Optimized poling of nonlinear optical polymers based on dipole-orientation and dipole-relaxation studies

Abstract

Nonlinear optical polymers contain molecular dipoles with very large hyperpolarizabilities in a glassy polymer matrix. Two typical examples—a guest-host system with dispersed polar dye molecules and a side-chain material with chemically attached molecular dipoles—were investigated by means of poling experiments, dielectric spectroscopy, thermally stimulated depolarization, and electro-optical thermal analysis. The dielectric behavior of both polymers can be described by the phenomenological Havriliak–Negami equation, and the existence of master curves for both materials demonstrates the validity of the time-temperature superposition principle above the respective glass transitions. Temperature-dependent mean relaxation times and relaxation-time distributions calculated from the dielectric data allow for an optimization of poling times. The dielectric relaxation strengths obtained from poling current and field, from dielectric measurements, and from thermally stimulated depolarization are in very good agreement and thus represent a useful measure of the polarization in poled polymers. From the temperature dependence of the polarization, optimal poling temperatures may be derived. Electro-optical thermal analysis yields the same temperature-stability curves as thermally stimulated depolarization and is therefore a valuable tool for investigating the stability of poled polymers, especially since it is not sensitive to charge effects. Optimal poling fields and currents must be selected as a compromise between high dipole mobilities (short relaxation times) and low bulk conductivities.

Nonlinear optical polymer electrets current practice

“…For constantvoltage corona poling, quasi-in situ determinations of the surface potential were demonstrated by Knoesen et al [70], who made equal currents to the sample and to an equivalently placed electrode, by compensating the sample's surface potential with a suitable rear-electrode bias voltage, and by Ren et al [67], who moved the sample for N 1 s from the corona discharge to a fieldcompensating surface-voltage probe and back. Because of their NLO properties, the poling of optically active polymer electrets may also be studied in situ by means of an all-optical technique, second-harmonic generation (SHG) 1711, which will be discussed in more detail in Section 6.3 below.…”

“…If one parameter is kept constant, such as the poling current in a constant-current corona, the other parameter, in this case the surface potential and thus also the effective poling field, can be determined directly. If all other parameters, and in particular the poling geometry, are left unchanged the setup may be calibrated so that the surface potential and the poling field may be calculated from the recorded poling current for a given polymer material [67]. [105].…”

Nonlinear dielectric response of poled amorphous polymer dipole glasses

“…With a dye loading of 90 mol%, the P(S-MA)-DR1 side-chain polymer showed a glass-transition temperature T g = 137°C, as measured with DSC at the same heating rate of 10°C/min [10]. After thermally poling the polymers for 10 min 20°C above their respective glass-transition temperature with a poling field of 80 V/lm, stable, non-resonant electro-optical coefficients r 33 = 1.8 pm/V @ 1.55 lm and r 33 = 8.5 pm/V @ 1.55 lm were achieved for the guest-host [12] and the side-chain polymer, respectively [13].…”

Chromofore Poling in Thin Films of Organic Glasses. 1. Overview of Corona Discharge Application

“…Temperature variations at poling affect the corona onset voltage, ion mobility, and, as a result, the V gap responsible for inaccuracies of the value of sample surface potential measured by this method. Versions of constant current corona triode poling setups [29][30][31][32][33][34][35][36][37] have been used in studies of polymer orientation, and their possible usage for poling NLO and HGP samples is still being examined [38,39]. As far as we know, the first system for measuring potential difference across a thin insulating film during the corona discharge has been reported by Weinberg [40].…”