- Email: [email protected]
Nonlinear optical properties and optical power limiting behavior of Leishman dye in solution and solid polymer film using z-scan
Accepted Manuscript Title: Nonlinear Optical Properties and Optical Power Limiting Behavior of Leishman Dye in Solution and Solid Polymer Film Using Z – Scan Author: Imad Al–Deen Hussein Al Saidi Saif Al–Deen Abdulkareem PII: DOI: Reference:
S0030-4026(15)00905-5 http://dx.doi.org/doi:10.1016/j.ijleo.2015.08.144 IJLEO 56068
To appear in: Received date: Accepted date:
20-8-2014 24-8-2015
Please cite this article as: I.A.D.H. Al, S.A.D. Abdulkareem, Nonlinear Optical Properties and Optical Power Limiting Behavior of Leishman Dye in Solution and Solid Polymer Film Using Z ndash Scan, Optik - International Journal for Light and Electron Optics (2015), http://dx.doi.org/10.1016/j.ijleo.2015.08.144 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ip t
Nonlinear Optical Properties and Optical Power Limiting Behavior of Leishman Dye in Solution and Solid Polymer Film Using Z – Scan
cr
Imad Al – Deen Hussein Al – Saidi* and Saif Al – Deen Abdulkareem
M
an
us
Department of Physics, College of Education for Pure Sciences, University of Basrah, Basrah-IRAQ * e-mail: [email protected]
Abstract
d
We have studied the nonlinear optical properties of Leishman dye in chloroform solution at different concentrations and solid film mixed with polymethylmethacrylate
te
(PMMA) polymer using a continuous wave (CW) laser at 532 nm as the excitation
Ac ce p
source. We have employed the z – scan technique to evaluate the sign and magnitude of the intensity dependent nonlinear refractive index (n2) , the nonlinear absorption coefficient (β), and the third – order nonlinear optical susceptibility (χ
(3)
). The obtained
results showed that the Leishman dye exhibits a negative nonlinear refraction (self – defocusing) and saturable absorption. It was found that the values of n2 , β , and χ (3) are dependent on the dye concentration, they increases when the dye concentration increases. Optical power limiting characteristics of the dye at different concentrations in solution and solid film were also studied. Our results showed that the Leishman dye has large third – order optical nonlinearity, thus it could be a potential candidate for opto – electronic and photonic devices. Key words: Leishman dye; Third – order optical nonlinearity; Z – scan technique; Optical power limiting.
1 Page 1 of 20
1. Introduction Nonlinear optical properties of materials have attracted considerable
ip t
attention owing to their applications in opto – electronic and photonic devices [1-5]. Great efforts devoted to search for nonlinear optical materials
cr
that can be used for optical devices applications. Organic materials are identified as promising candidates for nonlinear applications because they
us
can exhibit large nonlinearity, faster nonlinear responses when they interact with intense electromagnetic fields of laser beams [2, 6-9]. They exhibit
an
other additional advantages such as their broadband spectral responses, high thermal and chemical stability, along with their simple structures, low cost
M
and ease of preparation in solution and thin polymer film. Due to these advantages, the organic nonlinear materials have been extensively
d
investigated for useful optical applications, such as all – optical signal
te
processing, optical information storage, optical switching, and optical power limiting [ 10-14], which require large nonlinearities and fast response
Ac ce p
time. Dyes are a class of organic materials. They are very interesting materials for studying the optical nonlinear effects because they exhibit large optical nonlinearities, fast response time, and strong absorption in the visible spectral region. In addition, they are characterized by their flexibility and thermal and chemical stability in dye – doped polymer solid films. These very important advantages make the dyes suitable candidate for nonlinear optical investigations. Optical power limiting is an important nonlinear optical behavior exhibited by some nonlinear materials, it can be used to protect the eyes
2 Page 2 of 20
and the sensitive optical equipments from intense laser beams. In this optical process, the output intensity of the laser beam passing through the
ip t
nonlinear medium (the sample) initially increases with increased input laser beam intensity and then tends to saturated at higher input intensities. It was
cr
demonstrated that the dyes can exhibit significant and important optical
us
limiting behaviors [12,15,16]. In our study, we found that the Leishman dye exhibits large and negative nonlinearity and different nonlinear behaviors
an
were observed, thus it could be useful for optical applications. In this paper, we used the z – scan technique to determine the sign
M
and magnitude of the nonlinear refractive index (n2), the nonlinear absorption coefficient (β), and the third – order nonlinear optical (3)
) of the Leishman dye. The experiment was performed
d
susceptibility (χ
te
for different concentrations of Leishman dye solution and dye – doped film. The power limiting behavior was also studied using the z – scan
Ac ce p
technique.
2. Experimental
The Leishman dye was chosen for our study. The dye solution was
prepared by dissolving appropriate amount of the Leishman powder (depending on its molecular weight) in the chloroform as a solvent. Four samples of different concentrations of Leishman dye solution were prepared, these are : 0.03, 0.05, 0.07, and 0.09 mM. The dye – doped polymer
films
were
prepared
using
solution
casting method.
3 Page 3 of 20
The Methylmethacrylate (PMMA) was dissolved in Chloroform and the solution was stirred at room temperature for few hours to obtain a
ip t
homogeneous solution. The already prepared dye solution at concentration 0.09 mM was added to stirred solution (polymer with chloroform). The
cr
final mixture was cast on to microscope slides and allowed to evaporate
slowly at room temperature. After sometime solid films were obtained
us
with thickness varied from 0.80 to 0.85 mm. The optical quality of the films was checked by using He – Ne laser beam at wavelength 632.8 nm
an
and power 2 mW. The films show clear and uniform thickness. The film of thickness 0.08 mm was chosen for our present study.
M
The linear absorption spectra of both Leishman dye solution in 1 cm quartz cell for different concentrations and dye – doped polymer film
d
samples were recorded using UV – Vis spectrophotometer (Cecil double
te
– beam UV – Vis spectrophotometer model CE – 7500). The z – scan technique [17, 18] was used to measure the nonlinear
Ac ce p
optical properties of Leishman dye. This technique is a simple, highly sensitive, and straightforward method for determining the nonlinear refractive index (n2) and the nonlinear absorption coefficient of material. Both the sign and the magnitude of the real part and imaginary part of the third – order nonlinear optical susceptibility (χ
(3)
) can be determined by
this method. The z – scan technique relies on the distortions induced in the spatial and temporal profile of the input beam passing through the sample. Fig.1 shows the experimental setup of the z – scan technique. The experiment was carried out using an adjustable power CW solid-
4 Page 4 of 20
State
laser (SSL) operating at 532 nm wavelength as the source of
excitation. The output power of the laser can be varied over the range
ip t
0 – 100 mW. The laser Gaussian beam was focused to a beam waist (ω0) of 24 µm by a convex lens of focal length 5 cm and passed through the
cr
sample, which is either 1 mm quartz cell containing Leishman dye solution or dye – doped polymer film. The Rayleigh length (z0) was 3.4 mm, which
us
is satisfied the sample condition in the z – scan method, that is L < n0 z0 ,
an
where L is the sample thickness and n0 is the linear refractive index of the sample material.
M
The z – scan experiment was performed by translating the sample across the focal point of the lens along the z – axis direction. In the
d
closed – aperture z – scan, the transmitted power output was measured
te
through a small diameter aperture (S = 0.5) placed in the far field of the lens as a function of position z of the sample, with respect to the focal
Ac ce p
plane (z = 0) , using the photo - detector PD2 which is attached to a digital power meter. The photo - detector PD1 is also attached to a digital power meter was used to measure the input laser power. In the open – aperture z – scan, the aperture is fully opened (S = 1) and the power of the entire laser beam transmitted through the sample was measured by the photo - detector PD2 .
5 Page 5 of 20
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M
an
Fig. 1. Z – scan experimental setup. BS, is a beam splitter; PD1 and PD2 are Photo - detectors.
3. Results and Discussion
d
The linear absorption spectra of the Leishman dye at different
te
concentrations (0.03, 0.05, 0.07, 0.09 mM) and dye – doped polymer film at concentration 0.09 mM are shown in Fig. 2 (a) and (b), respectively.
Ac ce p
From these figures it can see that the absorption spectra of the Leishman dye exhibit a wide absorption band with two peaks, which are located at wavelengths 533 nm and 650 nm for the dye solution and a single peak at wavelength 653 nm for the dye – doped polymer solid film. We can also see from Fig. 2 (a) that the value the peak increases with increasing the Leishman dye concentration.
6 Page 6 of 20
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an
us
(a)
te
d
(b)
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Fig. 2. Linear absorption spectra of Leishman dye. (a) Dye solution at different concentrations. (b) Dye – doped polymer film of concentration 0.09 mM.
The transmittance
curves
(the
normalized
transmittance
as a
function of the sample position z) obtained for the Leishman dye in chloroform
at different concentrations and incident intensity I0 = 1.11
kW / cm 2 are shown in Fig. 3. The normalized transmittance curves of a closed – aperture z – scan in Fig. 3 (a) are characterized by a peak followed by a valley (peak – valley) behavior. This indicates that the 7 Page 7 of 20
sign of nonlinear refractive index is negative (n2 < 0) (self – defocusing effect). The normalized transmittance curves of the open aperture z –
ip t
scan in Fig. 3 (b) show saturable absorption behavior. Occurrence of the self – defocusing effect in the dye medium is due to the variation of
cr
its refractive index (n) with temperature (i.e., d n / d T).
detector PD2
us
In the closed – aperture z - scan measurements, the photo – is sensitive to both the nonlinear absorption and the
an
nonlinear refraction. Therefore, in order to obtain the pure nonlinear refraction, the closed – aperture data was divided by the open – aperture data [18]. The pure nonlinear refraction z – scan transmittance curves for
M
dye solution at different concentration are shown in Fig. 3 (c). Similar behaviors for closed - aperture and open – aperture z – scan were
d
observed in the case of the dye – doped polymer film at concentration
Ac ce p
te
0.09 mM as shown in Fig. 4 (a – c).
8 Page 8 of 20
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Ac ce p
te
(b)
d
M
an
us
(a)
(c)
Fig. 3. Normalized transmittance curves for Leishman dye solution at different concentrations. (a) Closed – aperture z – scan. (b) Open – aperture z – scan. (c) Pure nonlinear refraction. 9 Page 9 of 20
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Ac ce p
te
(b)
d
M
an
us
(a)
(c)
Fig. 4. Normalized transmittance curves for Leishman dye - doped polymer film at concentration 0.09 mM. (a) Closed – aperture z – scan. (b) Open – aperture z – scan. (c) Pure nonlinear refraction.
10 Page 10 of 20
For the calculation of the third – order nonlinear refractive index (n2) of the Leishman dye, the following standard relations were used
ip t
[17, 18]: ΔTP – V = 0.406 (1 – S) 0.25 |Δ Ø0|
cr
(1)
(2)
an
us
Δ Ø0 λ n2 = ────── 2 π I0 Leff
where ΔTP – V is the difference between the normalized peak and valley transmittance, TP – TV , |Δ Ø0| is the on axis nonlinear phase – shift of
M
laser beam at focus, and S is the linear aperture transmittance given by: S = 1 – exp (-2 ra 2 / ωa 2 ) , where ra is the aperture radius and ωa is
d
the laser beam radius at the aperture. λ is the laser wavelength
te
(λ = 532 nm), I0 = 2 P0 / π ω02 is the peak laser beam intensity within the
Ac ce p
the sample (I0 = 1.11 kW / cm2), and effective length (thickness) of
absorption coefficient of
Leff = (1 – exp(- α0 L) ) / α0
is
the sample, α0 is the linear
the sample medium, and L is the sample
length.
The nonlinear absorption coefficient (β) of the Leishman dye
was calculated from the following relation: 2√2 β = ──── ΔT I0 Leff
(3)
where ΔT is the normalized transmittance difference between peak at
11 Page 11 of 20
the focal point (z = 0) in the open – aperture z – scan curve and the baseline.
ip t
The real part (Re (χ (3))) and the imaginary part (Im (χ (3))) of the third – order nonlinear optical susceptibility (χ (3)) for the Leishman
cr
dye were calculated using the following relations [19]:
Im [χ (3)] (esu) = 10 – 2
ε0 c 2 n0 2 λ β ───────── 4 π2
us
Re [χ (3)] (esu) = 10 – 4
ε0 c 2 n0 2 n2 ──────── π
an
(cm 2 / W)
(5)
M
(cm / W)
(4)
d
where ε0 is the permittivity of free space, n0 is the linear refractive
The
te
index of the medium, and c is the velocity of light in vacuum. absolute value
of
the third – order nonlinear optical
Ac ce p
susceptibility was evaluated using the following relation: |χ (3)| = [(Re (χ (3))) 2 + (Im (χ (3))) 2]
The
calculated
nonlinear
½
parameters
(7) for the Leishman dye
solution and the dye doped – polymer film are summarized in Table 1.
12 Page 12 of 20
Table 1: Summary of the various calculated nonlinear parameters for Leishman dye solution and dye – doped polymer film. n2 (cm2 / W) × 10 - 7
β (cm / W) × 10 - 3
0.03
1.077
- 2.454
1.433
1.314
0.05
1.226
- 2.818
1.934
1.588
0.07
1.377
- 3.196
2.599
1.901
0.09
1.534
- 3.588
3.108
2.260
0.09
1.546
an
3.726
3.156
Polymer film
cr
us
Solution
ip t
ΔTP – V
- 4.178
M
Sample
|χ (3)| (esu) × 10 - 5
Concentration (mM)
The values of n2 , β , and |χ (3)| are related to the concentration of the dye
solution. The value of each one of these nonlinear
d
Leishman
te
parameters increases when the dye concentration increases as shown in Figs. 5, 6, and 7, respectively. This may attributed to the fact that the number
Ac ce p
of the dye molecules increases when concentration increases, more particles are thermally excited resulting in an enhanced nonlinear effect. The laser heating is produced while the laser beam passing through the sample medium. This process induces temperature and density gradients that change the refractive index of the dye medium and consequently thermal focusing effect arising.
13 Page 13 of 20
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Ac ce p
te
d
M
an
Fig. 5. The nonlinear refractive index (n2) as a function of dye Leishman concentration.
Fig. 6. The nonlinear absorption coefficient (β) as a function of dye Leishman concentration.
14 Page 14 of 20
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an
Fig. 7. The nonlinear third – order optical susceptibility ( |χ (3)|) as a function of dye Leishman concentration.
M
For optical power limiting measurements, based on the nonlinear refraction (self – defocusing), the sample (dye solution or dye – doped
d
polymer film) was located at the position where the valley falls in the
te
closed – aperture and the input power of the laser beam was varied.
Ac ce p
The input powers and the corresponding output powers of the laser beam were recorded by the power meters. Fig. 8 shows the optical limiting behavior of Leishman dye in solution and dye – doped polymer solid film. The laser output power was plotted as a function of the laser input power, varying over the range 0 – 40 mW. It is clearly seen that the output power initially varies linearly with increasing the input power (at low powers), but the transmitted output power starts to deviate from the linearity at high input powers. With still increasing the input power, the output power reaches a plateau region at certain value
15 Page 15 of 20
for the input
power and
the output power relatively remains
constant (saturated) with further
increase in the input power. The
ip t
value of the input power at which the output power starts to saturate is known as the power limiting threshold which defined as the input
cr
power at which the sample transmittance falls to half of its linear
us
transmittance.
The values of the power limiting threshold for the Leishman
an
dye solution at different concentrations and dye – doped polymer solid film at concentration 0.09 mM were estimated , Table 2 summarizes
M
these values.
It is evident that the optical power limiting effect depends on the
d
concentration of the Leishman dye and increases with increasing the dye
te
concentration, while the power limiting threshold decreases with increasing
Ac ce p
the dye concentration. At high Leishman dye concentrations, the output power reached a plateau at low input power and the dye medium exhibits strong optical power limiting effect.
16 Page 16 of 20
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d
M
an
Fig. 8. Optical power limiting behavior ( output laser power versus input laser power) for Leishman dye solution at different concentrations and dye – doped polymer film at concentration 0.09 mM.
Ac ce p
te
Table 2: The calculated values of the optical power limiting threshold for the Leishman dye solution and dye – doped polymer film. Sample
Solution
Polymer film
Concentration (mM) 0.03
Power limiting threshold (mW) 19.9
0.05
17.8
0.07
16.1
0.09
13.7
0.09
10.4
17 Page 17 of 20
4. Conclusion We have studied the nonlinear absorption and the nonlinear
ip t
refraction of Leishman dye, both in solution and polymer as a dye – doped polymer film using z – scan technique under excitation by a
cr
CW laser beam at 532 nm. We found that the Leishman dye
is
characterized by negative nonlinear refraction (self – defocusing) and
us
saturable absorption behavior. The observed nonlinearity are thermal in nature owing to the CW excitation and the nonlinear effect is caused
experimental
results
show that
M
The
an
by self – defocusing process.
exhibits large nonlinearities. Significant
values
the for
Leishman dye the nonlinear
d
refractive index (n2), the nonlinear absorption coefficient (β), and the
te
third – order nonlinear optical susceptibility (χ (3)) were obtained. These values can be easily varied by varying
the dye concentrations. The
Ac ce p
power limiting effect was observed in the Leishman dye and is affected by the variation of the concentration. These advantages give an indication that the Leishman is a promising material for potential applications in nonlinear optical devices such as photonic and signal processing devices.
18 Page 18 of 20
5. References [1] P. Günter, Ed., Nonlinear Optical Effects and Materials, Spriger –
ip t
Verlag, Berlin, Germany, 2000.
Ac ce p
te
d
M
an
us
cr
[2] H. S. Nalwa, Ed., Handbook of Advanced Electronic and Photonic Materials and Devices, Academic Press, New York , 2001. [3] Y. Guo, C. K. Kao, E. H. Li, K. S. Chang, Eds., Nonlinear Photonic, Springer – Verlag, Berlin, 2002. [4] P. N. Prasad, Introduction to Bio-Photonic, John Wiley & Sons Ltd., New York , 2003. [5] N. Costa, A. Cartaxo, Eds., Advances in Lasers and Electro Optics, InTech, 2010. [6] P. N. Prasad, D. J. Williams, Introduction to Nonlinear Optical Effects in Molecules and Polymers, John Wiley & Sons Ltd., New York, 1990. [7] S. R. Marder, J. E. Sohn, G. D. Stucky, Eds., Materials for Nonlinear Optics –Chemical Perspectives, ACS Symposium Series, Vol. 455, Academic Chemical Society, Washington, DC., 1991. [8] J. Zyss, Ed., Molecular Nonlinear Optics : Materials, Physics, and Devices, Academic Press, New York, 1994. [9] H. S. Nalwa, S. Miyata, Nonlinear Optics of Organic Molecules and Polymers, CRC Press, Boca Raton, 1997. [10] R. L. Sutherland, Ed., Handbook of Nonlinear Optics, 2nd Edition, Marcel Dekker, New York, 2003. [11] H. Stricker , W. W. Webb, Three – dimensional optical data storage in refractive media by two – photon excitation, Opt. Lett. 16 (1991) 1780-1782. [12] Z. G. Yong, W. Chun, L. Hong, W. Dong, S. Z. Shu, J. M. Hua, Two – photon absorption and optical power limiting based on new organic dyes, Chin. Phys. Lett. 18 (2001) 1120-1122.
19 Page 19 of 20
Ac ce p
te
d
M
an
us
cr
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[13] Purnima, D. Mohan, S. Rani, Optical nonlinear refractive and limiting behavior of Nickel complex dye doped solid – solid matrix for both visible and near infrared nanosecond excitation, Optik 124 (2013) 1741-1745. [14] L. Kamdth, Manjuntha K. B., S. Shettigar, G. Umesh, et al., Investigation of third – order and optical power limiting properties of Terphenyl derivatives, Opt. Laser Technol. 56 (2014) 425-429. [15] R. R. Krishnamurthy, R. Alkondan, Nonlinear characterization of Mercurochrome dye for potential application in optical limiting, Opt. Appl. 40 (2010) 187-196. [16] A. Thankappan, S. Thomas, V. P. N. Nampoon, Solvent effect on the third order optical nonlinearity and optical limiting ability of betanin natural dye extracted from red beet root, Opt. Mater. 35 (2013) 2332-2337. [17] M. Sheik – Bahae, A. A. Said, E. W. Van Stryland , High sensitive single beam n2 measurements, Opt. Lett. 14 (1989) 955-957. [18] M. Sheik – Bahae, A. A. Said, T. Wei, D. J. Hagan, E. W. Van Stryland , Sensitive measurement of optical nonlinearities using a single beam, IEEE J. Quantum Electron. QE-26 (1990) 760-769. [19] T. Cassano, R. Tommasi, M. Ferrara, F. Babudri, G. M. Farinola, F. Naso, Substituent-dependence of the optical nonlinearities in poly (2,5-diakoxy-p-phenylenevinylene) polymers investigated by z-scan technique , Chem. Phys. 272 (2001) 111-118.
20 Page 20 of 20
S0030-4026(15)00905-5 http://dx.doi.org/doi:10.1016/j.ijleo.2015.08.144 IJLEO 56068
To appear in: Received date: Accepted date:
20-8-2014 24-8-2015
Please cite this article as: I.A.D.H. Al, S.A.D. Abdulkareem, Nonlinear Optical Properties and Optical Power Limiting Behavior of Leishman Dye in Solution and Solid Polymer Film Using Z ndash Scan, Optik - International Journal for Light and Electron Optics (2015), http://dx.doi.org/10.1016/j.ijleo.2015.08.144 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ip t
Nonlinear Optical Properties and Optical Power Limiting Behavior of Leishman Dye in Solution and Solid Polymer Film Using Z – Scan
cr
Imad Al – Deen Hussein Al – Saidi* and Saif Al – Deen Abdulkareem
M
an
us
Department of Physics, College of Education for Pure Sciences, University of Basrah, Basrah-IRAQ * e-mail: [email protected]
Abstract
d
We have studied the nonlinear optical properties of Leishman dye in chloroform solution at different concentrations and solid film mixed with polymethylmethacrylate
te
(PMMA) polymer using a continuous wave (CW) laser at 532 nm as the excitation
Ac ce p
source. We have employed the z – scan technique to evaluate the sign and magnitude of the intensity dependent nonlinear refractive index (n2) , the nonlinear absorption coefficient (β), and the third – order nonlinear optical susceptibility (χ
(3)
). The obtained
results showed that the Leishman dye exhibits a negative nonlinear refraction (self – defocusing) and saturable absorption. It was found that the values of n2 , β , and χ (3) are dependent on the dye concentration, they increases when the dye concentration increases. Optical power limiting characteristics of the dye at different concentrations in solution and solid film were also studied. Our results showed that the Leishman dye has large third – order optical nonlinearity, thus it could be a potential candidate for opto – electronic and photonic devices. Key words: Leishman dye; Third – order optical nonlinearity; Z – scan technique; Optical power limiting.
1 Page 1 of 20
1. Introduction Nonlinear optical properties of materials have attracted considerable
ip t
attention owing to their applications in opto – electronic and photonic devices [1-5]. Great efforts devoted to search for nonlinear optical materials
cr
that can be used for optical devices applications. Organic materials are identified as promising candidates for nonlinear applications because they
us
can exhibit large nonlinearity, faster nonlinear responses when they interact with intense electromagnetic fields of laser beams [2, 6-9]. They exhibit
an
other additional advantages such as their broadband spectral responses, high thermal and chemical stability, along with their simple structures, low cost
M
and ease of preparation in solution and thin polymer film. Due to these advantages, the organic nonlinear materials have been extensively
d
investigated for useful optical applications, such as all – optical signal
te
processing, optical information storage, optical switching, and optical power limiting [ 10-14], which require large nonlinearities and fast response
Ac ce p
time. Dyes are a class of organic materials. They are very interesting materials for studying the optical nonlinear effects because they exhibit large optical nonlinearities, fast response time, and strong absorption in the visible spectral region. In addition, they are characterized by their flexibility and thermal and chemical stability in dye – doped polymer solid films. These very important advantages make the dyes suitable candidate for nonlinear optical investigations. Optical power limiting is an important nonlinear optical behavior exhibited by some nonlinear materials, it can be used to protect the eyes
2 Page 2 of 20
and the sensitive optical equipments from intense laser beams. In this optical process, the output intensity of the laser beam passing through the
ip t
nonlinear medium (the sample) initially increases with increased input laser beam intensity and then tends to saturated at higher input intensities. It was
cr
demonstrated that the dyes can exhibit significant and important optical
us
limiting behaviors [12,15,16]. In our study, we found that the Leishman dye exhibits large and negative nonlinearity and different nonlinear behaviors
an
were observed, thus it could be useful for optical applications. In this paper, we used the z – scan technique to determine the sign
M
and magnitude of the nonlinear refractive index (n2), the nonlinear absorption coefficient (β), and the third – order nonlinear optical (3)
) of the Leishman dye. The experiment was performed
d
susceptibility (χ
te
for different concentrations of Leishman dye solution and dye – doped film. The power limiting behavior was also studied using the z – scan
Ac ce p
technique.
2. Experimental
The Leishman dye was chosen for our study. The dye solution was
prepared by dissolving appropriate amount of the Leishman powder (depending on its molecular weight) in the chloroform as a solvent. Four samples of different concentrations of Leishman dye solution were prepared, these are : 0.03, 0.05, 0.07, and 0.09 mM. The dye – doped polymer
films
were
prepared
using
solution
casting method.
3 Page 3 of 20
The Methylmethacrylate (PMMA) was dissolved in Chloroform and the solution was stirred at room temperature for few hours to obtain a
ip t
homogeneous solution. The already prepared dye solution at concentration 0.09 mM was added to stirred solution (polymer with chloroform). The
cr
final mixture was cast on to microscope slides and allowed to evaporate
slowly at room temperature. After sometime solid films were obtained
us
with thickness varied from 0.80 to 0.85 mm. The optical quality of the films was checked by using He – Ne laser beam at wavelength 632.8 nm
an
and power 2 mW. The films show clear and uniform thickness. The film of thickness 0.08 mm was chosen for our present study.
M
The linear absorption spectra of both Leishman dye solution in 1 cm quartz cell for different concentrations and dye – doped polymer film
d
samples were recorded using UV – Vis spectrophotometer (Cecil double
te
– beam UV – Vis spectrophotometer model CE – 7500). The z – scan technique [17, 18] was used to measure the nonlinear
Ac ce p
optical properties of Leishman dye. This technique is a simple, highly sensitive, and straightforward method for determining the nonlinear refractive index (n2) and the nonlinear absorption coefficient of material. Both the sign and the magnitude of the real part and imaginary part of the third – order nonlinear optical susceptibility (χ
(3)
) can be determined by
this method. The z – scan technique relies on the distortions induced in the spatial and temporal profile of the input beam passing through the sample. Fig.1 shows the experimental setup of the z – scan technique. The experiment was carried out using an adjustable power CW solid-
4 Page 4 of 20
State
laser (SSL) operating at 532 nm wavelength as the source of
excitation. The output power of the laser can be varied over the range
ip t
0 – 100 mW. The laser Gaussian beam was focused to a beam waist (ω0) of 24 µm by a convex lens of focal length 5 cm and passed through the
cr
sample, which is either 1 mm quartz cell containing Leishman dye solution or dye – doped polymer film. The Rayleigh length (z0) was 3.4 mm, which
us
is satisfied the sample condition in the z – scan method, that is L < n0 z0 ,
an
where L is the sample thickness and n0 is the linear refractive index of the sample material.
M
The z – scan experiment was performed by translating the sample across the focal point of the lens along the z – axis direction. In the
d
closed – aperture z – scan, the transmitted power output was measured
te
through a small diameter aperture (S = 0.5) placed in the far field of the lens as a function of position z of the sample, with respect to the focal
Ac ce p
plane (z = 0) , using the photo - detector PD2 which is attached to a digital power meter. The photo - detector PD1 is also attached to a digital power meter was used to measure the input laser power. In the open – aperture z – scan, the aperture is fully opened (S = 1) and the power of the entire laser beam transmitted through the sample was measured by the photo - detector PD2 .
5 Page 5 of 20
ip t cr us
M
an
Fig. 1. Z – scan experimental setup. BS, is a beam splitter; PD1 and PD2 are Photo - detectors.
3. Results and Discussion
d
The linear absorption spectra of the Leishman dye at different
te
concentrations (0.03, 0.05, 0.07, 0.09 mM) and dye – doped polymer film at concentration 0.09 mM are shown in Fig. 2 (a) and (b), respectively.
Ac ce p
From these figures it can see that the absorption spectra of the Leishman dye exhibit a wide absorption band with two peaks, which are located at wavelengths 533 nm and 650 nm for the dye solution and a single peak at wavelength 653 nm for the dye – doped polymer solid film. We can also see from Fig. 2 (a) that the value the peak increases with increasing the Leishman dye concentration.
6 Page 6 of 20
ip t cr M
an
us
(a)
te
d
(b)
Ac ce p
Fig. 2. Linear absorption spectra of Leishman dye. (a) Dye solution at different concentrations. (b) Dye – doped polymer film of concentration 0.09 mM.
The transmittance
curves
(the
normalized
transmittance
as a
function of the sample position z) obtained for the Leishman dye in chloroform
at different concentrations and incident intensity I0 = 1.11
kW / cm 2 are shown in Fig. 3. The normalized transmittance curves of a closed – aperture z – scan in Fig. 3 (a) are characterized by a peak followed by a valley (peak – valley) behavior. This indicates that the 7 Page 7 of 20
sign of nonlinear refractive index is negative (n2 < 0) (self – defocusing effect). The normalized transmittance curves of the open aperture z –
ip t
scan in Fig. 3 (b) show saturable absorption behavior. Occurrence of the self – defocusing effect in the dye medium is due to the variation of
cr
its refractive index (n) with temperature (i.e., d n / d T).
detector PD2
us
In the closed – aperture z - scan measurements, the photo – is sensitive to both the nonlinear absorption and the
an
nonlinear refraction. Therefore, in order to obtain the pure nonlinear refraction, the closed – aperture data was divided by the open – aperture data [18]. The pure nonlinear refraction z – scan transmittance curves for
M
dye solution at different concentration are shown in Fig. 3 (c). Similar behaviors for closed - aperture and open – aperture z – scan were
d
observed in the case of the dye – doped polymer film at concentration
Ac ce p
te
0.09 mM as shown in Fig. 4 (a – c).
8 Page 8 of 20
ip t cr
Ac ce p
te
(b)
d
M
an
us
(a)
(c)
Fig. 3. Normalized transmittance curves for Leishman dye solution at different concentrations. (a) Closed – aperture z – scan. (b) Open – aperture z – scan. (c) Pure nonlinear refraction. 9 Page 9 of 20
ip t cr
Ac ce p
te
(b)
d
M
an
us
(a)
(c)
Fig. 4. Normalized transmittance curves for Leishman dye - doped polymer film at concentration 0.09 mM. (a) Closed – aperture z – scan. (b) Open – aperture z – scan. (c) Pure nonlinear refraction.
10 Page 10 of 20
For the calculation of the third – order nonlinear refractive index (n2) of the Leishman dye, the following standard relations were used
ip t
[17, 18]: ΔTP – V = 0.406 (1 – S) 0.25 |Δ Ø0|
cr
(1)
(2)
an
us
Δ Ø0 λ n2 = ────── 2 π I0 Leff
where ΔTP – V is the difference between the normalized peak and valley transmittance, TP – TV , |Δ Ø0| is the on axis nonlinear phase – shift of
M
laser beam at focus, and S is the linear aperture transmittance given by: S = 1 – exp (-2 ra 2 / ωa 2 ) , where ra is the aperture radius and ωa is
d
the laser beam radius at the aperture. λ is the laser wavelength
te
(λ = 532 nm), I0 = 2 P0 / π ω02 is the peak laser beam intensity within the
Ac ce p
the sample (I0 = 1.11 kW / cm2), and effective length (thickness) of
absorption coefficient of
Leff = (1 – exp(- α0 L) ) / α0
is
the sample, α0 is the linear
the sample medium, and L is the sample
length.
The nonlinear absorption coefficient (β) of the Leishman dye
was calculated from the following relation: 2√2 β = ──── ΔT I0 Leff
(3)
where ΔT is the normalized transmittance difference between peak at
11 Page 11 of 20
the focal point (z = 0) in the open – aperture z – scan curve and the baseline.
ip t
The real part (Re (χ (3))) and the imaginary part (Im (χ (3))) of the third – order nonlinear optical susceptibility (χ (3)) for the Leishman
cr
dye were calculated using the following relations [19]:
Im [χ (3)] (esu) = 10 – 2
ε0 c 2 n0 2 λ β ───────── 4 π2
us
Re [χ (3)] (esu) = 10 – 4
ε0 c 2 n0 2 n2 ──────── π
an
(cm 2 / W)
(5)
M
(cm / W)
(4)
d
where ε0 is the permittivity of free space, n0 is the linear refractive
The
te
index of the medium, and c is the velocity of light in vacuum. absolute value
of
the third – order nonlinear optical
Ac ce p
susceptibility was evaluated using the following relation: |χ (3)| = [(Re (χ (3))) 2 + (Im (χ (3))) 2]
The
calculated
nonlinear
½
parameters
(7) for the Leishman dye
solution and the dye doped – polymer film are summarized in Table 1.
12 Page 12 of 20
Table 1: Summary of the various calculated nonlinear parameters for Leishman dye solution and dye – doped polymer film. n2 (cm2 / W) × 10 - 7
β (cm / W) × 10 - 3
0.03
1.077
- 2.454
1.433
1.314
0.05
1.226
- 2.818
1.934
1.588
0.07
1.377
- 3.196
2.599
1.901
0.09
1.534
- 3.588
3.108
2.260
0.09
1.546
an
3.726
3.156
Polymer film
cr
us
Solution
ip t
ΔTP – V
- 4.178
M
Sample
|χ (3)| (esu) × 10 - 5
Concentration (mM)
The values of n2 , β , and |χ (3)| are related to the concentration of the dye
solution. The value of each one of these nonlinear
d
Leishman
te
parameters increases when the dye concentration increases as shown in Figs. 5, 6, and 7, respectively. This may attributed to the fact that the number
Ac ce p
of the dye molecules increases when concentration increases, more particles are thermally excited resulting in an enhanced nonlinear effect. The laser heating is produced while the laser beam passing through the sample medium. This process induces temperature and density gradients that change the refractive index of the dye medium and consequently thermal focusing effect arising.
13 Page 13 of 20
ip t cr us
Ac ce p
te
d
M
an
Fig. 5. The nonlinear refractive index (n2) as a function of dye Leishman concentration.
Fig. 6. The nonlinear absorption coefficient (β) as a function of dye Leishman concentration.
14 Page 14 of 20
ip t cr us
an
Fig. 7. The nonlinear third – order optical susceptibility ( |χ (3)|) as a function of dye Leishman concentration.
M
For optical power limiting measurements, based on the nonlinear refraction (self – defocusing), the sample (dye solution or dye – doped
d
polymer film) was located at the position where the valley falls in the
te
closed – aperture and the input power of the laser beam was varied.
Ac ce p
The input powers and the corresponding output powers of the laser beam were recorded by the power meters. Fig. 8 shows the optical limiting behavior of Leishman dye in solution and dye – doped polymer solid film. The laser output power was plotted as a function of the laser input power, varying over the range 0 – 40 mW. It is clearly seen that the output power initially varies linearly with increasing the input power (at low powers), but the transmitted output power starts to deviate from the linearity at high input powers. With still increasing the input power, the output power reaches a plateau region at certain value
15 Page 15 of 20
for the input
power and
the output power relatively remains
constant (saturated) with further
increase in the input power. The
ip t
value of the input power at which the output power starts to saturate is known as the power limiting threshold which defined as the input
cr
power at which the sample transmittance falls to half of its linear
us
transmittance.
The values of the power limiting threshold for the Leishman
an
dye solution at different concentrations and dye – doped polymer solid film at concentration 0.09 mM were estimated , Table 2 summarizes
M
these values.
It is evident that the optical power limiting effect depends on the
d
concentration of the Leishman dye and increases with increasing the dye
te
concentration, while the power limiting threshold decreases with increasing
Ac ce p
the dye concentration. At high Leishman dye concentrations, the output power reached a plateau at low input power and the dye medium exhibits strong optical power limiting effect.
16 Page 16 of 20
ip t cr us
d
M
an
Fig. 8. Optical power limiting behavior ( output laser power versus input laser power) for Leishman dye solution at different concentrations and dye – doped polymer film at concentration 0.09 mM.
Ac ce p
te
Table 2: The calculated values of the optical power limiting threshold for the Leishman dye solution and dye – doped polymer film. Sample
Solution
Polymer film
Concentration (mM) 0.03
Power limiting threshold (mW) 19.9
0.05
17.8
0.07
16.1
0.09
13.7
0.09
10.4
17 Page 17 of 20
4. Conclusion We have studied the nonlinear absorption and the nonlinear
ip t
refraction of Leishman dye, both in solution and polymer as a dye – doped polymer film using z – scan technique under excitation by a
cr
CW laser beam at 532 nm. We found that the Leishman dye
is
characterized by negative nonlinear refraction (self – defocusing) and
us
saturable absorption behavior. The observed nonlinearity are thermal in nature owing to the CW excitation and the nonlinear effect is caused
experimental
results
show that
M
The
an
by self – defocusing process.
exhibits large nonlinearities. Significant
values
the for
Leishman dye the nonlinear
d
refractive index (n2), the nonlinear absorption coefficient (β), and the
te
third – order nonlinear optical susceptibility (χ (3)) were obtained. These values can be easily varied by varying
the dye concentrations. The
Ac ce p
power limiting effect was observed in the Leishman dye and is affected by the variation of the concentration. These advantages give an indication that the Leishman is a promising material for potential applications in nonlinear optical devices such as photonic and signal processing devices.
18 Page 18 of 20
5. References [1] P. Günter, Ed., Nonlinear Optical Effects and Materials, Spriger –
ip t
Verlag, Berlin, Germany, 2000.
Ac ce p
te
d
M
an
us
cr
[2] H. S. Nalwa, Ed., Handbook of Advanced Electronic and Photonic Materials and Devices, Academic Press, New York , 2001. [3] Y. Guo, C. K. Kao, E. H. Li, K. S. Chang, Eds., Nonlinear Photonic, Springer – Verlag, Berlin, 2002. [4] P. N. Prasad, Introduction to Bio-Photonic, John Wiley & Sons Ltd., New York , 2003. [5] N. Costa, A. Cartaxo, Eds., Advances in Lasers and Electro Optics, InTech, 2010. [6] P. N. Prasad, D. J. Williams, Introduction to Nonlinear Optical Effects in Molecules and Polymers, John Wiley & Sons Ltd., New York, 1990. [7] S. R. Marder, J. E. Sohn, G. D. Stucky, Eds., Materials for Nonlinear Optics –Chemical Perspectives, ACS Symposium Series, Vol. 455, Academic Chemical Society, Washington, DC., 1991. [8] J. Zyss, Ed., Molecular Nonlinear Optics : Materials, Physics, and Devices, Academic Press, New York, 1994. [9] H. S. Nalwa, S. Miyata, Nonlinear Optics of Organic Molecules and Polymers, CRC Press, Boca Raton, 1997. [10] R. L. Sutherland, Ed., Handbook of Nonlinear Optics, 2nd Edition, Marcel Dekker, New York, 2003. [11] H. Stricker , W. W. Webb, Three – dimensional optical data storage in refractive media by two – photon excitation, Opt. Lett. 16 (1991) 1780-1782. [12] Z. G. Yong, W. Chun, L. Hong, W. Dong, S. Z. Shu, J. M. Hua, Two – photon absorption and optical power limiting based on new organic dyes, Chin. Phys. Lett. 18 (2001) 1120-1122.
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Ac ce p
te
d
M
an
us
cr
ip t
[13] Purnima, D. Mohan, S. Rani, Optical nonlinear refractive and limiting behavior of Nickel complex dye doped solid – solid matrix for both visible and near infrared nanosecond excitation, Optik 124 (2013) 1741-1745. [14] L. Kamdth, Manjuntha K. B., S. Shettigar, G. Umesh, et al., Investigation of third – order and optical power limiting properties of Terphenyl derivatives, Opt. Laser Technol. 56 (2014) 425-429. [15] R. R. Krishnamurthy, R. Alkondan, Nonlinear characterization of Mercurochrome dye for potential application in optical limiting, Opt. Appl. 40 (2010) 187-196. [16] A. Thankappan, S. Thomas, V. P. N. Nampoon, Solvent effect on the third order optical nonlinearity and optical limiting ability of betanin natural dye extracted from red beet root, Opt. Mater. 35 (2013) 2332-2337. [17] M. Sheik – Bahae, A. A. Said, E. W. Van Stryland , High sensitive single beam n2 measurements, Opt. Lett. 14 (1989) 955-957. [18] M. Sheik – Bahae, A. A. Said, T. Wei, D. J. Hagan, E. W. Van Stryland , Sensitive measurement of optical nonlinearities using a single beam, IEEE J. Quantum Electron. QE-26 (1990) 760-769. [19] T. Cassano, R. Tommasi, M. Ferrara, F. Babudri, G. M. Farinola, F. Naso, Substituent-dependence of the optical nonlinearities in poly (2,5-diakoxy-p-phenylenevinylene) polymers investigated by z-scan technique , Chem. Phys. 272 (2001) 111-118.
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