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Nonlinear Optics: An Overview
Dr. C. VijayanDept. of Physics
IIT Madras
www.physics.iitm.ac.in/~cvijayan
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The technology of generating and harnessing light
and other forms of energy whose quantum is the Photon
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From Stone Age to Photon AgeMechanical to Electrical to Electronic to Photonic
The emerging area of PhotonicsHarnessing energy and information carrying capacity of Photons
EM theory at the heartNonlinear Optics, Applied Optics, Optoelectronics,Electrooptics
The three `C’s of PhotonicsCommunication, Control and Computing
We are nonlinear!
Linear vs nonlinearStimulus vs response, Extreme stimulusLinear response theoryTransport properties, mass, charge, heat
Stress vs starin
Welcome to the nonlinear world!
Linear regime
NonLinear regime
Electric field
Polarization
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What exactly is NON LINEAR?Nonlinear dependence of polarization
on optical field
Pi=ε0 (χij(1) Ej + χijk
(2) EjEk + χijkl(3) Ej Ek El + …)
χ(n) : susceptibility of n th order
(n+1) th rank tensor with [3(n+1)] components
Linear optics : superposition
No energy transfer among waves
Nonlinearity Energy transfer; wave mixing
n th order, (n+1) wave mixing
Second Order Nonlinear Optical Processes• Second harmonic generation
• Linear electro-optic effect : Pockel’s effect
• Optical rectification
Third order Nonlinear Optical Effects
• Third harmonic generation
• Phase conjugation
• Stimulated Raman scattering
• Self focusing
• Bistability
• Quadratic electro-optic effect : Kerr Effect
Large and fast nonlinearity: A materials problem
Second order NLO effects
χ(2)
ω 2ω
SHG : Second harmonic generation
χ(2)ω1
Sum and difference frequency generation
ω2
ω1+ω2
ω1−ω2
• Optical parametric oscillation• Applications of wave mixing
today’s laser technology : Ti: Saphire
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Optical Phase Conjugation : idea
1 2
3
4
The phase of wave 4 is reversed w.r.t that of wave 3i.e. 4 is a time-reversed replica of 3
1 24
3
mediumOptical phase conjugation“Probe beam gets diffracted by gratings created by pump1 and pump2”
1 2
3 4
Experimental set-up
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Optical Phase Conjugation:Applications
Apart from measurement of chi-3 to characterize the NL material, wave front reversal (time-reversal) and distortion-healing properties of OPC are used in Adaptive Optics applications such as
Precise targeting of a beam,
Precise beam control in lithography,
Aberration-correction in amplifiersin fiber-optic communications etc
Optical data and image processing
Self focusing
Gaussian laser beam
Nonlinear medium
Applications :•Beam shaping•Pulse shaping – soliton propagation•Optical limiting•Measurement of n2
n(I) = n0 + n2I
IIIIIIII((((((
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Closed z scan
aperture
laser detector
Transmitted intensity against distance
Self-focusing defocusing
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Low power optical limiting“Smart materials”
KSB, PH, CV : Materials Letters, Volume 58(7-8), 1223-1226 (2004)
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Pulse shaping, solitonsA pulse can have a frequency that varies in time.
This pulse increases its frequency linearly in time; (from red to blue).In analogy to bird sounds, "chirped" pulse.
Group velocity dispersion and self focusing effects can be combined in certain nonlinear fibers so as to achieve soliton propagation where signals propagate without distortion for a large distance.
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Mechanisms of optical nonlinearity
Electronic, ionic, molecular :Free carriers, bound electrons, excitons.
Orientational, saturable absorption’
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Conventional Materials•Inorganic salts
KDP, ADP, BaTiO3, BBO
•Semiconductors GaAs, Si, Ge, InSb
•Organic MaterialsPolymers, dyes, urea
Required:Large and Fast nonlinearityNatural materials do not satisfy this twin requirement
Novel Artificial Materials Molecular engineering, band gap engineeringQD, CNT, PBG
Porphyrin : the Wonder Molecule
•Chemistry, Structure, •Molecular Engineering, •Charge transfer, •Biochemistry;Photosynthesis,secrets of life?
“Why Blood is red and Grass is green“
Nonlinear Optical Effects in engineered porphyrins
Nonlinear refractive index, self diffraction, self-focusing, optical bistability, limiting;
The splendor and glory ofCarbon the Great!
Diamonds, Organics, Fullerenes, Nanotubes,
What next?Your research results !
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Physics of nanoclusters
Plenty of room at the Bottom –R. P. Feynman
• Low-Dimensional Structures/Nanoclusters
• Quantum Mechanics in daily life -Particle in a boxCD players, satellite receivers
• Free electron-bound electrons-
Jailed electrons
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“‘Quantum Mechanics’ is the description of the behavior of matter and light in all its details and, in particular, of the happenings on an atomic scale. Things on a very small scale behave like nothing that you have any direct experience about. They do not behave like waves, they do not behave like particles, they do not behave like clouds, or billiard balls, or weights on springs, or like anything that you have ever seen.”
--Richard P. Feynman
Quantum Confinement Effects
Remarkable alteration of optical and electrical properties
The Exciton : Quasiparticle in a crystal lattice
•Bandgap breaks up into discretelevels
•Band-edge depends on dot size
•Modifiable absorption/emission – white light
•Sharp exciton peaks at RT : Signature blueshift in absorption and emission
•Photonic switching, limiting, smart materials
Exciton Energy levels near the edges of bands
0
0.5
1
1.5
2
2.5
3
3.5
250 350 450 550
Wavelength (nm)
O.D
.
CB
Bulk cut-off
Exciton peak
VB
PN, CV, YVGSM :Journal of Applied Physics, 91(3), 1509 (2002)
Bandgap engineered all the way from UV to IROptical absorption spectrum of nano PbS
From 3000 nm to 300 nm
Samples ‘a’ to ‘e’ : Size 14 nm to 4 nm
KSB and CV : Invited Chapter inAdvances in Nanoscience and Nanotechnology, (book)Publ. NISCAIR, CSIR, 2004
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Multiphton absorptione.g. in nano PbS with ultrashort pulses
Linear optics
Nonlinear optics
KSB, CV, PH, JT, RP : Accepted, SPIE Int. conf, Santiago,USA, 2005
When excited with high intensity light,more than one photon can be simultaneously excited
Circles denote experimental data;Red line : fit to two photon absorptionBlue line: fit to three photon absorption
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