Sir CV Raman was an Indian physicist who won the Nobel Prize in 1930 for his work on the Raman effect. He discovered that when light scatters from molecules, a small fraction of the light shifts to different wavelengths, which is now known as Raman scattering. Raman made many contributions in areas like X-ray diffraction, optics, and colloidal solutions. Raman spectroscopy uses the Raman effect to study materials by analyzing the scattering of monochromatic light. It provides a molecular fingerprint to identify compounds and detect molecular impurities. Both Raman and infrared spectroscopy are useful techniques to analyze materials, but Raman spectroscopy has advantages like avoiding interference from solvents and being able to detect IR-inactive modes.

3. 
November 7, 1888 - November 21, 1970

Won the Nobel prize in 1930 for Physics.

Raman effect was first reported by
Sir CV Raman and KS Krishnan.

Besides discovering the raman effect he studied extensively
in X-ray diffraction, optics , dielectrics and colloidal solutions.

4. 


Only objects whose dimensions are on the order of ~11.5 will scatter EM radiation (molecules).
Rayleigh scattering : the scattering of light by particles
in a medium, without change in wavelength.
Raman scattering : The scattering of radiation with
change of frequency is called Raman scattering.
RAMAN SPECTROSCOPY is a technique that uses
scattered light resulting from photon–molecule collisions
to investigate molecular properties.

5. 
When Light hits a sample, It is Excited, and is forced to
vibrate and move. It is these vibrations which we are
measuring.

6. Light is a travelling wave of electric and magnetic fields
 only the electric component gives rise to Raman
scattering.
 When a light wave meets a molecule consisting of
electrons and nuclei, the electric field of the wave at
any instant will be the same throughout the molecule.
 the field will exert the same force on all electrons in
the molecule and will tend to displace them.
 the displacements result in an induced dipole
moment, μ(ind) in the molecule.
Thus
μ(ind) = αE


7. 


α is called the electric polarizability of the molecule.
The Raman interaction leads to two possible
outcomes:
If the material absorbs energy and the emitted photon
has a lower energy than the absorbed photon. This is
Stokes Raman scattering while for antistockes raman
scattering reverse is true.
The spectrum of the scattered photons is the Raman
spectrum. It shows the intensity of the scattered light
as a function of its frequency difference Δν to the
incident photons.

8. The Raman effect comprises a very small fraction,
about 1 in 107 of the incident photons

9. A Raman spectrum is a plot of the intensity of Raman
scattered radiation as a function of its frequency
difference from the incident radiation (usually in units
of wave numbers, cm⁻¹). This difference is called the
Raman shift.

11. A modern Raman spectrometer

12. 
Identification of compound by matching the spectrum
of unknown with reference spectrum (fingerprint).



Determination of molecular composition of surfaces.
Identification of all type of inorganic compounds in
solid and aqueous solution.
Detection of molecular impurites and additives.

13. 




Advantages of Raman over IR:
Avoids many interferences from solvents, cells and sample
preparation methods.
Depolarization studies possible, enhanced effects in some cases.
Can detect IR-inactive vibrational modes.
Advantages of IR over Raman:

Raman lines are weaker, the Rayleigh line is also present.
Raman instruments can be more costly.
Raman can suffer from laser-induced fluorescence and degradation.

Final conclusion : Both techniques are complementary.



14. 
Experiments done in the mid 1970s demonstrated that
molecules adsorbed to a roughened metal surface
generated large Raman intensities. This is known as
surface-enhanced Raman spectroscopy (SERS).

SERS is a form of Raman spectroscopy that involves a
molecule adsorbed to the surface of a nanostructured
metal surface.

15. 
Raman intensity lines are 0.001% (at most) of the
source intensity.

The intensity can be increased by 10³ – 106 orders
of magnitude if the sample is adsorbed on the
surface of colloidal metal particles.

16. 
The mechanism of SERS is not completely understood.
 EM Enhancement
 Proposed by Jeanmarie and Van Duyne in 1977.
 Chemical enhancement
 Proposed by Albrecht and Creighton in 1977.

17. NanoRaman……………
To further expand the capabilities of a Raman
system, some manufacturers offers coupling solutions
to other analytical techniques.
Coupling to other non-optical imaging techniques like
AFM enables to go far beyond the diffraction
limit, while keeping the chemical information that
Raman spectroscopy brings.

18. Stanford scientists create a new way to scan for tumors
- a process that is potentially safer and more sensitive
than current cancer process.
 beam of laser light projected on the skin
surface, technique can spot with extraordinary
precision tiny particles that have been injected into the
bloodstream and attach themselves to cancer cells.
 PET scans, can pick up a tumor about 5 mm wide containing tens of millions of cancerous cells while
raman imaging has the potential to detect microscopic
lumps of only a few hundred cancer cells."


20. Thank you…..