Negative Nonlinear Refraction Research Articles

Structural, third-order optical nonlinearities and figures of merit of (E)-1-(3-substituted phenyl)-3-(4-fluorophenyl) prop-2-en-1-one under CW regime: New chalcone derivatives for optical limiting applications

In the present work, the crystal structures and third-order nonlinear optical (NLO) properties of two novel chalcone derivatives, (E)-1-(3-bromophenyl)-3-(4-fluorophenyl) prop-2-en-1-one (F3BC) and (E)-1-(3-nitrophenyl)-3-(4-fluorophenyl) prop-2-en-1-one (F3NC) have been experimentally investigated. Both chalcones were synthesized by Claisen–Schmidt condensation reaction. The single-crystals were obtained from slow evaporation solution growth method and were structurally characterized by single-crystal X-ray diffraction. Both studied crystals are crystallized in centrosymmetric space groups. The existence of CH⋯π interactions in F3BC and CH⋯O and CH⋯F hydrogen interactions in F3NC play important roles in creating supramolecular structures. The linear optical absorption coefficient (α) of F3BC and F3NC were analyzed by UV–Vis–NIR spectral analysis and the optical band gaps (Eg) were estimated. TG-DTA analysis revealed that the F3NC crystal has higher thermal stability than F3BC crystal. The third-order nonlinear optical properties of these crystals were studied in solution using Z-scan technique with a continuous wave (CW) DPSS laser operating at 532 nm wavelength. The molecules reveal a strong third-order nonlinear absorption (NLA) and negative nonlinear refraction (NLR). The calculated values of nonlinear absorption coefficient β, nonlinear refraction coefficient n2 and third-order nonlinear susceptibility χ(3) were found to be of the order of 10−5 cm/W, 10−8 cm2/W and 10−6 esu, respectively. The value of the two-photon absorption (2 PA) cross section at 532 nm for both chalcones is of the order of 108 GM. These crystals also exhibited optical limiting (OL) properties under CW laser excitation.

Dielectric, etching and Z-scan studies of glycine doped potassium thiourea chloride crystal

Abstract Glycine doped potassium thiourea chloride (PTC) crystal has been grown by slow solution evaporation technique. The dielectric studies have been employed to examine substantial improvement in dielectric constant and dielectric loss of glycine doped PTC crystal. The etching studies have been performed to investigate the surface quality of this crystal. The z-scan studies have been carried out at 632.8 nm to explore the third order nonlinear optical nature. The negative nonlinear refraction of glycine doped PTC crystal was found to be of 7.27 × 10−12 cm2/W. The origin of high magnitude of third order nonlinear optical susceptibility and reverse saturable nonlinear absorption have been investigated. The obtained results were explored to discuss the nonlinear optical applications of PTC crystal.

Femtosecond third order optical nonlinearity and optical limiting studies of (γ and β)—Barium borate nanostructures

Single phase (γ and β) barium borate with nanorod structures were prepared by hydrothermal method at reaction conditions of 433 and 1073K, respectively. FESEM images demonstrated the transformation of nanoclusters into elongated nanorods as the reaction time increased. The third order nonlinear optical (NLO) properties of the samples were investigated by the Z-scan technique (800nm, 150fs, 100MHz). Both phases of barium borate depicted nonlinear absorption and was assigned to the two-photon absorption mechanism. γ–BBO demonstrated negative nonlinear refraction (self-defocusing) while β-BBO showed positive nonlinear refraction (self-focusing). Both the phases exhibited optical limiting behavior and the limiting threshold was found to be in the order of μJ/cm2. Nanorods possessed superior third order NLO coefficients compared to nanoclusters of barium borate. Also γ–BBO possessed superior NLO properties compared to β–BBO and it can be strongly emphasized that γ–BBO nanorods can be used as a potential material for photonic applications.

Linear and nonlinear optical characterization of self-assembled, large-area gold nanosphere metasurfaces with sub-nanometer gaps.

We created centimeter-scale area metasurfaces consisting of a quasi-hexagonally close packed monolayer of gold nanospheres capped with alkanethiol ligands on glass substrates using a directed self-assembly approach. We experimentally characterized the morphology and the linear and nonlinear optical properties of metasurfaces. We show these metasurfaces, with interparticle gaps of 0.6 nm, are modeled well using a classical (without charge transfer) description. We find a large dispersion of linear refractive index, ranging from values less than vacuum, 0.87 at 600 nm, to Germanium-like values of 4.1 at 880 nm, determined using spectroscopic ellipsometry. Nonlinear optical characterization was carried out using femtosecond Z-scan and we observe saturation behavior of the nonlinear absorption (NLA) and nonlinear refraction (NLR). We find a negative NLR from these metasurfaces two orders of magnitude larger (n2,sat = -7.94x10-9 cm2/W at Isat,n2 = 0.43 GW/cm2) than previous reports on gold nanostructures at similar femtosecond time scales. We also find the magnitude of the NLA comparable to the largest values reported (β2,sat = -0.90x105 cm/GW at Isat,β2 = 0.34 GW/cm2). Precise knowledge of the index of refraction is of crucial importance for emerging dispersion engineering technologies. Furthermore, utilizing this directed self-assembly approach enables the nanometer scale resolution required to develop the unique optical response and simultaneously provides high-throughput for potential device realization.

Synthesis and properties of benzothiadiazole-pyridine system: The modulation of optical feature

In this work, two new benzothiadiazole (BTD)-based compounds 1 and 2 were elaborately designed and synthesized, to explore the modulation on the interesting optical properties. Briefly, bipyridine-substituted compound 1 was synthesized via a modified Buchwald-Hartwig amination reaction with relatively high yield, and then derivative 2 was prepared by a following dehydrogenation reaction. The result in steady-state spectroscopic analysis and DFT/TDDFT calculation suggest the readily polarized nature of 1. In contrast, the readily polarized nature was declined in π-conjugated molecule 2, indicating the blue-shifted absorption and emission. Interestingly, negative cubic nonlinear refraction behavior in 1 is greater than that in π-conjugated system 2. Furthermore, in case 1 or 2, the photophycal property was considerably influenced by the external transition metal ion (M = Ag+, Cu2+ or Fe3+). Especially, because of the existence of external Fe3+ in case 1, initially negative nonlinear refraction signal became a positive one. Such exciting result is quietly useful for the design and synthesis of new functional BTD-based dye material.

Linear and nonlinear optical properties of erbium doped zinc borotellurite glass system

A glass series of erbium doped zinc borotellurite glass system was prepared by using the melt-quenching method. The absorption spectra revealed several bands at visible range which correspond to the following transitions (from the ground state); 4G11/2 + 2H9/2 + 4F5/2 + 4F7/2 + 2H11/2 + 4S3/2 + 4F9/2 + 4I9/2 + 4I11/2. From the Judd–Ofelt analysis, it is found that the trend of Ω2 values is a non-linear variation along with erbium concentrations. Meanwhile, the value of Ω6 decreases as the erbium concentration increases. The photoluminescence analysis shows green emission which are attributed to the 4S3/2 level to the ground state at 4I15/2. Meanwhile, the upconversion analysis revealed several emission bands at 376nm, 424nm, 470nm and 558nm which correspond to 4G11/2 → 4I15/2, 4F3/2 → 4I15/2, 4F7/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions respectively. The non-linear refractive index spectra show self-defocusing behavior and negative nonlinear refraction (ƞ2<0) under laser excitation at 532nm of wavelength. The obtained values of nonlinear absorption and nonlinear susceptibility revealed nonlinear variations.

Structure and nonlinear optical properties of (E)-1-(4-aminophenyl)-3-(3-chlorophenyl) prop-2-en-1-one: A promising new D-π-A-π-D type chalcone derivative crystal for nonlinear optical devices

In this paper, we present the structure and nonlinear optical (NLO) studies of a D-π-A-π-D type chalcone derivative, (E)-1-(4-aminophenyl)-3-(3-chlorophenyl) prop-2-en-1-one (abbreviated as 3CAMC). The compound was synthesized by Claisen-Schmidt condensation and single crystals were grown by slow evaporation solution growth technique. The structure was confirmed by FT-IR, 1H NMR and single-crystal X-ray diffraction techniques. The 3CAMC crystal is crystallized in the monoclinic crystal system with non-centrosymmetric space group P21 with the unit cell parameters a = 8.0013 (19) Å, b = 4.6630 (11) Å, c = 16.883 (4) Å, β = 95.568 (3)° and Z = 2. The optical absorption spectrum was recorded using UV–Vis–NIR spectrophotometer and the band gap was calculated. The title crystal has a direct band gap of 2.96 eV. TGA/DTA thermal analysis revealed that the crystal has a good thermal stability. The second harmonic generation (SHG) efficiency was investigated using the modified Kurtz-Perry powder test at 1064 nm wavelength with nanosecond (ns) laser pulses. The SHG efficiency is found to be 7 times higher than the well-studied urea. The third-order nonlinear optical properties of 3CAMC at different concentrations were investigated in DMF using Z-scan technique with continuous wave (CW) DPSS laser at 532 nm wavelength. The molecule shows a strong two-photon absorption (2PA) and significant negative nonlinear refraction characteristic (self-defocusing) in the CW regime. Further, we observed the optical limiting behavior in the compound, and evaluated the one-photon and two-photon figures of merit. The encouraging results of NLO studies suggest that the 3CAMC crystal is a promising material for photonics devices, optical switches, and optical power limiting applications.

Dark-field Z-scan technique with highly nonlinear absorbing materials: Application to porphyrins

The newly introduced imaging Dark-field Z-scan (DFZ-scan) technique is applied here to demonstrate its ability to measure the optical third-order nonlinear (NL) index coefficient in the presence of nonlinear absorption (NLA). We present our experimental results for two compounds of Porphyrin molecules, known to have relatively high NLA in the picosecond regime, at 532[Formula: see text]nm, allowing to test both cases of positive and negative nonlinear refraction (NLR). Moreover, we show that, it is possible to increase the sensitivity of the method by introducing a circular aperture in the image plane. Also, limitations are discussed to process optically a pure NL refractive signal, not subject to the influence of the NLA one, at the output of the imaging setup.

Nonlinear negative refraction by difference frequency generation

Negative refraction has attracted much interest for its promising capability in imaging applications. Such an effect can be implemented by negative index meta-materials, however, which are usually accompanied by high loss and demanding fabrication processes. Recently, alternative nonlinear approaches like phase conjugation and four wave mixing have shown advantages of low-loss and easy-to-implement, but associated problems like narrow accepting angles can still halt their practical applications. Here, we demonstrate theoretically and experimentally a scheme to realize negative refraction by nonlinear difference frequency generation with wide tunability, where a thin Beta barium borate slice serves as a negative refraction layer bending the input signal beam to the idler beam at a negative angle. Furthermore, we realize optical focusing effect using such nonlinear negative refraction, which may enable many potential applications in imaging science.

Preparation and investigation on third-order nonlinear optical properties of ZnS/MWCNTs composite materials

ZnS/MWCNTs composite materials with different concentrations of ZnS were prepared and their third-order nonlinear optical properties were studied through experiments and theoretical analysis. Structure and morphology characterizations of the ZnS/MWCNTs composite materials showed that ZnS quantum dots (QDs) were uniformly attached on the surface of MWCNTs. Third-order nonlinear optical properties of all the MWCNTs samples, ZnS QDs and ZnS/MWCNTs composite materials were measured by using Z-scan technique with a picosecond pulse laser. Experimental results showed that the composite materials always presented saturated absorption properties of MWCNTs and a negative nonlinear refraction effect of ZnS.

Investigation on fluorescence, third order non-linear optical and mechanical performance of glycine doped ADP crystal for applications of photonic devices

Optically transparent glycine doped ammonium dihydrogen phosphate crystals have been grown from aqueous solution by slow solution evaporation method. Crystallographic data of the grown crystal has been determined using the single crystal X-ray diffraction technique. The photoexcited colour centred fluorescence emission spectrum of the grown crystal has been analysed at an emission wavelength of 254 nm in the range of 300 to 700 nm. Z-scan studies have been performed at 632·8 nm to confirm the negative third order non-linear refraction behaviour of the grown crystal. The non-linear refractive index (n2), non-linear absorption coefficient (β) and third order non-linearity susceptibility (χ3) of the grown crystal were calculated using the Z-scan data to explore the material suitability for photonic applications. Vicker's microhardness test was carried out to analyse the mechanical stability and determine the hardness parameters of the grown crystal.

Synthesis, growth and optical studies of novel organometallic NLO crystal: Calcium bis-thiourea chloride

A novel organometallic crystal calcium bis-thiourea chloride (CBTC) has been synthesized and confirmed by means of EDX and FT-IR analysis. The (25×9×10)mm3 CBTC crystal has been grown from aqueous solution by slow solution evaporation technique. The UV–visible spectral study has been carried in the range of 200–900nm to assess the optical transparency of CBTC crystal. The optical constants such as band gap, optical conductivity, refractive index and reflectance of grown crystal have been evaluated using the transmittance data. The color centered fluorescence behavior of grown crystal has been explored in visible region. The Z-scan technique has been employed to determine the negative third order nonlinear refraction behavior of CBTC crystal. The magnitude of third order nonlinear refraction (n2), nonlinear susceptibility (χ3), nonlinear absorption (β) and FOM of grown crystal has been calculated using the Z-scan data. The χ3 of magnitude 3.56×10−5esu confirms the strong polarizing nature of CBTC crystal. The Kurtz-perry test confirmed the SHG efficiency of CBTC crystal is 1.15 times higher than KDP crystal material.

Nonlinear negative refraction in reorientational soft matter

We analyze the propagation of self-trapped optical beams close to the Fr\'eedericksz threshold in nematic liquid crystals. Accounting for power-dependent changes in walk-off due to the all-optical response, we demonstrate that light beams can switch from positive to negative refraction according to the excitation.

Nonlinear optical properties and optical power limiting behavior of Leishman dye in solution and solid polymer film using z-scan

We have studied the nonlinear optical properties of Leishman dye in chloroform solution at different concentrations and solid film mixed with polymethylmethacrylate (PMMA) polymer using a continuous wave (CW) laser at 532nm as the excitation source. We have employed the z-scan technique to evaluate the sign and magnitude of the intensity dependent nonlinear refractive index (n2), the nonlinear absorption coefficient (β), and the third-order nonlinear optical susceptibility (χ(3)). The obtained results showed that the Leishman dye exhibits a negative nonlinear refraction (self-defocusing) and saturable absorption. It was found that the values of n2, β, and χ(3) are dependent on the dye concentration, they increases when the dye concentration increases. Optical power limiting characteristics of the dye at different concentrations in solution and solid film were also studied. Our results showed that the Leishman dye has large third-order optical nonlinearity, thus it could be a potential candidate for opto-electronic and photonic devices.

Dielectric Optical-Controllable Magnifying Lens by Nonlinear Negative Refraction.

A simple optical lens plays an important role for exploring the microscopic world in science and technology by refracting light with tailored spatially varying refractive indices. Recent advancements in nanotechnology enable novel lenses, such as, superlens and hyperlens, with sub-wavelength resolution capabilities by specially designed materials’ refractive indices with meta-materials and transformation optics. However, these artificially nano- or micro-engineered lenses usually suffer high losses from metals and are highly demanding in fabrication. Here, we experimentally demonstrate, for the first time, a nonlinear dielectric magnifying lens using negative refraction by degenerate four-wave mixing in a plano-concave glass slide, obtaining magnified images. Moreover, we transform a nonlinear flat lens into a magnifying lens by introducing transformation optics into the nonlinear regime, achieving an all-optical controllable lensing effect through nonlinear wave mixing, which may have many potential applications in microscopy and imaging science.

Study of nonlinear optical properties and optical power limiting of Leishman dye using z-scan technique

The third-order nonlinear optical properties of Leishman dye in ethanol at different concentrations for two different incident laser intensities were investigated. The z-scan technique with continuous wave solid-state laser operating at 532 nm wavelength was employed to measure the sign and magnitude of the nonlinear refractive index (n2) and the nonlinear absorption coefficient (β) of Leishman dye. The real and imaginary parts of the third-order nonlinear optical susceptibility (χ(3)) were determined. The experimental results show that the investigated Leishman dye exhibits saturation absorption and negative nonlinear refraction (self-defocusing). The optical power limiting behavior was also investigated for the Leishman dye solution at different concentrations. The results show that the Leishman dye is a good nonlinear material with large nonlinear response could be used as a potential material for devices in optical applications.

Surface Effects on Photoluminescence and Optical Nonlinearity of CdS Quantum Dots Stabilized by Sulfonated Polystyrene in Water

A simple aqueous method has been used for the direct synthesis of water-soluble sulfonated polystyrene (SPS) encapsulated CdS quantum dots (QDs). The aqueous solution of the QDs, stabilized by two SPSs of different sulfonation level, shows a blue shift in ultraviolet–visible (UV–vis) absorption and band edge emission. High resolution transmission electron microscope (HR-TEM) establishes the presence of quantum confined CdS particles. The sulfonation level of SPS influences the size of QDs and strongly affects the photoluminescence (PL). The CdS QDs passivated by SPS with less sulfonation level exhibit only band edge emission (463 nm), while QDs in aqueous solution of SPS with high sulfonic acid content emits predominantly defect state emission (610 nm) against the band edge emission (463 nm). The PL of the SPS-CdS nanocomposites demonstrates an interesting variation in emission spectra and quantum yield via the change in sulfonation level, the change in pH and on keeping in aqueous solution. In addition, the z-scan measurements show negative nonlinear refraction coefficient, indicating self-defocusing phenomena. The absolute value of the third order nonlinear refractive index and nonlinear absorption are decided by the CdS QDs surface chemistry.

Nonlinear optical properties of methyl blue dye by Z-scan technique

The third order nonlinear optical properties of methyl blue dye was studied using He–Ne laser light operated at 632.8nm wavelength, employing the standard Z-scan technique. The dye sample exhibited negative nonlinear refraction (self defocusing) with large nonlinear refractive index value and also the dye possesses saturable nonlinear absorption under the experimental conditions. The effective values of the nonlinear refractive index n2, the nonlinear absorption coefficient β, and the real and imaginary parts of the third order optical nonlinearity χ(3) were evaluated for two different concentrations which were found to be several times greater than the reported chalcone derivatives. The results imply that methyl blue dye can be used as a potential medium for various optoelectronic applications.

Low-threshold Optical limiting and Nonlinear refraction in Nanocomposite films of Light Green dye-polymer system

Poly(vinyl alcohol) (PVA) /Light Green (LG) dye nanocomposites were fabricated and their structure, microstructure, linear and nonlinear optical properties were investigated. The samples were characterized as nanocomposites with dye molecules encapsulated between the larger molecules (molecular chains) of the polymer host PVA. The nonlinear refraction behaviour was investigated employing the Z-scan technique, using a continuous wave (cw) He- Ne laser operating at 632.8 nm, as the excitation source. The samples displayed negative nonlinear refraction (self-defocusing) under the experimental conditions. Low-threshold optical limiting behaviour exhibited by the PVA based nanocomposites was demonstrated using an aperture limited geometry. The low limiting thresholds (~4 mW and ~2.4 mW) observed for the samples indicate that these low cost and durable nanocomposite films are potential media for optical limiting application under cw laser light excitation.

Nonlinear optical properties and optical power limiting of Leishman dye using z-scan technique

The third-order nonlinear optical properties of Leishman dye in ethanol at different concentrations for two different incident laser intensities were investigated. The z-scan technique with continuous wave solid-state laser operating at 532 nm wavelength was employed to measure the sign and magnitude of the nonlinear refractive index (n2) and the nonlinear absorption coefficient (β) of Leishman dye. The real and imaginary parts of the third-order nonlinear optical susceptibility (χ(3)) were determined. The experimental results show that the investigated Leishman dye exhibits saturation absorption and negative nonlinear refraction (self-defocusing). The optical power limiting behavior was also investigated for the Leishman dye solution at different concentrations. The results show that the Leishman dye is a good nonlinear material with large nonlinear response could be used as a potential material for devices in optical applications.