Download Ref. “Optical Materials”

Materials for Photonic Applications
Glasses, Optical Fibers and Sol-Gel Materials
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Sidney J.L. Ribeiro, Edison Pecoraro, Marcelo Nalin, Younes Messaddeq
and collaborators
[email protected]
Project UNESP-PROPG-NEaD-TIC (UNESP Graduate Studies Office)
Graduate Robson R. Silva and Undergraduate Fernando E. Maturi
April-June- 2013
Rio Grande do Sul
South of Brazil
Barbecue, chimarrão,
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GLASSES
OPTICAL PROPERTIES
CLASS 3
http://www.lehigh.edu/imi/
Professor Himanchu Jain
Lehigh University (Betelehem, PA, USA)
http://www.lehigh.edu/matsci/faculty/jain/jain.htm
The International Materials Institute for New Functionality in Glass (IMI-NFG) was
established in August 2004 through an initiative of the National Science Foundation
for enhancing research collaborations between US researchers and educators
and their counterparts worldwide.
It is also a collaboration between Lehigh University and Penn State University.
"To focus, coordinate and promote educational and research activities
across the globe to introduce new functionality in glass"
Go the IMI webiste or contact Professor Jain
for more informations!
Light- Special kind of electromagnetic energy
Propagates in space
c= 3.108 m/s in vacuum (0,03% less in air and 30% less in glass)
Refractive index- n
v(vacuum)/v(material)
Optical waves propagate through insulators
With characterisitics determined by:
-The dielectric constant and refractive index of the
material
-any absorptive or scattering process
As a consequence, insulators have a broad window of transparency
over somepart of the optical spectrum.
In this transparency window the dielectric constant generally has a weak dispersion.
Therefore the material transmits light with very little loss.
Wavelengths outside de transparency regions can induce strong polarization processes,
that can cause a dispersion in the dielectric constant or refractive index,
with an associated increase in propagation loss or absorption
Ordinary glasses are highly transparent in the visible
for three main reasons:
1- Their polatization processes are either too slow or too fast to keep up with
the oscillations in electromagnetic fields associated with the visible optical wave;
Consequently the refractive index is only weakly dependent on wavelength in that region
of the electromagnetic spectrum
2- Their constituents do not have electronic states that allow free-electron or
bound-electron transitions in the visible
3- Their microstructure is homogenous and isotropic, and their refractive index is
dependent on neither spatial position nor direction
Ref. “Optical Materials” by Joseph H. Simmons and Kelly S. Potter, Academic Press, 2000
Optical properties of glasses
-Good optical properties
-difficult preparation
-Bad optical properties
-easy preparation
-Good optical properties
-easy preparation
Ref- P.Lucas- Glass Properties- 2nd Virtual Glass Course - International Materials
Institute for New Functionalilty in Glasses (http://www.lehigh.edu/imi/)
INCIDENT LIGHT ON A MATERIAL SURFACE
REFLECTION
ABSORPTION
SCATTERING
TRANSMISSION
Glasses are
isotropic
REFLECTION
(FRESNEL EQUATION)
In the transparentregion =0
= extintion coeffcient
n= n+ i.
 n 1 
R

 n 1
If n=1.5
2
valid for  < 20o
R=4% at each surface
ABSORPTION
= absorption coefficient
Relationship between the absorption coefficient and the extinction coefficient
2

c
SCATTERING
Rayleigh scattering- results from microscopic fluctuations of the densityLight is sent to multiple directions. There is no energy transfer to the scatterer
Why is the sky blue??
Take a look at
http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html
Scattering from
particles.
Mie Scattering
Independent of the
wavelength
The change of sky colour at sunset (red nearest the sun, blue furthest away)
is caused by Rayleigh scattering by atmospheric gas molecules which are much
smaller than the wavelengths of visible light.
The grey/white colour of the clouds is caused by Mie scattering by water droplets
which are of a comparable size to the wavelengths of visible light.
http://en.wikipedia.org/wiki/Mie_theory
TRANSMISSSION
If the optical quality is good,
scattering may be descarded
and R+T+A=1
Reflection and refraction
Pencil in the
water
vertical
Pencil in the water
inclined
Refraction effect
n1sen1  n2 sen 2
Snell-Descartes Law
Total Internal Reflection
According to Snell-Descartes Law,
sen1 
n2
sen 2
n1
If n2>n1 then 1>2
For a given angle c the refracted beam will be paralel to the surface (1=90o)
We call this angle “critical angle”
The critical angle value will be given by senc=n1/n2
For any angle 2 larger that the critical angle, light will be completely
reflected to the medium. This process is what we call
Total internal reflection
We will come back to this to
explain light guiding in optical fibers
Refractive index- Basics
The deviation a light beam will suffer
will depend on its relative velocity in the two media
The relative refractive index (n21)- ratio of the two velocities
n21=v1/v2= n2/n1
Absolute value (n)- When the medium 1 is vacuum (v1=c)
C= 300000 km/s and n will be always larger than 1
In ordinary glass v=200000 km/s
And then n= 300000/200000=1.5
Refractive index for some materials
Material
Refractive index
air
water
glass
glicerine
Ethyl alcohol
diamond
Acrylic
Fused silica
ZBLAN glass
Lead silicate glass
1
1.33
1.5
1.9
1.36
2.42
1.49
1.46
1.5
2.5
What if the refractive index is negative??????
...the incident and the refracted waves lie on the same side of the normal to
the interface between a standard medium and the new medium with
negative refractive index (“left-handed refraction”)...
Normal refraction
Left-handed refraction
Coming back to normal refraction basics
Refractive index as a function of the wavelength
Dispersion of the refractive index
In the transparent region, dispersion
is “normal”
In resonance regions the dispersion
is “anomalous”. The refractive index
value goes to infinity
The optical dispersion may be evaluated
through the Abbe Number
Abbe number:

nd  1
nF  nC 
The lower the Abbe number
The greater the dispersive power
(Concerning the d-line some authors substitute the Na lamp line at 589,3nm for the He line at 587.56nm)
Ref. “Optical Materials” by Joseph H. Simmons and Kelly S. Potter, Academic Press, 2000
Crown glasses
Flint glasses
.
Glasses can then be categorised by their composition and position on the diagram.
This can be a letter-number code, as used in the Schott Glass catalogue
and shown in the figure
Abbe numbers are used to calculate the necessary focal lengths of achromatic
doublet lenses to minimize chromatic aberration.
Sellmeier equation- dispersion of the refractive index for a single-component glass
Sellmeier coefficients- A, B and C- determined experimentally for a variety of
different materials and may be found in the literature
In practice given the refractive index at some given wavelengths,
one can fit the Sellmeier equation to obtained the coefficients A, B and C
Silica
A=1.099433
B=10974.1
C=9.5988x10-9
Ref. “Optical Materials” by Joseph H. Simmons and Kelly S. Potter, Academic Press, 2000
Refractive index measurements
Abbe refractometer
Measures the angle of incidence required to just begin total internal reflection
(critical angle) for light propagating from a standard glass hemisphere of high
Index to a sample of lower index- Accuracy- 2x10-3
Ref. “Optical Materials” by Joseph H. Simmons and Kelly S. Potter, Academic Press, 2000
Refractive index measurements
Minimum-deviation prism goniometer
The most accurate method for measuring refractive index.
1- Position the source to one side of the unknown
prism and measure the minimum angle of deviation
2- Rotate the prism 1800 and repeat
3- This gives a measure of 2m from which the
refractive index can be calculated
The accuracy is 5x10-6 if the angle
can be measured with an accuracy
of 0.5 angular seconds
Refractive index measurements
Prism coupling
Critical angle
Metricom Model 2010- Prism Coupler
Lasers – 1540nm, 633nm, 543.5nm
Accuracy is comparable with that of
minimum deviation method
Ref. “Optical Materials” by Joseph H. Simmons and Kelly S. Potter, Academic Press, 2000
Refractive index measurements
Refractometers

The method consists of the measurement of the angle of a mirror required to send
a collimated optical beam back along its incoming track.
The refractive index of the V-block must be known to the same accuracy as the
desired for the unknown sample.
Ref. “Optical Materials” by Joseph H. Simmons and Kelly S. Potter, Academic Press, 2000
Refractive index measurements
Ellipsometry
An ellipsometer is usually used to measure the thickness and refractive index of
films deposited on a substrate.
With an appropriate standard, the same method can be applied to index measurements
on bulk samples.
Monochromatic light is passed through a polarizer (Glan-Thomson calcite prism)
and a quarter-wave compensator (mica plate with 45º retardation) to give
elliptically polarized light.
This light is incident upon a sample surface at a specified angle.
The reflected light is then detected through an analyser (Glan-Thomson calcite
prism) and both the polarizer and the analyser angles are varied to find the
maximum extinction of the reflected light. The values obtained consist of the
polarizer angle (P), the analyser angle (A) and the angle of incidence.
Ref. “Optical Materials” by Joseph H. Simmons and Kelly S. Potter, Academic Press, 2000
Refractive index measurements
Becke line method
Most used in optical mineralogy- Small glass fragments in an immersion liquid
of known refractive index, and observed under a microscope.
As the microscope stage is moved away from focus, there will be a bright line
contouring the perimeter of the glass sample. This is the “Becke Line”.
If the refractive index of the immersion liquid is lower than that of the glass, the
Becke line will move inside the object when the distance between the objective
lens and the specimen is increased. Decreasing the distance will cause the Becke
Line to move outside the sample.
If the immersion liquid index is higher that that of the sample,
the Becke line will move in the opposite direction
Different liquids are used so as to bracket the unknown index
The bracket is narrowed until the desired degree of accuracy is reached.
Finely graduated liquids can yield n= 0.02
Ref. “Optical Materials” by Joseph H. Simmons and Kelly S. Potter, Academic Press, 2000
Refractive index measurements
Femtosecond transit time method
100fs pulse width
The white light pulse from a Ti-sapphire femtosecond laser is used.
By decomposing the transmitted pulse into its component colors the time taken
for each wavelength to transmit through the sample can be calculated, giving
the refractive index for each wavelength directly.
Accuracy is good to the second decimal place for a sample1mm thick
Considering thin films,
refractive index and thickness
can be obtained together by using:
ref- P.Lucas- Glass Properties- 2nd Virtual Glass Course - International Materials
Institute for New Functionalilty in Glasses (http://www.lehigh.edu/imi/)
Soda-lime silica glass- Absorption spectrum
Multiphonon
processes
Harmonics of
fundamental
vibrational
modes
Minimum depends on the
glass composition
Energy gap
Electronic
transitions
valence band
conduction band
A=5.10-5 (1cm)
Attenuation- "decibels"
(dB)= 10 log(P1/P2) P1-in P2-out
 3dB  P1/P2= 2 (signal is half of the initial)
1ppm OH-- 4dB/k m at 1380nm
A=10-7(1cm)
96% of the
signal after
1km
Quizz number 3- question 1
Araraquara
1W, 1.5 m
270 kms of fiber
?W
São Paulo
Attenuation of a silica fiber at 1.5 m
0.2 dB/km
http://en.wikipedia.org/wiki/ZBLAN
ref- P.Lucas- Glass Properties- 2nd Virtual Glass Course - International Materials
Institute for New Functionalilty in Glasses (http://www.lehigh.edu/imi/)
Spectrometers
ref- P.Lucas- Glass Properties- 2nd Virtual Glass Course - International Materials
Institute for New Functionalilty in Glasses (http://www.lehigh.edu/imi/)
ref- P.Lucas- Glass Properties- 2nd Virtual Glass Course - International Materials
Institute for New Functionalilty in Glasses (http://www.lehigh.edu/imi/)
Fourier Transform Infrared (FTIR) spectrometers
In the infrared, which is the region of molecular vibrations,
wavenumbers range from 300 to 5000 cm-1 (33 to 2 m))
interferometers are used instead of dispersion monochromators
Light sources
-Black body radiation of a
heated silicon carbide coil
Detectors
-Pyroelectric detectors
-MCT (HgCdTe) – highly sensitive
Michelson Interferometer
The FT analysis of the
resulting interferogram (f(cm))
gives us
the infrared spectrum (f(cm-1))
ref- P.Lucas- Glass Properties- 2nd Virtual Glass Course - International Materials
Institute for New Functionalilty in Glasses (http://www.lehigh.edu/imi/)
Size effect in the band-gap value
“Quantum confinment in quantum dots” (“Quantum dots”- QD)
E
146 nm
1128 nm
ref- P.Lucas- Glass Properties- 2nd Virtual Glass Course - International Materials
Institute for New Functionalilty in Glasses (http://www.lehigh.edu/imi/)
ref- P.Lucas- Glass Properties- 2nd Virtual Glass Course - International Materials
Institute for New Functionalilty in Glasses (http://www.lehigh.edu/imi/)
Ref. “Optical Materials”
by Joseph H. Simmons and Kelly S. Potter,
Academic Press, 2000
The Bohr diameter defines the smallest
structure that will exhibit bulk behavior
ref- P.Lucas- Glass Properties- 2nd Virtual Glass Course - International Materials
Institute for New Functionalilty in Glasses (http://www.lehigh.edu/imi/)
Raman spectrum of a fluorindate glass
Silica- 1100cm-1 (9,1m)
Fluorides- 510 cm-1 (19,6m)
Chalcogenides- 300 cm-1 (33,3m)
Intensidade (un.arb.)
Highest energy vibrational modes
Highest energy
vibracional mode
510 cm-1 (19,6m)
100
200
300
400
500
600
Número de onda (cm-1)
2 important consequences
IR absorption edge
Non-radiative rates for transitions
Between lanthanides excited states
The lower the non-radiative rates,
The more efficient the radiative emission
will be!
We will come back to this!
http://electronics.howstuffworks.com/gadgets/automotive/in-dash-night-vision-system3.htm
ref- P.Lucas- Glass Properties- 2nd Virtual Glass Course - International Materials
Institute for New Functionalilty in Glasses (http://www.lehigh.edu/imi/)
Infrared Fibers
Chalcogenide glasses are transparent in the domain where the vibrational
signature of most molecules lies: 2-12 microns
From Laser Focus World
http://www.laserfocusworld.com/articles/print/volume-41/issue-4/features/chalcogenide-optical-fibers-target-mid-ir-applications.html
A cone penetrometer system using chalcogenide
fiber can be used for the in-situ detection of
contaminants and water in soil.
A chalcogenide fiber is connected to a
headened optical analysis system (top and center),
and is inserted into the soil to be tested.
The IR signals reflected from the soil and
transmitted through the fiber to the FTIR
in the truck are used to identify
the contaminant marine diesel fuel (DFM) (bottom)
Confederations Cup- 2013
Brazil Champion
Brazil 3 Spain 0
http://news.yahoo.com/brazil-beats-spain-3-0-win-confederations-cup-000418525.html
The champion is back!!!
http://www.youtube.com/watch?v=SS9k6ZoE3v0