Negative Nonlinear Refraction Research Articles

Third-harmonic optical process in Zn:NiO thin films under the influence of femtosecond and continuous wave laser excitation

In this study, we focused on the impact of nonlinear optical properties on Zn-doped NiO thin film, which was analyzed using z scan and THG technique. The z-scan technique was performed using a continuous wave laser. The open aperture shows that all films exhibit the reverse saturable absorption and the mechanism responsible for two-photon absorption, excited state absorption, and free carrier absorption. The closed aperture results in the negative nonlinear refraction caused by the thermal effects. The enhancement in the third-order susceptibility from 5.37 × 10−3 to 13.24 × 10−3 esu with Zn doping is due to the presence and increase in the concentration of defect levels in the films. The THG studies were performed using femtosecond and nanosecond lasers and revealed that the enhancement in the signal with the rise in Zn doping concentration was attributed to the enhancement of photoexcitation and relaxation processes within the sample. These results suggest that Zn-doped NiO films have significant potential for applications in the realm of optoelectronic applications.

Tailoring the optical limiting response of methyl orange via protonation

In order to realize effective optical limiting (OL), it is necessary to utilize materials that exhibit distinct traits, such as a large and rapid nonlinear optical response, high photothermal stability, and cost-effectiveness. In the present study, the nonlinear optical (NLO) response of methyl orange (MO) is modified by inducing conformational and structural changes through appropriate modification of pH conditions. The NLO properties of MO under two different pH conditions were investigated via the z-scan technique under 7 nanoseconds excitation in the visible region (532 nm). From z-scan results, the nonlinear absorption coefficient of pristine MO and protonated-MO (P-MO) was estimated. Compared to MO, the nonlinear absorption coefficient of P-MO increased by 3.6 times, and it can be attributed to the redistribution of energy levels of MO, which favored resonant absorption in the system. Molecular energy shift and the corresponding apparent red shift in the absorption spectrum of MO are confirmed from both experimental and theoretical analysis. The mechanism behind the nonlinear absorption (NLA) and OL activity of MO is found to be effective two-photon absorption. The closed aperture (CA) z-scan data reveal a negative nonlinear refraction response of MO and P-MO. These findings suggest an efficient way to tune the NLO response of MO through protonation, and this method readily applies to numerous nonlinear optical applications, including but not limited to OL.

The Comparative Third‐Order Nonlinearities of Titanium Carbide and Tungsten Carbide in the Visible Regain

AbstractThis study investigates the structure and properties of Titanium carbide (TiC) and Tungsten carbide (WC) nanoparticles. The X‐ray diffraction patterns confirm the presence of a hexagonal structure in WC nanoparticles and cubic structure in TiC nanoparticles. Transmission electron microscopy analysis reveals the particle sizes to be within the range of 30–50 nm. The bandgap of TiC and WC nanoparticles are 3.5 and 3.6 eV, respectively based on diffuse reflectance spectroscopy (DRS) along with Kubelka–Munk. Furthermore, the optical phonons and dielectric function of WC and TiC nanoparticles are investigated using the reflectance spectra along with the Kramers–Kronig (KK) method. Furthermore, the Z‐scan technique, employing a Nd:YAG laser operating at a wavelength of 532 nm, is utilized to assess the nonlinear optical (NLO) characteristics of WC and TiC nanoparticles. The open aperture Z‐scan measurements of WC nanoparticles indicate reverse saturable absorption (RSA) behavior and a positive nonlinear refraction (NLR) coefficient. On the other hand, TiC nanoparticles show RSA behavior with a negative NLR effect. The order of NLR, nonlinear absorption coefficient, and the susceptibility of TiC and WC are 10−8 cm2 W−1, 10−4 cm W−1, and 10−6 esu, respectively.

Impact of photoinduced energy transfer and LSPR of Au and Ag nanoparticles on nonlinear optical response of methyl orange

In order to realize effective optical limiting (OL), it is necessary to utilize materials that exhibit distinct traits, such as a large and rapid nonlinear optical (NLO) response, high photothermal stability, and cost-effectiveness. In this work, the NLO properties of methyl orange (MO), a popular pH indicator, a potential nonlinear material, and an azo dye of great industrial importance are modulated by forming nanohybrids with Ag and Au nanoparticles. The NLO properties of the samples were investigated via the Z-scan technique using 7 ns laser pulses at a wavelength of 532 nm. A huge enhancement is observed in the nonlinear absorption (NLA) and OL performance MO-Ag and MO-Au nanohybrid compared to its constituent compounds, and it is attributable to photoinduced energy transfer between MO and metal NPs as well as the local field effect of NPs. The mechanisms responsible for the NLA and OL activity are primarily Excited State Absorption (ESA) with contributions from a weak Two-Photon Absorption (TPA). Notably, the nanohybrid system incorporating Au NPs outperforms the one with Ag NPs in terms of nonlinear optical properties under 532 nm excitation, primarily due to the better resonant energy transfer of Au compared to the Ag nanoparticle and intense local field effects of Au on exciting at 532 nm due to resonant absorption. The Closed Aperture (CA) Z-scan measurements were employed to investigate the nonlinear refraction property of the compounds, and both the pristine MO and its nanohybrid exhibited negative nonlinear refraction. These findings indicate that forming nanohybrids is an efficient way to modify the NLO response of MO. It also suggests MO has the potential for a diverse array of nonlinear optical applications, including but not limited to optical limiting.

Annealing and intensity dependent femtosecond nonlinear optical studies of sodium zinc borate oxide glasses incorporated with gold nanoparticles

Herein, we explored the annealing and intensity–dependent femtosecond (fs) nonlinear optical (NLO) studies on sodium zinc borate (NZB) glasses embedded with gold nanoparticles (NPs). The glasses were prepared by the melt–quench process and subjected for thermal treatment at 450 °C at different schedules in a normal atmosphere. It was identified that the glass annealed for 12 hr (i.e., the NZBAu12 glass) had the maximum saturation intensity and negative nonlinear refraction values. Therefore, the intensity–sensitive NLO investigations then conducted on that glass to understand the influence of intensity of laser radiation on NLO proeprties on gold NPs embedded glasses. The saturable absorption observed at lower intensity was switched to reverse saturable absorption (two–photon absorption) during the exposure with high fluence laser pulses. However, the nonlinear refraction sign was unchanged with increase of intensity of laser radiation. The strategy explored in this work might pave the way for achieving the strong nonlinear traits in borate–based glasses routed with gold NPs. The study outcomes endorse the benefits of NZBAu12 glass for optical switching functionalities under low–intensity pulse excitation, as well as for optical limiting applications under high–intensity pulse excitation.

The rich nonlinear optical responses in a squaraine derivative: Nonlinear absorption and transient nonlinear refraction dynamics

The abundant nonlinear optical responses of a squaraine derivative (2, 4-bis[4-(diethylamino)-2-hydroxyphenyl]squaraine, SQ-640) are explored at visible and near-infrared (NIR) regions. The sign and magnitude of the third-order (intensity depend) nonlinear absorption and refraction for SQ-640 are determined under different pluses with Z-scan method. The results of this work show reverse saturable absorption (RSA) of SQ-640 at visible and NIR region and its potential for optical limiting (OL) application. Moreover, SQ-640 shows self-focusing at visible wavelength while shows self-defocusing at NIR wavelengths. The transient refraction dynamics indicate that positive excited-state refraction causes self-focusing at visible region while negative nonlinear refraction at NIR region mainly originates from bound electron response (Kerr effect) and negative excited state refraction. Besides, the nonlinear refraction index of SQ-640 under 532 nm ranges from ∼ 10-19 m2/W at femtosecond pulses to ∼ 10-16 m2/W at nanosecond pulses and the second order hyperpolarizability is about 4 × 10-28 esu at nanosecond case. The Kerr refraction coefficient is about −6.54 × 10-19 m2/W at 700 nm under femtosecond laser pulses. The obtained OL thresholds at 532 nm are ∼ 26.8 mJ/cm2 for picosecond pulses and ∼ 85.6 mJ/cm2 for nanosecond pulses. The enriching information extracted from NLR in SQ-640 may offer an optional perspective to understand the structure–property relationships in these compounds. The results of optical nonlinearities in SQ-640 gained from this study may be of assistance to its better applications in laser protection and optical switching.

Growth, characterizations and nonlinear optical studies of dimethylamine substituted anthracene chalcone single crystals

We report the structural, thermal, linear and nonlinear optical (NLO) properties of a newly grown anthracene based chalcone single crystal, (2E)-1-(anthracen-9-yl)-3-[4-(dimethylamino)phenyl]prop-2-en-1-one (abbreviated as DA-ANC). The chalcone was synthesized by Claisen-Schmidt condensation reaction and the single crystals were grown by slow evaporation of solution growth technique. Single-crystal XRD, NMR (1H & 13C), FT-IR, UV-Vis-NIR spectroscopies, TG/DTA, and computational DFT studies were performed to characterize the crystals. The intermolecular interactions were described by Hirshfeld surface analysis (HSA). The third-order NLO properties of DA-ANC were studied by Z-scan technique using CW-DPSS laser at 532 nm. Open aperture Z-scan exhibits strong two-photon assisted reverse saturation absorption (RSA) with two-photon absorption (TPA) coefficient (β) 6.9 × 10−5 cmW−1. Closed aperture Z-scan reveals the negative nonlinear refraction arising due to self-defocusing effect with nonlinear refractive index (n2) coefficient -1.31 × 10−8 cm2W−1. The optical limiting behavior based on TPA was performed and limiting-threshold was evaluated to be 6.47 kJ cm−2. The obtained one-photon and two-photon figures of merit satisfied the conditions of all-optical switching. The results show that DA-ANC can be a potential candidate for NLO applications.

Negative Refraction in Mechanical Rotator Lattices

This paper presents numerical and experimental investigations of negative refraction at the interface between two mechanical rotator lattices, adding to the recent body of anomalous wave behavior reported for such simple lattices. Each lattice implements easily reconfigured interrotator coupling which determines whether the lattice's passband is acoustic (with positive group velocity) or optic (with negative group velocity). Since the group velocities have opposite signs over the entirety of both lattices' Brillouin zones, the negative refraction at their interface is inherently broadband. The numerical study constructs a large lattice structure for full-wave simulation and quantitatively analyzes the linear and nonlinear negative refraction. The experimental study documents robust negative refraction in a smaller-scale fabricated system and serves as validation for the numerical findings. We observe frequency-dependent transmission in both simulations and experiments. A linear analysis captures the observed phenomenon at low amplitude. At larger amplitudes, numerical simulations are used to document amplitude-dependent transmission. This phenomenon is explained by a nonlinear dispersion shift and transitional evanescent waves analyzed using a perturbation method. A sensitivity test demonstrates the robustness of negative refraction in the proposed rotator lattice structure.

Molecular structure and third-order non-linear optical properties of two novel tetralone-based chalcone derivatives: Promising materials for optical limiting applications

Two novel tetralone-based chalcone derivatives (2E)-2-(3,4-dimethoxybenzylidene]-3,4-dihydro-2H-napthalen-1-one (DMDN) and (2E)-2-(3,4-dimethoxybenzylidene]-6-methoxy-3,4-dihydro-2H-napthalen-1-one (DM6MDN) have been synthesized via a Claisen–Schmidt condensation reaction. Single crystals were obtained using a slow evaporation solution growth method. Structural characterization was carried out using single crystal X-ray diffraction study. Non-centrosymmetric DMDN crystallized in the orthorhombic system with a P212121 space group. Centrosymmetric DM6MDN crystallized in the monoclinic system with a P21/c space group. Hirshfield analysis of both crystals revealed the existence of C–H···π and π···π interactions, which play an important role in creating supramolecular structures. Our TG-DSC study revealed that DM6MDN has higher thermal stability than DMDN. The linear absorption coefficient of DMDN and DM6MDN were calculated from our UV spectral analysis and their respective optical band gaps were calculated to be 2.88 and 3.05 eV, respectively. The photoluminescence spectra show emission peaks in the blue region. DMDN exhibits SHG activity and a large β value when compared to DM6MDN. The third-order NLO properties of the chalcone derivatives was investigated using the Z-scan technique. The obtained crystals show strong non-linear absorption (NLA) and negative non-linear refraction (NLR) for DMDN and a positive NLR for DM6MDN. The third-order non-linear susceptibility (χ(3)) was of the order 10−7 esu. DMDN and DM6MDN also exhibit optical limiting (OL) and optical switching behavior under continuous wave excitation. The static NLO parameters, such as dipole moment (μ), polarizability (α) and first order hyperpolarizability (β), were computed using the B3LYP/6–31++G(d,p) level of theory. The Donor-π-Acceptor-π-Donor (D-π-A-π -D) system of DMDN and DM6MDN also makes them promising materials for NLO applications.

Nonlinear absorption and nonlinear refraction in single-phased Ti1−xInxO2 (x = 0∼0.1) thin films

In this study, single-phased rutile T i 1 - x I n x O 2 ( x = 0 ∼ 0.1 ) thin films were deposited on fused quartz substrates using a pulsed laser deposition technique. The transmission spectra reveal that the films show good transparency in the wavelength range of 330–900 nm. The absorption edge of the T i 1 - x I n x O 2 thin films is blueshifted compared with that of undoped T i O 2 films. A single-beam z -scan method using a pulse laser operating at 532 nm with a duration of 55 ps was employed to evaluate the films’ nonlinear optical characteristics. The results show that the prepared T i 1 - x I n x O 2 films exhibit nonlinear saturable absorption and negative nonlinear refraction properties. The doping of In ions into T i O 2 does not change the nonlinear optical absorption significantly. However, the nonlinear refractive index of T i 1 - x I n x O 2 film obviously increases with the increasing doping of In ions. The local electron-pinned defect-dipoles and widening bandgaps in the T i 1 - x I n x O 2 thin films could be used to explain the observed results.

Third-order optical nonlinearity of indium-doped rutile TiO2 thin films

Rutile TiO2 and Ti0.9In0.1O2 thin films were fabricated using a pulsed laser deposition method. We employed the optical transmission spectra to reveal the good transparency of the films in the visible spectral range of 330 to 900 nm. The absorption edge of the Ti0.9In0.1O2 film is blue-shifted compared with that of undoped TiO2 film. The third-order optical nonlinearity of the films was investigated by using a z-scan method with a pulse laser operating at 532 nm with a duration of 55 ps. The results show that the Ti0.9In0.1O2 and TiO2 films exhibit nonlinear saturable absorption and negative nonlinear refraction. The doping of In ions does not change the nonlinear optical absorption of the TiO2 film significantly. However, the nonlinear refractive index of Ti0.9In0.1O2 film is about two times larger than that of undoped TiO2 film. The local electron-pinned defect-dipoles and widening bandgap in the Ti0.9In0.1O2 film can be used to explain the observed results.

Investigation of transient optical nonlinearity in pyrene-based ferrocene and its optical limiting potential for ultrafast laser absorption

The ultrafast optical nonlinearity of a pyrene-based ferrocene derivative (Py-Fc) is systematically studied via Z-scan, transient absorption spectrum (TAS), and phase object pump probe (POPP). An ultrafast broadband absorption in visible wavelength region is observed via TAS. Based on this finding, nonlinear optical absorption of the material is investigated at various wavelengths. Results indicate that different absorption mechanisms, including reverse saturable absorption and two-photon induced excited state absorption involve in the nonlinear absorption in visible spectrum. The cooperation between the two mechanisms brings strong optical limiting properties. In addition, negative nonlinear optical refraction from the excited state is observed in POPP experiment and its dynamics is discussed. These results demonstrate that the molecular Py-Fc exhibits strong optical limiting, suggesting it is a potential material for ultrafast laser protection.

Variation of the sign of nonlinear refraction of carbon disulfide in the short-wavelength region

We report the spectral dependence of the nonlinear refractive index (γ) of carbon disulfide (CS2) in the range of 400–1100 nm in the case of the femtosecond laser pulses. The positive sign of γ dominated in the region between 600 and 1100 nm. At a shorter wavelength (500 nm), we observed the intensity-dependent competition between the fifth-order related self-defocusing and third-order related self-focusing. Further decrease of the wavelength of the probe pulses (400 nm) resulted in domination of the negative nonlinear refraction. The fifth-order nonlinear refractive index of CS2 at λ = 400 nm (η = −4×10−22 cm4 W−2) is determined.

Optical nonlinearities of mercury telluride quantum dots measured by nanosecond pulses

We synthesized the colloidal mercury telluride quantum dots (QDs) and analyzed their low-order nonlinear optical properties using 1064 nm and 532 nm, 10 ns pulses. HgTe QDs colloidal suspension showed the strong saturable absorption and negative nonlinear refraction (saturation intensity ISA = 5 ×108W cm−2, nonlinear absorption coefficients attributed to saturable absorption and reverse saturable absorption βSA = −4 ×10−9cm W−1 and βRSA = 1 ×10−8 cm W−1, nonlinear refractive index γ = −6 ×10−13 cm2 W−1) while using the 532 nm probe pulses. The nonlinear optical parameters of this suspension at 1064 nm were smaller (nonlinear absorption coefficient attributed to the two-photon absorption β2PA = 6 ×10−10 cm W−1, γ = −5 ×10−14 cm2 W−1). The negative nonlinear refraction of HgTe QDs was attributed to the thermal and Kerr effects in the case of 532 nm and 1064 nm probe pulses, respectively.

Role of photoinduced destruction of gold nanorods in the formation of nonlinear optical response

In this work, we investigated the nonlinear optical response of ensembles of gold nanorods (Au NR) with an average size of 6 × 18 nm dissolved in water, passivated with cetyltrimethylammonium bromide (CTAB). Negative nonlinear refraction with an index γ = –3.5·10−15 cm2·W−1 and nonlinear absorption were found using Z-scan technique in a field of the second harmonic of 10 ns YAG:Nd3+ laser pulses with a wavelength of 532 nm. The Z-scan profile demonstrates the samples bleaching as well as an increase in absorption near the lens focal plane in the case the pulse energy increases to 0.16 mJ. It was shown that the sample bleaching is caused by a decrease of optical density at a wavelength of 532 nm as a result of the photoinduced transformation of nanoparticles from cylindrical to a spherical shape passing through the melting stage.

Third-order optical nonlinearity of DSR13/THF solutions under CW He–Ne laser irradiation using Z-scan method

The Z-scan technique was employed to explore the third-order nonlinear optical properties of disperse red 13 organic chromophore solutions in tetrahydrofuran. A continuous-wave He–Ne laser (632.8 nm) was used as a source of irradiation. The nonlinear absorption and nonlinear refractive index coefficients of this dye were investigated. The results showed that this dye has a good nonlinear response with its real and imaginary quantities of third-order susceptibility. The solutions showed negative nonlinear refraction. The best obtained value of the third-order susceptibility was 6.37 × 10–3 esu at a dye concentration of 3.15 × 10–4 mol/L. Moreover, the nonlinear optical properties were enhanced with higher dye concentrations, and an elevated trend in nonlinear absorption and nonlinear refractive index coefficients was observed. Also, it was found that the reverse saturable absorption was the main mechanism responsible for the two-photon absorption effect in DSR13/THF samples.

Low-order optical nonlinearities of PbS quantum dot liquids and films

We demonstrate the variations of the nonlinear optical parameters in the suspensions and thin films containing PbS quantum dots of different sizes (9 and 2.5 nm). We show that these colloidal quantum dots possess the thermal-lens induced negative nonlinear refraction and reverse saturable absorption in the case of the 532-nm, 10-ns probe pulses. The larger nonlinear absorption coefficients of 9-nm quantum dots compared with 2.5-nm species (1 × 10−7 and 8 × 10−9 cm W−1, respectively) in the case of 1064 nm, 10 ns probe pulses were determined. Similar relations between the nonlinear optical parameters of 9- and 2.5-nm species were maintained in the case of twice shorter wavelength (532 nm) of the probe pulses. The almost ten-fold growth of the nonlinear optical parameters in the visible range compared with the near infrared region was attributed to the stronger influence of the excitonic states on the propagation effects in the former case. We show that the thin films containing these quantum dots demonstrate saturable absorption, while the suspensions show mostly the reverse saturable absorption at 532 nm. A significant enhancement of the nonlinear refractive index of films compared with suspensions (−2 × 10−8 cm2 W−1 and -1 × 10−11 cm2 W−1), as well as a large negative nonlinear absorption coefficient (−3.2 × 10−5 cm W−1) in the former case are demonstrated. We discuss the signs of nonlinear refraction and nonlinear absorption of the quantum dots, as well as the role of the sizes of these species in variations of the nonlinear parameters.

Transformation from Self-Focusing to Self-Defocusing of Silver Nanoparticles.

The nonlinear refraction of silver nanoparticles (AgNPs) in n-hexane was studied by using the closed-aperture Z-scan technique with a 532 nm nanosecond laser. It was found that, the nonlinear refraction of AgNPs shows the coexistence and transformation from self-focusing to self-defocusing. Specifically, self-focusing occurs at low excitation intensity, self-defocusing occurs at high excitation intensity, and coexistence of self-focusing and self-defocusing occurs at relatively moderate excitation intensity. The experimental results were analysed and discussed in terms of third-order and fifth-order nonlinear refractive effect. Specifically, the self-focusing is caused by the positive third-order nonlinear refraction, the self-defocusing is induced by the negative fifth-order nonlinear refraction, and the transformation from the self-focusing to self-defocusing at medium excitation intensity is caused by the competition of third-order and fifth-order nonlinear refraction. Finally, the third-order refractive index and fifth-order refractive index were obtained.

Crystal structure, synthesis, growth and characterization of a non-linear chalcone crystal: (2E)-1-(4-chlorophenyl)-3-(4-diethylaminophenyl)-prop-2-en-1-one

A novel chalcone derivative (2E)-1-(4-chlorophenyl)-3-(4-diethylaminophenyl)-prop-2-en-1-one (CPDAPP) was synthesized and crystallized by slow evaporation growth method. Single crystal X-ray diffraction analysis confirmed the monoclinic system of the compound with P21/c space group. The molecular structure was confirmed by using FT-IR, FT-Raman, 1H NMR and 13C-NMR studies. Transparency of CPDAPP crystal was studied by UV-Vis spectrum analysis and band gap was found to be 2.7 eV. Thermo gravimetric analysis and DSC measurements revealed thermal stability, material decomposition and melting point of the grown crystal. Photoluminescence spectrum revealed emission peaks in green region. The third-order nonlinear optical properties of CPDAPP was investigated in DMF using Z-scan technique with continuous wave (CW) DPSS laser at 532 nm wavelength. The title chalcone exhibited significant two-photon absorption, negative nonlinear refraction (n2 = − 1.25 × 10−8 cm2W−1) and optical limiting threshold = 1.91 kW/cm2 under the CW regime. A comprehensive theoretical study was carried out on the molecule of CPDAPP using density functional theory (DFT) and compared with experimental results. The optimized geometry and frontier molecular orbitals were calculated by employing B3LYP/6-31++G(d,p) level of theory. The optimized molecular structure was confirmed computationally by IR and Raman vibrational and 1H NMR and 13C-NMR spectral analysis. The static NLO properties such as dipole moments (μ), polarizability (α), first (β) and second order hyperpolarizability (γ) were computed. The electronic excitation energies and HOMO–LUMO band gap for CPDAPP were also determined by DFT. The experimental and theoretical results were in good agreement and the NLO study shows that CPDAPP molecule can be a promising material for nonlinear optical applications.

Nonlinear Optical Characterization of InP@ZnS Core-Shell Colloidal Quantum Dots Using 532 nm, 10 ns Pulses.

InP@ZnS core-shell colloidal quantum dots (CQDs) were synthesized and characterized using the z-scan technique. The nonlinear refraction and nonlinear absorption coefficients (γ = −2 × 10−12 cm2 W−1, β = 4 × 10−8 cm W−1) of these CQDs were determined using 10 ns, 532 nm pulses. The saturable absorption (β = −1.4 × 10−9 cm W−1, Isat = 3.7 × 108 W cm−2) in the 3.5 nm CQDs dominated at small intensities of the probe pulses (I ≤ 7 × 107 W cm−2) followed by reverse saturable absorption at higher laser intensities. We report the optical limiting studies using these CQDs showing the suppression of propagated nanosecond radiation in the intensity range of 8 × 107–2 × 109 W cm−2. The role of nonlinear scattering is considered using off-axis z-scan scheme, which demonstrated the insignificant role of this process along the whole range of used intensities of 532 nm pulses. We discuss the thermal nature of the negative nonlinear refraction in the studied species.