule out severe thermally-induced degradation of the chromophore dipoles, at least in high-T g NLO polymers.…”

Pyro- and piezoelectric effects in nonlinear optical polymer electrets: New theoretical models

“…The response originates from organic NLO chromophores incorporated into the material and consisting of donor and acceptor end-groups connected by the conjugated p-electron bridge. The material exhibits the 2nd order NLO activity in the electret state, which is characterized by a frozen-in or induced polarization achieved by the aligning of chromophore dipoles in the external electric field [1][2][3][4]. In the electret state the polymer is known to manifest a variety of properties: pyroelectricity, piezoelectricity, birefringence, electrostriction, electrooptical and 2nd order NLO effects [4][5][6][7][8].…”

“…During recent decades the interest in the new polymer materials with a nonlinear optical (NLO) response to the external electric field has significantly grown, being stimulated by their possible applications in photonics and optoelectronics [1][2][3]. The response originates from organic NLO chromophores incorporated into the material and consisting of donor and acceptor end-groups connected by the conjugated p-electron bridge.…”

Electrochromic mechanism study of corona poled electro-optic polymer films

“…After poling, the polymer is a molecular dipole electret. Because the material has many unique features such as the controllable permittivity, assembled in the level of molecules, ease of processing and low cost [2]. It is thought that the material will become the basic material of photo-electronics and engineering in 2 1 century [3].…”