OPTICAL SUM FREQUENCY GENERATION STUDY OF ORGANIC MATERIALS

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OPTICAL SUM FREQUENCY GENERATION

STUDY OF ORGANIC MATERIALS

Student : Le Thi Kim Anh K56 Talented Program in Physics

Supervisor : Dr.Hoang Chi Hieu

*Nonlinear Optics

*Sum frequency generation (SFG) spectroscopy

*Organic materials

*Experiment

- Samples

- Experimental setup

- Results

* Conclusion

Contents

Nonlinear Optics

 Linear optics- ‘Optics of weak light’:

Light is deflected or delayed but its frequency is unchanged.

 Non-Linear optics-‘Optics of intense light’:

Describes the behavior of light in nonlinear media, in which the dielectric polarization P responds nonlinearly to the electric field E of the light.

Nonlinear Optics

Linear Optics

Light intensity does not affect optical

phenomenon.

Nonlinear Optics

- The refractive index ( velocity of light) in the optical media depends on light intensity.

-Superposition principle is violated.

- Light can interact with light

-Light frequency can be changed in the nonlinear media

 Linear  Nonlinear

P: the polarization of medium

ε0: the permittivity of free space E: electric field

χ(i): susceptibilities of ‘i’ order nonlinear

The second order polarization generates SFG

P( ω 1+ ω 2)= ε 0 χ (2) E 1 E2

Sum frequency generation (SFG)

 - Sum Frequency Generation (SFG)is a non-linear optical process in which 2 photons of angular

frequencies ω1 and ω2 annihilate, simultaneously, one photon of ω3=ω1+ω2 is generated.

ћω2

ћω1

ћω1+ ћω2

Vib level

Energy Diagram Schematic view

χ (2)

χ (2)

ω1

ω2

ωSFG =ω1 + ω2

SFG Spectroscopy:

The output intensity is given by

(χ(2) is the second-order susceptibility

A useful technique to analyze surfaces, interfaces and biomaterial

- The peaks appear when ω 2 matches ωq

- SFG is forbidden in centrosymmetric media

Analyze and selectively detect molecule vibrational modes with orientation

Why SFG is forbidden in centrosymetric media

The 2nd nonlinear polarization component that generates SFG:

Organic materials

 Almost organic materials belongs to molecule

chirality.

 Chiral structure which break centrosymmetric and

generates SFG signal

 SFG can provide the chemical

selectivity,interface specificity,chemical

indentification based on the changes of the

vibrational spectrum

Figure: Chirality in the amino-acid alanine Structures of the two mirror-image forms The image is part of the

EXPERIMENTAL

 Experimental Setup

SFG system optical layout

532 nm

Pulse lazer: 30 ps Pulse energy ∼ 200 mJ Repeatation rate 50Hz

Eskpla company

Recent studies

 Both experiment SFG study of Si (112) and Hydrated cellose

show advantages of SFG method and have succeeded in

carrying out the experiment to measure SFG spectra,using

the first in Vietnam.

 Mr Khien gets initial achievement to explain crystal tructures

Recent studies

Mr Long study dependence SFG

spectra of cellulose (HC) on the

hydration

SFG spectra of HC using pure water and NaOH

30%

0 5 10 15 20 25 30 35 40 45 50

3h H2O NaOH 3h Intens ity (a.u.)

IR Wavenumber (cm-1)

 SFG is a very new technology in the world with very high accuracy at monolayer level

 SFG is powerful to study on surface / interface and biological and biomedicalmaterials

 SFG has potential development for studying in Biology take 3D images, orientation

biological molecule by using SFG microscope

 Future works: we will study SFG spectra of some biomaterials like DNA and protein,

THANK YOU

FOR YOUR ATTENTION