Accepted Manuscript Thermally induced nonlinear optical response and optical power limiting of acid blue 40 dye S. Pramodini, P. Poornesh, K.K. Nagaraja PII:
S1567-1739(13)00113-2
DOI:
10.1016/j.cap.2013.03.002
Reference:
CAP 3253
To appear in:
Current Applied Physics
Received Date: 26 October 2012 Revised Date:
23 January 2013
Accepted Date: 3 March 2013
Please cite this article as: S. Pramodini , P. Poornesh , K.K. Nagaraja, Thermally induced nonlinear optical response and optical power limiting of acid blue 40 dye, Current Applied Physics (2013), doi: 10.1016/j.cap.2013.03.002. 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.
*Highlights (for review)
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The third-order optical nonlinearity and optical limiting properties for various concentrations of acid blue 40 dye were investigated by Z-scan technique under CW He-Ne laser at 633nm wavelength. For lower concentration, the samples display both saturable
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absorption (SA) and reverse saturable absorption (RSA); whereas with increase in concentration, RSA behaviour prevails.
The dyes exhibits multiple self-diffraction rings pattern when exposed to laser due to refractive index change and thermal lensing.
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Acid blue dyes exhibits good optical power limiting of cw laser beam at 633nm.
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*Manuscript Click here to view linked References
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Thermally induced nonlinear optical response and optical power limiting of acid blue 40 dye Pramodini S.a , Poornesh P.a,∗, K. K. Nagarajab,1 a
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Nonlinear Optics Research Laboratory, Department of Physics, Manipal Institute of Technology, Manipal University, Manipal, Karnataka, India-576 104. b Materials Research Laboratory, Department of Physics, National Institute of Technology Karnataka, Surathkal, D. K., Karnataka, India-575 025.
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Abstract
We report the investigations of thermally induced third-order nonlinear optical and optical limiting characterizations for various concentrations of acid blue 40 dye in N,N-Dimethyl Formamide, studied by employing Z-scan technique under cw He-Ne laser irradiation at 633 nm wavelength. The samples
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exhibited nonlinear absorption and nonlinear refraction under the experimental conditions. For lower concentration, the samples display both saturable absorption (SA) and reverse saturable absorption (RSA); whereas with increase in concentration, RSA behaviour prevails. The estimated values of
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the effective coefficients of nonlinear absorption βef f , nonlinear refraction n2 and third-order nonlinear susceptibility χ(3) were found to be of the order of
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10−2 cm/W, 10−4 esu and 10−6 esu respectively. Multiple diffraction rings were observed when the samples were exposed to laser beam due to refractive index change and thermal lensing. The effect of concentration and the laser
∗ Email address:
[email protected] (Poornesh P.) 1 Present address: Micro and Nanosystems Laboratory, Department of Instrumentation and Applied Physics, Indian Institute of Science, Benagaluru-560 012. ∗
Preprint submitted to Current Applied Physics
January 23, 2013
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intensity on the self-diffraction ring patterns were studied experimentally.
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The acid blue 40 dye also exhibited strong optical limiting properties under cw excitation and reverse saturable absorption is found to be the dominant nonlinear optical process leading to the observed nonlinear behaviour.
Keywords: Acid blue 40 dye, cw laser, Z-scan, NLO, optical limiting,
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diffraction rings.
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1. Introduction
Nonlinear optical materials are being greatly explored with great interest owing to their potential applications in all-optical switching, 3-D optical memory devices, optical modulation, telecommunications, human eyes and optical sensors protection, etc., and significant applications in biological and medical sciences [1–6]. Wide variety of materials are known to be optically
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nonlinear under cw laser illumination [7–16]. Optical materials with large nonlinearity, broad band spectral response and fast response time are the potential requirements for a good optical limiter. Optical limiting results from irradiance intensity dependent nonlinear optical properties of materi-
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als. Incident intense light alters the refractive and absorptive properties of the sample and hence it is important to determine the magnitude of the
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nonlinearity of a material so as to select a material as a possible optical limiter.
Among the various organic compounds, dyes are commercially available
and they are inexpensive. Azo, Anthraquinone and Indigo are the major chromophores found in commercial dyes. Acid blue 40 belongs to the anthraquinone class and represents second most important class of commercial 2
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dyes after azo dyes. Anthraquinone dyes have been under extensive research,
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since they have interesting optical properties and also for excellent properties that are not attainable by azo dyes including brilliancy of colours,
fastness and excellent dyeing properties such as leveling and dye bath stability [17, 18]. Linear absorption, SA, RSA are the basic absorption processes
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in dyes. Materials with SA behaviour are widely used in mode locking, laser
pulse compression, optical bi-stability, laser amplification. Whereas materi-
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als with RSA are used in optical limiting devices, two-photon fluorescence microscopy and imaging, 3D optical storage, up-conversion lasing, micro fabrication, etc. [19]. The study on third-order nonlinearity of acid blue 40 has not been reported. Further the transition behaviour of SA/RSA/SA is not addressed under cw laser at 633 nm wavelength till date. It is necessary to study the optical nonlinearity of present dye sample for its wide spread
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applications as mentioned above.
In this article, we report the results of thermally induced third-order nonlinear optical properties of acid blue 40 in solution investigated using zscan technique under cw He-Ne laser. Further, we present the strong optical
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power limiting of the samples under cw regime, based on reverse saturable absorption process. Also, the effect of thermally induced negative lens is
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demonstrated through diffraction ring patterns. 2. Experimental
2.1. Materials and methods Acid blue 40 dye (molecular weight 473.43 g mol−1 ) was purchased from Sigma Aldrich and used as received. The molecular formula of dye sample 3
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is C22 H16 N3 NaO6 S. For determining the absorptive and refractive nonlinear-
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ities, the dye sample solutions with 26.4, 30.2, 35.2, 42.2 and 52.8 micro
molar concentrations were prepared by dissolving them in research grade N,N-Dimethyl Formamide (DMF) separately and named as a, b, c, d and e. For optical limiting studies, we prepared additional samples along with
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above specified samples with 70.4 and 105.6 micro molar concentrations and named as f and g. The molecular structure of dye sample is shown in figure
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1. The optical characterization of the sample under investigation was studied by recording the electronic spectra in the wavelength range 300-800 nm using UV-1601PC Shimadzu spectrophotometer as shown in figure 2. 2.2. Z-scan experimental technique
The third-order nonlinear susceptibility χ(3) of acid blue 40 in DMF was
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evaluated by employing Z-scan technique developed by Sheik-Bahae et al. [20, 21]. Z-scan is a single-beam technique which offers simplicity as well as high sensitivity for measuring the nonlinear absorption (NLA) and nonlinear refraction (NLR) simultaneously. In the present experiment, a polarized
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Gaussian laser beam is focused to a narrow waist. The sample is mounted on the micro meter translation stage. By translating the sample between +z
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and -z positions along the z-direction, the transmitted intensity through the sample were measured. The measurements were recorded with and without the presence of aperture at far field in front of the photo detector. As the sample moves through the beam focus (z=0), self-focusing or self-defocussing modifies the wave front phase, there by modifying the detected beam intensity. Z-scan experiments were performed by using Thor labs HRP350-EC-1 CW He-Ne laser at 633 nm wavelength as an excitation source. The laser 4
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beam was focused to a spot size of 36.78 µm and the Rayleigh length ZR
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of 6.71 mm using a 5 cm focal length lens with input power 20.2 mW. The
samples were placed in a cuvette of 1 mm thickness. Hence, the thin sample approximation is valid as the sample thickness is less than the Rayleigh length ZR for all samples [20, 21].
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Optical power limiting measurements were carried out to investigate the
power limiting behaviour of the dye. The schematic experimental setup is
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shown in figure 3. The sample solutions were placed at the focal plane of the lens. The input power of the laser beam was varied by using neutral density filter and the resultant output power through the samples was recorded using a photo-detector fed to Thor labs PM320E dual channel optical power and energy meter.
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3. Results and discussions
3.1. Nonlinear absorption and refraction To examine nonlinear absorption and nonlinear refraction behaviours of
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the dye, open aperture and closed aperture z-scan experiments were carried out at an input intensity of 9.51 × 106 W/m2 . The open aperture z-scan traces obtained for dye samples are shown in figure 4. When the sample
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is away from the focus, the light intensity is low. For lower concentration (26.4 µM), at far field (figure 4 (a)) the transmittance increases with the increase in focal intensity and depicts SA type of behaviour. However, when the sample approaches focus (z=0), there is a shift in the behaviour and the transmittance decreases with increase in intensity indicating RSA. But again sudden switch over to SA from RSA is observed when the sample 5
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is at the focus. Therefore we can say that with increase in focal intensity,
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nonlinear absorption switches from SA/RSA/SA. In other words, for increase
in focal intensity, RSA response becomes weaker where upon SA occurs. For next higher concentration (30.2 µM) at the far field, the transmittance through the sample increases resulting in SA type of behaviour. However,
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as the sample approaches focus (z=0), the transmittance suddenly decreases
forming a well defined dip at the focus, indicating the occurrence of RSA
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behaviour as shown in figure 4 (b). Above results depicts the switch over of SA and RSA behaviour in the dye sample and this switch over behaviour of nonlinear absorption is in good agreement with reported results [19, 22–25]. For all other higher concentrations, at far field we did not observe SA behaviour that is, there was a disappearance of initial enhancement in the transmittance. Further as the sample is translated towards focus, the transmit-
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tance decreases forming a dip at the focus (z=0), indicating RSA behaviour. With the increase in the concentration of the samples and with increase in intensity (at focus, z=0) the variation in the dip (valley) transmission increases. For the sample concentration (52.8 µM), the nonlinear absorption
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dip transmission increases further at the focus (z=0) and the beam becomes little broader. In other words, the laser beam broadens comparatively with
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respect to the lower concentrations and its profile lowers in intensity and there is a significant increase in its full width at half maxima (FWHM) [9]. This effect is due to intensity dependent variation of the nonlinear refractive index, which makes the medium to behave like a concave lens [9]. This beam broadening phenomenon observed with increase in concentration is in good agreement with the reported results [9, 26].
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Reverse saturable absorption (RSA) results due to any of the nonlinear
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mechanisms such as two-photon absorption (TPA), excited free carrier absorption (ESA), free carrier absorption (FCA), nonlinear scattering or with
the combination of these processes [11, 12]. The origin of RSA is based on the two conditions, (i) the molecules present in ground state and excited states
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can absorb the incident photons of same wavelengths and (ii) the absorption
of excited states must be larger than that of the ground states. There are lit-
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eratures which reports the SA and RSA behaviour of the nonlinear medium investigated under cw regime [1, 3, 9, 14, 16, 22, 27, 28]. In the present case, the decrease in transmission with increase in the input intensity indicates that the sample exhibits RSA. This is because the radiative life time of the lowest triplet states are quite long, as a result, accumulation of population takes place in triplet states [12]. Under such conditions, non-radiative pro-
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cesses takes place and the molecules are further excited to the excited triplet state and this leads to RSA process. George et al., Riggs et al., and Harilal et al., reported that RSA is the major nonlinear absorption mechanism to occur in organic dyes [29–31]. With picosecond and nanosecond timescale,
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the RSA originates from the population of singlet states and for longer pulses the population of triplet state begins to dominate [32]. Henari reported that
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under cw excitation, the thermal effect will increase the excited state absorption (ESA) [32]. Thus we can say that RSA is the dominant mechanism leading to the observed nonlinearity in acid blue 40 dye samples. If the nonlinearity is due to TPA alone, the nonlinear absorption coefficient βef f should be a constant independent of on-axis input intensity I0 [6]. But from figure 5, the nonlinear absorption coefficient βef f value decreases with increase in
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on-axis input intensity I0 which is the consequence of sequential two-photon
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absorption, that is, it is due to the result of TPA and ESA assisted RSA process [6, 14, 33, 34]. Hence, in the present case the observed nonlinear absorption is attributed to TPA and ESA assisted RSA process and this is in good agreement with the reported results [6, 14, 33, 34].
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The closed aperture z-scan experiments were performed to determine the
sign and magnitude of the nonlinear refractive index n2 of the dye. The
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experiment is carried out by placing the aperture in front of the detector. The sensitivity to nonlinear refraction is entirely due to aperture, and absence of aperture completely eliminates the effect [20, 21]. Figure 6 illustrates the closed aperture z-scan profiles of the samples. The normalized closed aperture z-scan curve exhibits a pre-focal transmittance maximum (peak) followed by a post-focal transmittance minimum (valley) signature for the samples. This
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peak-valley signature indicates the self-defocussing and it is represented by negative nonlinear refractive index n2 . The sign of the nonlinear index of refraction n2 of a sample is thus immediately clear from the shape of graph. Since closed aperture data obtained from z-scan will contain both nonlinear
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refraction and nonlinear absorption components, it is necessary to separate the nonlinear absorption components from the nonlinear refraction so as to
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extract pure nonlinear refraction. The physical origin of nonlinear refraction can be electronic, molecular, electrostrictive or thermal in nature [11]. Under cw irradiation, the nonlinearity is due to thermal in nature and not because of other effects. This is confirmed from the following reasons; (i) the value of nonlinear refractive index n2 > 10−5 esu, (ii) for cw laser, the relaxation
time is in the order of milli seconds, (iii) The closed aperture z-scan curves
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for all concentrations of the samples show a peak-valley separation of 1.9
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ZR . A peak-valley separation of more than 1.7 times the Rayleigh range (ZR ) is the clear indication of thermal nonlinearity and indicates the observed
nonlinear effect is the third-order process [3, 4]. The difference in peak-valley normalized transmittance ∆TP −V can be defined as the difference between
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the normalized peak and valley transmittances TP − Tv . The variation of ∆TP −V quantity as a function of |∆φ0 | is given by [20, 21],
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∆TP −V = 0.406(1 − S)0.25 |∆Φ0 |
(1)
where |∆φ0 | is the on-axis phase shift, S is the aperture linear transmittance, which is equal to 0.7 in our experiments. The real and imaginary parts of the third-order nonlinear optical susceptibility χ(3) is determined by using the nonlinear refractive index n2 and nonlinear absorption coefficient βef f by
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the following equations [11], (3)
ε0 c2 n20 n2 (cm2 /W ) π
(2)
ε0 c2 n20 λ βef f (cm/W ) 4π 2
(3)
χR (esu) = 10−4
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and
(3)
χI (esu) = 10−2
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where ε0 is the vacuum permittivity and c is the light velocity in vacuum. We conducted a z-scan experiment on the N,N-Dimethyl Formamide (DMF) and found a negligible contribution to the observed nonlinearity. Therefore any contribution from the solvent to the observed nonlinearity is negligible at the laser input intensity used. The obtained values of nonlinear refractive index n2 , nonlinear absorption coefficient βef f and the real and imaginary parts of the third-order nonlinear susceptibility of dye samples are given in 9
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table 1. In table 1, for 26.4 ? concentration, β is negative. Because, at the
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focus, (z=0), there is a peak owing to SA type of behaviour (figure 4(a)). For SA type of behaviour β is negative [3, 9, 35]. The occurrence of -β (SA)
at the higher focal intensity (z=0), may be due to the large linear absorption
coefficient and cw laser irradiation which leads to SA rather than RSA [22].
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Whereas, for the increase in the concentration, may be the absorption of
excited states is larger than the ground states resulting in RSA (+β), due to
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more number of molecules participating in the interaction
Concentration dependence of the nonlinear absorption coefficient βef f was also studied. Figure 7 shows the nonlinear absorption coefficient βef f as a function of sample concentrations for dye sample in solution. The βef f increases with the concentration. This may be attributed to the fact that the number of molecules participating increases with increase in concentration
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and more number of particles are thermally agitated resulting in increase in third-order optical nonlinearity. To study the optical nonlinearity, we have selected the optimum concentration range of samples. For further lower concentrations, it was very difficult to record the z-scan signal as the variation
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was feeble. And for further higher concentrations, the sample was deep in colour and it was almost completely absorbing the incident light. That is,
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saturation of nonlinearity was observed. From the figure 4 and figure 6 it is clear that the acid blue 40 dye pos-
sess high nonlinear absorption and nonlinear refraction. The high nonlinear optical response is due to the presence of lone pairs of electrons and the influence of resonating structure. The linear absorption of acid blue 40 dye occur around 636 nm, which is very close to the wavelength of the light used
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for excitation. The linear absorption coefficient α calculated from figure 2,
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was in the range 0.43 to 6.8 cm−1 for various concentrations. Therefore, with 633 nm cw laser irradiation, which is near the resonance absorption peak,
light energy is absorbed significantly by the sample. This leads to the increase in local temperature by optimizing the absorbed energy in to heat in
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the sample. Also, it is clear from the same figures that the nonlinearity in-
creases with increase in concentration. This enhancement may be attributed
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to the fact that with increase in concentration, number of particles participating increases. When the medium is irradiated by laser, a small portion of its energy is absorbed by the particles. Hence at higher concentration, more number of particles is thermally agitated due to the local heating of the absorbed medium and results in temperature variation of the sample medium [11]. The nonlinearity is temperature dependent and results in in-
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crease in third-order optical nonlinearity which is here attributed to thermal nonlinearity and our results are in good agreement with the reported values [4, 11].The recently reported values for n2 and βef f of nonlinear materials under cw laser irradiation are listed in table 2. The nonlinear optical param-
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eters of present dye samples are higher than the reported results under cw
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regime [1, 4, 8–10, 12–16, 27, 36–41]. 3.2. Optical power limiting The development of modern optical technology demands the ability to
control the intensity of light and in this aspect optical power limiters have received significant attention. An ideal optical limiter exhibits a linear transmission below a threshold and clamps the output to a constant above it, thus providing safety to sensors and eyes. The optical limiting behaviour of acid 11
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blue dye was studied without aperture under cw laser illumination. To char-
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acterize the optical limiting behaviour of dye solutions, sample is located at the focal plane of the lens and the transmitted power is measured for different
input powers. Figure 8 shows the characteristic optical limiting curves as a function of incident power varying from 0.2 mW to 20 mW for various dye
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concentrations. For lower concentrations (curves a, b, c and d) we did not ob-
serve any clamping, as low concentration samples are much weaker than that
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of high concentration [42]. With the increase in concentration, we observed optical limiting property and clamping of output with respect to input power for the curves (e), (f) and (g). The deviation from linearity for (e), (f) and (g) began at 8 mW, 2.5 mW and 1.5 mW and the output clamping occurs at 4 mW, 0.9 mW and 0.2 mW respectively. The deviation from linearity is observed for all the samples and it is tabulated in table 3. From figure 8
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we can infer that, for the lower concentrations, there is a decrease (limiting threshold) in the output data with respect to the farfield for different input. That is, a slight deviation in the output takes place. This is because, for the lower concentrations, the number of particles participating in the interaction
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is relatively less. Whereas, for higher concentrations, both optical limiting and clamping are taking place. Since, with the increase in concentration,
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the number of particles participating in the interaction increases and more number of particles are thermally agitated to excited states. Hence at higher concentrations, better limiting and clamping is taking place. Thus it confirms from the observed data (table 3), that limiting threshold and clamping values are inversely proportional to the concentration of the sample. And also, with the increase in concentration, reduction in linear transmission below a
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threshold and optical clamping is observed. The results confirm that, the con-
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centration effect is remarkable and it is in good agreement with the observed
results reported in literatures [2, 3, 6, 9, 11, 13, 16, 28, 42]. Optical limit-
ing can be achieved by means of various nonlinear optical mechanisms, including self-focusing, self-defocussing, induced scattering, induced-refraction,
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induced aberration, excited state absorption (ESA), two-photon absorption
(TPA), photo-refraction and free-carrier absorption (FCA) in nonlinear opti-
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cal media [11]. As ours is energy absorbing type of optical limiter, the major nonlinear mechanism employed is ESA assisted RSA process. 3.3. Self-Diffraction pattern
When the Gaussian laser beam passes through a nonlinear medium, it tends to form concentric intensity distribution ring patterns in the far field.
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A nonlinear medium whose refractive index change is proportional to the light intensity (∆n= n2 I, where n2 is the nonlinear refractive index coefficient) then it can change an incident beam with a well-defined distribution. The refractive index change alters the transverse phase of the beam [22].
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This phenomenon is known as spatial self-phase modulation. Callen et al. [43] reported for the first time the annular concentric far field intensity dis-
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tribution in CS2 under He-Ne laser beam illumination. Later, Durbin et al. [44] observed similar effect in liquid crystals. Thereafter, the far field annular self-diffraction ring patterns were observed in many nonlinear media [1, 3, 4, 13, 16, 22, 27, 28, 37, 42]. With the incidence of high input power, one can study on the spatial self-phase modulation throughout the visible diffraction pattern of emergent laser light [22]. The self-diffraction ring pattern obtained for the samples are shown in figure 9. The diffraction 13
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pattern was recorded for a, b, c, d, e, f, g and an additional concentration
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of 211.2 µM named as h by using a digital camera. CW He-Ne laser at 633 nm wavelength with input power 20.2 mW was illuminated on the dye
samples by focusing through 5 cm lens. As, it is seen clearly, the fringe number increases with increase in dye concentration, which indicates that when
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laser passes, the sample acts like a negative lens [43]. This is because with
increase in concentration, more number of molecules per unit volume will
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participate in the interaction and this is due to nonlinear phase shift due to the intensity dependence of the refractive index and thermal lensing. A plot of concentration of the samples versus the variation in the number of diffraction rings is shown in figure 10. It is clear from the figure that there exists a linear relation between them at lower concentrations. Our results are in good agreement with the observed results [1, 4, 16, 22, 27, 28, 42].
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It is known that for the transmission of the laser beam through the sample, the induced variation in the refractive index is proportional to the number of fringes [4]. Further, with the increase in concentration the number of fringe pattern tends to saturate. With change in the position of the sample, the
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intensity of the transmitted laser beam spot distribution changes. Figure 11 shows the photographs of laser spot size variation as a function of sample
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position relative to lens focal point. By placing the sample at different positions that is, (a) far from focus, (b) pre-focus transmittance maximum, (c) post-focus transmittance minimum and (d) away from focus, the spot size variation was recorded. The spot of the transmitted laser beam has minimum size when the sample is at the focus and this is in good agreement with the reported literatures [1, 4, 14, 16, 28, 37, 40]. We observed self-focusing and
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self-defocussing ring patterns with naked eye, which confirms the nonlinear
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behaviour of the material before conducting the experiment. The contribu-
tion of cuvette used for the studies did not induce any change in the far field intensity and hence, its contribution is not considered in the analysis.
The dye samples were examined using optical microscopy before and after
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the laser irradiation to check any damage in the samples and we found no damage of the samples at the input intensity used.
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4. Conclusions
We have studied and presented the third-order nonlinear optical properties of acid blue 40 in DMF at various concentrations using Z-scan technique under continuous wave He-Ne laser at 633 nm wavelength. The samples were characterized with negative nonlinear refraction (self-defocussing). At
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lower concentration SA/RSA/SA behaviour was observed and with increase in concentration, RSA dominates. We observed the increase in induced selfdiffraction ring patterns with increase in concentration attributed to refrac-
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tive index change. The observed enhanced results are attributed to thermally induced nonlinearity. Also, Acid blue 40 dye exhibits strong optical power limiting based on RSA process under continuous wave laser at the experi-
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mental wavelength. Acknowledgement
This work is Catalyzed and Supported by Vision Group on Science and
Technology, Department of Science and Technology, Govt. of Karnataka.
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Figure 1.Molecular Structure of Acid blue 40.
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Figure captions
Figure 2.Absorbance spectra of Acid blue 40 in DMF.
Figure 3.The schematic optical limiting experimental setup.
Figure 4.Open aperture z-scan traces (a) 26.4, (b) 30.2, (c) 35.2, (d) 42.2
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and (e) 52.8 µM concentrations of acid blue 40 dye samples in DMF.
Figure 5.Nonlinear absorption coefficient βef f vs. on-axis input intensity
blue 40 dye samples in DMF.
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I0 (a) 26.4, (b) 30.2, (c) 35.2, (d) 42.2 and (e) 52.8 µM concentrations of acid
Figure 6.Pure nonlinear refraction z-scan traces (a) 26.4, (b) 30.2, (c) 35.2, (d) 42.2 and (e) 52.8 µM concentrations of acid blue 40 dye samples in DMF.
Figure 7.Concentration dependence of nonlinear absorption coefficient
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βef f of acid blue 40 in DMF.
Figure 8.Optical power limiting response (a) 26.4, (b) 30.2, (c) 35.2, (d) 42.2 and (e) 52.8, (f) 70.4, (g) 105.6 µM concentrations of acid blue 40 dye samples in DMF.
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Figure 9.Self-diffracted ring patterns (a) 26.4, (b) 30.2, (c) 35.2, (d) 42.2 and (e) 52.8, (f) 70.4, (g) 105.6 and (h) 211.2 µM concentrations of acid blue
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40 dye samples in DMF.
Figure 10.A plot of number of diffraction fringes vs. sample concentra-
tions of acid blue 40 dye samples in DMF. Figure 11.Photographs show the laser spot size variation as a function of
sample position relative to lens focal point of acid blue 40 (a) far from focus, (b) pre-focus transmittance maximum,(c) post-focus transmittance minimum
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and (d) away from focus.
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Table captions
DMF.
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Table1.Third-order nonlinear optical parameters of acid blue 40 dye in
Table2.Table depicting the recently reported βef f and n2 values of different materials with cw laser excitation.
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Table3.Optical power limiting parameters of acid blue 40 dye samples in
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DMF.
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Table 1: Third-order nonlinear optical parameters of acid blue 40 dye in DMF (3)
(3)
χ(3)
(esu)
(esu)
(esu)
×10−4
×10−6
×10−7
×10−6
−0.68
−0.23
−0.24
−0.30
0.25
0.31
−0.94
−0.32
−0.34
0.57
0.34
35.2(c)
0.55
−1.44
−0.49
−0.52
0.99
0.53
42.2(d)
1.59
−2.31
−0.78
−0.83
2.87
0.87
52.8(e)
3.14
−3.57
−1.20
−1.27
5.67
1.40
n2
n2
χR
Concn.
(cm/W)
(cm2 /W)
(esu)
(µM)
×10−2
×10−7
26.4(a)
−0.17
30.2(b)
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βef f
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Table 2: Table depicting the recently reported βef f and n2 values of different materials with cw laser excitation.
Sl.
Materials
βef f
(cm/W)
Reference
(cm2 /W)
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No.
n2
Fast green FCF dye
6.5 × 10−5
3.2 × 10−8
[1]
2
Congo red solution
−−
−1.17 × 10−10
[4]
3
Zinc tetraphenyl porphyrin
−−
−1.4 × 10−7
[8]
4
Basic violet 16 dye
−1.38 × 10−3
−2.81 × 10−8
[9]
5
Semiconductor ZnS nanoparticles
−3.2 × 10−3
−1.38 × 10−8
[10]
6
Polymer Nanocomposite films
45.5 × 10−2
−2.75 × 10−7
[12]
7
Solid films of amido black dye
−−
−1.57 × 10−7
[13]
8
ClAl-phthalocyanine
1.3 × 10−3
−18 × 10−8
[14]
9
2APS single crystal
−−
−2.42 × 10−8
[15]
11
Ag nanoparticles
−−
−1.941 × 10−7
[22]
10
Triphenylmethane dye
−3.08 × 10−3
−1.88 × 10−7
[35]
12
Azo dyes
−0.23 × 10−4
−0.54 × 10−8
[36]
PDPAlq3 solution
1.12 × 10−4
−1.76 × 10−8
[37]
Au and Ag colloids
−−
−2.23 × 10−8
[38]
−−
−1.6 × 10−8
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15
Organic dye nile blue
1.35 × 10−5
0.42 × 10−8
[39]
16
Tris(acetylacetonato)Manganese(III)
1.2 × 10−2
−1.17 × 10−7
[40]
17
Sudan I dye
−−
−2.8 × 10−8
[41]
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Table 3: Optical power limiting parameters of acid blue 40 dye samples in DMF.
Optical
Optical
concentration
limiting threshold
clamping
(µM)
(mW)
(mW)
∼ 12.5
−−
∼ 12.5
−−
35.2(c)
∼ 12.5
−−
42.2(d)
∼ 12
−−
52.8(e)
∼8
∼4
70.4(f )
∼ 2.5
∼ 0.9
∼ 1.5
∼ 0.2
26.4(a)
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30.2(b)
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105.6(g)
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