Raman spectroscopy and its applications in various field with the help of raman spectrometer

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APPLICATIONS OF
RAMAN
SPECTROSCOPY
Submitted by,
KAAVYA B
Holy Cross College,
Trichy 2

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• Resonance Raman Scattering
• Raman microscopy
• Surface Enhanced Raman scattering
• CARS
• Applications In
a) Medical
b) Forensic
c) Inspection of products
d) Art
e)Geology
f) Nanotechnology
• Conclusion 2
OUTLINE

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• Many substances, especially colored ones,
may absorb laser beam energy and generate
strong fluorescence, which contaminates
Raman spectrum.
• It was discovered that instead of fluorescence
some type of colored molecules could
produce strong Raman scattering at certain
condition.This effect is Resonance Raman.
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Resonance Raman Spectroscopy

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• In RRS the λ of incoming laser is selected
to coincide with an electronic transition of
the molecule or material.
• Raman signal is amplified for about 106
magnitude orders.
• Extensively used for biological molecules.
• Detection of dilution solution possible
(concentration—10-3 M)
• All kinds of samples are analyzed .
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• It can be used to measure the atomic
displacement between ground state &
excited state.
• It can be used in the analysis of air
pollutants,aerosol particles etc.,
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• Highly monochromatic tunable lasers are
used.
• Glass can be used for windows, lenses, and
other optical components.
• When resonance Raman spectra are recorded,
however, sample heating and photo-
bleaching can cause damage and a change to
the Raman spectrum obtained
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Instrumentation

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• Although scattered light leaves the sample
in all directions the collection of the
scattered light is achieved only over a
relatively small solid angle by a lens and
directed to the spectrograph and CCD
detector.
• The laser beam can be at any angle with
respect to the optical axis used to collect
Raman scattering.
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• The collected scattered radiation is focused
into a spectrograph, in which the light is
first collimated and then dispersed by a
diffraction grating and refocused onto a
CCD camera
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• It consists of optical microscope, and adds an
excitation laser, laser rejection filters, a
spectrometer or monochromator, and an
optical sensitive detector such as a charge-
coupled device (CCD)
• It uses 2 lasers---- one of them produces RR
spectrum & other monitors the position of the
objective over the sample through CCD.
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Raman Microscope

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• The optical microscope uses light to
magnify and identify samples while the
Raman spectrometer scatters light and
measures the excitation vibration.
• The back scattered radiation from the
sample is imagined on to the entrance slit
of a monochromator.
• The data by the computer gives details
regarding the sample at the position
monitored by the CCD camera. 12

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• Raman microscopy of inorganic specimens
such as rocks and ceramics can use a
broader range of excitation wavelengths.
• Optical microscope + Raman spectrometer
= high resolution images of small samples.
• It is useful in studying phase transition in
molecular crystals.
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• It is an ideal tool for trace analysis
• Better to study highly diluted solutions
• Raman signal can be amplified by the
adsorption of molecules in certain metallic
surfaces--- surface enhanced raman
scattering.
• It permits the study of surface interactions,
adsoption process, electrode reactions, single
molecule detection.
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Surface Enhanced Raman Spectroscopy

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• 2 mechanisms—
• A.Electromagnetic model: interactions
among the incident EM radiations with the
surfaces.
• B.Charge transfer/chemical model:
interactions between adsorbed molecules
with the metallic atoms involved in
adsorption.
• Greatest enhancement --when excitation λ
is near plasma frequency of metal. 17

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• Output is not linearly proportional to its
input.
• It can effectively reduce the influence of
fluorescence.
• Hyper Raman Spectroscopy, Coherent anti
stokes Raman Spectroscopy, Coherent stokes
Raman spectroscopy, Stimulated Raman gain
and inverse raman spectroscopy.
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Nonlinear Raman spectroscopy

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• When tunable lasers generate frequency
which equals the anti stokes scattering
frequency , there is a signal enhancement.
• And the vibrational transitions equals the
energy difference between the two light
sources.
• CARS signal is anti stokes region.
• It is useful for molecules with high
fluorescence effect.
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• Bio molecules are highly raman active due to
their non polar molecular structure, the
abundance of water do not interfere with the
spectra due to the extreme polarity of water
molecules.
• This dichotomy between the scattering cross
section of biological macromolecules and
water is what allows raman to be used on
both tissues.
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Medical

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• Quality control of crystalline silicon are
tested.
• Orientation of silicon molecular structure
will affect raman spectra.
• For pure crystalline silicon , there is only one
allowed molecular vibration peak 521cm-1
• If wafer undergoes any stress or strain
correspondingly the peak will reduce.
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Silicon Wafer Testing

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• Laser can be focused through optically
transparent packaging allowing the content
to be analyzed without opening it
• Ava spec mini weighs 175 grams and of
dimensions 95mm x65mm x20mm
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Inspection of products

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• Raman data can be obtained from almost any
surface, allowing minute traces of
explosives or a firearm’s discharge to be
detected without attempting to lift samples
from evidence.
• Raman spectroscopy is highly sensitive to
minute chemical differences between inks.
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Forensic

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• Identification of individual pigments and
their degradation product leads to
insight into the working method of
artist.
• It also gives information about the
original state of painting.
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ART

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• It helps us to know whether the sample
is polarizable or not.– Raman scattering
occur after a dipole is induced in a
molecule by the incident radiation.
• It also indicates the
compostion,structure,stability &
vibrational levels within the sample
• Concentration of the scatter is found.
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Conclusion

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