Third-order Nonlinear Polarization Research Articles

Effect of partial substitution of K2O by MgO on the structure, and thermal, physical, optical properties and crystallization behaviour of K2O–MgO–B2O3–P2O5 glasses

In this work, a series of K2O–MgO–B2O3–P2O5 (KMBP) glasses were prepared by the melt-quenching method and the glass-ceramics were prepared by the one-step heat treatment. The thermal, structural, physical and optical properties, as well as the crystallization behaviour of the KMBP system, were investigated in detail using characterization techniques such as DSC, XRD, SEM, FTIR, transmittance spectroscopy and microhardness. As indicated by DSC, the thermostability and glass-forming ability were gradually enhanced through the partial substitution of K2O by MgO. XRD showed that the main crystalline phases of the glass-ceramics (GC) were gradually converted from the P–Mg–K–O based crystalline phases to the P–Mg–O based and the P–Al–O based crystalline phases. The SEM results indicated that tiny grain-like crystals were successfully precipitated from the parent glasses after heat treatment. The deconvoluted FTIR spectra results showed a gradual conversion of the [BO3] and [PO3] units towards the [BO4] and [PO4] units with the increase of the MgO contents. The increase in the degree of glass network polymerization was the essential reason for the increment in the microhardness of the parent glasses. The microhardness of GC featured a trend concordant with the crystallinity of the crystalline phases. The values of metallization criteria (MC) between 0.34 and 0.45, as well as the higher values of third-order nonlinear polarizability (χ(3)) and nonlinear refractive index (nnl) are indicative of the good suitability of the KMBP glasses for the nonlinear optical applications.

Investigation of the third-order optical nonlinear enhancement properties of Ag doped chalcogenide glass films

Chalcogenide glass is widely recognized as an excellent nonlinear optical material. Enhancing its nonlinear optical properties through metal doping has emerged as a prominent research avenue in the field of chalcogenide glass. In this paper, silver (Ag) doped Ge28Sb12Se60 (GSS) chalcogenide glass films with different concentrations were prepared by co-evaporation method. The nonlinear absorption coefficients (β) of different samples were investigated by open-aperture top-hat Z-scan experiments and pump-probe experiments, and the nonlinear refractive index (γ) values were determined using the Tichy-Ticha relation. The results showed that the nonlinear absorption of GSS thin films can be improved by Ag doping. The nonlinear absorption coefficient β exhibits the maximum enhancement of about 2.5 times at 8.3% concentration, with the maximum β reaching 1.83×10−6 m/W. The nonlinear absorption mechanism observed in the thin films can be attributed to free carrier absorption, and the free carrier lifetime is positively correlated with the Ag doping concentration. Within the selected Ag concentration range, the nonlinear refractive index (γ) of Ag doped chalcogenide glass films continues to increase, reaching about 3 times at 30.7% concentration, with the maximum γ being 4.643×10−17 m2/W. Additionally, the third-order nonlinear polarizability (χ(3)) values can be increased from 1.014×10−11 esu to 3.314×10−11 esu with increasing Ag concentration. The research results in present paper are of great significance for further exploration of the optical nonlinear enhancement properties and carrier recombination dynamics in chalcogenide glass.

Nonlinear optical properties of novel crystalline complexes of cobalt (II) and nickel (II) with 4-bromo-3-methyl-1H-pyrazole: combined experimental and computational study

Two new isostructural cobalt [Co(II)(C4H5BrN2)4(Cl)2], I and nickel [Ni(II)(C4H5BrN2)4(Cl)2], II complexes were synthesized for linear and nonlinear optical (NLO) responses using the finite field method. The synthesized complexes were characterized using elemental analysis, infrared and H-NMR spectroscopy, TG/DSC analysis, and X-ray crystallography. The crystal analysis indicates that both complexes I and II are mononuclear, and crystallize in the monoclinic space group P21/c. The metal ion in each complex is six coordinated with four nitrogen atoms (from 4-bromo-3-methyl-1H-pyrazole ligand) and two chloride ligands adopting octahedral coordination geometry. Furthermore, the computational predictions for molecular geometries and average third-order nonlinear polarizabilities of I and II are made in current study. The average theoretically predicted third-order nonlinear polarizabilities 〈γ〉 of I and II are 95.50 × 10−36 and 91.25 × 10−36 esu, respectively. The 〈γ〉 amplitudes values of complexes I and II are ∼5.26 and ∼5.0 times greater than the prototype NLO molecule of para-nitroaniline (p-NA) at same level of theory, which indicates their decent potential as efficient NLO materials.

Electrically controlled liquid crystal nonlinear optical devices prepared by multi-layer composite structures

In this study, a multi-layer composite structure is used to prepare nonlinear optical devices from multi-walled carbon nanotubes (MWCNTs)/liquid crystal (LC) composite systems. Their third-order optical nonlinearity is investigated. The MWCNTs were coated and modified to improve their dispersion in the solvent. The coated and modified MWCNTs were characterized by IR absorption spectroscopy and transmission electron microscopy (TEM). The nonlinear optical (NLO) properties of the devices prepared by the multi-layer composite structures with varying design parameters were studied. The conventional devices were also prepared by mixed doping method for comparison with the proposed devices. Both devices underwent Z-scan testing. The third-order nonlinear polarizability of the conventional hybrid-doped devices was calculated with a value of 5.39 × 10-10 esu. The third-order nonlinear polarizability of the proposed devices prepared by the multi-layer composite structures has a value of 2.97 × 10-9 esu, which is about five times the corresponding value for the hybrid-doped devices. So, the devices prepared by the multi-layer composite structures have better NLO properties. Moreover, the third-order nonlinear polarizability of the proposed devices was further increased up to 3.88 × 10-9 esu, which is an increase of almost 31% after applying voltage to these devices prepared by the multi-layer composite structures. The limiting threshold of S-CTAB/MWCNTs@BHR33400 is 0.245 J/cm2 after voltage application. Applying voltage plays a role in promoting the NLO properties of the devices. Using the multi-layer composite structure to prepare the liquid crystal nonlinear optical devices can significantly improve the NLO properties of the devices. Such prepared devices can be electrically tuned, providing new avenues for preparing nonlinear optical devices.

Phenothiazine metal-organic framework materials with excellent third-order nonlinear properties

The third-order nonlinear optical material with excellent performance is a molecule with a large π-conjugated structure for absorption structure and a high degree of delocalization. Nitrogen-sulfur derivatives have lone pairs of electrons in their N and S atoms, which makes them have a strong intramolecular charge transfer ability, which is conducive to the formation of donor-acceptor molecules. In this paper, phenothiazine is used as the matrix structure of the third-order nonlinear optical material, modified, and then metal coordination is performed to obtain [Zn(Py)2Cl2]n and [Cd(Py)2Cl2]n. Its structure is characterized by infrared spectroscopy, single crystal X-ray diffraction and powder X-ray diffraction. The morphology of the material was characterized by scanning electron microscopy. The photophysical properties, thermal properties and third-order nonlinear properties were tested, and the theoretical verification was carried out with the DFT calculation method, and the relationship between the structure and the third-order nonlinear properties was summarized. The experimental results show that phenothiazine has good electron donating ability, the two-photon absorption coefficient β is between 1.334–38.400 × 10−10 m/W, and the third-order nonlinear polarizability χ(3) is between 2.752–79.247 × 10−11 esu, The second-order hyperpolarizability γ of the ligand molecule is 5.213 × 10−34 esu. The χ(3) values of [Zn(Py)2Cl2]n and [Cd(Py)2Cl2]n are 4 orders of magnitude higher than ordinary α-quartz (χ(3) = 2.6 × 10−14 esu).

Insighting the functionally modified C60 fullerenes as an efficient nonlinear optical materials: A quantum chemical study

It is well-known that π-conjugation plays an important role to tune the nonlinear optical (NLO) response of donor-π-conjugated-acceptor compounds. Fullerenes (C60) are one of a few compounds who are abounded with π-conjugation and perhaps are the largest π-conjugation compounds. In the present study, we systematically designed C60 derivatives (2 (fulleropyrrolidine) and 2a-2c (fulleropyrrolidine tetrathiafulvalene derivatives where 2a, 2b and 2c are with n = 0, n = 1 and n = 2) through the use of pyrrolidine and tetrathiafulvalene moieties. We applied density functional theory (DFT) methods to calculate their respective geometrical structures, electronic properties, linear and nonlinear optical response properties along with their respective UV–Visible spectra using CAM-B3LYP functional and 6-31G* basis set. The isotropic polarizability (αiso) and anisotropic polarizability (αaniso) of 2c was found to be 131.52 × 10-24 and 47.01 × 10-24 esu, respectively. Amongst our designed compounds, the maximum second-order nonlinear optical polarizability amplitude (β//) of 2c was found to be 15.69 × 10-30 esu. Interestingly, 2c shows the highest third-order nonlinear polarizability amplitude <γ> of 284.29 × 10-36 esu that is about three times higher than parent compound 1. Additionally, frontier molecular orbitals (FMOs), molecular electrostatic potential maps (MEPs), transition density matrix (TDM) analysis indicate more effective charge redistribution from donor moiety to acceptor fragments. The density of states (DOS) diagrams reveal distinct electronic contributions of various fragments in the formation of HOMO and LUMO orbitals resulting in efficient intramolecular charge transfer (ICT) and robust third-order NLO response properties of functionalized fullerene derivatives. The current study may arouse the attention of the scientific society to utilize the extensive π-conjugation of functionalized fullerenes for designing efficient NLO materials.

Structural, theoretical and third order nonlinear optical properties of (E)-N’-(4-chlorobenzylidene)-4-fluorobenzohydrazide monohydrate

The title compound (E)-N’-(4-chlorobenzylidene)-4-fluorobenzohydrazide monohydrate (CBFBH) is a novel hydrazone Schiff base compound, synthesized and characterized by FTIR, 1H and 13C NMR, UV-Vis and single crystal X-ray diffraction analyses. Quantum chemical computations were performed by Density Functional Theory (DFT) with B3LYP/6-311G (d,p) level to study the structural and spectral properties of the synthesized compound. Reliability of the crystal structure was visualized by Hirshfeld surface analysis. Third-order nonlinear optical polarization coefficient was calculated by Z-scan technique.

Synthesis, characterizations, crystal structures, and theoretical studies of copper(II) and nickel(II) coordination complexes

In the present study, we report synthesis, characterization, structural and theoretical studies of two copper(II) complexes, [Cu(py)2(L1)2] (1) and [Cu(phen)(Ac)2-Cu2(Ac)4]n (2), and a nickel(II) complex, [Ni(bipy)(L)(Ac)] (3), where py = pyridine, L1 = 3,5-dichloro-2-hydroxybenzaldehyde, phen = 1,10-phenanthroline, Ac = acetate ion, bipy = 2,2’-bipyridine and HL = 4-bromo-2-(Z)-(naphthalene-2-ylimino)methyl) phenol. The new complexes were fully characterized using microanalysis, FAB-mas (m/z), FT-IR, UV-Vis and fluorescence spectra, X-band EPR spectroscopy and then by single crystal X-ray diffraction studies. X-ray studies of 1 and 3 revealed distorted octahedral geometries. Complex 2 is a coordination polymer built by an octahedral copper unit Cu(phen)(Ac)2 alternating with paddle wheel species Cu2(Ac)4, located on a crystallographic center of symmetry, where an acetate anion bridges the two crystallographic independent copper ions. The fluorescence intensities and quantum yields of 1 and 2 were found to be more compared to 3. The preliminary tests in the potential application for theoretical biological activities of compounds have also been studied. Furthermore, we also performed quantum chemical calculations to get insights into the structure-property relationships of the synthesized complexes. The quantum chemical calculations were used for theoretical calculations of linear polarizability and third-order nonlinear optical polarizability (γ) for 1, 2 and 3. Besides this, the theoretical calculations, including the analysis of frontier molecular orbitals and electrostatic potential diagrams, are used to highlight the theoretical aspects of metal to ligand charge transfer (MLCT) processes in the studied complexes.

Spacing-dependent nonlinear optical study of FePt nanoparticles composited films

Abstract The self-organized FePt nanoparticles were embedded in single crystal MgO matrix using pulse laser deposition method. The increasing FePt nanoparticles spacing (2–10 nm) were observed as the decrease of FePt deposition pulse number. The spacing between the FePt nanoparticles changing causes many subbands rooting in superlattice structure. With the decrease of the spacing, the mechanism of samples third-order nonlinear optical property revealed that the two-photonic absorption replaces saturated absorption. By adjusting the FePt deposition pulse number from 100 to 900 P, the third-order nonlinear polarizability χ(3) initially increased, and then decreased. The highest third-order nonlinear polarizability χ(3) of 4.1 × 10−10 esu was obtained with the deposition pulse number of 500 P. In combination with the small linear absorption α, the FePt NPs: MgO system is enough to become a prime candidate for nonlinear application near 580 nm.

Study on third-order nonlinear optical properties of the composite films with Ag nanoparticles and CdSe quantum dots

Through the process of magnetron sputtering and spin-coating, CdSe/Al2O3/Ag and CdSe/PMMA/Ag composite films were fabricated. All the composite films' linear optical performances, morphology and structure have been concluded. Composite films' nonlinear refraction and absorption properties were investigated by fs Z-scan technique. When the laser energy is increased from 100nj to 500nj, the CdSe/PMMA/Ag composite films' saturated absorption (SA) are enhanced, and the CdSe/Al2O3/Ag composite films are converted from SA to reverse saturated absorption (RSA), the nonlinear absorption behavior can be explained by a three-level model. At 300nj laser energy, all the composite films exhibit SA. Both the composite films' nonlinear refraction and absorption were enhanced with the increasing of Ag nanoparticles (NPs) sputtering power. However, with the layers of CdSe quantum dots (QDs) increasing, the composite films' nonlinear absorption and refractive indexes were both decreased. Moreover, the CdSe/PMMA/Ag composite films’ third-order nonlinear polarization index, as compared with that of the CdSe/Al2O3/Ag composite films, are about ten times higher. Composite films can be used in many types of signal processing as well as in photonics and optoelectronic applications.

Exciton effects on the nonlinear optical properties of the endohedral La@C82 complex

Using the Hartree–Fock single-excitation configuration interaction (CI) model, we calculated the second-order and third-order nonlinear polarizability of the La@C82 molecule. Obtained results indicate that the third-order nonlinear polarizability $$ \gamma $$ is much larger than the second-order nonlinear polarizability $$ \beta $$ and linear polarizability. Also, our results show that the $$ \gamma $$ value of the La@C82 molecule is much larger than those of the C60 and C70 molecules. The spectral shapes of the third-order nonlinear polarizability tensor, the second-order nonlinear polarizability tensor and linear polarizability of the C82 molecule turn out to be determined mainly by the geometrical distributions of the pentagons in the fullerene structures.

Kerr Nonlinearity in germanium selenide nanoflakes measured by Z-scan and spatial self-phase modulation techniques and its applications in all-optical information conversion.

Germanium selenide (GeSe) has attracted considerable research interest due to its unique photoelectric characteristics: high abundance occurrence, low toxicity, high stability, and environmentally sustainable. To the best of our knowledge, less literature is available on the nonlinear optical (NLO) properties of GeSe and on its significance of the electronic structure. In this work, the GeSe nanoflake ethanol suspensions have been studied by using liquid phase exfoliation method and then characterized by Raman, transmission electron microscopy (TEM), transmittance and atomic force microscopy (AFM). The NLO properties of GeSe suspensions with different concentration are investigated by Z-scan and spatial self-phase modulation (SSPM) methods with continuous wave laser, which are coherent with the parameter nonlinear refractive index n2 and the third order nonlinear polarizabilities χ(3). The nonlinear refractive index n2 of GeSe dispersions basically occur in the order of 10-9 cm2/W for Z-scan methods and 10-6 cm2/W for SSPM technique, whereas the third-order nonlinear polarizabilities χ(3) total are within the range of 10-6 esu for SSPM method. On the basis of these substantial characteristics of the NLO response and high stability of the 2D GeSe, we have experimentally studied the applications of the GeSe suspensions on all-optical information conversion technique.

A dual approach to study the synthesis, crystal structure and nonlinear optical properties of binuclear Pd(II) complex of 3-methyl-5-(trifluoromethyl) pyrazole and its potential quantum chemical analogues

The transition metal complexes are playing the crucial role in advancement of modern chemical science. In the present study, we synthesized the Pd(II) complex [Pd2 (C5H5F3N2)2(C5H4F3N2)2Cl2]·3(C2H6O), 1 with 3-Methyl-5-(trifluoromethyl) pyrazoleligand. The complex 1 has been characterized by IR spectroscopy, elemental analysis and X-ray crystallography. The complex 1 crystallizes in triclinic space group P-1. Moreover, density functional theory (DFT) methods are successfully used not only to study the optical and nonlinear optical (NLO) properties of complex 1 but also to design its potential derivatives with Ni(II) and Pt(II) metals as complexes 2 and 3, respectively. The interaction energies are calculated for optimized complexes that are found to be −400, −524.41 and −504.16 kcal/mol for complexes 1, 2 and 3, respectively. The calculations for third-order nonlinear optical polarizability (γ) show that the average γ amplitudes for compounds 1, 2 and 3 are found to be 79.89 × 10−36, 71.24 × 10−36 and 102.09 × 10−36 esu, respectively. The γ amplitudes of compounds 1, 2 and 3 are about 4 times, 3 times and 5 times larger than that of para-nitroaniline (pNA), which is a prototype NLO molecule, respectively. The calculations of UV–Visible spectra show that the maximum absorption wavelength for complex 3 is around 260 nm with a significantly larger oscillator strength, which is about 4 times larger than the absorption spectra of complexes 1 and 2. The analysis of FMOs shows the ligand to metal intramolecular charge transfer (LMCT) process which might be the reason of larger NLO response properties in complex 3. Additionally, the calculations of global chemical reactivity descriptors indicate that the complexes are thermally and kinetically stable. Thus, we believe the present study will intrigue the scientific community to explore the designed complexes for optical and NLO applications.

Nonlinear polarization evolution using time-dependent density functional theory.

We propose a theoretical and computational approach to investigate temporal behavior of a nonlinear polarization in a perturbative regime induced by an intense and ultrashort pulsed electric field. First-principles time-dependent density functional theory is employed to describe the electron dynamics. Temporal evolution of third-order nonlinear polarization is extracted from a few calculations of electron dynamics induced by pulsed electric fields with the same time profile but different amplitudes. We discuss characteristic features of the nonlinear polarization evolution as well as an extraction of nonlinear susceptibilities and time delays by fitting the polarization. We also carry out a decomposition of temporal and spatial changes in the electron density in power series with respect to the field amplitude. It helps to get insight into the origin of the nonlinear polarization in atomic scale.

True versus effective Kerr nonlinear response in optical filamentation.

The optical Kerr effect, and the nonlinear polarization in general, represents an important light-matter interaction governing many regimes encountered in the nonlinear optics. We reason that in the context of optical filamentation one should distinguish the third-order Kerr effect occurring at relatively low light intensities from the effective Kerr nonlinearity relevant to higher intensity. While many properties of filaments can be captured well with a third-order nonlinear polarization model with a nonlinear index chosen somewhat higher than the true nonlinear index operative at low intensities, our comparative simulations indicate that some filamentation aspects carry significant signatures from the higher-order nonlinearity.

Crystal structure, spectroscopic and third-order nonlinear optical susceptibility of linear fused ring dichloro-substituent chalcone isomers

Two new anthracenyl chalcone isomers namely (E)-1-(anthracen-9-yl)-3-(2,4-dichlorophenyl)prop-2-en-1-one and (E)-1-(anhracen-9-yl)-3(2,6-dichlorophenyl)prop-2-en-1-one were successfully synthesized using Claisen Schmidt condensation method. The compounds were then characterized by using IR, 1H and 13C NMR and UV–Vis methods. The dichloro anthracene chalcone isomers have been solved and refined using X-ray single crystal diffraction data and optimized at the ground state using density functional theory (DFT) method with B3LYP/6-311G++(d,p) level. The experimental spectroscopic data were compared with the calculated TD-DFT spectra, where the values are in good agreement. The most stable conformer of the chalcones is identified from the computational results. Both compounds also show a good HOMO-LUMO energy gap values of 2.96 and 3.14 eV. The dipole moment at the different ortho-para and ortho-ortho position are 2.71D and 4.58D, respectively. The difference in orientation of the ortho-para and ortho- ortho position results affect the dipole moments and NLO properties response of the compounds. The analyses of nonlinear optical (NLO) properties were performed by calculating the third-order nonlinear polarizabilities. Both compounds show reasonably good NLO responds with the magnitude and sign of the third order optical susceptibility was determined. Based on the measured nonlinear susceptibility χ3 both structures offers great potential in applications such as optical switching and other optoelectronics devices.

Synthesis of four pyrene-containing chalcone derivatives: Achieving excellent third-order nonlinear optical properties by optimizing halopyridines

Four chalcone derivatives 3a–3d based on pyrenyl donor and different halopyridyl acceptors were synthesized successfully. The resultant chromophores 3a–3d were characterized by nuclear magnetic resonance (NMR), high resolution mass spectra (HR-MS) and ultraviolet (UV) spectra. The theoretical calculations and thermal properties of the materials 3a–3d were systematically studied to illustrate structure-performance relationship. Further, a novel and unique method, 4f phase coherent imaging technology, was introduced to investigate the third-order nonlinear optical properties of title compounds 3a–3d with 4 ns laser pulses at 460 nm. The thermal properties, the theoretical calculations and the experimental results consistently indicate that the compound 3b, namely 3-(5-bromopyridin-2-yl)-1-(pyren-1-yl) prop-2-en-1-one, is a more promising candidate for optoelectronic and nonlinear optical devices. Its third-order nonlinear absorption coefficient (β), refraction index (n2) and polarization (χ(33)) are found to be up to such order of magnitude as 10−9 m/W, 10−16 m2/W and 10−11 esu, respectively.

Strongly coupled bacteriochlorin dyad studied using phase-modulated fluorescence-detected two-dimensional electronic spectroscopy.

Fluorescence-detected two-dimensional electronic spectroscopy (F-2DES) projects the third-order non-linear polarization in a system as an excited electronic state population which is incoherently detected as fluorescence. Multiple variants of F-2DES have been developed. Here, we report phase-modulated F-2DES measurements on a strongly coupled symmetric bacteriochlorin dyad, a relevant 'toy' model for photosynthetic energy and charge transfer. Coherence map analysis shows that the strongest frequency observed in the dyad is well-separated from the excited state electronic energy gap, and is consistent with a vibrational frequency readily observed in bacteriochlorin monomers. Kinetic rate maps show a picosecond relaxation timescale between the excited states of the dyad. To our knowledge this is the first demonstration of coherence and kinetic analysis using the phase-modulation approach to F-2DES.

Efficient extreme-UV-to-extreme-UV conversion by four-wave mixing with intense near-IR pulses in highly charged ion plasmas

Nonlinear optics in the extreme-ultraviolet (EUV) has been limited by lack of transparent media and small conversion efficiency. To overcome this problem we explore the advantage of using multiply charged ion plasmas as the interacting media between EUV and intense near-infrared (NIR) pulses. Such media are transparent to EUV and can withstand intense NIR driving pulses without damage. We calculate the third-order nonlinear polarizabilities of ${\mathrm{Ar}}^{2+}$ and ${\mathrm{Ar}}^{3+}$ ions for EUV and NIR four-wave mixing by using the well-proven Cowan code and find that the EUV-to-EUV conversion efficiency as high as 26% can be expected for practical experimental configurations using multi-terawatt NIR lasers. Such a high efficiency is possible because the driving pulse intensity can be scaled up to several orders of magnitude higher than in conventional nonlinear media, and the group-velocity and phase mismatch are insignificant at the experimental plasma densities. This effective scheme of wave mixing can be utilized for ultrafast EUV waveform measurement and control as well as wavelength conversion.

Thermally induced self-phase modulation and optical limiting application of l-arginine hydrochloride (LAHCl) solutions

l-arginine hydrochloride (LAHCl) solutions of 1 M (A) and 2 M (B) concentrations have been investigated for optical nonlinearity under a continuous wave (CW) diode laser of wavelength 670 nm. Nonlinear absorption (β), nonlinear refraction (n2) and third-order nonlinear optical susceptibility (χ(3)) of LAHCl solutions (A and B) have been measured. Excited state absorption (ESA) assisted reverse saturable absorption (RSA) has been observed to be the reason for nonlinearity in the material. The nonlinear absorption has been observed to increase with increase in concentration of the solution. Thermal aberration rings have been formed by tightly focused Gaussian laser beam and also the beam suffered a self-phase modulation. The observed RSA has been effectively used to verify the optical limiting behaviour of LAHCl solutions. Theoretically predicted third-order nonlinear polarizability has a negative value that further conform the self-defocusing behaviour of LAHCl.