Journal of Materials Processing Technology 185 (2007) 173–177 Development of an electric field sensor based on second harmonic generation with electro-optic materials N.J. Vasa ∗ , Y. Kawata, R. Tanaka, S. Yokoyama Interdisciplinary Graduate School of Engineering Sciences, Department of Applied Science for Electronics and Materials, Kyushu University, Kasuga Kouen 6-1, Kasuga 816-8580, Japan Abstract A novel approach of measuring an impulse electric field is proposed by combining a nonlinear optical-frequency conversion technique, such as the second-harmonic generation (SHG), with the electro-optic effect. The technique involves measurement of an electric field based on the SHG output intensity. In the present work, a continuous-wave diode laser is used with nonlinear, electro-optic crystals, such as MgO:LiNbO 3 (MgO:LN) and KTiOPO 4 (KTP), and the feasibility of the SHG technique for impulse electric field measurements is studied. The experimental measurements combined with theoretical estimates show that even though the temperature control is a critical requirement, the SHG technique can be effectively used for electric field measurements with a wide dynamic range of the order of a few kV/cm. It was also possible to shift the electric field measurement range by offsetting the phase matching condition for SHG. © 2006 Published by Elsevier B.V. PACS: 85.60.Bt; 42.65.Ky; 42.70.Mp Keywords: Electric field sensor; Optical sensor; Second-harmonic generation; Electro-optic materials 1. Introduction Optical sensors for electric field and voltage measurements are of considerable interest to the electric power industry since electric field distortion during measurement can be avoided, remote measurements are possible with response over a wide frequency range, direct measurement of the electric field in the space is possible and contain no electronic circuit and power sources in the proximity of measurements resulting in reduced effect from electromagnetic induced noise [1]. Optical sensors are also useful in the measurement of impulse electric fields where high electrical noise and interference conditions, such as those produced during lightning strokes, switching surges, and electric-discharge experiments, result in expensive and dif- ficult electrical isolation. Traditionally, these optical sensors utilize electro-optic effect (Pockels effect), and they have been widely used for monitoring voltages and electric fields [2–4]. Fiber-optic based electric field sensors have also been reported by different research groups. One approach is to apply fiber- optic based Pockels sensors [5,6], and another approach is based ∗ Corresponding author. E-mail address: vasa@ence.kyushu-u.ac.jp (N.J. Vasa). on the converse piezoelectric effect of fiber-optic material [7]. Recently, Pockels field sensor with ferroelectric liquid-crystal phase modulator for measuring the electric field close to an elec- tric discharge has been reported [8]. On the other hand, in this study, a novel architecture of measuring the electric field is proposed by combining a nonlin- ear optical-frequency conversion technique, such as an optical second-harmonic generation (SHG), with the electro-optic effect in nonlinear crystals. In the SHG combined with a nonlinear electro-optic crystal, when the interacting input laser beam and the corresponding SHG wave satisfies the phase matching con- dition within certain limits, the second-harmonic output (SHG output) can be obtained [9]. However, when an external electric field is applied, the refractive indices in the birefringent crystal alter due to the electro-optic effect and in turn, the correspond- ing phase matching condition also changes. As a result, the SHG output intensity varies, which can be used for the measurement of the applied electric field [10]. The proposed technique pos- sesses following characteristics, which can be advantageously utilized for electric field sensing. (1) It incorporates direct mea- surement of the SHG output intensity and not the phase change of the transmitting light beam as in the case of Pockels method, therefore higher signal to noise ratio can be expected; (2) phase matching conditions can easily be offset to monitor different 0924-0136/$ – see front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.jmatprotec.2006.03.116