LASER-INDUCED PROCESSES IN FULLERENE-DOPED
ORGANIC STRUCTURES
Natalie V. Kamanina
Vavilov State Optical Institute, 12 Birzhevaya Line, St. Petersburg, 199034
Russia;
e-mail: kamanin@ffm.ioffe.ru
ABSTRACT. The laser-induced processes in the fullerene-doped -conjugated
organic systems based on 2-cyclooctylamino-5-nitropyridine, polyimide,
phthalocyanine, etc. have been studied. The optical limiting experiments have been
performed at wavelength of 532, 805, 1047, 1315 and 2940 nm. The reversible
holographic recording experiments have been carried out at 532 and 1315 nm under
the Raman-Nath diffraction conditions at spatial frequency of 100 mm-1. The
nonlinear refraction and third order susceptibility have been estimated from
holographic recording data. The place of the systems studied among other materials
used traditionally for nonlinear optics has been established.
INTRODUCTIONS
During last decade great interest has been expressed in laser-induced properties of
organic conjugated systems doped with fullerene (1-4). The optical properties, which
are conditioned by excitation of -electrons, demonstrate that a new charge-transfer
complex (CTC) is formed between donor fragment of an organic molecule and
fullerene one. The possible scheme of donor-acceptor (D-A) interaction in the
fullerene-doped structures is shown in Fig.1.
e

D
A
e
Fig. 1. The possible scheme of D-A interaction in the fullerene-doped structures
As the results of the CTC formation, the following evidences should be mentioned:
 This complex is of a higher excited state absorption cross section than the
ground state one. That is why fullerene-doped systems are reverse saturable
absorption (RSA) materials and may be used as nonlinear absorbers for a
sensors and eyes protection (5-9).
 Fullerene sensitization and complex formation provokes new spectral and
energy range for the conjugated structures treated. The bathochromic shift is
observed and new absorption band in the IR spectral range appears in the
fullerene-doped materials (4,10-12).
4-1
 The field gradient is formed as the charge transfer path changes (the charge is
transferred from the intramolecular donor fragment not to the intramolecular
acceptor one but to fullerene). As the result, the photorefractive effect is
possible in these structures. The drastic change in the refractive index has been
revealed. The large laser-induced change in the refractive index predicts large
nonlinear refraction n2 and third order susceptibility (3) (13,14).
 The temporal characteristics of the liquid crystal systems based on fullerenecontaining complexes are improved drastically (15,16). That is why the new
potentials to apply fullerene-doped structures for correction of phase
aberration and in display techniques should be detected.
In the present paper the optical limiting (OL) and holographic recording properties of
the materials based on 2-cyclooctylamino-5-nitropyridine (COANP), polyimide,
phthalocyanine have been studied. The place of the systems investigated among other
materials used traditionally for nonlinear optics has been established.
EXPERIMENTAL CONDITIONS, RESULTS AND DISCUSSIONS
3 % solutions of photosensitive components in 1,1,2,2–tetrachloroethane (TClE) were
generally used. The solution was doped with fullerenes C60 or/and C70. The fullerene
concentration was varied from 0.2 wt.% to 5 wt.%. It should be mentioned that
fullerenes are of relatively high solubility (about 5.3 mg mL-1) (17) in TClE. The 2.5–
5 µm films were spun on the glass substrates coated with transparent indium-tin-oxide
contacts. The general view of the thin films treated is shown in Fig.2.
Fig. 2. The general view of the thin fullerene-doped thin films
The optical limiting experiments have been performed at wavelength of 532, 805,
1047, 1315 and 2940 nm. The scheme was analogous to that shown in the papers
(18,19). More than 10-fold attenuation of the laser energy has been obtained for the
materials treated. It should be mentioned that the reverse saturable absorption is the
main OL mechanism in the visible spectral region. The shift of the absorption band
related to plasmon resonance; thermal change in permittivity of the components, lightinduced complex formation, nonlinear scattering; sublimation of carbon nanoparticles,
two-photon absorption, possible change of refractive index related to RF Kerr effect,
multiphoton processes, etc are responsible for the OL in the near and middle infrared
spectral region.
The basic results for the near infrared are presented in Table 1. For comparison, OL
materials data in IR obtained by other authors are shown in Table 1 as well.
4-2
Table 1. Comparative data on OL over the IR range
System
Initial
transmission,
%
Composite based
on silver halide
with nano-particles
of metallic silver
Wavelength,
nm
Pulse
width,
ns
OL
threshold,
Jcm-2
38004200
250
0.0050.025
Destruction
threshold,
Jcm-2
Ref.
(20)
2-(n-prolinol)-5nitropyridine-C60
65-70
2940
500 s
0.9-1
1.5
(21)
Polyimide-C70
~80
1315
50
0.08-0.1
~2
(12)
Zn-Pc-C60
75-80
1064
nanoseconds
Carbon-black
suspensions (SBS)
both in water and
in CS2
~80
1064
10
0.12-0.7
(23)
Carbon nanotube
suspensions both
in water and in
chloroform
90
1064
6
0.15-0.35
(24)
C60 (solution)
~85
1064
35 ps
~3
(25)
Polyimide-С70
~79-85
1047
8
0.6-0.7
~2.5-3
(26)
Mg-Pc-С60
70
1047
8
1.5
>3
(27)
Liquid
crystal+COANP+
C70
65
805
70 fs
>0.5
(28)
C60 (solution)
84
710740
10
(22)
2
(29)
The reversible holographic recording experiments have been carried out at 532 nm
(second harmonic of pulsed Nd-laser) and 1315 nm (pulsed iodine laser) under the
Raman-Nath diffraction conditions at spatial frequency of 100 mm-1. The change in
the light-induced refractive index ni has been estimated using equation given in the
paper (30). The calculated curves for polyimide materials, which correspond to the
previous experimental data, are shown in Fig. 3. ni increases from 2.1510-4 to
4.6810-3 and from 3.7110-4 to 5.0410-4 upon irradiation by nano- and by
picosecond pulses, respectively at wavelength of 532 nm. In this case, the incident
energy density increases from 0.03 to 0.6 Jcm-2. The value of ni is more than that
corresponding to the thermal nonlinearity (~10-4).
4-3
It should be noticed that ni ~ 10-3 has been obtain for the near IR at wavelength of
1315 nm as well.
-2
10
20 ns
C70-doped polyimide
-3
10
ni
400 ps
-4
10
pure polyimide (20 ns)
-5
10
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
-2
Win, J cm
Fig. 3. Dependence of the induced change in the refractive index on the incident
energy density for pure polyimide and polyimide with 0.2 wt.% С70
The large value of the light-induced refractive index in the fullerene-doped
compounds contributes significantly to the OL effect (due to energy losses by
diffraction), explains holographic recording in these media because of the
photorefractive effect even without an electrical control, and also predicts the large
values of nonlinear refraction n2 and third order susceptibility (3). These parameters
have been estimated using the relationships (31):
n2 
ni
I
 ( 3) 
(1)
n 2 n0 c
16 2
(2)
where ni is the laser-induced change of refractive index, I is the input laser intensity,
n0 and n2 is the linear and nonlinear refractive index, respectively, c is the velocity of
light. The corresponding data are presented in Table 2. The nonlinear refraction n2 and
the third order susceptibility (3) were determined to be 0,7810-10 cm2 W-1 and
2,6410-9 cm3 erg-1, respectively.
It should be mentioned that the data obtained are close to those for silicon and gives
an opportunity to estimate the place of fullerene-doped conjugated systems studied
among other materials used traditionally for nonlinear optics (32).
CONCLUSIONS
Nonlinear optical properties of the fullerene-doped conjugated structures and
polymer-dispersed liquid crystal ones based on 2-cyclooctylamino-5-nitropyridine,
polyimide, etc. have been studied to apply these materials as effective nonlinear
absorber, holographic recording element, and spatial light modulator in the visible and
in the near-infrared spectral ranges. To indicate the OL mechanisms and OL
threshold, the comparative results have been shown for different laser materials
4-4
successfully used in optoelectronics. From the induced changes of the refractive
index, the nonlinear refraction n2 and the third order susceptibility (3) were
determined. They were, respectively:~10-7 cm2kW-1 and ~10-9 esu for thin films of the
fullerene-doped organic structures; ~10-6 cm2kW-1 and ~10-8 esu for the fullerenedoped polymer-dispersed liquid crystals. The place of the materials studied has been
found among other nonlinear optical systems.
Table 2. Nonlinear optical coefficients of materials
Materials
CS2
Silica
С60 film
С60 film
С60 film
С70 film
С70 film
Cu - phthalocyanine
Pb - phthalocyanine
-TiO- phthalocyanine
Polyimide + С70
Polyimide + С70
COANP + C60
COANP + C70
PDLC based on COANP + C70
Si
Liquid crystal
n2,
cm2 W-1
310-14
310-16
0.7810-10
-1.210-9
0,6910-10
0,7710-10
1.610-9
10-10
10-4
(3),
cm3 erg-1
10-12
10-14
0.710-11
8.710-11
210-10
1.210-11
2.610-11
2.10.2 10-12
210-11
1.5910-10
2.6410-9
1.910-10
2,1410-9
2,410-9
4.8610-8
10-8
10-3
References
(31)
(31)
(33)
(34)
(35)
(36)
(34)
(37)
(38)
(39)
(13,14)
(40)
(9)
(9,41)
(42)
(31)
(31)
ACKNOWLEDGEMENTS
The author wish to thank Dr. V.I. Berendyaev (Karpov Research Physical-Chemical
Institute, Moscow, Russia), Dr. I.Yu.Denisyuk (Vavilov State Optical Institute, St.
Petersburg, Russia), Prof. I.M. Belousova, Dr. A.P. Zhevlakov and Dr.A.A.
Nikitichev (Institute for Laser Physics, St. Petersburg, Russia) for helpful discussions.
Young scientists M.M. Mikhailova and A.V. Varnaev have taken part in this study.
This work was partially supported by RFBR grant No. 04-03-32249-а.
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