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Introduction to Nonlinear Optics

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Introduction to Nonlinear Optics H. R. Khalesifard ... 10-14 Optical glass 30 ps 10-8 CdSxSe1-x doped glass 20 ns 6.5 10-4 GaAs (bulk room temperature) ... – PowerPoint PPT presentation

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Title: Introduction to Nonlinear Optics


1
Introduction to Nonlinear Optics
  • H. R. Khalesifard
  • Institute for Advanced Studies in Basic Sciences
  • Email khalesi_at_iasbs.ac.ir

2
Contents
  1. Introduction
  2. The essence of nonlinear optics
  3. Second order nonlinear phenomena
  4. Third order nonlinear phenomena
  5. Nonlinear optical materials
  6. Applications of nonlinear optics

3
Introduction
  • Question
  • Is it possible to change the color of a
    monochromatic light?
  • Answer
  • Not without a laser light

4
Stimulated emission, The MASER and The LASER
  • (1916) The concept of stimulated emission Albert
    Einstein
  • (1928) Observation of negative absorption or
    stimulated emission near to resonant wavelengths,
    Rudolf Walther Ladenburg
  • (1930) There is no need for a physical system to
    always be in thermal equilibrium, Artur L.
    Schawlow

5
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6
LASER (MASER)
7
The Maser
  • Two groups were working on Maser in 50s
  • Alexander M. Prokhorov and Nikolai G. Bassov
    (Lebedev institute of Moscow)
  • Charles H. Townes, James P. Gordon and Herbert J.
    Zeiger (Colombia University)

8
  • Left to right Prokhorov, Townes and Basov at
    the Lebede institute (1964 Nobel prize in Physics
    for developing the Maser-Laser principle)

9
  • Townes (left) and Gordon (right) and the
    ammonia maser they had built at Colombia
    University

10
The LASER
  • (1951) V. A. Fabrikant A method for the
    application of electromagnetic radiation
    (ultraviolet, visible, infrared, and radio
    waves) patented in Soviet Union.
  • (1958) Townes and Arthur L. Schawlow, Infrared
    and Optical Masers, Physical Review
  • (1958) Gordon Gould definition of Laser as
    Light Amplification by Stimulated Emission of
    Radiation
  • (1960) Schawlow and Townes
    U. S. Patent
    No. 2,929,922
  • (1960) Theodore Maiman Invention of the first
    Ruby Laser
  • (1960) Ali Javan The first He-Ne Laser

11
  • Maiman and the first ruby laser

12
  • Ali Javan and the first He-Ne Laser

13
Properties of Laser Beam
  • A laser beam
  • Is intense
  • Is Coherent
  • Has a very low divergence
  • Can be compressed in time up to few femto second

14
Applications of Laser
  • (1960s) A solution looking for a problem
  • (Present time) Medicine, Research, Supermarkets,
    Entertainment, Industry, Military, Communication,
    Art, Information technology,

15
Start of Nonlinear Optics
  • Nonlinear optics started by the discovery of
    Second Harmonic generation shortly after
    demonstration of the first laser.
  • (Peter Franken et al 1961)

16
2. The Essence of Nonlinear Optics
  • When the intensity of the incident light to a
    material system increases the response of medium
    is no longer linear

17
Response of an optical Medium
  • The response of an optical medium to the incident
    electro magnetic field is the induced dipole
    moments inside the medium

18
Nonlinear Susceptibility
Dipole moment per unit volume or polarization
  • The general form of polarization

19
Nonlinear Polarization
  • Permanent Polarization
  • First order polarization
  • Second order Polarization
  • Third Order Polarization

20
How does optical nonlinearity appear
  • The strength of the electric field of the
    light wave should be in the range of atomic fields

21
Nonlinear Optical Interactions
  • The E-field of a laser beam
  • 2nd order nonlinear polarization

22
2nd Order Nonlinearities
  • The incident optical field
  • Nonlinear polarization contains the following
    terms

23
Sum Frequency Generation
Application Tunable radiation in the UV
Spectral region.
24
Difference Frequency Generation
25
Phase Matching
  • Since the optical (NLO) media are dispersive,
  • The fundamental and the harmonic signals have
  • different propagation speeds inside the media.
  • The harmonic signals generated at different
    points
  • interfere destructively with each other.

26
SHG Experiments
  • We can use a resonator to increase the efficiency
    of SHG.

27
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28
Third Order Nonlinearities
  • When the general form of the incident electric
    field is in the following form,
  • The third order polarization will have 22
    components which their frequency dependent are

29
The Intensity Dependent Refractive Index
  • The incident optical field
  • Third order nonlinear polarization

30
The total polarization can be written as
One can define an effective susceptibility
The refractive index can be defined as usual
31
By definition
where
32
Typical values of nonlinear refractive index
Mechanism n2 (cm2/W) (esu) Response time (sec)
Electronic Polarization 10-16 10-14 10-15
Molecular Orientation 10-14 10-12 10-12
Electrostriction 10-14 10-12 10-9
Saturated Atomic Absorption 10-10 10-8 10-8
Thermal effects 10-6 10-4 10-3
Photorefractive Effect large large Intensity dependent
33
Third order nonlinear susceptibility of some
material
Material ? 1111 Response time
Air 1.210-17
CO2 1.910-12 2 Ps
GaAs (bulk room temperature) 6.510-4 20 ns
CdSxSe1-x doped glass 10-8 30 ps
GaAs/GaAlAs (MQW) 0.04 20 ns
Optical glass (1-100)10-14 Very fast
34
Processes due to intensity dependent refractive
index
  1. Self focusing and self defocusing
  2. Wave mixing
  3. Degenerate four wave mixing and optical phase
    conjugation

35
Self focusing and self defocusing
  • The laser beam has Gaussian intensity profile. It
    can induce a Gaussian refractive index profile
    inside the NLO sample.

36
Wave mixing
37
Optical Phase Conjugation
  • Phase conjugation mirror

38
Aberration correction by PCM
39
What is the phase conjugation
The signal wave
The phase conjugated wave
40
Degenerate Four Wave Mixing
  • All of the three incoming beams A1, A2 and A3
    should be originated
  • from a coherent source.
  • The fourth beam A4, will have the same Phase,
    Polarization, and
  • Path as A3.
  • It is possible that the intensity of A4 be more
    than that of A3

41
Mathematical Basis
The four interacting waves
The nonlinear polarization
The same form as the phase conjugate of A3
42
Holographic interpretation of DFWM
Bragg diffraction from induced dynamic gratings
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