Using the dielectric of a capacitor irradiated with a diode laser as a new optoelectronic switch

Cristian Bahrim

5th Southeast Symposium on Contemporany Engineering Topics (SSCET)  September 19, 2014 •  New Orleans, LA

Joint appointment with the Phillip Drayer Department of Electrical Engineering

Department of Physics

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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.

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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.

UEE 12

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The Poynting vector of the

EM radiation experiences a discontinuity

at reflection or refraction.

1. Dispersion - light of different colors travel at different speeds through the same material.

Spectrometry

2. Reflection of polarized light

Measurements of refractive indices

Ind

ex o

f re

frac

tion

Wavelength [nm] 2/sin

2/sin min

n

Minimum deviation method:

i

90oSi

Sr

St

BES1

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Our Experimental Method

di n1tan:law sBrewster'

The parallel component of the reflected E-field vanishes.

Plane of incidence

Based on measurements of the polarized light reflected by a dielectric surface near the Brewster angle.

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.

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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 exactly at the Brewster angle, but within a range of about 1°.

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Interest in the study of polarized light:

Bio-chemistry - Brewster angle microscopy (it is used for physical and morphological analysis in microbiology).

Spectro-polarimetric astronomical measurements (spectroscopic analysis 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).

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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:

ri

rrii nn sinsin

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2 2

2 2

2 cos

cos cos

2 cos

cos cos

t i i

i i t t i

t i i

i i i t t

E nT

E n n

E nT

E n n

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:

2 2

2 2

cos cos

cos cos

cos cos

cos cos

t i i tr

i i t t i

i i t tr

i i i t t

n nER

E n n

n nER

E n n

Fresnel’s equations for the parallel and the perpendicular components of the reflectance

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2

tan

tan

t

tR

2

sin

sin

t

tR

Parallel and perpendicular components of the reflectance:

Total reflectance:

RRR

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Both components of the reflectance normalized to the total reflectance have a parabolic shape!

@ Brewster

angle

0

1@ Brewster

angle

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Reflectance versus the angle of incidence

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Dipole Oscillator (Lorentz-Cauchy) Model

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Interpretation of the interaction between light and atomic dipoles on the dielectric surface.

2212 1 oCCn

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Experimental setup with PASCO equipment

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Data acquisition with the Data Studio software

Raw data – normalized reflectances

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Parabolic fit of the raw data

Parallel Component

0

0.01

0.02

0.03

0.04

0.05

50 52 54 56 58 60 62 64 66 68

Angle (degrees)

Rat

io

Brewster Angle

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Resolution (required) Better than 0.01 degrees!

Visible range

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Computer-based analysis of raw data

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Computer-based analysis of raw data

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Analysis of raw data for flint glass

irradiated with 532 nm

Range of thermal stability

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Correction of the wrong data

during the measurementA 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!

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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.

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Results for two glasses irradiated with two lasers

SystemMDM

( degrees )RPL

( degrees )Index

of refraction

F650F532C650C532

58.210 ± 0.00158.380 ± 0.00256.475 ± 0.00156.555 ± 0.001

58.213 ± 0.00358.388 ± 0.00856.470 ± 0.00656.553 ± 0.003

1.6141 ± 0.00021.6252 ± 0.00061.5096 ± 0.00031.5143 ± 0.0002

Legend: F= Flint; C= Crown; Wavelengths of 650 and 532 in nm.

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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.

UEE 12

1E2E o

U

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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.

Capacitor-type configuration

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Shifted wavelengths of the probe laser signal (of 532nm)

at different voltages applied across the capacitor :

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RESULTS

(t)

1.o I t

Pr E

2

.d rn tan .

d

BI

n

n

Optoelectronic switch

Linear regimeF = -kx

UEE 12

At 0 and 3V r is the same.

Degree of polarization

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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.

The E-field of the laser ispolarized at 45 degrees.

ANALYSIS

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ANALYSIS

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