ABSTRACT
In an effort to optimize magnetic field detection sensitivities, the Faraday responsivity vector, which determines the relationship between the Faraday rotation angle and an externally applied magnetic field, was investigated in magneto-optic sensors based on bismuth-doped iron-garnet films. Under externally applied fields, Faraday rotation is produced principally by domain rotation and domain wall motion, whose relative contributions depend on the domain geometry and the direction of laser propagation. When optically probed along a principal magnetization axis, Faraday rotation is driven by a single magnetization mechanism, and the responsivity is linearized (reduced to an effective Verdet constant). When the films are probed along an oblique angle to the principal axes, the relationship between the Faraday rotation and the external field becomes tensorial and much more complex. Although this may lead to more complicated phenomena, the interplay of domain rotation and domain wall bowing can be exploited to improve responsivity or bandwidth. A generalized model for the magnitude and direction of the responsivity vector is formulated, which gives predictions that are consistent with the experimental data. Applications to arrayed sensors and three-axis field measurements are discussed.
ABSTRACT
For optimal sensitivity in electric field measurements, electro-optic (EO) crystals are typically selected based on their EO coefficients and dielectric constants. However, the conventional figure of merit yields sensitivity predictions regarding EO materials that are inconsistent with experimental data. In this Letter, we demonstrate that depolarization effects, which are often ignored, can dramatically enhance responsivity depending on the shape and orientation of the EO crystal. For optimal sensitivity, these effects are best exploited in longitudinal EO sensors, where they yield an optical modulation depth that increases quadratically with crystal length.
ABSTRACT
Quantum tunneling rates through a barrier separating two-dimensional, symmetric, double-well potentials are shown to depend on the classical dynamics of the billiard trajectories in each well and, hence, on the shape of the wells. For shapes that lead to regular (integrable) classical dynamics the tunneling rates fluctuate greatly with eigenenergies of the states sometimes by over two orders of magnitude. Contrarily, shapes that lead to completely chaotic trajectories lead to tunneling rates whose fluctuations are greatly reduced, a phenomenon we call regularization of tunneling rates. We show that a random-plane-wave theory of tunneling accounts for the mean tunneling rates and the small fluctuation variances for the chaotic systems.
ABSTRACT
Electro-optic (EO) modulation devices, which utilize an external electric field to modulate a beam of optical radiation, are strongly affected by parasitic effects, which change the polarization state of the optical beam. As a result, very small changes in the birefringence or optical path length within the EO material can result in very large fluctuations of the amplitude and phase of the optical modulation signal. A method of actively analyzing the modulated beam is described and demonstrated, which eliminates these fluctuations and keeps the modulation device stably operating at its peak responsivity. Applications to electric field detection and measurements are discussed.
ABSTRACT
The sensitivity of an electro-optic (EO) field sensor depends inversely on the dielectric constant of the nonlinear crystal. In EO sensors based on lithium niobate the effective value of this dielectric constant is affected by dielectric relaxation effects and is identified with its smaller, high-frequency component. Because of this effect, the EO modulation is significantly enhanced, thus improving the field strength sensitivity.
