Optics and Photonics Journal, 2013, 3, 34-37
doi:10.4236/opj.2013.32B008 Published Online June 2013 (http://www.scirp.org/journal/opj)
Optical Limiting and Stabilization Properties of a Liquid
Dye on 1064 nm Nanosecond Laser Pulses
Liuheng Wang1,2, Rongzong Peng1,2, Yuxia Zhao1, Feipeng Wu1
1Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, P. R. China
2Graduate University of Chinese Academy of Sciences, Beijing, P. R. China
Email: fpwu@mail.ipc.ac.cn
Received 2013
A novel liquid dye 2-((2E,5E)-2,5-bis(4-(methyl(2,5, 8,11-tetraoxatridecan-13-yl)amino)benzylidene)cyclopentylidene)
malononitrile (TO-BDCM) was synthesized by incorporating two oligo(ethenyl glycol) groups into the backbone of a
prototype malononitrile derivative (BDCM) for the purpose of increasing its solubility in organic solvents. The nonlin-
ear absorption properties of this liquid dye on 1064 nm ns pulsed laser were investigated in DMF with remarkably high
concentration up to ~1M, showing a superior large nonlinear absorption coefficient of 55.6 cm3/GW2. Fairly good opti-
cal limiting and stabilization effects were achieved. Meanwhile, the liquid dye exhibited equivalent stability under laser
irradiation compared to its prototype dye BDCM.
Keywords: Liquid Dye; Multiphoton Absorption; Optical Limiting; Optical Stabilization
1. Introduction
Optical limiting and stabilization techniques become
more and more important as the fast development of ultra
short pulsed lasers. Using these techniques can protect
human eyes and optical sensors from damages induced
by intense laser pulses, or stabilize the temporal fluctua-
tion of laser pulses to keep the peak energy of all pulses
at a certain level [1,2]. Materials based on multiphoton
absorption are most widely used to fabricate optical lim-
iter or stabilizer because of their fast response of the ultra
short pulses, as well as the remarkably high linear trans-
mission at low energy, compared with other materials,
such as reverse saturable absorption or induced scattering
materials [3,4].
In order to improve the optical limiting and stabiliza-
tion properties of multiphoton absorption (MPA) materials,
researchers have reported a number of methods to in-
crease the multiphoton absorption cross section of MPA
materials, such as elongating the conjugation length of
the molecule, or using a dendritic structure [5]. However,
in most of the cases, the solubility of such materials in
organic solvents is a big problem. Except to increase the
multiphoton absorption cross section of materials, to in-
crease the concentration of a given materials is also an
effective strategy for enhancing its optical limiting and
stabilization performance [6].
In our previous work, we have reported a malononi-
trile derivative (BDCM) with relatively large two-photon
absorption cross section [7], and can be potential choice
as good optical limiter and stabilizer. But the maximum
concentration of the dye in organic solvents limits to
~10-2 M, which may restrict its optical limiting properties
in some extent. In order to increase the solubility, In this
work, oligo(ethenyl glycol) groups were introduced to
the backbone of BDCM and 2-((2E,5E)-2,5-bis (4-
cyclopentylidene) malononitrile (TO-BDCM) was ob-
tained. It is a dark-blue with highly viscous oil at room
temperature. By mixing with one or two parts (mess ratio)
of DMF, a uniform optical solution can be obtained. The
solubility of TO-BDCM is remarkably increased to a
magnitude larger than that of BDCM. The high concen-
tration of effective dyes in the solution should signifi-
cantly improve the final optical limiting and stabilization
performance of TO-BDCM.
2. Results and Discussion
2.1. Synthesis
The chemical structure and synthetic procedure of TO-
BDCM is shown in Figure 1. Two oligo (ethenyl glycol)
groups were incorporated into BDCM to decrease the
glass transition temperature and improve its solubility in
organic solvents. The target liquid dye TO-BDCM was
obtained through Knoevenagel condensation between the
benzaldehyde 1 [8] and 2-cyclopentylidenemalononitrile.
It was a dark-blue and highly viscous oil at room tem-
Copyright © 2013 SciRes. OPJ
L. H. WANG ET AL. 35
Figure 1. Chemical structure and synthetic route of the
liquid chromophore TO-BDCM.
TO-BDCM). Yield 42%. 1H NMR (CDCl3, 400 MHz)
δ8.04 (s, 2 H), 7.42 (d, 4 H, J=8.9 Hz), 6.75 (d, 4 H,
J=8.9 Hz), 3.69-3.60 (m, 28 H), 3.55-3.53 (m, 4 H), 3.37
(s, 6 H), 3.08 (s, 6 H), 2.91 (s, 4 H).
2.2. Optical Properties
The linear attenuation of pure TO-BDCM and its DMF
solution was as shown as in Figure 2. From Figure 2
one can see that the transmission of the pure TO-BDCM
was much lower than its DMF solution. This is because
the refractive index distribution in the viscous TO-BDCM
is not homogeneous. So the TO-BDCM can not be di-
rectly applied in optical limiting and stabilization as its
original form. Figure 2 shows that the linear attenuation
of the DMF solution is less than 1% at 1064 nm (after
subtracting the effect of the cuvette). As a result, diluted
DMF solution is the better sample medium for optical
limiting and stabilization application, compared with
pure TO-BDCM. The linear attenuation was carried out
on a Virian Cary 5000 UV-vis-NIR spectrophotometer.
The DMF solution was prepared by mixing DMF and
TO-BDCM in volume ratio of ~1/1. The solution con-
centration was about ~0.75 M. Both the pure TO-BDCM
and the DMF solution were filled in 1-cm length cuvette.
The UV-Vis and fluorescence spectrum of TO-BDCM
and BDCM were shown in Figure 2. From the spectrum
one can see that the maximum absorption of TO-BDCM
was located at 577 nm. This indicates that possible two-
photon absorption may occur around 1064 nm. Both the
UV-Vis and fluorescence spectrum of TO-BDCM are
similar to BDCM, so the incorporation of oligo(ethenyl
glycol) groups to the backbone has little influence on
both ground and excited state of BDCM. The UV-Vis
spectrum was measured on a Hitachi U3900 spectropho-
tometer by using 1×10-5 M DMF solution. The fluores-
cence spectrum was investigated on a Hitachi F4500 FL
spectrophotometer. For the fluorescence spectrum meas-
urement, the concentration of the DMF solution was
~10-4 M, besides, the exciting and emission slit of the
spectrophotometer were set to the largest. This is because
the Fluorescence quantum yield of these two compounds
are very low.
2.3. Photostability
The photobleaching of TO-BDCM and BDCM is shown
in Figure 3. ln(A/A0) is plotted as a function of irradia-
tion time, where A0 and A were the maximum absorption
before and after every 10 min of irradiation. The linear
fitting of the plot yields the first order rate constant of 6.2
×10-4/min and 6.6×10-4/min for BDCM and TO-
BDCM, respectively. TO-BDCM and BDCM exhibit
equivalent photochemical stability. The photobleaching
was carried out by irradiating the DMF solution filled in
1-cm cuvette with a 532 nm Semiconductor solid-state
laser (MGL-532 nm--30 mW, Changchun New Indus-
tries Optoelectronics Tech. Co., Ltd). The solutions are
prepared with the same absorption at 532 nm. The UV-
Vis spectrum was measured every 10 min of irradiation
Figure 2. UV-Vis and fluorescence spectrum for diluted
TO-BDCM (solid lines) and BDCM (dashed lines) solutions;
Linear transmission curve of pure TO-BDCM filled in
1-mm cuvette (dot line) and a slightly diluted solution of
0.75 M in DMF (dash-dot line).
Figure 3. Plot of ln(A/A0) vs irradiation time, the slope of
the linear fitting curve is the first order photobleaching rate
Copyright © 2013 SciRes. OPJ
on Hitachi-U3900 UV-Vis spectrophotometer. The con-
centrated solution of ~0.75 M was also directly irradiated
by 1064 nm pulsed laser (Quantum Ray). The pulse du-
ration, repetition rate and beam radius were 8 ns, 10 Hz,
and 45 mm, respectively. The beam diameter was smaller
than the width of the cuvette so that the entire of the
beam can pass through the sample solution. In this condi-
tion, the pulse intensity was about 0.2 GW/cm2. After
irradiation of 2 h, the solution was diluted to ~10-5 M and
then the UV-Vis spectrum was measured on Hitachi
U-3900 spectrophotometer. we found that there was little
change between the UV-Vis spectrum before and after
irradiation. The liquid chromatography also found no
new substance generated. This result may also indicate a
good photochemical stability of TO-BDCM.
2.4. Optical Limiting and Stabilization
For all solution samples applied in optical limiting and
stabilization, the multi-photon absorption (MPA) proper-
ties are proportional to the effective concentration of the
solutions. The dye BDCM has been reported as an effec-
tive optical limiter on 1064 nm fs pulsed laser [8]. It has
large two-photon absorption (TPA) cross section as hun-
dreds of GM. But the effective concentration of this dye
is limited to ~10-2 M. After modifying the molecular, the
effective concentration of TO-BDCM can reach up to ~1
In nonlinear absorption experiment, a 1064 nm Nd:
YAG pulsed laser (Quanta-Ray, Spectra Physics) was
used as the excitation beam with pulse duration 8 ns and
repetition rate 10 Hz. The laser beam was focused by a
lens (f=500 mm) and then passed through a cuvette filled
with sample solutions. The cuvette was placed between
the focus and the lens in the experiment, so that the laser
beam in the sample solutions can approximately be sup-
posed as parallel in this case. Meanwhile, this arrange-
ment also can avoid the damage of the cuvette by the
focused beam. In the case of ns pulsed laser, it is com-
mon to observe stronger nonlinear absorption compared
to that in fs case because of the TPA induced excited
state absorption. In such a case, a three-photon absorp-
tion model was more effective to be used to evaluate the
experimental data compared to a two-photon absorption
model. The plot of the output intensity vs input intensity
can be fitted by (1) [9,10]
where I was the output intensity, I0 was the iput intensity,
γ was the effective three-photon absorption coefficient,
and L was the path length of the sample solutions.
Figure 4 (a) shows the optical limiting behavior of the
~0.75 M TO-BDCM solution filled in a 1-cm cuvette.
The output intensity was plotted as a function of input
intensity. One can see that the transmitted/input intensity
characteristic curve starts to deviate from the linear
transmission at about 0.05-0.06 GW/cm2, and becomes
flattened when the input intensity is higher than about
0.10 GW/cm2. Specifically, in the experimental condition,
the input intensity increased from 0.01 to 0.81 GW/cm2
(81 times increase), while the output intensity only in-
creased from 0.01 to 0.10 GW/cm2 (10 times increase).
The solid line is the theoretical curve predicted by (1),
and the nonlinear fitting gives γ as large as 55.6 cm3/GW2.
Figure 4(b) shows the nonlinear transmission as a
function of input intensity. The solid line is the best fit-
ting curve using the three-photon absorption theory with
the γ value obtained above. In the experimental condition,
the nonlinear transmission is as low as 12.6% at the
highest input intensity.
For most pulsed laser-based application, the intensity
stability is very important. In other words, the fluctuation
of the intensity among different pulses is harmful. MPA
materials are one of the best approaches to stabilize the
pulse energy. From Figure 4(a) one can see that in the
experimental condition, when the intensity of the input
pulses is higher than 0.10 GW/cm2, the optical limiting
curve becomes flat, and the output intensity tends to a
fixed value of ~0.10 GW/cm2. So if the intensity of the
input pulses varies between 0.10 GW/cm2 and any value
larger than 0.10 GW/cm2, the intensity of transmitted
pulses fluctuates around 0.10 GW/cm2 within a small
variation range. This is a simple example for the prin
ciple of optical stabilization based on MPA.
Figure 5 shows the optical stabilization of the 0.75 M
TO-BDCM solution filled in a 2-mm cuvette. The trans-
mitted and input beam power were measured by two
Figure 4. (a) Output intensity as a function of input inten-
sity, dashed and solid line represent the theoretical linear
and nonlinear absorption curve, respectively, (b) Nonlinear
transmission as a function of input intensity, solid line
represents theoretical nonlinear transmission curve.
Copyright © 2013 SciRes. OPJ
Copyright © 2013 SciRes. OPJ
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3. Conclusions
In conclusion, we have synthesized a new liquid com-
pound TO-BDCM by incorporating oligo(ethenyl glycol)
groups into the backbone of a prototype chromophore
BDCM. TO-BDCM has remarkable solubility in organic
solvent. Its effective concentration can reach up to ~1 M
in DMF, which results in remarkable nonlinear absorb-
ability. The solution of this liquid dye with high effective
concentration shows fairly good optical limiting and sta-
bilization behavior on 1064 nm ns pulsed laser. Mean-
while, the liquid dye shows equivalent photochemical
stability under irradiation compared to its prototype
compound BDCM.
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4. Acknowledgements
This research was supported by NSAF projects (10776033,