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Nonlinear studies of Acid Fuchsin dye in liquid and solid media
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Spectrochimica Acta Part A 69 (2008) 1160–1164
Nonlinear studies of Acid Fuchsin dye in liquid and solid media G. Vinitha ∗ , A. Ramalingam Centre for Laser Technology, Department of Physics, Anna University, Chennai 600025, India Received 15 December 2006; received in revised form 4 June 2007; accepted 15 June 2007
Abstract Solid-state dye-doped polymers are attractive alternative to the conventional liquid dye solutions. In this paper, nonlinear properties of the dye Acid Fuchsin has been studied. The third-order nonlinear optical properties of Acid Fuchsin dye in 1-butanol and dye-doped polymer film were measured by the Z-scan technique using 532 nm diode pumped Nd:Yag laser. This material exhibits negative optical nonlinearity. The dye at 0.4 mM concentration exhibited nonlinear refractive coefficient (n2 = −8.72 × 10−8 and −10.308 × 10 −8 (cm2 /W) in liquid and solid media, respectively), nonlinear absorption coefficient (β = −7.69 × 10−4 and −8.294 × 10−4 cm/W in liquid and solid media, respectively) and susceptibility (χ(3) = 4.33 × 10−6 and 5.13 × 10−5 esu in liquid and solid media, respectively). These results show that Acid Fuchsin dye has potential applications in nonlinear optics. © 2007 Elsevier B.V. All rights reserved. Keywords: Acid Fuchsin; Solid-state dye laser; Z-scan; Nonlinear refraction index; Nonlinear absorption
1. Introduction There has been a large need for nonlinear optical materials that can be used with low intensity lasers for applications such as phase conjugation, image processing, and optical switching [1,2]. Large nonlinear optical susceptibility resulting from the nonlinear response of organic molecules has attracted much attention. Study of nonlinear optical properties on dye IR 140 [3], series hydroxy porphyrin [4], bismuth-based glasses [5], ultrafast optical nonlinearity in polymethylmethacrylate–TiO2 nanocomposites [6], has been reported recently. Nonlinear optical phenomena can be due to electronic and nonelectronic processes. The former refers to those radiative interactions between the active electron and the optical electric field. Nonelectronic processes are nonradiative interactions such as temperature, density, cis–trans isomerism, phase transition, etc. Among various techniques developed to measure the nonlinear optical refractive index, the single beam Z-scan technique, developed by the Mansoor et al. [7], is a simple and effective tool. It provides not only the magnitudes of the real and imaginary parts of the nonlinear susceptibility, but also the sign of the real part. It is a method, which can rapidly measure both
nonlinear refraction and nonlinear absorption in solids and liquid samples. It is the simple single beam method, which utilizes self-focusing or self-defocusing phenomena in optical nonlinear materials. In this article, we report results of experiments performed by us using the Z-scan technique to measure the sign and magnitude of the optical nonlinearity of an organic dye, namely Acid Fuchsin in 1-butanol and dye-doped polymer film. The sample is found to exhibit a large and negative optical nonlinearity. 2. Experiment The dye, Acid Fuchsin, obtained from CDH, India, was chosen for this study. Thin layer chromatography (TLC) test confirms the absence of any impurities in this dye. methylmethacrylate (MMA) (Lancaster) was used as monomer. Initial MMA compositions were cleared of foreign inclusions. Spectroscopic grade 1-butanol purchased from Merck (India) was chosen as an additive because it combines good solubility for Acid Fuchsin dye. Chemical structure of organic dye, Acid Fuchsin is as in Fig. 1. The absorption spectra of the dye in solvent and in dye-doped polymer film is as shown in Fig. 2. 2.1. Synthesis of dye-doped polymer film
∗
Corresponding author. Tel.: +91 44 22203162; fax: +91 44 22301369. E-mail addresses: [email protected] (G. Vinitha), ramalingam [email protected] (A. Ramalingam). 1386-1425/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2007.06.016
The dye-doped polymer film of dye concentration 0.4 mM was synthesized by thermal bulk free radical polymerization
G. Vinitha, A. Ramalingam / Spectrochimica Acta Part A 69 (2008) 1160–1164
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Fig. 1. Chemical structure of Acid Fuchsin dye belonging to triarylmethane family.
method [8]. MMA and 1-butanol are taken in the ratio 4:1 (v/v). Known weights of dyes are dissolved in this mixture. Three grams of 2,2-azobis (isobutyronitrile) per litre of MMA, 1-butanol mixture solution is used as an initiator for polymerization. The solution is taken in polymerizing tubes and kept in the nitrogen atmosphere. Bulk polymerization is carried out in a temperature controlled water bath. Once the solution is viscous, the viscous dye solution with initiator mixture is poured on to a petridish placed in a glass enclosure, kept at a temperature of 40 ◦ C in a temperature controlled water bath and a film of thickness 0.9 mm was obtained. 2.2. Nonlinear studies The Z-scan technique [7] is a simple but very accurate method to determine both nonlinear index of refraction n2 and nonlinear absorption coefficient β. Nonlinear index of refraction is proportional to the real part of the third-order susceptibility [Re χ(3) ] and the nonlinear absorption coefficient is proportional to [Im χ(3) ]. The Z-scan experiments were performed using a 532 nm diode pumped Nd:Yag laser beam (Coherent CompassTM 215M50), which was focused by 3.5 cm focal length lens. The laser beam waist ω0 at the focus is measured to be 15.84 m and the Rayleigh length to be 1.48 mm. The schematic of the experimental setup used is shown in Fig. 3. A 1 mm wide optical cell containing the dye in 1-butanol is translated across the focal region along the axial direction that is the direction of the propagation laser beam. The transmission of the beam through an aperture placed in the far field was measured using photo detector fed to the digital power meter (Field master GS-coherent).
Fig. 2. Absorption spectrum of dye Acid Fuchsin in (a) 1-butanol; (b) PMMA + 1-butanol.
Fig. 3. Schematic diagram of experimental arrangement for the Z-scan measurement.
For an open aperture Z-scan, a lens to collect the entire laser beam transmitted through the sample replaced the aperture. The same was repeated for the polymer film. 3. Results and discussions The third-order nonlinear refraction index n2 , and the nonlinear absorption coefficient β, of Acid Fuchsin in solution and in polymer film were evaluated by the measurements of Zscan. Fig. 4 shows the Z-scan of Acid Fuchsin in 1-butanol and thin polymer film at concentration 0.4 mM at incident intensity 4.38 kW/cm2 . The peak followed by a valley-normalized transmittance obtained from the closed aperture Z-scan data, indicates that the sign of the refraction nonlinearity is negative, i.e. selfdefocusing. Self-defocusing effect is due to local variation of refractive index with temperature. Fig. 4(b) shows the typical Z-scan data for the open aperture (S = 1) setup for solution of Acid Fuchsin in 1-butanol and in polymer film at concentration of 0.4 mM. The enhanced transmission near the focus is indicative of the saturation of absorption at high intensity. Absorption saturation in the sample enhances the peak and decreases the valley in the closed aperture Z-scan thus distorting the symmetry of the Z-scan curve about z = 0. The defocusing effect shown in Fig. 4(a) is attributed to a thermal nonlinearity resulting from absorption of radiation at 532 nm. Localized absorption of a tightly focused beam propagating through an absorbing dye medium produces a spatial distribution of temperature in the dye solution and consequently,
Fig. 4. Z-scan data of the 0.4 mM Acid Fuchsin dye in (A) 1-butanol (liquid medium) and (B) dye-doped polymer film (solid medium) at I0 = 4.38 kW/cm2 (a) closed aperture scan (S = 0.035), (b) open aperture scan (S = 1) and (c) the division of a by b.
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Table 1 Values of peak to valley distance (Tp − Tv ), nonlinear refraction coefficient (n2 ), change in refractive index (n), absorption coefficient (β), susceptibility (χ(3) ) for different concentrations of Acid Fuchsin dye solution in 1-butanol and in dye-doped polymer film Acid Fuchsin dye
Tp-v
n2 (×10−8 cm2 /W)
n (×10−4 )
β (×10−4 cm/W)
χ(3) (×10−6 esu)
In 1-butanol (0.4 mM) In 1-butanol (0.3 mM) In 1-butanol (0.2 mM) In 1-butanol (0.1 mM) In 1-butanol (0.05 mM) Polymer film (0.4 mM)
1.703 1.510 1.409 1.247 0.949 1.795
−8.72 −7.91 −7.03 −6.16 −4.64 −10.31
−3.79 −3.09 −3.06 −2.68 −2.02 −4.48
−7.69 −5.71 −3.55 −2.85 −2.64 −4.48
4.33 3.94 3.49 3.06 2.31 5.13
a spatial variation of the refractive index, that acts as a thermal lens resulting in phase distortion of the propagating beam. |ϕ0 |, the on-axis phase shift at the focus is related to the difference in the peak and valley transmission, Tp-v as Tp-v = 0.406(1 − S)0.25 |ϕ0 |
(1)
where S = 1 − exp(−2r02 /ω02 ) is the aperture linear transmittance with r0 denoting the aperture radius and ω0 denoting the beam radius at the aperture in the linear regime. Then nonlinear refractive index is given by [7] n2 = ϕ0 λ2πI0 Leff
(2)
where λ is the laser wavelength, I0 the intensity of the laser beam at focus z = 0, Leff = [1 − exp(−αL)/α] the effective thickness of the sample, α the linear absorption coefficient and L is the thickness of the sample. Generally the measurements of the normalized transmittance versus sample position, for the cases of closed and open aperture, allow determination of the nonlinear refractive index, n2 and the saturation absorption coefficient, β. Here, since the closed aperture transmittance is affected by the nonlinear refraction and absorption, the determination of n2 is less straightforward from the closed aperture scans. It is necessary to separate the effect of nonlinear refraction from that of the nonlinear absorp-
tion. A method [7] to obtain purely effective n2 is to divide the closed aperture transmittance by the corresponding open aperture scans. The ratio of Fig. 4(a) and (b) scans is shown in Fig. 4(c). The data obtained in this way reflects purely the effects of nonlinear refraction. The nonlinear absorption coefficient β can be estimated from the open aperture Z-scan data. √ T β=2 2 (3) I0 Leff The real and imaginary parts of the third-order nonlinear optical susceptibility χ(3) are defined as [9] Re χ(3) (esu) =
ε0 c2 n20 n2 (×10−4 cm2 /W) π
(4)
Im χ(3) (esu) =
ε0 c2 n20 λβ (×10−2 cm/W) 4π2
(5)
where ε0 is the vacuum permittivity and c is the light velocity in vacuum. The values of change in peak to valley distance (Tp − Tv ), nonlinear refraction coefficient (n2 ), change in refractive index (n), Absorption coefficient (β), susceptibility (χ(3) ) for different concentrations of Acid Fuchsin dye solution in 1-butanol and in dye-doped polymer film are as tabulated in Table 1.
Fig. 5. Z-scan data of (A) closed, (B) open and (C) ratio of closed to open of dye solution at various concentrations (a) 0.05 mM, (b) 0.1 mM, (c) 0.2 mM, (d) 0.3 mM and (e) 0.4 mM.
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Fig. 6. The change in the peak-to-valley transmission for different concentrations.
Fig. 9. Variation of χ(3) of dye solution in 1-butanol for different concentrations.
The value of Tp-v has increased for the dye-doped polymer film when compared to the dye in 1-butanol. This may be due to the heat dissipation being faster in liquids as compared to that in solid medium. Experiment is performed for different concentrations of the dye solution. Fig. 5 gives the Z-scan signatures of
the dye in 1-butanol for various concentrations. Fig. 6 shows the change in the peak-to-valley distance for different concentrations. It is inferred that the Tp-v value increases with increase in concentration. From Figs. 7–9, we can see an increasing trend in values of n2 , β and χ(3) as the concentration increases. This may be attributed to the fact that as the number of dye molecules increases when the concentration increases, more particles get thermally agitated resulting in an enhanced effect. 4. Conclusion
Fig. 7. Variation of n2 of dye solution in 1-butanol for different concentrations.
We have measured the nonlinear refraction index coefficient, n2 , the nonlinear absorption coefficient, β and susceptibility, χ(3) for solution of Acid Fuchsin in 1-butanol and in dye-doped polymer film (liquid and solid environments) using the Z-scan technique with 532 nm diode pumped Nd:Yag laser. The Zscan measurements indicated that the dye exhibited negative nonlinear optical properties. We have shown that the nonlinear absorption can be attributed to a saturation absorption process, while the nonlinear refraction leads to self-defocusing in this dye. It is worth noting that the value of χ(3) for the dye studied is larger than those of some representative third-order nonlinear optical materials such as organic polymers and organic metal [10–12]. All these experimental results show that Acid Fuchsin dye is a promising material for applications in nonlinear optical devices. Acknowledgement The authors wish to thank the DAE-BRNS for their financial support. References
Fig. 8. Variation of β of dye solution in 1-butanol for different concentrations.
[1] M.A. Kramer, W.R. Tompkin, R.W. Boyd, Phys. Rev. A 34 (1986) 2026. [2] F.E. Hernandez, A.O. Marcano, Y. Alvarado, A. Biondi, H. Maillotte, Opt. Commun. 152 (1998) 77. [3] U. Tripathy, R.J. Rajesh, P.B. Bisht, A. Subrahmanyam, Chem. Sci. 114 (2002) 557.
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[4] X. Li, F. Wang, S. Pei, W. Peng, Y. Shi, X. Wang, Proc. SPIE 6029 (2006) 370. [5] H. Tomoharu, T. Nagashima, N. Sugimoto, Opt. Commun. 250 (2005) 411. [6] H.I. Elim, W. Ji, A.H. Yuwono, J.M. Xue, J. Wang, Appl. Phys. Lett. 82 (2003) 2691. [7] S.-B. Mansoor, A.A. Said, T.-H. Wei, D.J. Hagan, E.W. Van Stryland, IEEE J. Quant. Electron. 26 (4) (1990) 760.
[8] A. Costela, I. Garcia-marino, J.M. Figuera, F. Amat Guerri, J. Barroso, R. Sastre, Opt. Commun. 130 (1996) 44. [9] T. cassano, R. Tommasi, M. Ferrara, F. Babudri, G.M. Farinola, F. Naso, Chem. Phys. 272 (2001) 111. [10] F. Li, Y. Song, K. Yang, S. Liu, C. Li, Appl. Phys. Lett. 71 (1997) 2073. [11] G. Ravindra Kumar, F.A. Rajgara, Appl. Phys. Lett. 67 (1995) 3871. [12] A. Clementi, N. Chiodini, A. Pleari, Appl. Phys. Lett. 84 (2004) 960.
Spectrochimica Acta Part A 69 (2008) 1160–1164
Nonlinear studies of Acid Fuchsin dye in liquid and solid media G. Vinitha ∗ , A. Ramalingam Centre for Laser Technology, Department of Physics, Anna University, Chennai 600025, India Received 15 December 2006; received in revised form 4 June 2007; accepted 15 June 2007
Abstract Solid-state dye-doped polymers are attractive alternative to the conventional liquid dye solutions. In this paper, nonlinear properties of the dye Acid Fuchsin has been studied. The third-order nonlinear optical properties of Acid Fuchsin dye in 1-butanol and dye-doped polymer film were measured by the Z-scan technique using 532 nm diode pumped Nd:Yag laser. This material exhibits negative optical nonlinearity. The dye at 0.4 mM concentration exhibited nonlinear refractive coefficient (n2 = −8.72 × 10−8 and −10.308 × 10 −8 (cm2 /W) in liquid and solid media, respectively), nonlinear absorption coefficient (β = −7.69 × 10−4 and −8.294 × 10−4 cm/W in liquid and solid media, respectively) and susceptibility (χ(3) = 4.33 × 10−6 and 5.13 × 10−5 esu in liquid and solid media, respectively). These results show that Acid Fuchsin dye has potential applications in nonlinear optics. © 2007 Elsevier B.V. All rights reserved. Keywords: Acid Fuchsin; Solid-state dye laser; Z-scan; Nonlinear refraction index; Nonlinear absorption
1. Introduction There has been a large need for nonlinear optical materials that can be used with low intensity lasers for applications such as phase conjugation, image processing, and optical switching [1,2]. Large nonlinear optical susceptibility resulting from the nonlinear response of organic molecules has attracted much attention. Study of nonlinear optical properties on dye IR 140 [3], series hydroxy porphyrin [4], bismuth-based glasses [5], ultrafast optical nonlinearity in polymethylmethacrylate–TiO2 nanocomposites [6], has been reported recently. Nonlinear optical phenomena can be due to electronic and nonelectronic processes. The former refers to those radiative interactions between the active electron and the optical electric field. Nonelectronic processes are nonradiative interactions such as temperature, density, cis–trans isomerism, phase transition, etc. Among various techniques developed to measure the nonlinear optical refractive index, the single beam Z-scan technique, developed by the Mansoor et al. [7], is a simple and effective tool. It provides not only the magnitudes of the real and imaginary parts of the nonlinear susceptibility, but also the sign of the real part. It is a method, which can rapidly measure both
nonlinear refraction and nonlinear absorption in solids and liquid samples. It is the simple single beam method, which utilizes self-focusing or self-defocusing phenomena in optical nonlinear materials. In this article, we report results of experiments performed by us using the Z-scan technique to measure the sign and magnitude of the optical nonlinearity of an organic dye, namely Acid Fuchsin in 1-butanol and dye-doped polymer film. The sample is found to exhibit a large and negative optical nonlinearity. 2. Experiment The dye, Acid Fuchsin, obtained from CDH, India, was chosen for this study. Thin layer chromatography (TLC) test confirms the absence of any impurities in this dye. methylmethacrylate (MMA) (Lancaster) was used as monomer. Initial MMA compositions were cleared of foreign inclusions. Spectroscopic grade 1-butanol purchased from Merck (India) was chosen as an additive because it combines good solubility for Acid Fuchsin dye. Chemical structure of organic dye, Acid Fuchsin is as in Fig. 1. The absorption spectra of the dye in solvent and in dye-doped polymer film is as shown in Fig. 2. 2.1. Synthesis of dye-doped polymer film
∗
Corresponding author. Tel.: +91 44 22203162; fax: +91 44 22301369. E-mail addresses: [email protected] (G. Vinitha), ramalingam [email protected] (A. Ramalingam). 1386-1425/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2007.06.016
The dye-doped polymer film of dye concentration 0.4 mM was synthesized by thermal bulk free radical polymerization
G. Vinitha, A. Ramalingam / Spectrochimica Acta Part A 69 (2008) 1160–1164
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Fig. 1. Chemical structure of Acid Fuchsin dye belonging to triarylmethane family.
method [8]. MMA and 1-butanol are taken in the ratio 4:1 (v/v). Known weights of dyes are dissolved in this mixture. Three grams of 2,2-azobis (isobutyronitrile) per litre of MMA, 1-butanol mixture solution is used as an initiator for polymerization. The solution is taken in polymerizing tubes and kept in the nitrogen atmosphere. Bulk polymerization is carried out in a temperature controlled water bath. Once the solution is viscous, the viscous dye solution with initiator mixture is poured on to a petridish placed in a glass enclosure, kept at a temperature of 40 ◦ C in a temperature controlled water bath and a film of thickness 0.9 mm was obtained. 2.2. Nonlinear studies The Z-scan technique [7] is a simple but very accurate method to determine both nonlinear index of refraction n2 and nonlinear absorption coefficient β. Nonlinear index of refraction is proportional to the real part of the third-order susceptibility [Re χ(3) ] and the nonlinear absorption coefficient is proportional to [Im χ(3) ]. The Z-scan experiments were performed using a 532 nm diode pumped Nd:Yag laser beam (Coherent CompassTM 215M50), which was focused by 3.5 cm focal length lens. The laser beam waist ω0 at the focus is measured to be 15.84 m and the Rayleigh length to be 1.48 mm. The schematic of the experimental setup used is shown in Fig. 3. A 1 mm wide optical cell containing the dye in 1-butanol is translated across the focal region along the axial direction that is the direction of the propagation laser beam. The transmission of the beam through an aperture placed in the far field was measured using photo detector fed to the digital power meter (Field master GS-coherent).
Fig. 2. Absorption spectrum of dye Acid Fuchsin in (a) 1-butanol; (b) PMMA + 1-butanol.
Fig. 3. Schematic diagram of experimental arrangement for the Z-scan measurement.
For an open aperture Z-scan, a lens to collect the entire laser beam transmitted through the sample replaced the aperture. The same was repeated for the polymer film. 3. Results and discussions The third-order nonlinear refraction index n2 , and the nonlinear absorption coefficient β, of Acid Fuchsin in solution and in polymer film were evaluated by the measurements of Zscan. Fig. 4 shows the Z-scan of Acid Fuchsin in 1-butanol and thin polymer film at concentration 0.4 mM at incident intensity 4.38 kW/cm2 . The peak followed by a valley-normalized transmittance obtained from the closed aperture Z-scan data, indicates that the sign of the refraction nonlinearity is negative, i.e. selfdefocusing. Self-defocusing effect is due to local variation of refractive index with temperature. Fig. 4(b) shows the typical Z-scan data for the open aperture (S = 1) setup for solution of Acid Fuchsin in 1-butanol and in polymer film at concentration of 0.4 mM. The enhanced transmission near the focus is indicative of the saturation of absorption at high intensity. Absorption saturation in the sample enhances the peak and decreases the valley in the closed aperture Z-scan thus distorting the symmetry of the Z-scan curve about z = 0. The defocusing effect shown in Fig. 4(a) is attributed to a thermal nonlinearity resulting from absorption of radiation at 532 nm. Localized absorption of a tightly focused beam propagating through an absorbing dye medium produces a spatial distribution of temperature in the dye solution and consequently,
Fig. 4. Z-scan data of the 0.4 mM Acid Fuchsin dye in (A) 1-butanol (liquid medium) and (B) dye-doped polymer film (solid medium) at I0 = 4.38 kW/cm2 (a) closed aperture scan (S = 0.035), (b) open aperture scan (S = 1) and (c) the division of a by b.
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Table 1 Values of peak to valley distance (Tp − Tv ), nonlinear refraction coefficient (n2 ), change in refractive index (n), absorption coefficient (β), susceptibility (χ(3) ) for different concentrations of Acid Fuchsin dye solution in 1-butanol and in dye-doped polymer film Acid Fuchsin dye
Tp-v
n2 (×10−8 cm2 /W)
n (×10−4 )
β (×10−4 cm/W)
χ(3) (×10−6 esu)
In 1-butanol (0.4 mM) In 1-butanol (0.3 mM) In 1-butanol (0.2 mM) In 1-butanol (0.1 mM) In 1-butanol (0.05 mM) Polymer film (0.4 mM)
1.703 1.510 1.409 1.247 0.949 1.795
−8.72 −7.91 −7.03 −6.16 −4.64 −10.31
−3.79 −3.09 −3.06 −2.68 −2.02 −4.48
−7.69 −5.71 −3.55 −2.85 −2.64 −4.48
4.33 3.94 3.49 3.06 2.31 5.13
a spatial variation of the refractive index, that acts as a thermal lens resulting in phase distortion of the propagating beam. |ϕ0 |, the on-axis phase shift at the focus is related to the difference in the peak and valley transmission, Tp-v as Tp-v = 0.406(1 − S)0.25 |ϕ0 |
(1)
where S = 1 − exp(−2r02 /ω02 ) is the aperture linear transmittance with r0 denoting the aperture radius and ω0 denoting the beam radius at the aperture in the linear regime. Then nonlinear refractive index is given by [7] n2 = ϕ0 λ2πI0 Leff
(2)
where λ is the laser wavelength, I0 the intensity of the laser beam at focus z = 0, Leff = [1 − exp(−αL)/α] the effective thickness of the sample, α the linear absorption coefficient and L is the thickness of the sample. Generally the measurements of the normalized transmittance versus sample position, for the cases of closed and open aperture, allow determination of the nonlinear refractive index, n2 and the saturation absorption coefficient, β. Here, since the closed aperture transmittance is affected by the nonlinear refraction and absorption, the determination of n2 is less straightforward from the closed aperture scans. It is necessary to separate the effect of nonlinear refraction from that of the nonlinear absorp-
tion. A method [7] to obtain purely effective n2 is to divide the closed aperture transmittance by the corresponding open aperture scans. The ratio of Fig. 4(a) and (b) scans is shown in Fig. 4(c). The data obtained in this way reflects purely the effects of nonlinear refraction. The nonlinear absorption coefficient β can be estimated from the open aperture Z-scan data. √ T β=2 2 (3) I0 Leff The real and imaginary parts of the third-order nonlinear optical susceptibility χ(3) are defined as [9] Re χ(3) (esu) =
ε0 c2 n20 n2 (×10−4 cm2 /W) π
(4)
Im χ(3) (esu) =
ε0 c2 n20 λβ (×10−2 cm/W) 4π2
(5)
where ε0 is the vacuum permittivity and c is the light velocity in vacuum. The values of change in peak to valley distance (Tp − Tv ), nonlinear refraction coefficient (n2 ), change in refractive index (n), Absorption coefficient (β), susceptibility (χ(3) ) for different concentrations of Acid Fuchsin dye solution in 1-butanol and in dye-doped polymer film are as tabulated in Table 1.
Fig. 5. Z-scan data of (A) closed, (B) open and (C) ratio of closed to open of dye solution at various concentrations (a) 0.05 mM, (b) 0.1 mM, (c) 0.2 mM, (d) 0.3 mM and (e) 0.4 mM.
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Fig. 6. The change in the peak-to-valley transmission for different concentrations.
Fig. 9. Variation of χ(3) of dye solution in 1-butanol for different concentrations.
The value of Tp-v has increased for the dye-doped polymer film when compared to the dye in 1-butanol. This may be due to the heat dissipation being faster in liquids as compared to that in solid medium. Experiment is performed for different concentrations of the dye solution. Fig. 5 gives the Z-scan signatures of
the dye in 1-butanol for various concentrations. Fig. 6 shows the change in the peak-to-valley distance for different concentrations. It is inferred that the Tp-v value increases with increase in concentration. From Figs. 7–9, we can see an increasing trend in values of n2 , β and χ(3) as the concentration increases. This may be attributed to the fact that as the number of dye molecules increases when the concentration increases, more particles get thermally agitated resulting in an enhanced effect. 4. Conclusion
Fig. 7. Variation of n2 of dye solution in 1-butanol for different concentrations.
We have measured the nonlinear refraction index coefficient, n2 , the nonlinear absorption coefficient, β and susceptibility, χ(3) for solution of Acid Fuchsin in 1-butanol and in dye-doped polymer film (liquid and solid environments) using the Z-scan technique with 532 nm diode pumped Nd:Yag laser. The Zscan measurements indicated that the dye exhibited negative nonlinear optical properties. We have shown that the nonlinear absorption can be attributed to a saturation absorption process, while the nonlinear refraction leads to self-defocusing in this dye. It is worth noting that the value of χ(3) for the dye studied is larger than those of some representative third-order nonlinear optical materials such as organic polymers and organic metal [10–12]. All these experimental results show that Acid Fuchsin dye is a promising material for applications in nonlinear optical devices. Acknowledgement The authors wish to thank the DAE-BRNS for their financial support. References
Fig. 8. Variation of β of dye solution in 1-butanol for different concentrations.
[1] M.A. Kramer, W.R. Tompkin, R.W. Boyd, Phys. Rev. A 34 (1986) 2026. [2] F.E. Hernandez, A.O. Marcano, Y. Alvarado, A. Biondi, H. Maillotte, Opt. Commun. 152 (1998) 77. [3] U. Tripathy, R.J. Rajesh, P.B. Bisht, A. Subrahmanyam, Chem. Sci. 114 (2002) 557.
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G. Vinitha, A. Ramalingam / Spectrochimica Acta Part A 69 (2008) 1160–1164
[4] X. Li, F. Wang, S. Pei, W. Peng, Y. Shi, X. Wang, Proc. SPIE 6029 (2006) 370. [5] H. Tomoharu, T. Nagashima, N. Sugimoto, Opt. Commun. 250 (2005) 411. [6] H.I. Elim, W. Ji, A.H. Yuwono, J.M. Xue, J. Wang, Appl. Phys. Lett. 82 (2003) 2691. [7] S.-B. Mansoor, A.A. Said, T.-H. Wei, D.J. Hagan, E.W. Van Stryland, IEEE J. Quant. Electron. 26 (4) (1990) 760.
[8] A. Costela, I. Garcia-marino, J.M. Figuera, F. Amat Guerri, J. Barroso, R. Sastre, Opt. Commun. 130 (1996) 44. [9] T. cassano, R. Tommasi, M. Ferrara, F. Babudri, G.M. Farinola, F. Naso, Chem. Phys. 272 (2001) 111. [10] F. Li, Y. Song, K. Yang, S. Liu, C. Li, Appl. Phys. Lett. 71 (1997) 2073. [11] G. Ravindra Kumar, F.A. Rajgara, Appl. Phys. Lett. 67 (1995) 3871. [12] A. Clementi, N. Chiodini, A. Pleari, Appl. Phys. Lett. 84 (2004) 960.