Large Nonlinear Optical Susceptibility Research Articles

Large in-plane negative piezoelectricity and giant nonlinear optical susceptibility in elementary ferroelectric monolayers

Large in-plane negative piezoelectricity and giant nonlinear optical susceptibility in elementary ferroelectric monolayers

SnP2S6: A Promising Infrared Nonlinear Optical Crystal with Strong Nonresonant Second Harmonic Generation and Phase-Matchability

High-power infrared laser systems with broadband tunability are of great importance due to their wide range of applications in spectroscopy and free-space communications. These systems require nonlinear optical (NLO) crystals for wavelength up/down conversion using sum/difference frequency generation, respectively. NLO crystals need to satisfy many competing criteria, including large nonlinear optical susceptibility, large laser induced damage threshold (LIDT), wide transparency range and phase-matchability. Here, we report bulk single crystals of SnP_2S_6 with a large non-resonant SHG coefficient of d33= 53 pm/V at 1550nm and a large LIDT of 350 GW/cm^2 for femtosecond laser pulses. It also exhibits a broad transparency range from 0.54 {\mu}m to 8.5{\mu}m (bandgap of ~2.3 eV) and can be both Type I and Type II phase-matched. The complete linear and SHG tensors are measured as well as predicted by first principles calculations, and they are in excellent agreement. A proximate double-resonance condition in the electronic band structure for both the fundamental and the SHG light is shown to enhance the non-resonant SHG response. Therefore, SnP2S6 is an outstanding candidate for infrared laser applications.

Tunable broadband light emission from graphene

Graphene is an ideal material for integrated nonlinear optics thanks to its strong light–matter interaction and large nonlinear optical susceptibility. It has been used in optical modulators, saturable absorbers, nonlinear frequency converters, and broadband light emitters. For the latter application, a key requirement is the ability to control and engineer emission wavelength and bandwidth, as well as electronic temperature. Here, we demonstrate that the emission wavelength of graphene’s broadband hot carrier photoluminescence can be tuned by integration in photonic cavities, while thermal management can be achieved by out-of-plane heat transfer to hexagonal boron nitride. Our results pave the way to graphene-based ultrafast broadband light emitters with tunable emission.

Spatial mapping of exciton transition energy and strain in composition graded WS2(1−x)Se2x monolayer

We studied the optical properties of a composition graded WS2(1−x)Se2x alloy monolayer. A symmetric gradual composition gradient from a Se-rich center to the relatively less Se-rich edges of an equilateral triangle shaped flake is confirmed by Raman mapping. Photoluminescence (PL) mapping shows a large 100 meV variation in the exciton energy, resulting from the composition dependent bandgap variation and carrier localization. The alloying leads to symmetry breaking and large nonlinear optical susceptibility. Second harmonic generation (SHG) mapping was carried out to study the non-linear properties and additionally to determine the lattice strain of the alloy flake. In contrast to PL and Raman mappings, SHG intensity is found to be spatially uniform. However, polarization dependent SHG reveals a unidirectional strain parallel to the (zigzag) edge of the flake, in addition to the sixfold symmetry expected from the transition metal dichalcogenide (TMD) lattice. Our results suggest potential applications of composition graded TMD alloys as ultra-compact color-tunable light sources and miniaturized spectrometers.

First-principles investigation of the ferroelectric, piezoelectric and nonlinear optical properties of LiNbO3-type ZnTiO3

The newly synthesized LN-type ZnTiO3 (J. Am. Chem. Soc. 2014, 136, 2748) contains cations with the electronic configurations nd10 (Zn2+: 3d10) along with second-order Jahn-Teller (SOJT) nd0 (Ti4+: 3d0) cations. This is different from traditional ferroelectrics with the electric configurations of d0 transition metal ions or/and lone pair electrons of ns2. Using a first-principles approach based on density functional theory, we investigate the electronic structure, zone-center phonon modes, piezoelectric and nonlinear optical properties of the LiNbO3-type ZnTiO3. The electronic structure indicates that this compound is a wide direct-band-gap insulator. The results reveal that this compound is a good ferroelectric material with a large spontaneous polarization of 90.43μC/cm2. The Raman scattering peaks of A1 and E modes are assigned to their zone-center optical modes. Additionally, the large piezoelectric and nonlinear optical susceptibilities reveal that LiNbO3-type ZnTiO3 is a high-performance lead-free piezoelectric and nonlinear optical crystal.

Dielectric, piezoelectric and nonlinear optical properties of polar iodate BiO(IO3) from first-principles studies

The electronic structure, dielectric, piezoelectric, and nonlinear optical properties of recently synthesized polar iodate BiO(IO3) are systematically investigated by density functional theory calculations. The energy band structure shows that it is an indirect-band-gap semiconductor. The analyses of its zone-center phonon modes, it is found that there are 17A1, 18A2, 17B1, and 17 B2 optical phonon modes. The elastic stiffness tensors satisfy the Born stability restriction, indicating that this compound is mechanically stable. Importantly, the large piezoelectric and nonlinear optical susceptibilities show that polar iodate BiO(IO3) is a highly competitive piezoelectric and nonlinear optical material.

Third-harmonic generation in multilayer Tin Diselenide under the influence of Fabry-Perot interference effects.

Two-dimensional layered materials are in general known to exhibit strong layer dependent nonlinear optical response owing to the crystal symmetry and associated phase matching considerations. Here we report up-conversion of 1550 nm incident light using third-harmonic generation (THG) in multilayered tin di-selenide (SnSe2) and study its thickness dependence by simultaneously acquiring spatially-resolved images in the forward and backward propagation direction. We find good agreement between the experimental measurements and a coupled-wave equation model we have developed when including the effect of Fabry-Perot interference between the SnSe2 layer and the surrounding medium. We extract the magnitude of the third order electronic nonlinear optical susceptibility of SnSe2, for the first time to our knowledge, by comparing its nonlinear response with a glass substrate and find this to be ∼1500 times higher than that of glass. We also study the polarization dependence and find good agreement with the expected angular dependence of nonlinear polarization considering the crystal symmetry of SnSe2. The large nonlinear optical susceptibility of multi-layer SnSe2 makes it a promising material for studying nonlinear optical effects. This work demonstrates that in addition to the large inherent nonlinear optical susceptibility, the high refractive index of these materials and optical absorption above the bandgap strongly influence the overall nonlinear optical response and its thickness dependence characteristics.

Structural, Electronic, Mechanical, Thermodynamic, and Linear and Nonlinear Optical Properties of MoS2, MoSe2, and their MoS2xSe2(1−x) Alloys: Ab Initio Calculations

The Born effective charge tensors, high-frequency dielectric constants, phonon frequencies at Г symmetry point, and phonon dispersion curves of MoS2xSe2(1−x) (x = 0, 0.25, 0.5, 0.75, and 1) alloys are calculated based on density functional perturbation theory using optimized lattice parameters. The structural stability, stiffness, ductility, and plasticity of these alloys are explored in detail by calculating the polycrystalline structural properties. The calculated Born effective charges and Poisson’s ratio indicate the existence of a combination of ionic and covalent bonding between the transition metal and chalcogens in each layer. Based on the calculated phonon frequencies, the temperature dependence of the specific heat at constant volume, entropy, and Helmholtz free energy of MoS2xSe2(1−x) (x = 0, 0.25, 0.5, 0.75, and 1) alloys are calculated in the harmonic approximation. Structurally, the spatial inversion symmetry in the MoS2xSe2(1−x) (x = 0.25, 0.5, and 0.75) alloys is broken. This leads MoS2xSe2(1−x) (x = 0.25, 0.5, and 0.75) alloys to exhibit novel nonlinear optical properties that do not exist in the 2H-MoX2 (X = S, Se) compounds. So, the nonlinear optical properties are calculated by applying the 2n + 1 theorem to an electric-field-dependent energy functional. It is found that MoS2xSe2(1−x) (x = 0.25, 0.5, and 0.75) alloys exhibit remarkable large nonlinear optical susceptibility and electro-optic coefficients and would be promising candidates for use in nonlinear optical applications. Van der Waals interactions are included in all the first-principles calculations, to correctly describe the interaction between adjacent layers. The calculated lattice parameters, electronic energy bandgaps, phonon frequencies, and high-frequency dielectric constants of 2H-MoX2 (X = S, Se) compounds are in good agreement with available theoretical and experimental results.

Study of zinc doped tellurite glasses using XRD, UV-Vis and FTIR

Abstract Tellurite glasses possess many useful properties like high refractive index, wide band infrared transmittance and large third order non-linear optical susceptibility etc. There are many applications of theses glasses in the area of infrared amplifier, solar cell coating, fibre lasers, non-linear devices etc. Four glass samples of ZnO-TeO2 systems with varying concentration of zinc doping were prepared using melt-quench method. This glass matrix is a wonderful host of rare-earth ions doping and need to be studied thoroughly. The densities of prepared samples were found using standard displacement method. XRD spectrums of the samples were recorded for the 2θ range of 10°-100°. It was seen that the samples were purely amorphous. The transmittance of samples for wavenumber 400-4000cm-1 was recorded using FTIR. The transmittance peak corresponding to Te-O resonant stabilized bonds was achieved in 600-700cm-1. Optical absorption spectra of all samples were recorded using UV-VIS spectrophotometer in the wavelength range of 200-800nm. The values of Band gap energy were found to lie between 3.46-3.58eV and Urbach energy was found to lie between 0.9-1.3eV.

Ba2NaClP2O7: Unprecedented Phase Matchability Induced by Symmetry Breaking and Its Unique Fresnoite-Type Structure.

To combine noncentrosymmetry, large second order nonlinear optical (NLO) susceptibility, deep UV transparency, and phase matchability simultaneously into a single structure is a great challenge. Especially, the relationship between the macrophase matchability and microstructure has been less investigated. Herein, we report a unique Ba2NaClP2O7 representing the first phase-matchable example of the fresnoite family, which exhibits excellent NLO properties, including short absorption edge (<176 nm, ca. 7.0 eV), strong second-harmonic generations at the incident lasers of 850-1110 nm (obv. 0.9-1.3 × KDP; cal. dave, 1.11 vs 0.96 pm/V of KDP), and large laser-induced damage threshold (1.4 × KDP). More interestingly, Ba2NaClP2O7 illustrates an unprecedented mechanism of phase matchability that is promoted by crystallographic disorder. The uniaxial symmetry breaking caused by the disorder of [P2O7]4- group results in a structural anisotropy that changes the band dispersions along k-paths of G-Y and G-X, resulting in an increase of refractive index n x and a n y decrease, eventually enlarging the birefringence.

Alkynyl Pyridinium Crystals for Terahertz Generation

AbstractThe design and synthesis of three organic nonlinear optical crystals is presented for terahertz (THz) generation that incorporates the optimal characteristics of known organic nonlinear optical crystals 4‐(4‐(dimethylamino)styryl)‐1‐methylpyridinium 4‐methylbenzenesulfonate (DAST) and 2‐(4‐hydroxy‐3‐methoxystyryl)‐1‐methylquinolinium 2,4,6‐trimethylbenzenesulfonate (HMQ‐TMS). The three crystals feature the 4‐((4‐(dimethylamino)phenyl)ethynyl)‐1‐methylpyridin‐1‐ium (4DEP) cation and three different anion combinations. Gas phase ab initio calculations of the cation show that 4DEP has a larger hyperpolarizability than cations from both DAST and HMQ‐TMS. To obtain the molecular packing needed for large nonlinear optical susceptibility and efficient THz generation, three anions are tested that result in noncentrosymmetric crystals: 4‐methylbenzenesulfonate, 3‐nitrobenzenesulfonate, and napthalene‐2‐sulfonate. After synthesis and crystallization, the crystal structure is characterized via X‐ray diffraction (XRD) analysis, and the relative THz generation efficiency for ideal crystals is predicted. 4DEP‐N2S shows a roughly 30% larger relative second‐order nonlinear optical susceptibility compared to HMQ‐TMS and DAST and, therefore, shows promise as a new advanced THz generation crystal.

AgGa2 PS6 : A New Mid-Infrared Nonlinear Optical Material with a High Laser Damage Threshold and a Large Second Harmonic Generation Response.

To develop new mid-infrared (MIR) nonlinear optical (NLO) materials, which can overcome the low laser damage threshold (LDT) of the commercial MIR-NLO crystals (AgGaS2 , AgGaSe2 and ZnGeP2 ) and simultaneously keep the large NLO susceptibility, is necessary for high-power MIR laser frequency conversion technology. To improve the LDT, a new strategy of increasing lattice stability was adopted. Here, the strongly covalent structural unit of the PS4 tetrahedron was introduced into AgGaS2 (AGS), and that led to the isolation of the first compound in AgI -GaIII -PV -S system, namely, AgGa2 PS6 (Cc). It retains a large SHG efficiency (1.0×AGS) with phase-matchable ability, and also exhibits an improved LDT (5.1×AGS), indicating AgGa2 PS6 is a new promising MIR-NLO crystal. Moreover, a novel 3D framework of [Ga2 PS6 ]- , with triangular-shaped channels, as well as interesting single triangular geometry of AgS3 -both of which are very rare in reported sulfides-was discovered in AgGa2 PS6 . Furthermore, theoretical calculations, and lattice energy and thermal expansions analyses suggest that the PS4 group makes a large contribution to the large SHG efficiency and high LDT.

Temperature Dependence of Crystal Structure and THz Absorption Spectra of Organic Nonlinear Optical Stilbazolium Material for High-Output THz-Wave Generation

A stilbazolium material comprising 4-dimethylamino-N′-methyl-4′-stilbazolium tosylate (DAST), which has a large nonlinear optical susceptibility, was studied for application in terahertz (THz)-wave generation. The temperature-dependent structure of the DAST crystal was measured by using powder X-ray diffraction from −100 to 200 °C, indicating a volume expansion of 4.6 %. The lattice constants show anisotropic thermal expansion. Also, the temperature dependence of THz absorption spectra was measured by terahertz time-domain spectroscopy (THz-TDS) in the temperature range varying from −80 to 88.1 °C. A strong absorption peak was found at around 1 THz, shifting slightly toward a lower frequency with increasing temperature. The temperature dependence of the THz spectra was compared with that of X-ray diffraction. The shifting of THz-vibrational frequencies of the DAST crystal suggests that the change in its lattice structure is temperature dependent.

Pb5Ga6ZnS15: a noncentrosymmetric framework with chains of T2-supertetrahedra.

A novel noncentrosysmmetric sulfide, Pb5Ga6ZnS15 (1), was synthesized for the first time. Its crystal structure revealed the presence of [GaS2](-)∞ (chain 1, chains of [GaS4](5-) tetrahedra) and [Ga4S9](6-)∞ (chain 2, chains of T2-supertetrahedra) connected by isolated [ZnS4](6-) tetrahedra. Structure correlation with the network constructed solely using chain 1 (Pb4Ga4GeQ12-type) is discussed. Pb5Ga6ZnS15 was calculated to have a suitable static briefringence (Δn) of 0.1137, and a large nonlinear optical susceptibility d31 of 58.32 pm V(-1) at a wavelength of 2.05 μm (0.6 eV), much higher than that of the benchmark AgGaS2 (18.14 pm V(-1)).

New trans-stilbene derivatives with large two-photon absorption cross-section and non-linear optical susceptibility values--a theoretical investigation.

A detailed theoretical study of linear and non-linear optical susceptibilities (NLOS), one- and two-photon absorption (OPA and TPA) properties for a series of push-pull trans-stilbene (TSB) derivatives with introduction of different electron donor (D) and acceptor (A) groups on either side of the TSB ring system is presented. The objective of the work is to design new TSB derivatives with large TPA cross-section values and to explore their linear and non-linear optical susceptibilities, OPA and TPA properties. We have used linear and quadratic response theory methods and CAM-B3LYP functional in conjunction with the 6-31+G* basis set for all property calculations. We have explained the results of the first hyperpolarizability and TP transition probability using two-state model (2SM) calculations, the results of which are in excellent agreement with the response theory methods. The TP tensor elements have been analysed to explain the large TP activity of molecules. Orbitals involved in the transition processes have been studied both qualitatively (molecular orbital pictures) and quantitatively (Λ-values) in order to explain the nature of charge transfer in different TSB derivatives. The study reveals that the novel derivatives TSBD-10, TSBD-11, TSBD-12 and TSBD-13 have large non-linear optical susceptibilities and TPA cross-section values, the largest being found for TSBD-13 (5560 G.M.).

Optical second harmonic generation in a low-bandgap polymer

Recently, much research has been performed on developing low-bandgap polymers for e.g. harvesting solar energy. In the quest to improve these properties, little attention has been paid to their nonlinear optical properties, despite their interesting linear optical spectra and structural similarities to certain nonlinear optically active compounds. We characterized the optical second harmonic generation of corona poled films of poly(cyclopenta[2,1-b;3,4-b′] dithiophen-4-ylidenedioctylmalonate). The unexpectedly large nonlinear optical susceptibilities and the thermal and temporal stability of the material compare favorably to other novel nonlinear optical materials despite the lack of a donor-acceptor dye. Additionally, the polymer displays a very low absorption in the relevant wavelength region. These results demonstrate the promise of these materials for nonlinear optical devices.

Tailoring the size and distribution of Ag nanoparticles in silica glass by defects

The composites embedded with metallic nanoparticles show large nonlinear optical susceptibility and strong surface plasmon resonance absorption, which enable potential application in opto-electronics. Ion implantation has been proven to be a powerful technique of synthesis of metallic nanoparticles due to its versatility and compatibility. However, the synthesis of nanoparticles by ion implantation inevitably leads to a broad size distribution due to Ostwald ripening process. The broad size distribution has a negative effect on improving the figure of merits for nonlinear optics. In this paper, we tried to introduce defects in silica glass to act as pre-nucleation centers to mediate the size and distribution of Ag nanoparticles. In experiment, the silica glass samples were pre-irradiated by 200keV Ar ions to fluences of 0.8, 2.0 and 5.0×1016ions/cm2, and then 200keV Ag ions were implanted into the pre-irradiated samples to fluence of 2.0×1016ions/cm2. UV–VIS results show that the absorbance intensity of Ag SPR peak initially increases and then decreases with pre-irradiation fluence, which implies the change in size and density of Ag nanoparticles in samples. TEM results verify that Ag nanoparticles in the sample pre-irradiated to the fluence of 0.8×1016ions/cm2 grow bigger and distribute in a relatively narrow region comparing with that without pre-irradiation. With further increase of pre-irradiation fluence, the size of Ag nanoparticles shows a depth dependent distribution. A boundary can be clear seen at the depth of 110nm, larger Ag nanoparticles disperse in region shallower than 110nm, and smaller Ag nanoparticles disperse in the region deeper than 110nm. The average size of Ag nanoparticles initially increases and then decreases with pre-irradiation fluence. Therefore, the introduction of defects by pre-irradiation could be an effective way to tailor the size and distribution of metallic nanoparticles in matrix.

Synthesis and optical properties of hyperbranched PAEKs containing porphyrin and its metal derivatives

Novel functional hyperbranched poly(aryl ether ketone)s (HPAEKs) bonded with nonlinear optical chromophores (meso-tetrakis(4-hydroxyphenyl) porphyrin, THPP and its metal derivatives) were synthesized and characterized by 1H-NMR and UV-Vis absorption spectra. The incorporation of chromophores into HPAEKs endowed HPAEKs novel NLO and OL properties. Indeed, dendritic architecture allowed for maximum dispersion of the chromophores, avoided aggregation, more optical limiting property was obtained. Simultaneously, they retained the excellent properties of the materials, particularly in thermal stability. Their optical properties were evaluated by nonlinear optical analyses and optical limiting. The results showed that these polymers possessed good optical limiting (OL) property and large nonlinear optical (NLO) susceptibilities (ca. 10−12 esu). All polymers containing chromophores presented excellent thermal stability (DT 5 > 524.17 °C).

Assessment of long-range corrected functionals for the prediction of non-linear optical properties of organic materials

We calculate the hyperpolarizability of the prototypical chromophore p-nitroaniline in gas phase using different long-range corrected Density Functional Theory (LC-DFT) methods and compare it with experimental data. While traditional DFT methods are inadequate for predicting hyperpolarizabilities, LC-DFT functionals provide very good agreement with experiment (less than 10% error) for this archetypal organic molecule with large nonlinear optical (NLO) susceptibility. Additionally, we use the LC-ωPBE functional to calculate the structures and predict the hyperpolarizabilities of two recently synthesized potential organic NLO materials. The structures are compared with experimental measurements and found to be in excellent agreement.

Synthesis and optical properties of poly (aryl ether ketone)s-containing nonlinear optical chromophores

Novel functional poly (aryl ether ketone)s bonded nonlinear optical chromophores (meso-tetrakis (4-hydroxyphenyl) porphyrin, THPP) with different backbone structures were synthesized and characterized using proton nuclear magnetic resonance, Fourier transform infrared, and ultraviolet–visible absorption spectra. Their optical properties were evaluated by nonlinear optical analyses and optical limiting (OL). The results showed that these polymers possessed good OL properties and large nonlinear optical (NLO) susceptibilities. All polymer films-containing THPP presented excellent thermal stability (&gt;460°C). Polymers bonded with –CH3 to the backbone exhibited better performances in OL and NLO properties than those bonded with –CF3; however, the thermal stability of the former was slightly inferior. Backbone bonded with electron donating groups was conducive to the OL and NLO properties.