1. Raman spectroscopy Solid state spectroscopy class
Miss pimpika pimsorn ID: D

2. outline
INTRODUCTION
PRINCIPLE
INSTRUMENT
APPLICATION

3. Introduction Raman spectroscopy is a spectroscopic technique.
bases on inelastic scattering of monochromatic light, usually from a laser source. (in the visible, near-infrared, and near-ultraviolet range.)
can be used to study solid, liquid and gaseous samples.
measures the vibration, rotation and other low frequency transitions in molecules.

4. Introduction Sir Chandrasekhara Ventaka Raman is Indian physicist.
Discovered the “Raman effect”.
Studied extensively in X-ray Diffractions, Acoustics, Optics, Dielectrics and Colloidal solutions.

5. Introduction Raman effect P = αE
is based on molecular deformations in electric field E determined by molecular polarizability α.
occurs when monochromatic light impinges upon a molecule and interacts with the electron cloud and the bonds of this molecule.
requires a changing induced dipole moment.
P = αE
α is the polarizability of the molecule
E is the electronic field

6. PRINCIPLE
Monochromatic laser light with frequency υ0 excites molecules and transforms them into oscillating dipoles. Such oscillating dipoles emit light of three different frequencies
I. Rayleigh scattering (no exchange of energy: incident and scattered photons have the same energy)
II. Stokes Raman scattering (atom or molecule absorbs energy: scattered photon has less energy than the incident photon)
III. Anti-Stokes Raman scattering
(atom or molecule loses energy: scattered photon has more energy than the incident photon)

7. PRINCIPLE I = CNI0F(T) Concentration measurement C - is a constant,
I - Raman signal intensity
C - is a constant,
N - the number density,
I0 - the laser intensity,
 - the Raman cross-section,
 - the scattering solid angle,
- the length of the observed segment of the laser beam,
F(T) - a temperature dependent factor determined by the spectral width and resolution of the detection system and the investigated molecule
I = CNI0F(T)

8. INSTRUMENT
A Raman system typically consists of four major components: 1. Excitation source (Laser). 2. Sample illumination system and light collection optics. 3. Wavelength selector (Filter or Spectrophotometer). 4. Detector (Photodiode array, CCD or PMT).

9. INSTRUMENT 1 2 3 4
Schematic of the Raman instrumentation.

10. INSTRUMENT
{J. Phys. Chem. C, 2011, 115 (46) pp }. Copyright {2011} American Chemical Society.

11. INSTRUMENT

12. application 1. Stimulated Raman Scattering : SRS
Very strong laser pulse with electric field strength > 109 V·cm-1 transforms up to 50% of all laser pulse energy into coherent beam at Stokes frequency 0 - m
CH2-stretching vibration
SRS tissue imaging of fresh mouse skin.
Stimulated Raman transitional schemes

13. application 2. Coherent Anti-Stoke Raman : CARS
Instead of the traditional one laser, two very strong collinear lasers irradiate a sample.
 lipid storage in Caenorhabditis elegans
Transitional scheme for CARS
CARS spectra of C. elegans. Thomas Hellerer et al. PNAS 2007;104:

14. application 3. Resonance Raman : RR
The intensity of a given vibrational mode is enhanced when the molecule is in resonance with the excitation wavelength
Parts of the polyhedral network in the TS-I (a) and CS-II (b) bromine hydrate structures. D (512), T(51262), P(51263), and H(51264) are standard notations for the convex polyhedra formed by hydrogen-bonded water molecules.
Resonance Raman transitional schemes

15. application 4. Surface-Enhanced Raman Spectroscopy: SERS
It utilizes both Surface-Enhancement effect and Raman Resonance effect so the resulting enhancement in Raman signal intensity can be as high as 1014.

16. application
The capacity of Raman spectroscopy and endoscopic imaging for improving the noninvasive, in vivo diagnosis and detection of epithelial precancer and cancer in humans (e.g., GI, ENT, lung, and the cervix, etc). 

17. Advantages
• Raman experiments do not require any tuneable laser source, any laser with high average power can be used, but since the signal is proportional to -4, short wavelengths are preferred. • Both rotational and vibrational temperatures can be obtained • Atoms, radicals as well as molecules that absorb well down in the VUV region can be measured • Raman are best suited for major species detection, i.e. N2, O2, H2, CO, CO2, H2O, hydrocarbons, normally with a single shot detection limit ~1000 ppm. • The signal is linear in laser intensity, no saturation effects

18. disAdvantages
• The Raman weak scattering signal is very weak, ~1000 times weaker than Rayleigh scattering. • It is very hard to make 2D-visualization. • The technique is sensitive to background fluorescence and stray light. • It is an incoherent technique, which means that background emission can be a problem. • It requires a laser with high average power. • Trade-off between having a sufficient signal and not damaging the windows.

19. THANK YOU FOR YOUR ATTENTION