presentation by depositing dielectric and metallic Anti

March 21, 2019 History

presentation by
Krishna Manoj Aavula
Optical Technologies

Agenda
1. What are optical thin films ?
2. What is nonlinear refractive index?
3. How are we going measure it?
4. Manufacturing of optical thin films.
5. Measurement of optical thin film.
6. Conclusion
7. References
2
Nonlinear optics

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3
1.
What are
optical thin
films ?
Nonlinear optics
Thin -film optics is the branch of
optics that deals with very thin
structured layers of different
materials.
Applications:
Optical Thin Films: – What is Thin film ?
– What is Optical Thin Films ?
– Coating Materials
– Applications
Coating Materials:
Optical Coatings are created
by depositing dielectric and
metallic
Anti -Reflection (AR) Coatings,
High Reflective (Mirror)
Coatings,
Beam splitter coatings, and
Filter coatings such as short
pass, long pass, and notch
filters.
Al 2O 3 Ta 2O 5

4
2.
what is
nonlinear
refractive
index?
Nonlinear optics
• linear optical properties of materials as thin films are known to differ
from the linear optical properties of the corresponding bulk materials.
? What is refractive index?
? What is Nonlinear Refractive index?
? why do we have to consider nonlinear optical effects?
? How are we going to measure it? Nonlinear Refractive index
which changes the refractive
index depending on the intensity
of the incident radiation and a
material constant.
refractive index
the refractive index or index of
refraction of a material is a
dimensionless number that
describes how light propagates
through that medium.
How to measure it?
classical z -scan technique
combined with a Mach –
Zehnder -interferometer

5
3.
How are we
going to
measure it?
– How are we going to measure nonlinear refractive index?
The approach is based on the classical z-scan technique combined with a
Mach -Zehnder -interferometer.
– What is z -scan technique?
In nonlinear optics z-scan technique is used to measure the non -linear index
and the non -linear absorption coefficient.
The Mach –Zehnder interferometer is a device used to determine the
relative phase shift variations between two collimated beams derived by
splitting light from a single source.
– What is Mach -Zehnder -interferometer?
Nonlinear optics

6
3.
How are we
going to
measure it?
? What is Z -Scan?
• This change of beam diameter is converted into a measurable
power variation by measuring the radiation transmitted through a
small pinhole .
Nonlinear optics
• The method is based on the change of the beam diameter caused
by the self -focusing in the sample while moving the sample along
the path of a focused beam.
= Power Detector
M. Steinecke at al 2018

7
3.
How are we
going to
measure it?
? What is Mach -Zehnder -interferometer?
• A collimated beam is split by a half -silvered mirror . The two
resulting beams are each reflected by a mirror .
• The two beams then pass a second half -silvered mirror and
enter two detectors .
Nonlinear optics
Stigmatella aurantiaca at al 2013

8
3.
How are we
going to
measure it?
• Interferometric Setup and Laser System
• Before entering the interferometer itself, the beam is collimated to
initially create a very plane wave front . The reference beam then
proceeds unchanged to a camera, which is used to record the
resulting interference pattern .
• The beam in the sample – arm is focused for greater intensity, and,
after passing the sample, the beam is collimated again to allow a
superposition
Nonlinear optics
M. Steinecke at al 2018

9
3.
How are we
going to
measure it?
» Retrieval of Wave Front Curvature
• To achieve the linear carrier, the two beams are superimposed
under a small angle, which changes the interference pattern to a
sequence of stripes . The recorded interference pattern is then
transformed by a 2D -Fast -Fourier -Transformation (FFT) to obtain
the spatial frequency spectrum .
(a) (b)
Nonlinear optics
M. Steinecke at al 2018

To create optical thin films
for the measurement of
the nonlinear refractive
index, two main factors
have to be kept in mind
and optimized:
10
4.
Manfacturing
of Optical Thin
films
• Absorption
• Layer Stress
? To create the layers, an Ion Beam Sputtering (IBS)
deposition with the special co -sputtering technique
was applied .
? The application of the co -sputter technique allows
manufacturing mixtures of two coating materials .
? The atoms sputtered from the target materials are
then oxidized by inserted oxygen gas and create a
ternary oxidic layer on the substrates .
Nonlinear optics

11
• heating during the coating
process seems to reduce the
layer stress in the process,
which allows for thicker
coatings without interruptions
for annealing, while also
reducing the absorption in the
manufactured layers .
Nonlinear optics
Ion Beam Sputtering
Cristian Gómez Camacho at al 2017

12
5.
Measurement
of thin films
Nonlinear optics
• Thick substrates produce a signal with two distinguished peaks, which are
caused by the surfaces of the sample .When an optical layer is deposited on one
of these surfaces, the corresponding peak will change, while the other peak
almost perfectly retains its shape .
• An example for this procedure is presented. The sample consists of a 6mm
quartz substrate coated on one side with an 85µm layer of niobium oxide (91%)
mixed with aluminum oxide (9%).

13
5.
Measurement
of thin films
Nonlinear optics
Fig 5a
Fig 5b M. Steinecke at al 2018

14
6.
conclusion
? A novel measurement method for the nonlinear refractive index is
presented and evaluated .
? The measurement is based on the established z-scan approach, but uses
an interferometric procedure
? This new approach could provide a higher sensitivity and is less influenced
by nonlinear absorption caused by excited electrons in the material .
? This will enable a more detailed knowledge of the nonlinear properties of
coating materials and, in this way, allow a compensation or even
exploitation of nonlinear effects in dielectric layer stacks.
Nonlinear optics

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Nonlinear optics

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REFERENCES
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