Towards clinico-pathological application of Raman spectroscopy

�
incident light
�
incident light
Introduction
Figure 1. Schematic representation of the interaction of light and matter. The major fraction of
incident light with wavelength � is scattered with the identical wavelength (Rayleigh scattering). A
Figure 1. Schematic representation small fraction of of the the interaction incident light of however, light and is scattered matter. at The altered major wavelengths fraction due of to so-called
incident light with wavelength inelastic � is light scattered scattering, with in which the identical energy is wavelength exchanged between (Rayleigh an incident scattering). photon A and the molecule.
small fraction of the incident light however, is scattered at altered wavelengths due to so-called
inelastic light scattering, in which energy is exchanged between an incident photon and the molecule.
excited
electron state
vibrational
levels
ground state
A B C D
λ
�
�
�
Figure 1. Schematic representation of the interaction of light and matter. The major fraction of incident
light with wavelength λ is scattered with the identical wavelength (Rayleigh scattering). A small fraction of
the incident light however, is scattered at altered wavelengths due to so-called inelastic light scattering, in
which energy is exchanged between an incident photon and the molecule.
excited
electron state
vibrational
levels
ground state
λ
�−
λ+∆ λ−∆
λ λ
λ+∆ λ−∆
λ Rayleigh
scattering
Stokes λ shifted
Raman scattering
�
anti-Stokes shifted
Raman λscattering
λ
infrared
absorption
Rayleigh Figure 2. Energy
Stokes
level diagrams
shifted
showing
anti-Stokes
A) elastic scattering
shifted
(Rayleigh),
infrared
B) en C) inelastic scattering
scattering
(Stokes and anti-Stokes, resp.) and D) infrared absorption (IR).
Raman scattering Raman scattering absorption
�
�
�+
A B C D
λ
�
�
λ
�−
Figure 2. Energy level diagrams showing A) elastic scattering (Rayleigh), B) en C) inelastic scattering (Stokes
and anti-Stokes, Figure 2. resp.) Energy and level D) diagrams infrared showing absorption A) elastic (IR). scattering (Rayleigh), B) en C) inelastic scattering
(Stokes and anti-Stokes, resp.) and D) infrared absorption (IR).
Intensity
778
-800
anti-Stokes
Raman shift
803
-400
819
823
laser
-170
-100
0
830
837
842
100
170
�
�
�+
Stokes
Raman shift
859
400
889
800
wavelength (nm)
- 1
Raman shift (cm )
Figure Figure 3. A theoretical 3. A theoretical Raman spectrum Raman with spectrum the Stokes and with anti-Stokes the Stokes shifted and Raman anti-Stokes lines symmetrically shifted Raman lines
distributed symmetrically around the distributed laser line (in around this example the laser 830 line nm).
(in this example 830 nm).
∆cm
−1
� 1 1 � −
= �
� − �
� * 10
� λ 0 λ S �
2
1
1
13