Nonlinear Optics Lab
Nonlinear Optics Lab . . Hanyang Univ. Hanyang Univ.
Chapter 8. Second-Harmonic Generation
and Parametric Oscillation
8.0 Introduction
Second-Harmonic generation : Parametric Oscillation :
2
) (
1 2 32 1
3
Reference :
R.W. Boyd, Nonlinear Optics,
Chapter 1. The nonlinear Optical Susceptibility
Nonlinear Optics Lab
Nonlinear Optics Lab . . Hanyang Univ. Hanyang Univ.
The Nonlinear Optical Susceptibility
General form of induced polarization :
( ) ( ) ( )
)
(t (1)E t (2)E2 t (3)E3 t
P
P(1)(t) P(2)(t) P(3)(t)
: Linear susceptibility where,
(1): 2
nd(2 order nonlinear susceptibility) : 3
rd(3 order nonlinear susceptibility)) 2
P(
: 2nd order nonlinear polarization
) 2
P(
: 3rd order nonlinear polarization
Maxwell’s wave equation :
2 2 2
2 2 2 2
t P t
E c
E n
Source term : drives (new) wave
Nonlinear Optics Lab
Nonlinear Optics Lab . . Hanyang Univ. Hanyang Univ.
Second order nonlinear effect
) ( )
( (2) 2
) 2
( t E t
P
Let’s us consider the optical field consisted of two distinct frequency components ; c.c.
)
(t E1ei 1tE2ei 2t
E
] [
2
] c.c.
2 2
[ )
(
* 2 2
* 1 1 ) 2 (
) (
* 2 1 )
( 2 1 2
2 2 2
2 1 ) 2 ( )
2
( 1 2 1 2 1 2
E E E E
e E E e
E E e
E e
E t
P
i t i t i t i t
(OR) )
( 2
) 0 (
) DFG (
2 ) (
) SFG (
2 ) (
) SHG (
) 2 (
) SHG (
) 2 (
* 2 2
* 1 1 ) 2 (
* 2 1 ) 2 ( 2
1
2 1 ) 2 ( 2
1
2 2 ) 2 ( 2
2 1 ) 2 ( 1
E E E E P
E E P
E E P
E P
E P
: Second-harmonic generation: Sum frequency generation
: Difference frequency generation : Optical rectification
# Typically, no more than one of these frequency component will be generated Phase matching !
Nonlinear Optics Lab
Nonlinear Optics Lab . . Hanyang Univ. Hanyang Univ.
Nonlinear Susceptibility and Polarization
1) Centrosymmetric media (inversion symmetric) : V ( x ) V ( x )
Potential energy for the electric dipole can be described as
4 ...
) 2
(
02 2 m Bx
4 m x
x
V
Restoring force :
3
...
2
0
m x mBx
x
F V
Equation of motion :
m t eE Bx
x x
x 2
02
3 ( )/
Damping force
Restoring force
Coulomb force
Nonlinear Optics Lab
Nonlinear Optics Lab . . Hanyang Univ. Hanyang Univ.
Purtubation expansion method :
c.c.
)
(t E1ei 1tE2ei 2t
E
Assume,
) ( )
(t E t E
x(1) (2)x(2) (3)x(3)
x
Each term proportional to n should satisfy the equation separately
m t eE x
x
x(1)2
(1)
02 (1) ( )/0 2 (2) 02 (2)
) 2
( x x
x
0 2 (3) 02 (3) 3(1)
) 3
( x x Bx
x
: Damped oscillator
x
(2) 0
Second order nonlinear effect in centrosymmetric media can not occur !
Nonlinear Optics Lab
Nonlinear Optics Lab . . Hanyang Univ. Hanyang Univ.
2) Noncentrosymmetric media (inversion anti-symmetric) : V ( x ) V ( x )
Potential energy for the electric dipole can be described as
3 ...
) 2
(
02 2 m Dx
3 m x
x
V
Restoring force :
2
...
2
0
m x mDx
x
F V
Equation of motion :
m t eE Dx
x x
x 2
02
2 ( )/
Damping force
Restoring force
Coulomb force
Nonlinear Optics Lab
Nonlinear Optics Lab . . Hanyang Univ. Hanyang Univ.
Similarly,
c.c.
)
(t E1ei 1tE2ei 2t
E
Assume,
) ( )
(t E t E
x(1) (2)x(2) (3)x(3)
x
Each term proportional to n should satisfy the equation separately
m t eE x
x
x(1)2
(1)
02 (1) ( )/0 ] [
2 (2) 02 (2) (1) 2
) 2
( x x D x
x
0 2
2 (3) 02 (3) (1) (2)
) 3
( x x DBx x
x
Solution :
c c e
x e
x t
x(1)( ) (1)(
1) i1t (1)(
2) i2t .
j j
j j
j
j i
E m
e L
E m x e
2 )
) (
( 2 2
0 )
1 (
: Report
Nonlinear Optics Lab
Nonlinear Optics Lab . . Hanyang Univ. Hanyang Univ.
Example) Solution for SHG
) ( ) / 2 (
1 2
2 1 2
2 )
2 ( 2 0 ) 2 ( )
2
( 1
L
E e
m e x D
x x
t
i
Put general solution as x(2)(t)x(2)(2
1)e2i1t) ( ) 2 (
) / ) (
2 (
1 2 1
2 1 2 1
) 2 (
L L
E m e
x D
: Report Similarly,
) ( ) 2 (
) / ) (
2 (
2 2 2
2 2 2 2
) 2 (
L L
E m e x D
) ( ) ( ) (
) / ( ) 2
(
2 1
2 1
2 1 2 2
1 ) 2 (
L L L
E E m e x D
) ( ) ( ) (
) / ( ) 2
(
2 1
2 1
* 2 1 2 2
1 ) 2 (
L L L
E E m e x D
) (
) ( ) 0 (
) / ( 2 )
( ) ( ) 0 (
) / ( ) 2
0 (
2 2
* 2 2 2
1 1
* 1 1 ) 2
2 (
L L
L
E E m e D L
L L
E E m e x D
Nonlinear Optics Lab
Nonlinear Optics Lab . . Hanyang Univ. Hanyang Univ.
Susceptibility
) ( )
(j Nex j
P
( ) ( ) ( ))
(t P( ) (1)E t (2)E2 t (3)E3 t P
j
j
Polarization :
( )) / ) (
(
2 )
1 (
j
j L
m e N
: linear susceptibility
2 )
1 ( )
1 ( 3 2 2
2 ) 3
2
( (2 )[ ( )]
) ( ) 2 (
) / ) (
, , 2
( j j
j j
j j
j N e
mD L
L
a m e
N
: SHG
) ( ) ( ) (
) / ) (
, , (
2 1
2 1
2 3 2
1 2 1 ) 2 (
L L L
D m e N
2 3(1)(12)(1)(1)(1)(2) e
N mD
) ( ) ( ) (
) / ) (
, , (
2 1
2 1
2 3 2
1 2 1 ) 2 (
L L
L
D m e N
: SFG
: DFG
: OR
) ( ) ( )
( 1 2 (1) 1 (1) 2
) 1 ( 3
2
N e mD
) (
) ( ) 0 (
) / ) (
, , 0 (
2 ) 3
2 (
j j
j
j L L L
D m e N
2 3 (1)(0) (1)( j) (1)( j)
e N
mD
Nonlinear Optics Lab
Nonlinear Optics Lab . . Hanyang Univ. Hanyang Univ.
<Miller’s rule>
- empirical rule, 1964) ( ) ( ) (
) , , (
2 ) 1 ( 1 ) 1 ( 2 1 ) 1 (
2 1 2 1 ) 2 (
3 2e N
mDis nearly constant for all noncentrosymmetric crystals.
# N ~ 1023 cm-3 for all condensed matter
# Linear and nonlinear contribution to the restoring force would be comparable when the displacement is approximately equal to the size of the atom (~order of lattice constant d) :
m02d=mDd D=w02/d : roughly the same for all noncentrosymmetric solids.
4 4 0 2
3 )
2 (
d m
e
(non-resonant case) : used in rough estimation of nonlinear coefficient.
2 0 2
2
0 2
)
(j j ij
L N1 d/ 3 D02/d
60
2 0 2 3 3
2 1
2 1
2 3 2
1 2 1 ) 2
( (1/ )( / )( / )
) ( ) ( ) (
) / ) (
, ,
(
d e m d
L L
L
D m e
N
3108esu
: good agreement with the measured values
Nonlinear Optics Lab
Nonlinear Optics Lab . . Hanyang Univ. Hanyang Univ.
Qualitative understanding of Second order nonlinear effect
in a noncentrosymmetric media
Nonlinear Optics Lab
Nonlinear Optics Lab . . Hanyang Univ. Hanyang Univ.
2 component
Nonlinear Optics Lab
Nonlinear Optics Lab . . Hanyang Univ. Hanyang Univ.
General expression of nonlinear polarization and
Nonlinear susceptibility tensor
General expression of 2nd order nonlinear polarization :
t i
m n
i t i
m n
i
i t P e n m P e n m
P(r, ) (
) ( ) (
) ( )), (
) ( ) , , (
) (
) (
) 2 (
m k n j m n m n jk nm
ijk m
n
i E E
P
where,
2nd order nonlinear susceptibility tensor
# Full matrix form of Pi(nm)
) ( ) ( ) , , (
) ( ) ( ) , , (
) ( ) ( ) , , (
) ( ) ( ) , , (
) (
2 2
2 2 2 2 ) 2 (
1 2
1 2 1 2 ) 2 (
2 1
2 1 2 1 ) 2 (
1 1
1 1 1 1 ) 2 (
k j
jk ijk
k j
jk ijk
k j
jk ijk
k j
jk ijk m
n i
E E
E E
E E
E E
P
2 , 1 , m n
: SHG
: SHG : SFG : SFG
Nonlinear Optics Lab
Nonlinear Optics Lab . . Hanyang Univ. Hanyang Univ.
Example 1. SHG
1 2
2 1
1 3
3 1
2 3
3 2
3 3
2 2
1 1
321 312
331 313
332 323
333 322
311
221 212
231 213
232 223
233 222
211
121 112
131 113
132 123
133 122
111
) 2 (
) 2 (
) 2 (
E E
E E
E E
E E
E E
E E
E E
E E
E E
P P P
n z
n y
n x
Example 2. SFG
.
) ( ) (
. .
. .
. ) , , (
.
. .
.
.
) ( ) (
. .
. .
. ) , , (
.
. .
. ) (
) (
) (
n k m j n
m m n ijk
m k n j m
n m n ijk m
n z
m n y
m n x
E E
E E
P P P
Nonlinear Optics Lab
Nonlinear Optics Lab . . Hanyang Univ. Hanyang Univ.
Properties of the nonlinear susceptibility tensor
1) Reality of the fields
) , r ( ), , r( t E t
Pi are real measurable quantities : )*
( )
( n m i n m
i P
P
*
*
) ( )
(
) ( )
(
m k m
k
n j n
j
E E
E E
ijk(2)(
n
m,
n,
m)
ijk(2)(
n
m,
n,
m)
*2) Intrinsic permutation symmetry
) , , (
) , , (
)
( n m ijk(2) n m n m ijk(2) n m m n Pi
Nonlinear Optics Lab
Nonlinear Optics Lab . . Hanyang Univ. Hanyang Univ.
4) Kleinman symmetry (nonresonant, is frequency independent)
) () (
) (
) (
) (
) (
2 1 3 ) 2 ( 2
1 3 ) 2 ( 2
1 3 ) 2 (
2 1 3 ) 2 ( 2
1 3 ) 2 ( 2
1 3 ) 2 (
kji jik
ikj
kij jki
ijk
intrinsic
3) Full permutation symmetry (lossless media : is real)
) (
* ) (
) (
) (
3 2 1
) 2 (
3 2 1
) 2 ( 3
2 1 )
2 ( 2
1 3 ) 2 (
jki
jki jki
ijk
: Indices can be freely permuted !
Nonlinear Optics Lab
Nonlinear Optics Lab . . Hanyang Univ. Hanyang Univ.
Define, 2
ndorder nonlinear tensor, d
ijk
21
ijk(2)) ( ) ( 2
) (
) (
m k n jk nm
j ijk m
n
i
d E E
P
## If the Kleinman’s symmetry condition is valid, the last two indices can be simplified to one index as follows ;
6 5
4 3
2 1 :
21 , 2 1 13 , 31 32 , 23 33 22 11 : l
jk
and,
36 35 34 33 32 31
26 25 24 23 22 21
16 15 14 13 12 11
d d d d d d
d d d d d d
d d d d d d
dil : 18 elements
d
can be represented as the 3x6 matrix ;ijkNonlinear Optics Lab
Nonlinear Optics Lab . . Hanyang Univ. Hanyang Univ.
Again, by Kleinman symmetry (Indices can be freely permuted),
14 13
23 33
24 15
12 14
24 23
22 16
16 15
14 13
12 11
d d
d d
d d
d d
d d
d d
d d
d d
d d
d
il : Reportdil has only 10 independent elements :
Nonlinear Optics Lab
Nonlinear Optics Lab . . Hanyang Univ. Hanyang Univ.
Example 1. SHG
) ( ) ( 2
) ( ) ( 2
) ( ) ( 2
) (
) (
) (
2 ) 2 (
) 2 (
) 2
( 2
2 2
36 35
34 33
32 31
26 25
24 23
22 21
16 15
14 13
12 11
y x
z x
z y
z y x
z y x
E E
E E
E E
E E E
d d
d d
d d
d d
d d
d d
d d
d d
d d
P P P
Example 2. SFG
) ( ) ( ) ( ) (
) ( ) ( ) ( ) (
) ( ) ( ) ( ) (
) ( ) (
) ( ) (
) ( ) (
4 ) (
) (
) (
2 1
2 1
2 1
2 1
2 1
2 1
2 1
2 1
2 1
36 35
34 33
32 31
26 25
24 23
22 21
16 15
14 13
12 11
3 3 3
x y
y x
x z
z x
y z
z y
z z
y y
x x
z y x
E E
E E
E E
E E
E E
E E
E E
E E
E E
d d
d d
d d
d d
d d
d d
d d
d d
d d
P P P
: Report
Nonlinear Optics Lab
Nonlinear Optics Lab . . Hanyang Univ. Hanyang Univ.
8.2 Formalism of Wave Propagation in Nonlinear Media
Maxwell equation
t
d
i
h t
h
e
d
0eP i σ e Polarization :P
0
ee P
NLAssume, the nonlinear polarization is parallel to the electric field, then
2 NL 2 2
2
e
2e P (r , )
e
tt t
t
Total electric field propagating along the z-direction :
.]
. )
( 2[ ) 1 , ( e
.]
. )
( 2[ ) 1 , ( e
.]
. )
( 2[ ) 1 , ( e
) (
3 )
(
) (
2 )
(
) (
1 )
(
3 3 3
2 2 2
1 1 1
c c e
z E t
z
c c e
z E t
z
c c e
z E t
z
z k t i
z k t i
z k t i
) , ( e ) , ( e ) , ( e
e (1) z t (2) z t (2) z t
where,
2 1
3
and
Nonlinear Optics Lab
Nonlinear Optics Lab . . Hanyang Univ. Hanyang Univ.
1term
. .
2
) ( ) ( e
e e
[( ) ( )* 2 3
2 2 2
) 2 ( 1 )
( 1 )
(
2 1 1 1 E z E z e 3 2 3 2 cc
d t t
t
z k k t i
( )
( )
. .
) 2 ( 2
1
( )1 2 1 ) 1 (
1 )
( 2
1 2
1 1 1
1 1
1
e k E z e c c
z z ik E
z e z
E
i t k z i t k z i t k z. ) .
2 ( ) 2 (
1
1 ( )1 1
2
1
e
1 1c c
dz z ik dE
z E
k
i t k z
2 1 2 1 1
) ( )
(
dz z E d dz
z
k dE (slow varying approximation)
...
TextNonlinear Optics Lab
Nonlinear Optics Lab . . Hanyang Univ. Hanyang Univ.
z k k k
e
iE E i d
dz E
dE
* ( )3 1 2
* 2 2 2 2
*
2 1 3 2
2 2
z k k k
e
iE E i d
dz E
dE
( )2 1 3
3 3
3 3
3 1 2 3
2 2
z k k k
e
iE E i d
dz E
dE
* ( )2 3 1
1 1 1 1
1 3 2 1
2 2
Similarly,