Biomedical Engineering Reference
In-Depth Information
Table 3.2 Third-order non-linear optical (NLO) properties measured in
nanocomposite materials
1
3
measured
a
Measured
NLO strength
Unit
Part of w
λ (nm)
Composite
CdS in Nafion
10
7
cm
2
/W Im
6.1
6
ðw
3
Þ=a
480
10
7
cm
2
/W Im
CdS in Nafion/NH
3
8.3
6
ðw
3
Þ=a
450
10
5
Capped CdSe in PMMA 1.2
6
cm/W Im
ðw
3
Þ
544-560
10
8
2
2
0:5
CdS
x
Se
1-x
glass
1.3
6
esu
½
Re
ðw
3
Þ
þ
Im
ðw
3
Þ
532
10
12
2
2
0:5
CdS in sol-gel glass
5
6
esu cm
½
Re
ðw
3
Þ
þ
Im
ðw
3
Þ
=a
380
10
10
3
2
3
2
0
:
5
PPV in SiO
2
3
6
esu
½
Re
ðw
Þ
þ
Im
ðw
Þ
602
2
2
0
:
5
10
10
3
3
PPV in V
2
O
5
6
6
esu
½
Re
ðw
Þ
þ
Im
ðw
Þ
602
10
12
cm
2
/W Re
3
GaAS in Vycor glass
5.6
6
ðw
Þ
1064
Standard NLO materials
Fused quartz
10
14
3
8.5
6
esu
Re
ðw
Þ
1064
10
13
3
SF
6
8
6
esu
Re
ðw
Þ
1064
10
11
3
CdS
5
6
esu
Re
ðw
Þ
610
a
α
is the absorption coefficient
5
D
0
-
7
F
2
transition of Eu
3+
ions (614 nm) in densified silica and Al
3+
co-
doped silica matrices. The sharp lines observed between 200 and 500 nm are
assigned to the f-f transitions of the Eu
3+
ions in the glasses. However, a
broad band with a peak at 300 nm is observed only in the aluminum co-
doped sample that contains both Eu
2+
and Eu
3+
ions. The excited Eu
2+
ions in the 4f
6
5d (e
g
) level can relax to the ground state by transferring
energy to the Eu
3+
ions which, in turn, are excited to the
5
D
2
level.
3.4
Non-linearity
Non-linear optics is the branch of optics that describes the behavior of light
in non-linear media, that is, media in which the dielectric polarization P
responds non-linearly to the electric field E of the light (i.e electric
polarization is the cause of optical non-linearity), which can be expressed
as
31
P
NL
¼ w
ð
2
Þ
EE
þ w
ð
3
Þ
EEE
þ
½
3
:
2
where P
NL
is non-linear electric polarization, E is the incident electric field
and
(3)
are the second- and third-order non-linear optical
susceptibility terms, respectively. Theoretically,
(2)
χ
χ
and
(2)
is zero for materials
having inversion symmetry in a region whose size is of the order of the
wavelength of an incident beam but
χ
(3)
has a finite value in all substances
χ
(Table 3.2).
Glasses are optically isotropic so they should not have second-order
