Nonlinear Refractive Index Coefficient Research Articles

Nonlinear refraction and absorption of spectrally tuneable picosecond pulses in carbon disulfide

We analyze the spectral dependence of the nonlinear refractive index and nonlinear absorption coefficient of carbon disulfide (CS2) in the spectral range of 400–1100 nm using picosecond laser pulses. An increase of the nonlinear refractive index of CS2 at the shorter wavelength region compared with the near infrared region (9 × 10−14 cm2 W−1 (λ = 700 nm) and 4 × 10−14 cm2 W−1 (λ = 1000 nm), respectively) follows by a decrease of this parameter at the wavelengths below 600 nm. We compare the spectral dependences of the lower- and higher-order nonlinear absorption coefficients in carbon disulfide. The three-photon absorption coefficient was found to be maximal at λ = 1000 nm (β3PA = 2 × 10−19 cm3 W−2), while analyzing between 700 and 1100 nm. The maximal value of the two-photon absorption coefficient was determined at λ = 400 nm (1.8 × 10−9 cm W−1).

Nonlinear optical properties of human cornea measured by spectral domain Z-scan method.

In the myopia correction surgery by femtosecond laser, such as Laser in Situ Keratomileusis (LASIK) and Small Incision Lenticule Extraction (SMILE), the nonlinear refractive index of the cornea may cause the deviation of cutting depth. In order to improve the cornea cutting's accuracy and reduce the possibility of undercorrection, the nonlinear refractive index coefficient n2 of the human cornea must be measured with high accuracy. The spectral domain Z-scan technique can measure n2 of the highly scattering biological tissues with much better signal to noise ratio and thus better accuracy than the conventional methods. In this paper, the n2 coefficient of one ex-vivo human corneal sample was measured by the spectral domain Z-scan technique. Experimental results show that as this corneal sample gradually dehydrates, its n2 coefficients are 1.1 ± 0.1×10-19 m2/W, 1.4 ± 0.2×10-19 m2/W and 1.6 ± 0.2 ×10-19 m2/W respectively for the corneal sample with water contents of 89%, 82%, and 78%. The increase of the water content reduces the value of n2, which is reasonable since the nonlinear refractive index coefficient of water is one order of magnitude smaller than that of the cornea.

Fused ring effect on optical nonlinearity and structure property relationship of anthracenyl chalcone based push-pull chromophores.

The Ultraviolet-visible (UV-Vis) spectra indicate that anthracenyl chalcones (ACs) have high maximum wavelengths and good transparency windows for optical applications and are suitable for optoelectronic applications owing to their HOMO–LUMO energy gaps (2.93 and 2.76 eV). Different donor substituents on the AC affect their dipole moments and nonlinear optical (NLO) responses. The positive, negative, and neutral electrostatic potential regions of the molecules were identified using molecular electrostatic potential (MEP). The stability of the molecule on account of hyperconjugative interactions and accompanying charge delocalization was analyzed using natural bond orbital (NBO) analysis. Open and closed aperture Z-scans were performed using a continuous-wave frequency-doubled diode-pumped solid-state (DPSS) laser to measure the nonlinear absorption and nonlinear refractive index coefficients, respectively. The valley-to-peak profile of AC indicated a negative nonlinear refractive index coefficient. The obtained single crystals possess reverse saturation absorption due to excited-state absorption. The structural and nonlinear optical properties of the molecules have been discussed, along with the role of anthracene substitution for enhancing the nonlinear optical properties. The calculated third-order susceptibility value was 1.10 x10-4 esu at an intensity of 4.1 kW/cm2, higher than the reported values for related chalcone derivatives. The NLO response for both ACs offers excellent potential in optical switching and limiting applications.

Methotrexate Detection Based On The Optical Properties Of Carbon Nanotubes And Silver Nano Particles Nanocomposites

<p>In this experiment, glassy carbon electrode with multi walled carbon nanotubes<br />nanocomposites have been prepared in different concentration in order to see if<br />methotrexate is anticancer drug. For the purpose of characterizing the structures,<br />nanocomposites were analyzed by scanning electron microscope. Optical measurements of different concentrations were conducted by z-scan method and the results show that by rising the concentration, nonlinear refractive index and linear absorption coefficient increases. The values of nonlinear refractive index are in orders of 𝟏𝟎−𝟖 𝒄𝒎𝟐 𝒘.</p>

Study of Third-order Nonlinear Optical Properties of Basic Violet 3 Dye in Polar Protic and Aprotic Solvents.

The present work aims to study of third-order nonlinear optical (TONLO) behavior of basic violet 3 dye dissolved in polar protic and aprotic solvents, namely, ethanol, 1-propanol, acetone and dimethyl sulfonate (DMSO), respectively. The polarity of the solvent used to have a substantial impact on the linear and TONLO properties of the dye sample. The dye exhibits self-defocusing nonlinearity due to thermally induced nonlinear refractive index and nonlinear absorption coefficient reveals the character of both saturable and reverse saturable absorption (RSA). The order of magnitude of nonlinear refractive index (n2) and nonlinear coefficient of absorption (β) of dye sample was determined to be 10-7 cm2/W and 10-3cm/W, respectively. The real and imaginary factors of the TONLO susceptibility of basic violet 3 dye were measured to be the power of 10-5 esu. The obtained results reveal that the dye sample seems to have the potential candidate for use in various photonics and optoelectronics applications.

Enhancement of Optical Nonlinearity in the Triangular Gold Nanoplates on Indium Tin Oxide

The nonlinear optical materials with small footprint, low operating energy, ultrafast and large nonlinear optical response are highly required for the signal processing. Here, we investigated the broadband optical nonlinear response of the triangular gold nanoplates on indium tin oxide (ITO) coated glass, and obtained a large optical nonlinear enhancement at its localized surface plasmon resonance (LSPR) region at the wavelength of 780 nm, far from the ENZ (epsilon-near-zero) region of ITO. The measured nonlinear refractive index and nonlinear absorption coefficient can reach up to 8.39×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-15</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /W and 5.81×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> m/W, respectively. The experimental results highlight the noble metals' potential for nonlinear optics and nanophotonics.

Photoluminescence and nonlinear optical investigations on Eu2O3 doped sodium bismuth borate glasses for solid state lighting and near-infrared optical limiting applications

Tri–positive rare earth ions activated alkali heavy metal borate glasses were designed and synthesised using melt–quenching process. Photoluminescence (PL), nonlinear optical (NLO), and optical limiting (OL) attributes of titled glasses have been systematically investigated in order to understand the efficacy of tri–valent europium ions and the obtained results are discussed in detail. The PL attributes were assessed with the blue light pumping. The NLO and OL features were evaluated in 700–1000 nm spectral region using femtosecond laser pulses. The two–photon absorption and nonlinear refractive index coefficients were found to be increased with elevation of Eu2O3 content to higher doping whereas the OL threshold factors exhibited an opposite behaviour. The PL and Judd–Ofelt analysis revealed the glass matrices containing high concertation of tri–valent europium ions are more useful for red lighting applications when excited with blue light. NLO and OL results suggest the strong Eu3+ containing glasses are ideal materials for designing optical limiters of high power to work in near infrared region with femtosecond pulses.

Giant Third-Order Nonlinear Response of Liquids at Terahertz Frequencies

The nonlinear response of liquids in the terahertz regime has recently attracted significant interest, even though very few measurements have been reported. Here, we report on our measurements based on a $z$-scan technique of the nonlinear refractive-index coefficient ${n}_{2}$ at terahertz frequencies for several liquids with noncentrosymmetric molecules, specifically, water, ethanol, and $\ensuremath{\alpha}$-pinene. We describe how the value of ${n}_{2}$ depends on the physical parameters of these molecules. The measured values of ${n}_{2}$ of the liquids in the terahertz region are as much as 6 orders of magnitude larger than their corresponding values in the visible or near-IR. Through a simple theoretical model, we confirm that the predominant source of this large third-order nonlinearity is the second-order perturbative component of the vibrational response of these molecules, which have resonances in the mid-IR.

Third-order nonlinear optical properties of the small-molecular organic semiconductor tris (8-Hydroxyquinoline) aluminum by CW Z-scan technique

The linear optical and electroluminescence properties of small molecular organic material tris-(8-hydroxyquinoline) aluminum (Alq3) are known and extensively investigated by many studies. However, the studies on the nonlinear optical (NLO) properties of this material are still scarce. Herein, the third-order NLO (TONLO) properties of Alq3 chloroform solutions with different concentrations have been examined using the Z-scan technique. At different laser powers and different laser wavelengths, the Z-scan signals were recorded using a continuous-wave (CW) laser beam. The open-aperture (OA) and closed- aperture (CA) Z-scan signals revealed strong TONLO properties. Both nonlinear refractive index (n2) and nonlinear absorption coefficient (β) showed negative values, and their smallest values were in the fold of 10−8 cm2/W and 10−2 cm/W, respectively. The negative values of n2 and β suggest thermal nonlinearity and saturable absorption (SA), respectively. The TONLO susceptibility (χ(3)) was calculated and found to be in the order of 10−6 esu. Besides, they increased with increasing the concentrations of Alq3 and laser powers. Therefore, the results indicate that Alq3 could be one of the potential materials as a saturable absorber for starting a passive mode-locking operation.

Improved third-order optical nonlinearities in Ag/MoS2 Schottky-type nano/hetero-junctions

Molybdenum disulfide (MoS2) nanostructures have been prepared by a hydrothermal treatment and were decorated with metallic silver (Ag) using the conventional wet incipient impregnation process to form Ag/MoS2 nano/hetero-junctions. The physiochemical functionalities were characterized using X-ray diffraction, Fourier transfer infrared spectroscopy, Raman spectroscopy, field emission scanning electron microscopy, energy dispersive spectroscopy and transmission electron microscopy. UV–Vis (ultraviolet–visible) spectroscopy shows an improved light absorption in visible region for Ag/MoS2 nano/hetero-junctions due to the surface plasmon resonance absorption. Photoluminescence (PL) studies suggest efficient photoexcited charge separation to occur in Ag/MoS2 nano/hetero-junctions due to an internal electric field formed across Schottky interface. The nonlinear responses of as-prepared samples to intense laser fields were examined using standard single-beam Z-scan technique under a 532 nm CW second-harmonic Nd:YAG laser irradiation wherein demonstrated reverse saturable absorption behaviors and self-defocusing responses due to negative lens effects were observed. The third-order nonlinear refractive index and absorption coefficient for Ag/MoS2 nano/hetero-junctions were found to be 6.5 × 10-7 cm2/W and 3.5 × 10-4 cm/W, respectively, showing 1.44 and 1.5 times enhancement than in MoS2 nanostructures.

Nonlinear optical properties of 6H-SiC and 4H-SiC in an extensive spectral range

Silicon carbide (SiC), which is the leading representative of the third-generation of semiconductors, possesses many excellent physical properties. However, its advantages also incur difficulties in processing, which calls for special processing techniques, such as femtosecond laser machining. In addition, SiC has shown unprecedented potential for optoelectronic applications. Knowledge of the nonlinear absorption coefficient and the nonlinear refractive index coefficient of SiC is required in both of the fields. In this work, the nonlinear absorption coefficient and the nonlinear refractive index coefficient of semi-insulating (SI) 6H-SiC and SI 4H-SiC, the most pervasive SiC polytypes, are measured in an extensive spectral range from 400 nm to 1000 nm with the Z-scan technique. Besides, the spectral dependence of the nonlinear optical properties is analyzed, facilitated by linear absorption spectrum. Especially, two-photon absorption (2PA) and three-photon absorption (3PA) coefficients of SI 6H-SiC and SI 4H-SiC are characterized in the respective spectral ranges. From the characterization of SiC, we can observe self-focusing phenomenon for nonlinear refraction. In the end, we unravel the potential of SiC for ultrafast all-optical switching based on the measured nonlinear optical properties.

Comparative Study on Au-Ag composition in Lithium Zinc Calcium Fluroborate Glasses: Nonlinear Optics Perspective

20Li2O-15CaF2-20ZnO-45B2O3- 0.XAu-(0.5-X) Ag, (where X= 0.2, 0.3) glasses were prepared by the conventional melt quench technique and coded as 2G3S and 3G2S respectively. The idea of this current work is to check the compositional dependence on the gold and silver nanoparticles in the glass. The XRD results confirmed presence of Au-Ag (111) peak at 38.11. The Infrared spectral study confirms the presence of borate segments. The UV Visible Spectroscopic studies confirms the presence of surface plasmon resonance shoulder peak for Ag nanoparticles around 490nm and 509 nm for glass 2G3S and 3G2S which had overlapped with SPR resonance peak of Au around 603 nm for glass 2G3S and around 559nm for glass 3G2S. The nonlinear optical properties were characterized using Z-Scan experimental technique for these glasses and it suggests the Glass 3G2S exhibited better nonlinear refractive index and nonlinear absorption coefficient compared to Glass 2G3S

Impact of Zn2+ introduced into the central cavity of meso-tetra(4-pyridyl)porphine on its spectroscopic features

Abstract The effect of metal ion (Zn2+) introduced into the center cavity of macrocyclic meso-tetra(4-pyridyl)porphine, H2TPyP, on its spectroscopic feature is explored. Thin films of H2TPyP and ZnTPyP are successfully prepared using the thermal evaporation technique. The linear and nonlinear spectroscopic characterizations of H2TPyP and ZnTPyP films are investigated as comparative study. Our results indicate that some perturbations in the absorption spectroscopy of the H2TPyP due to Zn complexation to form ZnTPyP led to reduce four quasi degenerated Q-bands to two Q-bands and in addition to the Soret (B) band splits into two sub-bands (Bx & By) called Davydov splitting. The indirect allowed transition dominated the electronic absorption bands for both H2TPyP and ZnTPyP films and the values of optical band gap enhanced due to metalation of H2TPyP into ZnTPyP. A single oscillator model is applied to normal dispersion behavior of refractive index spectrum for H2TPyP and ZnTPyP films and from which, the dispersion parameters are calculated and exhibited an increased in their values due to insertion of Zn atom into H2TPyP. The nonlinear optical parameters such as third order susceptibility (χ(3)), nonlinear refractive index (n2) and nonlinear absorption coefficient (βc) are derived from dispersion parameters and showed a decrease in their values for ZnTPyP films with respect to H2TPyP films due to the introduction of Zn atom in central cavity of porphyrin macrocycle.

Studies on the third-order nonlinear behaviour of Itaconic acid single crystal using femto-second laser

This work focuses on the bulk growth of Itaconic acid (ITA) single crystal from aqueous solution by slow evaporation solution growth technique. The detailed structural, optical, laser studies have been carried out for the title compound by adopting different instrumentation techniques. The cut-off wavelength of ITA crystal was obtained at 268 nm shows good nonlinear response. From the PL measurement, the high intense emission peak was observed at 442 nm corresponds to blue emission. The dominant emission colour of the grown specimen was estimated by CIE plot. The fast and slow decay of ITA single crystal were studied by time resolved PL. The laser resistive nature was examined by Nd-YAG laser and found that it is having good laser damage threshold (LDT) property. The third-order nonlinear optical behaviour of ITA crystal has been analyzed with the help of a femto-second laser using Z-scan technique. The value of various parameters like nonlinear refractive index (n2) and nonlinear absorption coefficient (β) is estimated using the theoretical calculations. The values of n2 and β were found to be 3.13 $$\times$$ 10–17 cm2/W and 1.57 $$\times$$ 10–12 cm/W, respectively. Such values of nonlinear parameters shows that grown crystal can be useful in optoelectronics applications.

Femtosecond nonlinear refraction of 2D semi-metallic redox exfoliated ZrTe2 at 800 nm

Zirconium telluride, a transition metal dichalcogenide, was synthesized by a redox exfoliated method to obtain a 2D monolayer semi-metal. After being characterized for compositional and optical analysis, its third-order nonlinear optical (NLO) properties were studied by the Z-scan technique in the femtosecond (100 fs) regime at 800 nm. Interestingly, in this spectro-temporal regime and in the intensity range exploited, the only third-order NLO effect observed was nonlinear refraction, giving rise to a positive value of the nonlinear refractive index coefficient, n2 = +(4.2 ± 0.3) × 10−16 cm2/W. Based on the calculated band structure and the excitation photon energies employed, the physical origin of the refractive nonlinearity is discussed.

Synthesis, Fluorescence and Nonlinear Optical Properties of Phthalocyanine Derivatives in the Continuous-wave and Pulsed Excitation Regimes-=SUP=-*-=/SUP=-

In this work, the photo-physical properties of seven different phthalocyanine derivatives are studied, with a focus on their transparency spectral range. Two compounds among them are recently synthesised. The investigations include synthesis, photoluminescence, absorptive and refractive nonlinear properties, and optical limiting performances. The compounds are found to be emitting interesting broad fluorescence bands in the visible range. The nonlinear optical properties are investigated with the help of Z-scan technique, with both a continuous laser at 488, 514.5 and 632.8 nm, and with a pulsed laser at 532 nm. The sign and the magnitude of the nonlinear refractive index, third-order susceptibility, and nonlinear absorption coefficient have been evaluated in the seven compounds. The optical limiting performance of each compound was also evaluated in the continuous and pulsed laser excitation regimes. Keywords:

О возможности исследования доли неоднородностей оптических нелинейных сред с помощью осевой цифровой голографии с временным разрешением

An approach to determining the fraction of local inhomogeneities nonlinear refractive index n2 in a transparent medium is considered. Data recording was performed using inline digital holography with femtosecond time resolution, where a set of probe beam inline digital holograms in the Fresnel diffraction zone to be recorded at various time delays between the pump and probe pulses. Digital holograms contain diffraction patterns that have information about the induced degenerate non-collinear phase modulation formed in the presence of nonlinear refractive index inhomogeneities. The developed algorithm is based on the calculation of the diffraction patterns Fourier spectrum and analysis of the intensity at zero spatial frequency. The proposed method has been validated in numerical modeling. An approach to determining the fraction of local inhomogeneities nonlinear refractive-index coefficient n2 in a transparent medium is considered. Data recording was performed using time-resolved inline digital holography, where a set of inline digital holograms in the Fresnel diffraction zone to be recorded in a probe beam at various time delays between the pump and probe pulses. Digital holograms contain diffraction patterns that have information about the induced degenerate noncollinear phase modulation formed in the presence of nonlinear refractive index inhomogeneities. The developed algorithm is based on the calculation of the diffraction patterns Fourier spectrum and analysis of the intensity at zero spatial frequency. The proposed method has been validated in numerical simulation.

Third order nonlinear optical, spectral, luminescence, mechanical strength and electrical properties of d – Alanine bulk crystals

Abstract Optical quality d - Alanine bulk crystals were grown by slow evaporation technique. The grown crystal is confirmed by single crystal XRD. The functional parameters are analysed by the FTIR and powder XRD implicates its crystalline nature. The optical constants of the as-grown crystal were determined from the uv visible spectral studies. The third order nonlinear refractive index and nonlinear absorption coefficient of the grown crystal were measured by Z-scan studies. The third order nonlinear susceptibility was found to be 2.2545 х 10−6 esu which seems to be fairly high. The Photoluminescence spectra reveal the emission bands for d -Alanine crystals. The hardness testing was accomplished by Vickers and Knoop testing to determine the Young's Modulus of the crystal. The d.c. conductivity of the grown crystal was measured by the complex impedance analysis wherein the obtained plot in the form of semicircle finds application in Debye relaxation for materials having large dc conductivity.

Refractive Index Border Associated with Nonlinear Optical Properties in Superhybrid Transparent TiO2 Nanoparticles-Polymer: Great Potential for Ultrafast Optical Waveguide in Optical Communication

The excellency of a superhybrid material based TiO2 nanoparticles (NPs) has been improved by the surface modification of the TiO2 with a coupling agent of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane to render them highly compatible with organic monomer mixtures avoiding aggregation. Such TiO2 NPs are then attached with a polymer. The border of linear refractive index of hybrid TiO2 NPs-polymer is enhanced in comparison with that of pure epoxy resin or polymer. Nonlinear refractive index and nonlinear absorption coefficient of hybrid TiO2 NPs-polymer are measured by femtosecond Z-scan technique at 800 nm. This hybrid material has been fabricated and studied to have a great potential for ultrafast optical waveguide in optical communication quantified by the propagation loss of the hybrid TiO2 NPs-polymer optical waveguide in the range of 4.79 to 11.90 dB/cm, which is depending on the volume percent of TiO2 NPs

Estimations of Low-Inertia Cubic Nonlinearity Featured by Electro-Optical Crystals in the THz Range

Despite the growing interest in nonlinear devices and components for light by light control in the terahertz range, there is a shortage of such materials and media used for these purposes. Here, we present the calculated values of low-inertia nonlinear refractive index coefficient for electro-optical crystals used in THz time-domain spectroscopy systems such as ZnSe, ZnTe, CdTe, GaP, and LiNbO3. The medium parameters affecting the cubic nonlinearity of the vibrational nature increase in the range of 0.5–1 THz have been determined. Comparison of theoretical calculations with known experimental results confirm the theoretical model as well as our analysis of media parameter influence on the cubic nonlinearity. In terms of applications, results obtained open up new perspectives for studying various materials in the THz frequency range.