Ex) Article Title, Author, Keywords
Current Optics
and Photonics
Ex) Article Title, Author, Keywords
Curr. Opt. Photon. 2023; 7(6): 721-731
Published online December 25, 2023 https://doi.org/10.3807/COPP.2023.7.6.721
Copyright © Optical Society of Korea.
Fadhil Abass Tuma1, Hussain Ali Badran1 , Harith Abdulrazzaq Hasan1,2, Riyadh Chassib Abul-Hail1
Corresponding author: *hussain_badran@yahoo.com, ORCID 0000-0002-2865-7907
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
This paper studies various roughness parameters, besides waviness, texture, and nonlinear parameters of Bismarck brown Y (BBY)-doped Poly(methyl methacrylate) (PMMA) films based on the computed values of optical limiting (OL) threshold power and nonlinear refractive index. The films’ morphology, grain size, and absorption spectra were investigated using atomic force microscopy in conjunction with ultraviolet-visible (UV-Vis) spectrophotometer. The particle size of the films ranged between 4.11–4.51 mm and polymer films showed good homogeneity and medium roughness, ranging from 1.11–4.58 mm. A polymer film’s third-order nonlinear optical features were carried out using the Z-scan methodology. The measurements were obtained by a continuous wave produced from a solid-state laser with a 532 nm wavelength. According to the results, BBY has a nonlinear refractive index of 10−6 cm2/W that is significantly negative and nonlinear. The optical limiting thresholds are roughly 10.29, 13.52, and 18.71 mW, respectively. The shift of nonlinear optical features with the film’s concentration was found throughout the experiment Additionally, we found that the polymer samples have outstanding capabilities for restricting the amount of optical power that may be transmitted through them. We propose that these films have the potential to be used in a wide variety of optoelectronic applications, including optical photodetectors and optical switching.
Keywords: Azo dye, Grain size, Nonlinear materials, Optical limiting, Roughness
OCIS codes: (140.0140) Lasers and laser optics; (190.0190) Nonlinear optics; (310.0310)Thin films
In recent years, there has been an increasing need for nonlinear optical materials that are compatible with low-intensity lasers and can be employed in a number of applications. Some examples of these applications include all-optical switching [1–3], optical bistability, phase conjugation, data and image processing [4–7], eye and sensor protection [8–11], nonlinear optical fiber and limiter devices [12–15] and optical switching [16–27]. Organic dyes have a variety of advantages over traditional nonlinear optical materials, which differentiate them from such materials [28, 29]. Organic compounds fall within the category of dyes. They show substantial optical nonlinearities, short response times, and strong absorption in the visible spectrum range, making them particularly attractive materials for the investigation of the impacts of optical nonlinearity. In addition, dye-doped polymer solid films made with these materials are characterized by their flexibility as well as their thermal and chemical durability. Because of these extremely significant benefits, the dyes are good candidates for nonlinear optical research. The capacity of these dyes to capture optical information [30–34] sets azo dyes apart from the others currently on the market and has proven their high efficiency in a variety of photonic devices and applications.
Bismarck brown Y (BBY) dye belongs to a family of chemicals known as azo dyes. Not only can BBY be used for staining mucin, the cartilage in histological sections, and the Papanicolaou technique for vaginal smears [35, 36], but it has also draw attention among several new organic materials due to usage in photonic devices such as optical limiters [37]. BBY belongs to an organic material, and has received special attention among several new organic materials. Because of its superior quality and excellent performance, BBY dye is used in a wide variety of dyeing processes in various industrial applications such as colored paper, pulp, wool, leather, and other materials [38, 39].
This study aims to identify a substance with high characteristics in nonlinear optics and the potential to be used in optical devices. Thus BBY was selected as a sample, while Poly(methyl methacrylate) (PMMA) served as the host.
In earlier research, BBY, an industrial essential with unique qualities, was selected due to the interest in azo dye’s high nonlinear optical qualities as follows: Hardness and chemical resistance to many kinds of solvents and dilute acids, high adhesion, and outstanding electrical insulation capabilities. PMMA is a very flexible material that has been used in many ways. It is used to replace shatterproof glass, especially in plastic optical fiber, and has become the most common plastic used in dentistry.
The use of PMMA goes all the way back to when the material was first found. Since then, PMMA has been used as a reference material to compare other intraocular lens and hard contact lens materials. Extensive work has also been done to find more ways to use PMMA in building and construction.
In addition to knowing how polymers work chemically, it would be very helpful to know how they behave physically. Many studies have been done on the physical properties of the material, such as in electrical devices [40], dosimetry [41], dental bases [42], optical switching, electrical and thermal conductivity, and thermal lenses [43]. Several methods have been developed to keep track of the physical changes that happen to a PMMA polymer after it is exposed to something like radiation. In turn, these changed how the PMMA material works.
In this study, BBY azo dye was introduced into PMMA, which served as a host for the dye. The Z-scan approach was used to study the optical nonlinearity that was created in an azo dye film by a continuous-wave (CW) diode-pumped laser (DPL) (SDL-532-100T; Shanghai Dream Lasers Co., Shanghai, China) with an output power of 18 mW at 532 nm. This study was based on the sample-driven variations in the beam profile that were seen in the far field. During the experiment, the azo dye BBY was present in a variety of quantities. Also, the power-limiting behavior was investigated for its potential implication through the Z-scan approach, and the film sample’s surface morphology was looked at.
In the current experiment, PMMA was a host for the dye because of it’s superior optical transparency in the visible spectral range, optical stability, and resistance to laser damage. The linear absorption spectrum of PMMA is shown in Fig. 1.
The chemical structure of the azo dye BBY (Central Drug House, New Delhi, India) can be seen in Fig. 2. The PMMA films are manufactured in the following way: First, the azo dye and the PMMA are dissolved in chloroform (Merck KGaA, Mumbai, India), and then the solutions of the azo dye and the PMMA are completely mixed. Finally, chloroform solvent is evaporated to remove any remaining traces of the azo dyed in PMMA film. After combining the ingredients and stirring them for half an hour, the mixture is spread out evenly on a clean glass slide and left to air-dry at room temperature for 24 hours. The quantity of BBY dye and PMMA in chloroform is 0.94 mM, and the other two amounts of BBY films are created using the same technique and have concentrations of 0.68 mM and 0.36 mM, respectively.
The polymer film samples were found to have a uniform thickness as well as a high degree of purity. After being measured using a digital micrometer head, the thickness of films (type M 98, IP 65, range 0–25 mm-MI-02031095; SanTool Werkeuge Gmbh., Heidenheim, Germany) were 8 mm. The range of the instrument was 0 to 25 mm. The absorption spectra of the polymer films were examined at normal incidence in the spectral range of (300–700) nm using a Cecil Reflecta-scan Reflectance Spectrophotometer (CE-3055; Cecil Instruments, Cambridge, UK).
Figure 2 depicts the absorption spectrum of a concentration of 0.68, 0.36, and 0.94 mM, respectively. In Fig. 2, the ultraviolet-visible (UV–vis) absorption spectra of the samples that varied in concentration are presented. Within the visible spectrum, it was possible to make out a number of bands. High delocalization of electrons in the azo chromophore group, which is responsible for the color of the dye, can be said to be the cause of the visible bands that can be seen in Fig. 2. As predicted, there is an inexorable correlation between the concentration of the dye solution and the linear absorbance. Visibility in some bands increased in proportion to the dye concentration, particularly in the regions around 468.5 and 536 nm, and the production of dimers was supposed to be the reason.
The capacity of a substance to retard the propagation speed of electromagnetic waves as they go through it is referred to as its optical density. Figure 2 presents an illustration of the observed absorbance spectra (A) of azo dye BBY-doped PMMA sheets. This diagram represents an absorbance curve that can be broken down into two distinct humps and a single large area. This area, which is known as the high absorption zone, can be described as extending from a wavelength of around 300 nm to approximately 700 nm. It represents the absorption of polymer films for electromagnetic waves is particularly high in this particular location. This occurs as a result of the impact of resonance caused by light photons and the polarization of electrons. Because of this, electron coupling occurs in the polymer films when exposed to an oscillating electric field [44].
Furthermore, electrons that are oscillating in semiconductor materials retain a little bit of the energy that they absorb from electromagnetic waves in the form of vibrational energy at shorter wavelengths. This absorbed energy is then released into the environment in the form of a new wave disturbance. Consequently, the optical density of the film samples grows as the obstruction to the propagation of electromagnetic waves inside the substance of the film increases [45, 46].
A helium-neon laser beam with a power of 5 mW was incident normally on the films to test their optical quality. Because the output laser beam exhibited no signs of distortion, this is further evidence that the films had a high level of optical quality. It is essential for optical devices to have a surface topography that can be characterized. In general, it has been discovered that the average roughness contributes to an increase in diffusion transmission. In linear and nonlinear optics, roughness characteristics have essential uses, such as the linear electro-optical effect, optical filters, and optical storage systems. The atomic force microscopy analysis of the surface morphology of BBY films with the application of image processing and the examination of the surface morphology of thin films can be described. It does this by simulating an optical method that is used to quantify the roughness of surfaces.
Figures 3(a)–3(f) show surface scans of thin films in two dimensions and corresponding images. A visual examination of either Fig. 3(a) or 3(b) present two typical morphological characteristics. The first is that the film has granular characteristics at a variety of scales, and these features are practically uniformly dispersed throughout several ranges. In addition, the surface profile should be imaged along with graphs of the intensity. In the sample, there was no discernible aggregation to be seen. The plots on the right (where there is the angle between the incident beam and the scattering plane, in degrees) vs. the intensity of the film are shown in Figs. 3(d)–3(f), respectively. The range of the azimuthal angle (chi), goes from 0 degrees to 360 degrees.
Since the samples do not need to be coated with any conductive materials during the imaging process, recent research on the structure of polymer films has been conducted using atomic force microscopy rather than scanning electron microscopy and transmission electron microscopy [47]. All atomic force microscope’s (AFM) supplies have combined to produce a surface that is completely scratch-free and free of additional particles, including dust and grime. The AFM can perform both touch and tapping modes. The tapping method was used throughout this research to analyze the surface morphology of specimens. Figure 3 shows in two dimensions the AFM surface images obtained from polymer films. The characterization of surface roughness is a very powerful tool for solving a wide variety of important issues [48], including fractions, contact deformation, tightness, and many others.
The BBY:PMMA film roughness parameters are reported in Table 1. As can be observed, a reduction in surface roughness followed a rise in the ratio of BBY, which led to the decline. An inverse association was observed between surface pore size and surface roughness. This means that the smoother the sample surface, the smaller the surface pore size, and vice versa [49].
TABLE 1 Roughness average, diameter, grain size and average height of the BBY:PMMA films
Polymer Film (mM) | Grain Size (nm) | Average Height (nm) | Average Diameter (nm) | Roughness Average (nm) |
---|---|---|---|---|
−0.36 | 4.11 | 7.52 | 2.21 | 1.11 |
−0.68 | 4.32 | 12.43 | 2.36 | 2.22 |
−0.94 | 4.51 | 19.25 | 2.38 | 4.58 |
By scanning the sample along the x-axis, we could examine the surface roughness of the films that had been created. Figure 4 shows the homogeneous surface roughness and waviness distribution along the two axes for each polymer film. As can be seen in Fig. 4, the surface waviness as well as the polymeric texture was individually investigated for each film. This became readily apparent when the height of the grain size of the films decreased in conjunction with an increase in the quantities of BBY to PMMA polymer. As a result, the surface of the films has a rather smooth texture.
A diagrammatic depiction of the Z-scan approach is shown in its overall arrangement in Fig. 5. It is possible to quantify the size of the phase shift by carefully observing the change in transmittance through a small aperture in the far field location (closed aperture, CA). This observation must be made in order to measure the phase shift. One way to determine the intensity-dependent absorption of a sample is to move the sample through the focus of the detector while maintaining what is referred to as an open aperture (OA). The signal ratio received from open and closed measurement methods can be used to calculate the nonlinear refraction of the sample when both open and closed measurement techniques are used to make the measurements.
The Z-scan method, well-known technique that provides the simultaneous measurement of both the nonlinear absorption coefficient (NBC) and the nonlinear refractive coefficient (NRC), was used to measure the nonlinear coefficients of the BBY:PMMA films.
Following the completion of these measurements, an analysis of the findings was carried out. By using an aperture scheme with a CA, we were able to get an estimate of the value of the NRC of the sample. On the other hand, we used an aperture scheme with an open aperture to obtain an estimate of the value of the NBC. A CA Z-scan of a polymer film (azo dye BBY:PMMA) with different concentrations is shown in Fig. 6. The data obtained from a CA Z-scan displayed a peak that was immediately followed by a valley-normalized transmittance implies that the sign of the refraction nonlinearity is negative or that the object in question is self-defocusing.
The defocusing effect is the result of thermal nonlinearity (Fig. 6), when light with a wavelength of 532 nm is absorbed. The sample goes through spatial dispersion in temperature, and as a consequence, there is a spatial change in the refractive index as a direct result of the localized absorption of a tightly focused beam as it passes through a polymer medium. The phase of the beam is distorted as a result of this spatial variation in the refractive index, which acts as a thermal lens and produces the distortion as it travels.
Z-scan is a technique used to measure the difference between the normalized peak transmittance and the valley transmittance. This difference can be found by comparing the peak transmittance to the valley transmittance. The peak-to-valley ratio, also known as ∆TPV, has a linear connection with the on-axis phase distortion, also known as ∆Θ″, of the radiation that has been transmitted through the sample. Both quantities are indicated by their respective acronyms. The connection can be described as follows [50–52]:
and
where SLT = 1 − exp(−2ra/ωa) is the linear transmittance of the aperture [53, 54], ra is the radius of the aperture, ωa is the beam radius at the aperture in the linear region, Io is the intensity (Io = 1.56 kW/cm2) of the laser beam at focus z = 0, L′eff = (1 − exp(−αcoDth))/αco [55] is the polymer film effective thickness, Dth is the thickness of the BBY film, αco is the linear absorption coefficient of the polymer film (αco = 2.303 A/Dth [56–58]), and k = 2π/λ is the wave number. Equations 1 and 2 and the change in the refractive index ∆n = n2 I0 can be used to figure out nonlinear refractive index (NRX). The NBC (β cm/W) can be calculated using the equation below [59, 60]:
where ∆T is the normalized transmittance for the OA.
The natural effect of nonlinear refraction in nonlinear optical material may be caused by various physical mechanisms, including electronic, molecular, and thermal processes. It is anticipated that the thermal effect will be responsible for the BBY films produced by the CW laser. The fact that the closed aperture Z-scan curves meet the electronic refractive nonlinearity criterion is one way this can be proved.
In addition, the physical process of nonlinear absorption might be owed to a shift in absorption with either an increase or decrease in intensity. This may be either saturable absorption (SA), which results in a reduction in the amount of light that is absorbed by the material, or reverse SA (RSA), increases in the amount of light that is absorbed by the material. RSA and SA both have the potential to be brought about through nonlinear scattering, free carrier absorption (FCA), and two-photon absorption (TPA). When the energy band gap Eg is more than 2Ephoton, the TPA mechanism becomes the predominant one. In this particular piece of research, the conclusions are credited to RSA as being the cause of the inception of BBY films. As a result, the TPA is of little consequence.
The usual Z-scan data for polymer films are shown in Fig. 7, acquired using an OA (S = 1). When the intensity is great, complete absorption enhances emission towards the center. The sample has reached its maximum capacity for absorption, which causes the top of the CA Z-scan to become larger while the valley becomes smaller (Fig. 8). This results in a modification to the form of the Z-scan curve that surrounds z = 0.
A CW DPL emitting light at a wavelength of 532 nm was used to conduct optical limiting (OL) experiments. The optical geometry used for OL measurement is shown in Fig. 9. A positive lens with a focal length of 5 cm was used to focus the light coming from the laser beam on the object being examined. BBY:PMMA was used as the polymer sample. Following that, the polymer was shifted in such a way that it was now located behind the focal length. Whole trials were conducted in settings that were as close to real life as possible and at temperatures that were equivalent to those in a normal living room (25 ℃). To detect the incident beam that was sent from the polymer sample, a photo detector (PD) that was attached to a power meter device was used. There was a round opening with a diameter of 2.5 mm in front of the PD. In order to accomplish OL, we were required to make adjustments to the input power while maintaining a close watch on the power being produced.
In order to investigate the effect that the concentration has on the OL characteristics, the experiment was carried out with concentrations of 0.36, 0.68, and 0.94 mM for BBY-doped PMMA film. Nonlinear emissions of BBY: PMMA films were tested to find out how the polymer film limits light. An immediate reaction can be seen as a result of the incident light in Fig. 10, which depicts the relationship between the amount of power that is produced and the amount of power that is input.
The polymer samples clearly exhibit an OL behavior, as shown in Fig. 10. The output samples grow with increasing incident power up to a limiting threshold and concentration, where the output power is restricted. After reaching this threshold and concentration, the output power no longer rises. The OL threshold is what affects the functionality of the limiter, and it is common knowledge that a limiter with a lower threshold value would function more effectively.
The transmission curves that have been normalized and shown as a function of the incident input power for various polymer film concentrations are shown in Fig. 11. The optical limiting thresholds are roughly 10.29, 13.52, and 18.71 mW, respectively. These thresholds are defined as the incident input power at which transmission drops by 50%.
The input power is in the range of (0–30) mW. When the incident laser beam power is greater than 18 mW, the transmission transforms into a nonlinear state, as clearly shown. Because its nonlinear absorption coefficient rises with an increase in the incoming irradiance, the output power tends to remain constant when the incident power is over 20 mW. This is because of how photovoltaic cells work. The high absorbance of the nonlinear material at the corresponding wavelength often causes a rise in the sample’s temperature. This occurs in polymer samples, which have substantial thermal expansion because of their low thermal conductivity. The absorption of laser light causes heating, which is the process responsible for the change in the coefficient of absorption and the OL effect [59]. It demonstrates that BBY is a promising candidate for OL using a CW laser operating at 532 nm.
The normalized transmittance curves of BBY-doped PMMA films are shown in Fig. 11. These curves are a function of the input power. This form is designed to determine the value of the BBY-doped PMMA film’s limiting threshold. These values represent the value of the input power at the instant in time when the transmittance dropped by a factor of half, and they are shown in Table 2.
TABLE 2 Z-scan parameters of polymer film
Concentration (mM) | α (cm−1) | ∆Θ″ | n2 × 10−6 (cm2/W) | β × 10−3 (cm/W) | ∆n × 10−3 |
---|---|---|---|---|---|
0.36 | 4767.21 | 0.85 | 22.14 | 154.82 | 34.72 |
0.68 | 5470.83 | 1.10 | 32.58 | 230.08 | 51.07 |
0.94 | 6424.50 | 1.46 | 50.81 | 350.05 | 79.65 |
As seen in Table 2, the value of the limiting threshold drops as the concentration of the polymer film rises, and the OL features become better as the concentration of the polymer film rises within the concentration range that was used for this inquiry. This may be seen when one examines the relationship between the value of the limiting threshold and the concentration. The following is an example that may explain this behavior: The sample with the greatest concentration has a higher number of molecules packed into each volume unit as compared to the sample with the lowest concentration.
Consequently, the sample with the greatest concentration will have more molecules interacting with one another throughout the process of nonlinear absorption. This is because more molecules will be present in the sample. When compared with the film that had a high concentration, the polymer film, which had a lower concentration, had an OL response that was less pronounced.
When the input power is increased throughout the measuring procedure, the transmitted beam is photographed at a greater distance from the sample than it was initially. Photographs of this kind are shown in Fig. 12 for a sample solution containing 0.94 mM concentration when the input powers are 1, 3, 4, 6, 12, 15, 16, 17, 18, 19, 24, and 30 mW, correspondingly. It is evident from images 12(a)–12(f) that the size of the spot grows with an increase in the input power, which indicates an increase in the output power. Figure 12 shows these photographs. This provides an explanation for the precipitous rises in output power shown in the limiting curve of Fig. 10 for input powers of 1, 3, 4, 6, 12, and 15 mW. It is possible to notice that there has been a little expansion of the spot size by looking at Figs. 12(g)–12(j). The limiting curve in Fig. 10 shows that there is a little rise in the output power for 16, 17, 18, and 19 mW of input power. Figures 12(k) and 12(l) in demonstrate how comparable the spot sizes are to one another. This indicates that the output power stabilized at a constant level for an input power of 24 and 30 mW, as shown by the limiting curve in Fig. 10.
In order to investigate how the location of the sample influenced the optical limiting, the sample was put in the exact center of the lens’s focus point. Diffraction rings were seen to appear throughout the process of the laser’s strength being steadily raised. Figure 13 depicts the limiting behaviors of the polymer films at concentrations of 0.36, 0.68, and 0.96 mM correspondingly. It is clear from looking at Figs. 10 and 13 that the optical limiting behavior of the sample varies greatly depending on the location of the sample in space. Because all the diffraction rings are contained inside the aperture, it is possible to observe, as in Fig. 13, that the output power via the aperture rises linearly with the input power when the input power is below the threshold value. Because the diameters of the outer rings are larger than the aperture size, the output power drops precipitously when the input power is greater than the threshold value. Then, as the power that is fed into the system increases, the power that is output approaches a specific value. This is due to both the number and the power of the inner rings that pass through the aperture remain almost constant.
The photos that were studied showed that the sample had a surface that was consistent and smooth, without any cracks or holes, and that material (azo dye and PMMA) spread on it in a regular pattern. To report the nonlinear optical characteristics of BSB:PMMA film, the Z-scan method was used under CW illumination at a wavelength of 532 nm. It was discovered that the value of the nonlinear refractive index (n2), is dependent on the sample absorption coefficient (αco). This is due to the sample with the biggest absorption coefficient also having the highest nonlinear refractive index. The produced samples showed signs of having a self-defocusing impact.
Based on these findings, it seems that there is potential for the BBY films to be used in optical device applications. The optical limiting features of sample films were investigated with the assistance of a CW laser whose wavelength was set at 532 nm. Research was done to investigate the impact of the concentration on the optical limiting characteristics. It was discovered that the limiting threshold of the samples used in this investigation decreased as the concentration increased; In other words, the features of the optical limiting became better as the concentration increased. In addition to this, it was discovered that the limiting threshold is lower at the wavelength that has a greater linear absorption coefficient, denoted by αco. Doping the dye with PMMA polymer leads to an improvement in its optical limiting qualities, which in turn allows the current research to accomplish its goal. This new dye has superior optical limiting properties compared to many other materials that are currently known.
Casting was the procedure that was used in this study for the preparation of a BBY:PMMA film. In order to acquire the characterization of the surface morphology of the film, AFM and ImageJ software (National Institutes of Health, MD, USA) were used to conduct an analysis of the image that was captured by the AFM microscope. The photos that were studied showed that the sample had a surface that was consistent and smooth, without any cracks or holes, and that material (azo dye and PMMA) spread on it in a regular pattern. The Z-scan method was used under CW illumination at a wavelength of 532 nm to report the nonlinear optical characteristics of BSB:PMMA film. It was discovered that the value of the nonlinear refractive index (n2) is dependent on the sample absorption coefficient (αco). This is due to the sample with the biggest absorption coefficient also has the highest nonlinear refractive index. The produced samples showed signs of having a self-defocusing impact.
Based on these findings, it seems that there is potential for the BBY films to be used in optical device applications. The optical limiting features of sample films were investigated with the assistance of a CW laser whose wavelength was set at 532 nm. Research was done to investigate the impact of the concentration on the optical limiting characteristics. It was discovered that the limiting threshold of the samples used in this investigation decreased as the concentration increased; in other words, the features of the optical limiting became better as the concentration increased. In addition to this, it was discovered that the limiting threshold is lower at the wavelength that has a greater linear absorption coefficient (αco). Doping the dye with PMMA polymer leads to an improvement in its optical limiting qualities, which in turn allows the current research to accomplish its goal. This new dye has superior optical limiting properties compared to many other materials that are currently known.
The authors would like to thank Prof. Falih Hussain Al- Khudair for his assistance, guidance, intellectual support and expertise in LabView programming.
This work was supported by the first author.
The authors declare no conflicts of interest.
The data underlying the results presented in this manuscript are not publicly available at the time of publication.
Curr. Opt. Photon. 2023; 7(6): 721-731
Published online December 25, 2023 https://doi.org/10.3807/COPP.2023.7.6.721
Copyright © Optical Society of Korea.
Fadhil Abass Tuma1, Hussain Ali Badran1 , Harith Abdulrazzaq Hasan1,2, Riyadh Chassib Abul-Hail1
1Department of Physics, Education College for Pure Sciences, University of Basrah, Basrah 61004, Iraq
2Department of Material Science, Polymer Research Center, University of Basrah, Basrah 61004, Iraq
Correspondence to:*hussain_badran@yahoo.com, ORCID 0000-0002-2865-7907
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
This paper studies various roughness parameters, besides waviness, texture, and nonlinear parameters of Bismarck brown Y (BBY)-doped Poly(methyl methacrylate) (PMMA) films based on the computed values of optical limiting (OL) threshold power and nonlinear refractive index. The films’ morphology, grain size, and absorption spectra were investigated using atomic force microscopy in conjunction with ultraviolet-visible (UV-Vis) spectrophotometer. The particle size of the films ranged between 4.11–4.51 mm and polymer films showed good homogeneity and medium roughness, ranging from 1.11–4.58 mm. A polymer film’s third-order nonlinear optical features were carried out using the Z-scan methodology. The measurements were obtained by a continuous wave produced from a solid-state laser with a 532 nm wavelength. According to the results, BBY has a nonlinear refractive index of 10−6 cm2/W that is significantly negative and nonlinear. The optical limiting thresholds are roughly 10.29, 13.52, and 18.71 mW, respectively. The shift of nonlinear optical features with the film’s concentration was found throughout the experiment Additionally, we found that the polymer samples have outstanding capabilities for restricting the amount of optical power that may be transmitted through them. We propose that these films have the potential to be used in a wide variety of optoelectronic applications, including optical photodetectors and optical switching.
Keywords: Azo dye, Grain size, Nonlinear materials, Optical limiting, Roughness
In recent years, there has been an increasing need for nonlinear optical materials that are compatible with low-intensity lasers and can be employed in a number of applications. Some examples of these applications include all-optical switching [1–3], optical bistability, phase conjugation, data and image processing [4–7], eye and sensor protection [8–11], nonlinear optical fiber and limiter devices [12–15] and optical switching [16–27]. Organic dyes have a variety of advantages over traditional nonlinear optical materials, which differentiate them from such materials [28, 29]. Organic compounds fall within the category of dyes. They show substantial optical nonlinearities, short response times, and strong absorption in the visible spectrum range, making them particularly attractive materials for the investigation of the impacts of optical nonlinearity. In addition, dye-doped polymer solid films made with these materials are characterized by their flexibility as well as their thermal and chemical durability. Because of these extremely significant benefits, the dyes are good candidates for nonlinear optical research. The capacity of these dyes to capture optical information [30–34] sets azo dyes apart from the others currently on the market and has proven their high efficiency in a variety of photonic devices and applications.
Bismarck brown Y (BBY) dye belongs to a family of chemicals known as azo dyes. Not only can BBY be used for staining mucin, the cartilage in histological sections, and the Papanicolaou technique for vaginal smears [35, 36], but it has also draw attention among several new organic materials due to usage in photonic devices such as optical limiters [37]. BBY belongs to an organic material, and has received special attention among several new organic materials. Because of its superior quality and excellent performance, BBY dye is used in a wide variety of dyeing processes in various industrial applications such as colored paper, pulp, wool, leather, and other materials [38, 39].
This study aims to identify a substance with high characteristics in nonlinear optics and the potential to be used in optical devices. Thus BBY was selected as a sample, while Poly(methyl methacrylate) (PMMA) served as the host.
In earlier research, BBY, an industrial essential with unique qualities, was selected due to the interest in azo dye’s high nonlinear optical qualities as follows: Hardness and chemical resistance to many kinds of solvents and dilute acids, high adhesion, and outstanding electrical insulation capabilities. PMMA is a very flexible material that has been used in many ways. It is used to replace shatterproof glass, especially in plastic optical fiber, and has become the most common plastic used in dentistry.
The use of PMMA goes all the way back to when the material was first found. Since then, PMMA has been used as a reference material to compare other intraocular lens and hard contact lens materials. Extensive work has also been done to find more ways to use PMMA in building and construction.
In addition to knowing how polymers work chemically, it would be very helpful to know how they behave physically. Many studies have been done on the physical properties of the material, such as in electrical devices [40], dosimetry [41], dental bases [42], optical switching, electrical and thermal conductivity, and thermal lenses [43]. Several methods have been developed to keep track of the physical changes that happen to a PMMA polymer after it is exposed to something like radiation. In turn, these changed how the PMMA material works.
In this study, BBY azo dye was introduced into PMMA, which served as a host for the dye. The Z-scan approach was used to study the optical nonlinearity that was created in an azo dye film by a continuous-wave (CW) diode-pumped laser (DPL) (SDL-532-100T; Shanghai Dream Lasers Co., Shanghai, China) with an output power of 18 mW at 532 nm. This study was based on the sample-driven variations in the beam profile that were seen in the far field. During the experiment, the azo dye BBY was present in a variety of quantities. Also, the power-limiting behavior was investigated for its potential implication through the Z-scan approach, and the film sample’s surface morphology was looked at.
In the current experiment, PMMA was a host for the dye because of it’s superior optical transparency in the visible spectral range, optical stability, and resistance to laser damage. The linear absorption spectrum of PMMA is shown in Fig. 1.
The chemical structure of the azo dye BBY (Central Drug House, New Delhi, India) can be seen in Fig. 2. The PMMA films are manufactured in the following way: First, the azo dye and the PMMA are dissolved in chloroform (Merck KGaA, Mumbai, India), and then the solutions of the azo dye and the PMMA are completely mixed. Finally, chloroform solvent is evaporated to remove any remaining traces of the azo dyed in PMMA film. After combining the ingredients and stirring them for half an hour, the mixture is spread out evenly on a clean glass slide and left to air-dry at room temperature for 24 hours. The quantity of BBY dye and PMMA in chloroform is 0.94 mM, and the other two amounts of BBY films are created using the same technique and have concentrations of 0.68 mM and 0.36 mM, respectively.
The polymer film samples were found to have a uniform thickness as well as a high degree of purity. After being measured using a digital micrometer head, the thickness of films (type M 98, IP 65, range 0–25 mm-MI-02031095; SanTool Werkeuge Gmbh., Heidenheim, Germany) were 8 mm. The range of the instrument was 0 to 25 mm. The absorption spectra of the polymer films were examined at normal incidence in the spectral range of (300–700) nm using a Cecil Reflecta-scan Reflectance Spectrophotometer (CE-3055; Cecil Instruments, Cambridge, UK).
Figure 2 depicts the absorption spectrum of a concentration of 0.68, 0.36, and 0.94 mM, respectively. In Fig. 2, the ultraviolet-visible (UV–vis) absorption spectra of the samples that varied in concentration are presented. Within the visible spectrum, it was possible to make out a number of bands. High delocalization of electrons in the azo chromophore group, which is responsible for the color of the dye, can be said to be the cause of the visible bands that can be seen in Fig. 2. As predicted, there is an inexorable correlation between the concentration of the dye solution and the linear absorbance. Visibility in some bands increased in proportion to the dye concentration, particularly in the regions around 468.5 and 536 nm, and the production of dimers was supposed to be the reason.
The capacity of a substance to retard the propagation speed of electromagnetic waves as they go through it is referred to as its optical density. Figure 2 presents an illustration of the observed absorbance spectra (A) of azo dye BBY-doped PMMA sheets. This diagram represents an absorbance curve that can be broken down into two distinct humps and a single large area. This area, which is known as the high absorption zone, can be described as extending from a wavelength of around 300 nm to approximately 700 nm. It represents the absorption of polymer films for electromagnetic waves is particularly high in this particular location. This occurs as a result of the impact of resonance caused by light photons and the polarization of electrons. Because of this, electron coupling occurs in the polymer films when exposed to an oscillating electric field [44].
Furthermore, electrons that are oscillating in semiconductor materials retain a little bit of the energy that they absorb from electromagnetic waves in the form of vibrational energy at shorter wavelengths. This absorbed energy is then released into the environment in the form of a new wave disturbance. Consequently, the optical density of the film samples grows as the obstruction to the propagation of electromagnetic waves inside the substance of the film increases [45, 46].
A helium-neon laser beam with a power of 5 mW was incident normally on the films to test their optical quality. Because the output laser beam exhibited no signs of distortion, this is further evidence that the films had a high level of optical quality. It is essential for optical devices to have a surface topography that can be characterized. In general, it has been discovered that the average roughness contributes to an increase in diffusion transmission. In linear and nonlinear optics, roughness characteristics have essential uses, such as the linear electro-optical effect, optical filters, and optical storage systems. The atomic force microscopy analysis of the surface morphology of BBY films with the application of image processing and the examination of the surface morphology of thin films can be described. It does this by simulating an optical method that is used to quantify the roughness of surfaces.
Figures 3(a)–3(f) show surface scans of thin films in two dimensions and corresponding images. A visual examination of either Fig. 3(a) or 3(b) present two typical morphological characteristics. The first is that the film has granular characteristics at a variety of scales, and these features are practically uniformly dispersed throughout several ranges. In addition, the surface profile should be imaged along with graphs of the intensity. In the sample, there was no discernible aggregation to be seen. The plots on the right (where there is the angle between the incident beam and the scattering plane, in degrees) vs. the intensity of the film are shown in Figs. 3(d)–3(f), respectively. The range of the azimuthal angle (chi), goes from 0 degrees to 360 degrees.
Since the samples do not need to be coated with any conductive materials during the imaging process, recent research on the structure of polymer films has been conducted using atomic force microscopy rather than scanning electron microscopy and transmission electron microscopy [47]. All atomic force microscope’s (AFM) supplies have combined to produce a surface that is completely scratch-free and free of additional particles, including dust and grime. The AFM can perform both touch and tapping modes. The tapping method was used throughout this research to analyze the surface morphology of specimens. Figure 3 shows in two dimensions the AFM surface images obtained from polymer films. The characterization of surface roughness is a very powerful tool for solving a wide variety of important issues [48], including fractions, contact deformation, tightness, and many others.
The BBY:PMMA film roughness parameters are reported in Table 1. As can be observed, a reduction in surface roughness followed a rise in the ratio of BBY, which led to the decline. An inverse association was observed between surface pore size and surface roughness. This means that the smoother the sample surface, the smaller the surface pore size, and vice versa [49].
TABLE 1. Roughness average, diameter, grain size and average height of the BBY:PMMA films.
Polymer Film (mM) | Grain Size (nm) | Average Height (nm) | Average Diameter (nm) | Roughness Average (nm) |
---|---|---|---|---|
−0.36 | 4.11 | 7.52 | 2.21 | 1.11 |
−0.68 | 4.32 | 12.43 | 2.36 | 2.22 |
−0.94 | 4.51 | 19.25 | 2.38 | 4.58 |
By scanning the sample along the x-axis, we could examine the surface roughness of the films that had been created. Figure 4 shows the homogeneous surface roughness and waviness distribution along the two axes for each polymer film. As can be seen in Fig. 4, the surface waviness as well as the polymeric texture was individually investigated for each film. This became readily apparent when the height of the grain size of the films decreased in conjunction with an increase in the quantities of BBY to PMMA polymer. As a result, the surface of the films has a rather smooth texture.
A diagrammatic depiction of the Z-scan approach is shown in its overall arrangement in Fig. 5. It is possible to quantify the size of the phase shift by carefully observing the change in transmittance through a small aperture in the far field location (closed aperture, CA). This observation must be made in order to measure the phase shift. One way to determine the intensity-dependent absorption of a sample is to move the sample through the focus of the detector while maintaining what is referred to as an open aperture (OA). The signal ratio received from open and closed measurement methods can be used to calculate the nonlinear refraction of the sample when both open and closed measurement techniques are used to make the measurements.
The Z-scan method, well-known technique that provides the simultaneous measurement of both the nonlinear absorption coefficient (NBC) and the nonlinear refractive coefficient (NRC), was used to measure the nonlinear coefficients of the BBY:PMMA films.
Following the completion of these measurements, an analysis of the findings was carried out. By using an aperture scheme with a CA, we were able to get an estimate of the value of the NRC of the sample. On the other hand, we used an aperture scheme with an open aperture to obtain an estimate of the value of the NBC. A CA Z-scan of a polymer film (azo dye BBY:PMMA) with different concentrations is shown in Fig. 6. The data obtained from a CA Z-scan displayed a peak that was immediately followed by a valley-normalized transmittance implies that the sign of the refraction nonlinearity is negative or that the object in question is self-defocusing.
The defocusing effect is the result of thermal nonlinearity (Fig. 6), when light with a wavelength of 532 nm is absorbed. The sample goes through spatial dispersion in temperature, and as a consequence, there is a spatial change in the refractive index as a direct result of the localized absorption of a tightly focused beam as it passes through a polymer medium. The phase of the beam is distorted as a result of this spatial variation in the refractive index, which acts as a thermal lens and produces the distortion as it travels.
Z-scan is a technique used to measure the difference between the normalized peak transmittance and the valley transmittance. This difference can be found by comparing the peak transmittance to the valley transmittance. The peak-to-valley ratio, also known as ∆TPV, has a linear connection with the on-axis phase distortion, also known as ∆Θ″, of the radiation that has been transmitted through the sample. Both quantities are indicated by their respective acronyms. The connection can be described as follows [50–52]:
and
where SLT = 1 − exp(−2ra/ωa) is the linear transmittance of the aperture [53, 54], ra is the radius of the aperture, ωa is the beam radius at the aperture in the linear region, Io is the intensity (Io = 1.56 kW/cm2) of the laser beam at focus z = 0, L′eff = (1 − exp(−αcoDth))/αco [55] is the polymer film effective thickness, Dth is the thickness of the BBY film, αco is the linear absorption coefficient of the polymer film (αco = 2.303 A/Dth [56–58]), and k = 2π/λ is the wave number. Equations 1 and 2 and the change in the refractive index ∆n = n2 I0 can be used to figure out nonlinear refractive index (NRX). The NBC (β cm/W) can be calculated using the equation below [59, 60]:
where ∆T is the normalized transmittance for the OA.
The natural effect of nonlinear refraction in nonlinear optical material may be caused by various physical mechanisms, including electronic, molecular, and thermal processes. It is anticipated that the thermal effect will be responsible for the BBY films produced by the CW laser. The fact that the closed aperture Z-scan curves meet the electronic refractive nonlinearity criterion is one way this can be proved.
In addition, the physical process of nonlinear absorption might be owed to a shift in absorption with either an increase or decrease in intensity. This may be either saturable absorption (SA), which results in a reduction in the amount of light that is absorbed by the material, or reverse SA (RSA), increases in the amount of light that is absorbed by the material. RSA and SA both have the potential to be brought about through nonlinear scattering, free carrier absorption (FCA), and two-photon absorption (TPA). When the energy band gap Eg is more than 2Ephoton, the TPA mechanism becomes the predominant one. In this particular piece of research, the conclusions are credited to RSA as being the cause of the inception of BBY films. As a result, the TPA is of little consequence.
The usual Z-scan data for polymer films are shown in Fig. 7, acquired using an OA (S = 1). When the intensity is great, complete absorption enhances emission towards the center. The sample has reached its maximum capacity for absorption, which causes the top of the CA Z-scan to become larger while the valley becomes smaller (Fig. 8). This results in a modification to the form of the Z-scan curve that surrounds z = 0.
A CW DPL emitting light at a wavelength of 532 nm was used to conduct optical limiting (OL) experiments. The optical geometry used for OL measurement is shown in Fig. 9. A positive lens with a focal length of 5 cm was used to focus the light coming from the laser beam on the object being examined. BBY:PMMA was used as the polymer sample. Following that, the polymer was shifted in such a way that it was now located behind the focal length. Whole trials were conducted in settings that were as close to real life as possible and at temperatures that were equivalent to those in a normal living room (25 ℃). To detect the incident beam that was sent from the polymer sample, a photo detector (PD) that was attached to a power meter device was used. There was a round opening with a diameter of 2.5 mm in front of the PD. In order to accomplish OL, we were required to make adjustments to the input power while maintaining a close watch on the power being produced.
In order to investigate the effect that the concentration has on the OL characteristics, the experiment was carried out with concentrations of 0.36, 0.68, and 0.94 mM for BBY-doped PMMA film. Nonlinear emissions of BBY: PMMA films were tested to find out how the polymer film limits light. An immediate reaction can be seen as a result of the incident light in Fig. 10, which depicts the relationship between the amount of power that is produced and the amount of power that is input.
The polymer samples clearly exhibit an OL behavior, as shown in Fig. 10. The output samples grow with increasing incident power up to a limiting threshold and concentration, where the output power is restricted. After reaching this threshold and concentration, the output power no longer rises. The OL threshold is what affects the functionality of the limiter, and it is common knowledge that a limiter with a lower threshold value would function more effectively.
The transmission curves that have been normalized and shown as a function of the incident input power for various polymer film concentrations are shown in Fig. 11. The optical limiting thresholds are roughly 10.29, 13.52, and 18.71 mW, respectively. These thresholds are defined as the incident input power at which transmission drops by 50%.
The input power is in the range of (0–30) mW. When the incident laser beam power is greater than 18 mW, the transmission transforms into a nonlinear state, as clearly shown. Because its nonlinear absorption coefficient rises with an increase in the incoming irradiance, the output power tends to remain constant when the incident power is over 20 mW. This is because of how photovoltaic cells work. The high absorbance of the nonlinear material at the corresponding wavelength often causes a rise in the sample’s temperature. This occurs in polymer samples, which have substantial thermal expansion because of their low thermal conductivity. The absorption of laser light causes heating, which is the process responsible for the change in the coefficient of absorption and the OL effect [59]. It demonstrates that BBY is a promising candidate for OL using a CW laser operating at 532 nm.
The normalized transmittance curves of BBY-doped PMMA films are shown in Fig. 11. These curves are a function of the input power. This form is designed to determine the value of the BBY-doped PMMA film’s limiting threshold. These values represent the value of the input power at the instant in time when the transmittance dropped by a factor of half, and they are shown in Table 2.
TABLE 2. Z-scan parameters of polymer film.
Concentration (mM) | α (cm−1) | ∆Θ″ | n2 × 10−6 (cm2/W) | β × 10−3 (cm/W) | ∆n × 10−3 |
---|---|---|---|---|---|
0.36 | 4767.21 | 0.85 | 22.14 | 154.82 | 34.72 |
0.68 | 5470.83 | 1.10 | 32.58 | 230.08 | 51.07 |
0.94 | 6424.50 | 1.46 | 50.81 | 350.05 | 79.65 |
As seen in Table 2, the value of the limiting threshold drops as the concentration of the polymer film rises, and the OL features become better as the concentration of the polymer film rises within the concentration range that was used for this inquiry. This may be seen when one examines the relationship between the value of the limiting threshold and the concentration. The following is an example that may explain this behavior: The sample with the greatest concentration has a higher number of molecules packed into each volume unit as compared to the sample with the lowest concentration.
Consequently, the sample with the greatest concentration will have more molecules interacting with one another throughout the process of nonlinear absorption. This is because more molecules will be present in the sample. When compared with the film that had a high concentration, the polymer film, which had a lower concentration, had an OL response that was less pronounced.
When the input power is increased throughout the measuring procedure, the transmitted beam is photographed at a greater distance from the sample than it was initially. Photographs of this kind are shown in Fig. 12 for a sample solution containing 0.94 mM concentration when the input powers are 1, 3, 4, 6, 12, 15, 16, 17, 18, 19, 24, and 30 mW, correspondingly. It is evident from images 12(a)–12(f) that the size of the spot grows with an increase in the input power, which indicates an increase in the output power. Figure 12 shows these photographs. This provides an explanation for the precipitous rises in output power shown in the limiting curve of Fig. 10 for input powers of 1, 3, 4, 6, 12, and 15 mW. It is possible to notice that there has been a little expansion of the spot size by looking at Figs. 12(g)–12(j). The limiting curve in Fig. 10 shows that there is a little rise in the output power for 16, 17, 18, and 19 mW of input power. Figures 12(k) and 12(l) in demonstrate how comparable the spot sizes are to one another. This indicates that the output power stabilized at a constant level for an input power of 24 and 30 mW, as shown by the limiting curve in Fig. 10.
In order to investigate how the location of the sample influenced the optical limiting, the sample was put in the exact center of the lens’s focus point. Diffraction rings were seen to appear throughout the process of the laser’s strength being steadily raised. Figure 13 depicts the limiting behaviors of the polymer films at concentrations of 0.36, 0.68, and 0.96 mM correspondingly. It is clear from looking at Figs. 10 and 13 that the optical limiting behavior of the sample varies greatly depending on the location of the sample in space. Because all the diffraction rings are contained inside the aperture, it is possible to observe, as in Fig. 13, that the output power via the aperture rises linearly with the input power when the input power is below the threshold value. Because the diameters of the outer rings are larger than the aperture size, the output power drops precipitously when the input power is greater than the threshold value. Then, as the power that is fed into the system increases, the power that is output approaches a specific value. This is due to both the number and the power of the inner rings that pass through the aperture remain almost constant.
The photos that were studied showed that the sample had a surface that was consistent and smooth, without any cracks or holes, and that material (azo dye and PMMA) spread on it in a regular pattern. To report the nonlinear optical characteristics of BSB:PMMA film, the Z-scan method was used under CW illumination at a wavelength of 532 nm. It was discovered that the value of the nonlinear refractive index (n2), is dependent on the sample absorption coefficient (αco). This is due to the sample with the biggest absorption coefficient also having the highest nonlinear refractive index. The produced samples showed signs of having a self-defocusing impact.
Based on these findings, it seems that there is potential for the BBY films to be used in optical device applications. The optical limiting features of sample films were investigated with the assistance of a CW laser whose wavelength was set at 532 nm. Research was done to investigate the impact of the concentration on the optical limiting characteristics. It was discovered that the limiting threshold of the samples used in this investigation decreased as the concentration increased; In other words, the features of the optical limiting became better as the concentration increased. In addition to this, it was discovered that the limiting threshold is lower at the wavelength that has a greater linear absorption coefficient, denoted by αco. Doping the dye with PMMA polymer leads to an improvement in its optical limiting qualities, which in turn allows the current research to accomplish its goal. This new dye has superior optical limiting properties compared to many other materials that are currently known.
Casting was the procedure that was used in this study for the preparation of a BBY:PMMA film. In order to acquire the characterization of the surface morphology of the film, AFM and ImageJ software (National Institutes of Health, MD, USA) were used to conduct an analysis of the image that was captured by the AFM microscope. The photos that were studied showed that the sample had a surface that was consistent and smooth, without any cracks or holes, and that material (azo dye and PMMA) spread on it in a regular pattern. The Z-scan method was used under CW illumination at a wavelength of 532 nm to report the nonlinear optical characteristics of BSB:PMMA film. It was discovered that the value of the nonlinear refractive index (n2) is dependent on the sample absorption coefficient (αco). This is due to the sample with the biggest absorption coefficient also has the highest nonlinear refractive index. The produced samples showed signs of having a self-defocusing impact.
Based on these findings, it seems that there is potential for the BBY films to be used in optical device applications. The optical limiting features of sample films were investigated with the assistance of a CW laser whose wavelength was set at 532 nm. Research was done to investigate the impact of the concentration on the optical limiting characteristics. It was discovered that the limiting threshold of the samples used in this investigation decreased as the concentration increased; in other words, the features of the optical limiting became better as the concentration increased. In addition to this, it was discovered that the limiting threshold is lower at the wavelength that has a greater linear absorption coefficient (αco). Doping the dye with PMMA polymer leads to an improvement in its optical limiting qualities, which in turn allows the current research to accomplish its goal. This new dye has superior optical limiting properties compared to many other materials that are currently known.
The authors would like to thank Prof. Falih Hussain Al- Khudair for his assistance, guidance, intellectual support and expertise in LabView programming.
This work was supported by the first author.
The authors declare no conflicts of interest.
The data underlying the results presented in this manuscript are not publicly available at the time of publication.
TABLE 1 Roughness average, diameter, grain size and average height of the BBY:PMMA films
Polymer Film (mM) | Grain Size (nm) | Average Height (nm) | Average Diameter (nm) | Roughness Average (nm) |
---|---|---|---|---|
−0.36 | 4.11 | 7.52 | 2.21 | 1.11 |
−0.68 | 4.32 | 12.43 | 2.36 | 2.22 |
−0.94 | 4.51 | 19.25 | 2.38 | 4.58 |
TABLE 2 Z-scan parameters of polymer film
Concentration (mM) | α (cm−1) | ∆Θ″ | n2 × 10−6 (cm2/W) | β × 10−3 (cm/W) | ∆n × 10−3 |
---|---|---|---|---|---|
0.36 | 4767.21 | 0.85 | 22.14 | 154.82 | 34.72 |
0.68 | 5470.83 | 1.10 | 32.58 | 230.08 | 51.07 |
0.94 | 6424.50 | 1.46 | 50.81 | 350.05 | 79.65 |