S. Jeyaram’s research while affiliated with The Takshashila Institution and other places

Third-order nonlinear optical (NLO) properties of Acridine Orange (AO) dye were studied using Z-scan method under low power conditions and DFT method. The dye was completely dissolved in polar solvents, including ethanol, methanol, acetone, and 1-propanol. Significant optical nonlinearity was observed in polar liquids, with methanol showing the largest optical susceptibility for the AO dye. The open aperture (OA) Z-scan results indicate both positive and negative nonlinearities, attributed to saturable absorption (SA) and reverse saturable absorption (RSA). The closed aperture (CA) Z-scan results for the AO dye in all solvents demonstrated self-defocusing phenomena, as evidenced by a curve that displayed a peak followed by a valley in transmittance. The nonlinear absorption coefficient and nonlinear refractive index of the AO dye were measured to be the order of 10–7cm²/W and 10–2 cm/W, respectively. The third-order NLO susceptibility (χ³) of the AO dye was found to be the order of 10–7 esu. The effect of solvents on the solute molecules were examined using Kamlet-Abboud-Taft multi-parameter scale, which quantified the contribution percentages of solvent spectral features. Additionally, the NLO properties of the AO dye were investigated using density functional theory (DFT) at the B3LYP/6–311 + + G(d,p) level. Analyses were performed on geometry optimization, Frontier Molecular Orbital (FMO), and Electrostatic Potential (ESP). Furthermore, linear polarizability (α), first-order hyperpolarizability (β), and second-order hyperpolarizability (γ) were computed in various solvents, revealing a solvent-dependent enhancement of NLO properties that aligns with the experimental data.

The present work outlines the third-order nonlinear optical (TNLO) features of triphenylmethane dye, namely crystal violet (CV) dye dissolved in ethanol, methanol, DMF and DMSO using low power diode laser employed at 650 nm wavelength. The nonlinear refractive index (n2) and nonlinear absorption coefficient (β) of CV dye were determined from closed aperture (CA) and open aperture (OA) Z–scan approaches, respectively. The order of n2 and β of the CV dye in polar liquids were computed to be 10–7 cm2/W and 10–3 cm/W, respectively. The β of CV dye exhibited both positive and negative nonlinearity as a result of reverse saturable absorption (RSA) and saturable absorption (SA). The existence of RSA in CV dye dissolved in DMF and DMSO was confirmed by measured ground and excited state absorption cross-section. The CV dye displayed a self-defocusing NLO refraction in all the liquids due to thermal nonlinearity. The order of TNLO susceptibility and second order hyperpolarizability of the CV dye in polar liquids were determined to be 10–6 esu and 10–31 esu. The optical limiting (OL) study was employed and the dye exhibited low OL threshold of 1.97 × 102 W/cm2 in DMSO under low power laser.

Nonlinear optical (NLO) susceptibility of Ethidium Bromide (EB) dye, an excellent NLO material, dissolved in different solvents, including ethanol, methanol, acetone, 1-propanol, DMF, and DMSO is reported. Z-scan tool is used to measure the NLO features of EB dye using open and closed aperture methods. The peak-valley transmittance graph indicating self-defocusing nonlinearity in the nonlinear refractive index of EB dye in different solvents. The nonlinear absorption coefficient showed both positive and negative nonlinearity is the result of saturable and reverse saturable absorption behavior from the open aperture curve. The absorption coefficient and nonlinear refractive index of EB dye in various solvents are found to be the order of 10⁻⁴ m/W and 10⁻¹¹ m²/W, respectively. Significant second-order hyperpolarizability and third-order NLO susceptibility are observed in EB dye dissolved in DMSO. The effect of the solvent on the solute molecule is assessed using a multi-parameter scale that considered both specific and non-specific interactions. The investigation of NLO properties of EB dye is carried out using the DFT method at the B3LYP/6-311 + + G(d, p) level to compute the linear polarizability (α), first-order hyperpolarizability (β), and second-order hyperpolarizability (γ) values in different solvents. These theoretical findings are further supported by experimental results, highlighting the solvent-dependent enhancement of NLO properties.

Microplastic (MP) pollution has become a growing concern due to its potential environmental and health impacts. The present study aimed to investigate the presence of MPs in specific brands of drinking water bottle and milk packets. To identify the MPs, researchers employed microscopic techniques, FTIR spectroscopy, and FESEM with EDS. The types of polymers were determined by comparing the obtained values with reference standards. The study also assessed the potential daily microplastic exposure from drinking water and milk consumption. MPs were detected in the samples in three different shapes: filaments, fibers, and fragments. Four types of polymers were identified: polypropylene (PP), polyamide (PA), polysulfone (PSU), and polyethersulfone (PES). The colors observed included violet, blue, green, red, and black. In the analyzed drinking water samples, a total of 13 MPs sized 1–3 mm and 7 MPs sized 3–6 mm were found. In the milk samples, there were 2 MPs sized 4–5 mm and 4 MPs sized 2–3 mm. The results of the study indicate that MPs are present in the examined drinking water and milk, which are directly consumed by humans. This suggests that microplastic pollution may occur during the manufacturing or packaging processes of these products. The study recommends implementing measures to reduce microplastic contamination at the beginning of the production process for drinking water and milk.

This study reveals the solvent dependent third-order nonlinear optical (NLO) features of malachite green (MG) dye using Z–scan technique. MG dye is dissolved in polar solvents, including DMF, DMSO, ethanol, acetone, methanol, and 1-propanol. The study employs the Z–scan instrument, using a continuous wave (CW) laser as the excitation source, operating at a wavelength of 650 nm. The closed aperture (CA) and open aperture (OA) Z–scan techniques are used to assess the nonlinear indices of refraction (n2) and nonlinear coefficient of absorption (β) of MG dye. MG dye demonstrates both saturable absorption (SA) and reverse saturable absorption (RSA) in the OA Z–scan results, due to negative and positive NLO absorption coefficients. MG dye proves a self-defocusing NLO refractive index while operating under low-power conditions. The third-order NLO susceptibility (χ³) of MG dye in various liquids are calculated to be the order of 10–6 esu. Multilinear regression fit is applied here to investigate the various intermolecular interactions between the solute and solvent. MG dye exhibited large thermo-optic coefficient of the order of 10− 3 K− 1 is observed. The results give important new information about the characteristics of MG dye and indicate potential sources of material for NLO applications in future.

The objective of this study is to examine the third-order nonlinear optical (NLO) characteristics of acid green (AG) 16 dye dissolved in polar liquids, including methanol, ethanol, DMF, and DMSO. The study employed a Z–scan instrument using a low power laser as the excitation source, operating at a wavelength of 650 nm with a power output of 5 mW. The closed-aperture (CA) and open-aperture (OA) Z–scan experiments were applied to estimate the nonlinear indices of refraction (n2) and nonlinear coefficient of absorption (β) of AG 16 dye in polar liquids. AG 16 dye demonstrates both saturable absorption and reverse saturable absorption in the OA Z–scan results, due to negative and positive NLO absorption coefficients. The dye sample proves a self-defocusing NLO refractive index while operating under low-power conditions. The third-order NLO susceptibility (χ3) of AG 16 dye in various polar liquids are calculated to be the order of 10–6 esu. The solvent spectral parameters effect on χ(3) of AG 16 dye is studied by multi-parameter scale. The results provide a significant insight into the properties of AG 16 dye, suggesting a potential material for future NLO applications.

This article reports the nonlinear refractive index (n2) and nonlinear absorption coefficient (β) of acid blue 129 (AB 129) dye-doped polyvinyl alcohol (PVA) thin film with different dye concentrations using Z-scan technique. The experimental technique consists of a continuous wave laser with 5 mW power working at 635 nm wavelength. The normalized transmittance curve suggests that the dye-doped polymer film exhibits a self-defocusing nonlinear index of refraction and a large nonlinear absorption coefficient ascribed to the behaviour of reverse saturable absorption. The order of third-order NLO susceptibility of the sample is estimated to be 10‒5 esu. The dye-doped polymer films show a low-limiting threshold of 0.15 kW cm–2 at 0.04 mM dye concentration and believed that the prepared thin film is a suitable candidate for application in optical limiting. The self-diffraction pattern is observed at far-field and estimated the nonlinear refractive index of the thin film using this technique. The results of the nonlinear refractive index of the sample obtained from the self-diffraction method are comparable with Z-scan results.

Herein, we report the nonlinear refractive index and nonlinear absorption coefficient of anthraquinone dye (disperse blue 14)-doped polymer film using a facile Z-scan technique. The Z-scan studies were carried out using a semiconductor diode laser with a constant power output of 5 mW at a wavelength of 635 nm as the source of excitation. The Z-scan technique consists of closed and open aperture methods, which revealed the self-defocusing and reverse saturable absorption mechanisms based optical nonlinearity. The third-order nonlinear optical susceptibility (χ(3)) of dye-doped polymer film was estimated to be in the order of 10–5 esu. Optical limiting (OL) behaviour of the polymer film with different dye concentrations was performed under the same experimental conditions and found to be a low OL threshold of 1.45 × 102 W cm–2 at 0.04 mM dye concentration. Self-diffraction ring pattern of the polymer film was also noticed in the far field. The overall results found that the dye-doped polymer film is a potential material for photonics and optoelectronics applications.