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5 th Southeast Symposium on Contemporany Engineering Topics (SSCET) September 19, 2014 • New Orleans, LA. Using the dielectric of a capacitor irradiated with a diode laser as a new optoelectronic switch. Cristian Bahrim. Department of Physics.
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5th Southeast Symposium on Contemporany Engineering Topics (SSCET) September 19, 2014 • New Orleans, LA Using the dielectric of a capacitor irradiated with a diode laser as a new optoelectronic switch Cristian Bahrim Department of Physics Joint appointment with the Phillip Drayer Department of Electrical Engineering
Collaborators: • Dr. Wei-Tai Hsu – Former postdoc at the Research Center for Adaptive Data Analysis at the National Central University • Nick Lanning – Graduate student at LSU • Don Duplan – Engineering firm in Dallas. • Md Mozammal Raju – EE alumni (Aug. 2014). • Md Khairuzzaman – EE graduate student.
Objectives • Accurate measurements of indices of refraction (and relative permittivity) from the analysis of the polarized light reflected by the dielectric surface near the Brewster angle. • Best precision: - for the Brewster angle is 0.001 degrees. - for indices of refraction is 10-4. • Shift of the photon’s energy from a laser source as perceived by the dielectric due to an additional (uniform) external source of energy, U: • Analysis of the optical response of a non-magnetic dielectric materials using a low voltage applied across, while a laser radiation illuminates the dielectric surface.
Index of refraction Wavelength [nm] Measurements of refractive indices • Dispersion - light of different colors travel at different speeds through • the same material. • Spectrometry • 2. Reflection of polarized light Minimum deviation method: i The Poynting vector of the EM radiation experiences a discontinuity at reflection or refraction. Sr Si 90o St
Our Experimental Method • Based on measurements of the polarized light reflected by a dielectric surface near the Brewster angle. The parallel component of the reflected E-field vanishes. Plane of incidence Precision: 1) The Brewster angle is measured with 0.001 deg precision. 2) The index of refraction is calculated with a precision of 10-4.
Disadvantages of MDM: • Uneven dispersion - violet wavelengths are spread out more than the red ones. • Rayleigh effect - violet-blue wavelengths are scattered more than the red wavelengths (the violet part of the spectrum appears less intense than in standard spectrum charts/spectroscopic tables). Advantages of RPL versus MDM: • It is not restricted to solid materials of triangular shape. • The local non-homogeneity of the material is not a problem. Only a locally smooth surface is necessary for having specular reflection. • It does not require experimental data exactlyat the Brewster angle, but within a range of about 1°.
Bio-chemistry - Brewster angle microscopy (it is used for physical and morphological analysis in microbiology). Spectro-polarimetric astronomical measurements (spectroscopicanalysis of stellar nebulas). Forensic analysis (detecting latent fingerprints in a crime scene). Imaging nano-particles. Material science (reducing the reflectance of materials). Analysis of gemstones (such as measuring high index of refraction). Interest in the study of polarized light:
Basic Physics: Maxwell equations with boundary conditions for dielectrics: the Fresnel’s equations. • We impose the optical E-field to be continuous across a non-magnetic dielectric: • Laws of geometric optics:
Fresnel’s equations for the parallel and the perpendicular components of the reflectance • The reflectance R is the ratio of the reflected irradiance to the incident irradiance (irradiance ~ E2): • The transmittance T is the ratio of the transmitted irradiance to the incident irradiance:
Parallel and perpendicular components of the reflectance: Total reflectance:
@ Brewster angle 0 @ Brewster angle 1 Both components of the reflectance normalized to the total reflectance have a parabolic shape!
Interpretation of the interaction between light and atomic dipoles on the dielectric surface.
Data acquisition with the Data Studio software Raw data – normalized reflectances
Parabolic fit of the raw data Brewster Angle
Resolution (required) Visible range • Better than 0.01 degrees!
Range of thermal stability Analysis of raw data for flint glass irradiated with 532 nm
A small error of 1.5% in the location of only three experimental data points leads to about 0.1o shift in the position of Brewster angle! Correction of the wrong data during the measurement
Advantages of using a computer–based procedure for collecting and processing data in real time. • Allows to recognize during measurements when the surface is overheated. • Allows to re-measure the data which are out of trend during data acquisition.
Results for two glasses irradiated with two lasers Legend: F= Flint; C= Crown; Wavelengths of 650 and 532 in nm.
Our apparatus/methodology allows measurements of any small variation of the indices of refraction. Influence of an isotropic and uniform external energy to the index of refraction of the dielectric material.
Capacitor-type configuration The setup used to observe the changes in the refractive index of a dielectric surface at the Brewster angle when a capacitor voltage is applied across the dielectric.
Shifted wavelengths of the probe laser signal (of 532nm) at different voltages applied across the capacitor :
RESULTS Degree of polarization Linear regime F = -kx At 0 and 3V r is the same. Optoelectronic switch
ANALYSIS The E-field of the laser is polarized at 45 degrees. • A capacitor voltage lower than 0.5V aligns the electric dipoles on the dielectric surface along the E-field of the laser. The polarized dipoles reduce the net charge on the plates, and implicitly the capacitance. • The decrease in the electric permittivity is actually the effect of an increase in the inertial resistance of the dipoles to the alignment under the influence of the probe laser due to the presence of a relative weak capacitor voltage.
