Study on third-order nonlinear optical properties of 4-methylsulfanyl chalcone derivatives using picosecond pulses

Article abstract of DOI:10.1016/j.materresbull.2012.06.063

In this paper we present results from the experimental study of third-order nonlinear optical (NLO) properties of three molecules of Br and NO₂ substituted chalcone derivatives namely (2E)-1-(4-bromophenyl)-3- [4(methylsulfanyl)phenyl]prop-2-en

Full text of DOI:10.1016/j.materresbull.2012.06.063

Materials Research Bulletin 47 (2012) 3552–3557
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Study on third-order nonlinear optical properties of 4-methylsulfanyl chalcone
derivatives using picosecond pulses
b
b
a
E.D. D’silva a, , G. Krishna Podagatlapalli , S. Venugopal Rao , S.M. Dharmaprakash
*
a Department of Studies in Physics, Mangalore University, Mangalagangotri, Mangalore 574199, India
b Advanced Centre of Research in High Energy Materials (ACRHEM), University of Hyderabad, Hyderabad 500046, India
A R T I C L E I N F O
A B S T R A C T
Article history:
In this paper we present results from the experimental study of third-order nonlinear optical (NLO)
properties of three molecules of Br and NO2 substituted chalcone derivatives namely (2E)-1-(4-
bromophenyl)-3-[4(methylsulfanyl)phenyl]prop-2-en-1-one (4Br4MSP), (2E)-1-(3-bromophenyl)-3-
[4-(methylsulfanyl) phenyl]prop-2-en-1-one (3Br4MSP) and (2E)-3[4(methylsulfanyl) phenyl]-1-(4-
nitrophenyl)prop-2-en-1-one (4N4MSP). The NLO properties have been investigated by Z-scan
technique using 2 ps laser pulses at 800 nm. The nonlinear refractive indices, nonlinear absorption
coefficient, and the magnitude of third-order susceptibility have been determined. The values obtained
are of the order of 10ꢀ7 cm2/GW, 10ꢀ3 cm/GW and 10ꢀ14 esu respectively. The molecular second
hyperpolarizability for the chalcone derivatives is of the order of 10ꢀ32 esu. The coupling factor, excited
state cross section, ground state cross section etc. were determined. The optical limiting (OL) property
was studied. The results suggest that the nonlinear properties investigated for present chalcones are
comparable with some of the reported chalcone derivatives and can be desirable for NLO applications.
ß 2012 Elsevier Ltd. All rights reserved.
Received 21 May 2012
Accepted 19 June 2012
Available online 29 June 2012
Keywords:
A. Optical materials
A. Organic compounds
D. Optical properties
1. Introduction
belong to the class of low molecular charge transfer (CT)
compounds that show strong nonlinear optical properties without
The application of nonlinear optics in optoelectronic and
photonic devices grasped the attention on nonlinear optical
materials. Especially, nonlinear optical materials exhibiting strong
two-photon absorption (TPA) are in great demand, due to their
applications in three-dimensional fluorescence imaging and multi-
photon microscopy, eye and sensor protection, frequency up
conversion lasing, optical signal reshaping and stabilizing fast
fluctuations of laser power [1–5]. There is a need to design and
develop novel nonlinear materials with large molecular two-
photon absorption cross-sections to meet the present demand.
However, such attempts toward understanding the third-order
NLO properties of organic crystals are very limited [6–8]. Organic
materials are attractive because of their optical and electronic
properties which can be tuned by structural modifications. Organic
materials with large third-order nonlinear optical (NLO) properties
will be the key elements for future photonic technologies [9–11].
The large and ultrafast NLO response has made organic molecules
attractive candidates for high bandwidth applications. Chalcones
longer wavelength absorption. These emerged as promising
candidates for third order nonlinear optics because of their
noticeable third order nonlinearity and good optical power
limiting properties [12–15]. Since the chalcone backbone is an
asymmetric transmitter, it strongly increases the molecular
nonlinearity for the electron donating and withdrawing group
substitutions. Generally in charge transfer compounds, large
nonlinear electronic polarization arises due to the large dipole
moment change from ground state to an excited state by optical
radiation [16]. The other advantage of chalcone molecules is that it
offers greater flexibility in adopting suitable design strategies
[17,18], and thereby enhancing the nonlinear optical coefficients.
In this paper we report our investigations on third ordered
nonlinear optical properties of three chalcone molecules namely,
(2E)-1-(4-bromophenyl)-3-[4-(methylsulfanyl)phenyl]prop-2-en-
1-one (4Br4MSP), (2E)-1-(3-bromophenyl)-3-[4 (methylsulfanyl)
phenyl]prop-2-en-1-one (3Br4MSP) and (2E)-3[4(methylsulfanyl)
phenyl]-1-(4-nitrophenyl)prop-2-en-1-one (4N4MSP) by adopting
the picosecond (ps) Z-scan technique. The ps studies are important
to identify the electronic part of nonlinearity. Open aperture data
provided the nonlinear absorption coefficients while the closed
aperture data provided nonlinear refractive index. The contribu-
tion of solvent is also identified.
* Corresponding author. Tel.: +91 8970093263; fax: +91 8242287367.
E-mail addresses: deepak.dsilva@gmail.com (E.D. D’silva),
soma_venu@yahoo.com (S. Venugopal Rao).
0025-5408/$ – see front matter ß 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.materresbull.2012.06.063

E.D. D’silva et al. / Materials Research Bulletin 47 (2012) 3552–3557
3553
2. Experimental procedure
measurements were done at room temperature. Sample in the
cuvette moved from the extreme end of the translation stage to the
other end in steps of 1 mm, and transmitted power is noted down
for each position of the sample using a power sensor (COHERENT
The compounds were synthesized by following the standard
procedure namely Clainsen–Schmidt condensation method [19–
21]. This is
a
reaction of substituted acetophenone with
Power Max, measuring range: 1 mW–1 W). We also demonstrate
substituted benzaldehyde in the presence of an alkali. Commer-
cially available 4-bromoacetophenone, 3-bromoacetophenone, 4-
nitroacetophenone was treated with 4-methylthiobenzaldehyde
to get 4Br4MSP, 3Br4MSP, 4N4MSP respectively. The compounds
were used without further purification. The synthesis of the
compounds follows literature method. The resulting crude after
synthesis reaction was collected by filtration, dried and purified by
repeated crystallization from acetone. The structures of the
compounds are shown in Fig. 1. The linear absorption spectra of
the samples recorded at room temperature in dilute DMF solution
(2 ꢁ 10ꢀ2 mol/L) using a spectrophotometer (SHIMADZU UV-
1800) is shown in Fig. 2. The linear absorption spectrum of
solutions shows that all the compounds are transparent at 800 nm.
The linear refractive index of these samples dissolved in DMF was
measured using an Abbe refractometer. The single beam Z-scan
technique was employed to study the nonlinear optical properties
of these compounds [22,23]. This technique is particularly useful
when the nonlinear refraction is accompanied by nonlinear
absorption and allows one to measure both sign and magnitude
of the nonlinear refractive index. The transmittance of the
nonlinear medium through a finite aperture in the far field as a
function of the sample position is measured with respect to the
focal plane of the focused Gaussian laser beam. Here the sample
itself acts as a thin lens with varying focal length as it moves
through the focus. When the intensity of the laser beam is
sufficient to induce the nonlinearity in the sample, the laser beam
either focuses or defocuses depending upon the nature of the
nonlinearity of the material.
The experiment is performed by using Z-scan experimental
setup with a ps amplifier [seeded by Micra laser oscillator
(COHERENT)] generating pulses of duration ꢂ2 ps at a repetition
of 1 kHz. The experiment has been done at 800 nm wavelength
only. The maximum average and peak powers are ꢂ2 W and
ꢂ1 GW, respectively. The diameter of the beam from the amplifier
is 4 mm. Using ND filters power has been reduced to avoid sample
damage. Sample solutions are prepared using DMF as a solvent.
4N4MSP, 3Br4MSP are made of 10 mM and 4Br4MSP is prepared
with a concentration of 15 mM. The 800 nm beam is focused using
a 20 cm biconvex lens and allowed to pass through a 1 mm quartz
cuvette that contained sample solution. The resulting beam waist
the strong optical power limiting property of ps laser pulses at
800 nm based on the two photon absorption (TPA) process. In the
open aperture (OA) scheme the aperture of the power sensor is
fully opened and transmission is noted down where as in closed
aperture (CA) scheme the aperture of the power sensor is partially
closed and the transmittance is recorded. In both of the cases plots
had been taken for position versus normalized transmittance using
MATLAB and ORIGIN. From the open aperture analysis we can find
out the nonlinear absorption coefficient/two photon absorption
coefficient (b). From the closed aperture analysis we can calculate
intensity dependent refractive index (n2) of the sample.
3. Result and discussion
The nonlinear absorption in the materials arising from either
direct multi-photon absorption, saturation of the single photon
absorption, or dynamic free carrier absorption has strong effect on
the measurements of nonlinear refraction using the Z-scan
technique. When Z-scan with open aperture (S = 1) is performed,
will be insensitive to nonlinear refraction (thin sample approxi-
mation). Such Z-scan traces with no aperture are expected to be
symmetric with respective to the focus (z = 0) where they have a
minimum transmittance (e.g. multi-photon absorption) or maxi-
mum transmittance (e.g. saturation of absorption). In fact the
coefficient of nonlinear absorption can be easily calculated from
such transmittance curves. The third order nonlinear susceptibility
is a complex quantity
xð3Þ
¼
xðR3Þ þ ixðI3Þ
(1)
where the imaginary part is related to the 2PA coefficient
through
b
n20 0c2
e
v
xðI3Þ
¼
b
(2)
and the real part is related to
g through
xðR3Þ ¼ 2n20
e
0c
g
(3)
In the case of 2PA the nonlinear absorption coefficient
b
is related
radius at the focus was 25.44
mm that corresponds to the Rayleigh
to linear absorption coefficient by the relation
a
ðIÞ ¼ a0
þ
bI. This
length of 2.54 mm. The sample thickness of 1 mm is lesser than
Rayleigh length and therefore could be treated as thin medium. The
Z-scan performed at laser pulse energy of 1 mW, which resulted in
an on-axis peak irradiance of 49 GW/cm2. All the sample
yields the irradiance distributionandphaseshift ofthebeamatthe exit
a
L
surface of the sample as Ieðz; r; tÞ ¼ ðIðz; r; tÞeꢀ Þ=ð1 þ qðz; r; tÞÞ and
Dfðz; r; tÞ ¼ ðk
g
=
b
Þln ½1 þ qðz; r; tÞꢃ, where qðz; r; tÞ ¼
b
Iðz; r; tÞLe f f
.
In the case of open aperture Z-scan (S = 1), for a Gaussian beam, the
O
O
Br
SCH3
O
O2N
SCH3
Br
SCH3
Fig. 1. Molecular structure of 4Br4MSP, 4N4MSP and 3Br4MSP.

3554
E.D. D’silva et al. / Materials Research Bulletin 47 (2012) 3552–3557
The open aperture Z-scan curves are shown in Fig. 3. The
experimental data was fitted with the theoretical formula for two
photon absorption. The presence of valley in normalized transmit-
tance in open aperture scans indicates strong reverse saturation
absorption (RSA) at peak intensities. The closed aperture measure-
ments were carried at the input energy of 1 mW. The nonlinear
refraction (NLR) curves of the compounds are shown in Fig. 4. The
valleyfollowed by peakinthe normalized transmittancedata clearly
suggests that the sample possesses positive type of nonlinearity and
self-focusing behavior. In order to identify the contribution from the
solventDMF, theZ-scanwasperformed onitand observedsamesign
and a higher value of n2 (n2 = 3 ꢁ 10ꢀ16 cm2/W) indicating that the
solute had an opposite sign of nonlinearity (Fig. 5). The magnitudes
of n2 are estimated to be ꢂ10ꢀ16 cm2/W. The slightly deviation for
the fitted line and the experimental data for closed aperture fit of
4N4MSP may be due to thermal contribution to the nonlinearity,
higher order nonlinear effect or nonlinear scattering [15]. The
experimentally determined values of be f f , n2, Re x3 and Im x3 are
given in the Table 1. The values calculated in Table 1 include the
3
2
1
0
3Br4MSP
4Br4MSP
4N4MSP
300 400 500 600 700 800 900 1000
Wavelength (nm)
Fig. 2. Linear absorbance spectrum of chalcone derivatives.
transmittance can be given by the equation [22], TðzÞ ¼ ln½1 þ
q0ðzÞꢃ=q0ðzÞ for jq0ðzÞj < 1, where q0ðzÞ ¼
b
I0Le f f =ð1 þ z2=z02Þ.
sqoffilffivffiffiffieffiffinffiffiffitffiffiffiffiffiffiffiffifficffiffioffiffiffinffiffiffitffiffirffiffiiffibffiffiffiuffiffiffitffiiffiffioffiffinffiffiffi.ffi The
calculated
value of x3
¼
2
2
Þ
For a cubic nonlinearity and a small phase it can be shown that
the normalized transmittance in the case of closed aperture z-scan is
ðRe xð3ÞÞ þ ðIm xð3Þ
(using Eqs. (2) and (3)) for the samples is
of the order of 10ꢀ14 esu and is influenced by different donor or
acceptor group substitutions and their position on the aromatic ring
in the molecular structure of chalcone [24]. The value of n2 is found
to be of the order of 10ꢀ14 esu.
4
Df0x
2
Df0ð3 þ x2Þ
TðzÞ ¼ 1 þ
ꢀ
;
ð1 þ x2Þð9 þ x2Þ ð1 þ x2Þð9 þ x2Þ
0:25
Among the compounds studied, 4N4MSP shows high x3 value
compared with 4Br4MSP. The Br acts as an electron donating
group, whereas SCH3 is also an electron donor group. 4Br4MSP can
be considered as effective D–A–D (donor–acceptor–donor) type of
molecule. In the case of 4N4MSP, the nitro group present is a strong
acceptor group and a molecule is A–A–D type. In the case of D–A–D
type of molecules charge transfer takes place through donor to
acceptor and in A–A–D type through acceptor end to donor end
(between two end groups of the molecules). x3 value found to
increase with the presence of strong acceptor or donor groups.
3Br4MSP shows less value of x3 when compared with other two
where Df0
Df0 ¼ ð1=2Þ
¼
D
T
PꢀV =0:406ð1 ꢀ SÞ
for
j
Df0j ꢄ
p
and
b
I0Le f f
.
For a pure nonlinear refraction curve, obtained by division of
closed aperture scan by open aperture scan, the normalized
transmittance is shown to be
4Df0x
TðzÞ ¼ 1 þ
ð1 þ x2Þð9 þ x2Þ
OnceDf0 is calculated, one can readily calculate
[24] Df0l=2
the conversion formula given by n2ðesuÞ ¼ ðcn0=40
g
usingequation
g
¼
pLe f f I0, from which one can obtained n2 through
p
Þg
ðm2=WÞ.
Fig. 3. Open Z-scan data of chalcone solutions of DMF. The open aperture Z-scan data represented by open circle and solid line is the fit to the experimental data.

E.D. D’silva et al. / Materials Research Bulletin 47 (2012) 3552–3557
3555
Fig. 4. Closed aperture Z-scan data of chalcone solutions of DMF. The closed aperture Z-scan data represented by open circle and solid line is the fit to the experimental data.
Fig. 5. Open and closed aperture Z-scan data of pure DMF solution.
Table 1
Third order nonlinear parameters of 4-methylsulfanyl chalcone derivatives.
Sample
n0
n2 (ꢁ10ꢀ7 cm2/GW) n2 (ꢁ10ꢀ14 esu) be f (ꢁ10ꢀ5 cm/GW) Rejx3j (ꢁ10ꢀ22 m2/V2) Imjx3j (ꢁ10ꢀ22 m2/V2)
j
x3j (ꢁ10ꢀ19 m2/V2)
j
x3j (ꢁ10ꢀ14 esu)
f
4Br4MSP 1.363 2.30
3Br4MSP 1.365 2.00
4N4MSP 1.360 2.40
7.49
6.52
7.79
5.5
3.8
4.0
2.27
1.98
2.36
0.046
0.047
0.097
2.30
1.99
2.37
1.65
1.43
1.70
molecules. Here in this molecules Br is present at the meta position
on the aromatic ring and the length of the charge transfer axis is
less compared to other two molecules. It was observed that as the
length of the charge transfer axis contributes to nonlinearity [25].
The dihedral angle between aromatic rings is 47.828, 50.038
respectively for 4Br4MSP and 3Br4MSP. The large dihedral angle of
3Br4MSP causes less efficient charge transfer through its backbone
than compared with 4Br4MSP and show less nonlinearity. Third-
order susceptibility values are of same order when compared with
some chalcone derivatives reported earlier [15].
r
¼ Im xð3Þ=Re xð3Þ. The observed values of coupling factor for the
samples 4Br4MSP, 3Br4MAP and 4N4MSP are 0.208, 0.121, and
0.106 respectively. The nonlinear induced polarization per
molecule is described by the microscopic susceptibilities known
as the hyperpolarizabilities. For third-order effects the corre-
sponding hyperpolarizability gh (second order hyperpolarizabil-
ity) is related to the third order susceptibility xð3Þ by the equation
[26]
xð3Þ
gh
¼
The coupling factor
r, the ratio of imaginary part to real part of
4
½ð1=3Þðn20 þ 2Þꢃ N
third-order nonlinear susceptibility can be measured as [24],

3556
E.D. D’silva et al. / Materials Research Bulletin 47 (2012) 3552–3557
Table 2
Linear and non-linear optical parameters of chalcones.
Sample
a
(mmꢀ1
)
gh (ꢁ10ꢀ32 esu)
s
2(ꢁ10ꢀ46 cm4 s/photon)
sex (ꢁ10ꢀ19 cm2)
sg (ꢁ10ꢀ19 cm2)
4Br4MSP
3Br4MSP
4N4MSP
0.116
0.163
0.151
0.070
0.100
0.104
1.51
1.56
1.65
11.67
5.78
6.55
1.29
2.69
2.51
where N is the density of molecules in the unit of molecules per
cm3 and n0 is the linear refractive index of the medium. The value
of gh obtained are tabulated in Table 2. The gh of 4N4MSP and
3Br4MSP is one order less compared with the reported values of
polymer doped chalcones [14,27] and have equal order with the
values reported for chalcones by Ravindra et al. [15]. But the value
of gh 4Br4MSP is found to be one order less than the literature
value [15].
The TPA cross section depends on type of functional group and
its position on the aromatic ring of the chalcone molecule [24].
The excited state cross section sex (Table 2) for all the samples
can be determined from the procedure described in the
literature [29]. The ground state absorption cross section sg
(Table 2) can be calculated from the equation
NA is the Avogadro number, C is the concentration in mol/cm3
and is the linear absorption coefficient. The value of sex was
found to be larger than the value of g, which is in agreement
a
¼
sgNAC, where
a
The two photon absorption (TPA) cross section, s2 (in units of
cm4 s/photon), which defines the transition rate for TPA was
calculated for all the samples using the equation [24]
s
with the condition for observing reverse saturable absorption
[30].
be f f
¼
s
2NAd ꢁ 10ꢀ3=h
n
, where NA is the Avogadro number, d is
The knowledge of the on-axis irradiance dependence of the
nonlinear absorption (NLA) coefficient gives the information about
the mechanism of the nonlinear absorption. If the mechanism
belongs to simple two photon absorption (TPA), then be f f should
be a constant that is independent of the on-axis peak irradiance I0.
If the mechanism is due to direct three-photon absorption then
be f f should be a linearly increasing function of I0 and the intercept
at the vertical axis must be zero [31]. We used three different input
intensities I0 = 49 GW/cm2, I0 = 98 GW/cm2, I0 = 147 GW/cm2 to
the concentration of the samples in mol/L and h
n
is the energy of
an incident photon (in J). The measured s2 values are in the
order of 10ꢀ46 cm4 s/photon (Table 2). ESA data is of interest
because on one hand it provides fundamental information about
the nature of the lying excited states often inaccessible from the
ground state, and on the other hand, it can provide important
information to assess the lasing potential of the medium [28].
measure
beff. It is observed that beff increases with increase in I0
7.2
7.0
6.8
6.6
6.4
(Fig. 6) even with the excited-state absorption being greater than
that of the ground state and the intercept on the vertical axis is non
zero, this suggests that a higher order effect, such as excited state
absorption (ESA) via two photon absorption, could be contributing
to the nonlinear absorption (NLA).
3Br4MSP
4Br4MSP
6.2
4N4MSP
6.0
5.8
5.6
5.4
5.2
5.0
4.8
4.6
4.4
4.2
4.0
3.8
Optical limiting is a phenomena observed when the transmis-
sion of a medium decreases with increasing input laser intensity
(or fluence). OL can be achieved through various nonlinear optical
mechanisms such as multi-photon absorption (MPA), excited state
absorption (ESA), free carrier absorption (FCA), self-focusing, self-
defocusing, nonlinear scattering, photo-refraction etc. Coupling
two or more of these mechanisms has also causes OL like self de-
focusing along with MPA [32]. The present chalcone samples have
negligible linear absorption at the operating laser wavelength
800 nm. The relation for intensity dependant nonlinear absorption
coefficient is given by [14]
40
60
80
100
I0(GW/cm2)
120
140
160
dI
¼ ꢀb 2
I
(4)
Fig. 6. A plot of be f vs. I0 for chalcone derivatives.
dz
f
where
b
is the nonlinear absorption coefficient. The solution of
Eq. (4) may be written as IðzÞ ¼ I0=ð1 þ
intensity. Hence dynamic transmissivity can be given by
TðI0; zÞ ¼ IðzÞ=I0 ¼ 1=ð1 þ zI0Þ. We plotted the graph of transmis-
b
zI0Þ, where I0 is the input
0.06
b
0.05
3Br4MSP
sion versus input peak laser intensity, is shown in Fig. 7. An
effective optical limiter will have low limiting threshold, high
optical damage threshold and stability, fast response time, high
linear transmittance throughout the sensor bandwidth, optical
clarity and robustness. In the case of present chalcone samples, it is
observed that sample exhibits strong two-photon absorption and
therefore is responsible for the limiting reported here.
4Br4MSP
4N4MSP
0.04
0.03
0.02
0.01
4. Conclusions
40
60
80
100
120
140
160
The third order nonlinear optical properties of donor and
acceptor substituted chalcones was investigated at 800 nm
using picosecond laser pulses by Z-scan technique. The
dependence of nonlinear responses of these sample molecules
I0 (GW/cm2)
Fig. 7. A plot of dynamic transmission vs. intensity for chalcone derivatives.

E.D. D’silva et al. / Materials Research Bulletin 47 (2012) 3552–3557
3557
[11] A. John Kiran, K. Chandrasekharan, Satheesh Rai Nooji, H.D. Shashikala, G. Umesh,
Chem. Phys. 324 (2006) 699.
[12] A. John Kiran, Ashok Mithun, B. Shivaram Holla, H.D. Shashikala, G. Umesh, K.
Chandrasekharan, Opt. Commun. 269 (2007) 235.
[13] S. Shettigar, K. Chandrasekharan, G. Umesh, B.K. Sarojini, B. Narayana, Polymer 47
(2006) 3565.
[14] S. Shettigar, G. Umesh, K. Chandrasekharan, B.K. Sarojini, B. Narayana, Opt. Mater.
30 (2008) 1297.
[15] H.J. Ravidra, A. John Kiran, K. Chandrasekharan, H.D. Shashikala, S.M. Dharam-
prakash, Appl. Phys. B: Lasers Opt. 88 (2007) 105.
[16] L.H. Hornak, Polymers for Light Wave and Integrated Optics, Marcel Dekker, New
York, 1992.
[17] Marius Albota, David Beljonne, Jean-Luc Brebas, E. Jaffrey Ehrlich, Jia-Ying Fu, A.
Ahmed Heikal, E. Samuel Hess, Thierry Kogej, D. Michael Levin, R. Seth Marder, D.
McCord Maughon, W. Joseph Perry, Harald Rockel, M. Rumi, G. Subramaniam, W.
Watt Webb, L. Xiang Wu, Science 281 (1998) 1653.
on substituent groups is discussed. The presence of strong
donor or acceptor functional group enhanced the third-order
susceptibility x3 and second order hyperpolarizability gh
which can be comparable with some of reported chalcone
molecules. All the three samples show pleasing optical limiting
behavior at 800 nm. The present results show that the samples
exhibit satisfactory optical responses in the picosecond domain
thus can be considered for designing suitable optical devices
for eye and sensor protection, optical limiting and for
electronic applications.
Acknowledgement
[18] B.A. Reinhardt, L.L. Brott, S.J. Clarson, A.G. Dillard, J.C. Bhatt, R. Kannan, L. Yuan,
G.S. He, P.N. Prasad, Chem. Mater. 10 (1998) 1863.
[19] E.D. D’silva, D. Narayana Rao, Reji Philip, J. Ray Butcher, Rajnikant, S.M. Dharma-
prakash, Physica B 406 (2011) 2206–2210.
Authors acknowledge the Department of Science and Technol-
ogy (DST), Government of India for financial assistance.
[20] E.D. D’silva, D. Narayana Rao, Reji Philip, J. Ray Butcher, Rajnikant, S.M. Dharma-
prakash, J. Phys. Chem. Solids 72 (2011) 824–830.
References
[21] R.J. Butcher, J.P. Jasinki, H.S. Yathirajan, B. Narayana, A. Mithun, Acta Cryst. E63
(2007), o3731-o3732.
[22] M. Sheik-Bahae, A.A. Said, T.H. Wei, D.J. Hagan, E.W. Van Stryland, IEEE J. Quant.
Electron. 26 (1990) 760.
[23] M. Sheik-Bahae, A.A. Said, E.W. Van Stryland, Opt. Lett. 14 (1989) 955.
[24] S. Vijayakumar, Adithya Adhikari, Balakrishna Kalluraya, K.N. Sharafudeen, K.
Chandrasekharan, J. Appl. Polym. Sci. 119 (2011) 595–601.
[25] P. Poornesh, K. Ravi, G. Umesh, P.K. Hegde, M.G. Manjunatha, K.B. Manjunatha,
A.V. Adhikari, Opt. Commun. 283 (2010) 1519–1527.
[26] M.-T. Zhao, P.B.P. Singh, P.N. Prasad, J. Chem. Phys. 89 (1988) 5535.
[27] A. John Kiran, N. Satheesh Rai, K. Chandrasekharan, B. Kalluraya, F. Rotermund,
Jpn. J. Appl. Phys. 47 (2008) 6312.
[1] P.N. Prasad, David J. Williams, Introduction to Nonlinear Optical Effects in
Molecules and Polymers, Wiley, New York, 1992.
[2] J.W. Perry, K. Mansour, I.-Y.S. Lee, X.-L. Wu, P.V. Bedworth, C.-T. Chen, D. Ng, S.R.
Marder, P. Miles, T. Wada, M. Tian, H. Sasabe, Science 273 (1996) 1533.
[3] M. Fakis, G. Tsigaridas, I. Polyzos, V. Giannetas, P. Persephonis, I. Spiliopoulos, J.
Mikroyannidis, Chem. Phys. Lett. 342 (2001) 155.
[4] L. De Boni, A.A. Andrade, S.B. Yamaki, L. Misoguti, S.C. Zilio, T.D.Z. Atvars, C.R.
Mendonca, Chem. Phys. Lett. 463 (2008) 360.
[5] A.A. Andrade, S.B. Yamaki, L. Misoguti, S.C. Zilio, T.D.Z. Atvars Jr., O.N. Oliveira, C.R.
Mendonca, Opt. Mater. 27 (2004) 441.
[6] Y. Morela, A. Ibanez, C. Nguefack, C. Andraud, A. Collet, J.-F. Nicoud, P.L. Baldeck,
Synth. Met. 115 (2000) 265.
[7] T. Saito, Y. Yamaoka, Y. Kimura, R. Morita, M. Yamashita, Jpn. J. Appl. Phys. 35
(1996) 4649.
[28] Hacene Manaa, Opt. Quant. Electron. 41 (2009) 761–770.
[29] F.Z. Henari, W.J. Blau, L.R. Milgrom, G. Yahioglu, D. Philips, J.A. Lacey, Chem. Phys.
Lett. 267 (1997) 229.
[30] L.W. Tutt, T.F. Boggess, Prog. Quant. Electron. 17 (1993) 299.
[31] S.-L. Guo, L. Xu, H.T. Wang, X.Z. You, N.B. Ming, Optik 114 (2003) 58.
[32] S. Venugopal Rao, P.T. Anusha, T. Shuvan Prashant, D. Swain, P. Surya Tewari,
Mater. Sci. Appl. 2 (2011) 299–306.
[8] C. Bosshard, R. Spreiter, P. Gunter, J. Opt. Soc. Am. B 18 (2001) 1620.
[9] Hari Singh Nalwa, Siezo Miyata, Nonlinear Optics of Organic Molecules and
Polymers, CRC Press, USA, 1997.
[10] C. Li, L. Zhang, M. Yang, H. Wang, Y. Wang, Phys. Rev. A 49 (1994) 1149.