Harmonic Generation Capability Research Articles

Diisopropylammonium hydrogen squarate: Synthesis and comprehensive analysis of non-linear optical co-crystal using X-ray, Hirshfeld, mechanical, optical and DFT methods

This research successfully synthesized a single co-crystal of diisopropylammonium hydrogen squarate using prolonged vaporization for crystal growth. Single-crystal X-ray spectrometry confirmed its monoclinic structure, and morphological predictions were made. UV–visible spectroscopy revealed its optical transmittance with a direct optical energy band gap of 3.45 eV. Photoluminescence studies showed a strong violet emission at 402 nm when excited by a 260 nm source. Microhardness study examined the crystal's mechanical attributes portraying the normal indentation size effect followed by a qualitative overview of half-penny crack dynamics. FTIR study aided in the discernment of varied vibrational modes with NH stretching being observed at 3078 cm−1. Thermal examination further revealed the crystal's stability up till 244 °C. Proton and carbon-13 NMR spectra were analyzed to verify the presence of functional groups and the overall molecular integrity. Intermolecular interactions were analyzed using Hirshfeld surface and fingerprint mapping. The Z-scan technique demonstrated the crystal's applicative potential in its third harmonic generation capability. Theoretical calculations with Density Functional Theory (DFT) supported the experimental findings, offering insights into optimized geometries, frontier molecular orbitals, natural population and bond orbital distributions, hyperpolarizability, molecular electrostatic potentials, IR vibrational modes, and UV absorbance profiles.

Introducing a Symmetry‐Breaking Coupler into a Dielectric Metasurface Enables Robust High‐Q Quasi‐BICs

Dielectric metasurfaces supporting quasibound states in the continuum (quasi‐BICs) exhibit very high‐quality factor resonances and electric field confinement. However, accessing the high‐Q end of the quasi‐BIC regime usually requires marginally distorting the metasurface design from a BIC condition, pushing the needed nanoscale fabrication precision to the limit. This work introduces a novel concept for generating high‐Q quasi‐BICs, which strongly relaxes this requirement by incorporating a relatively large perturbative element close to high‐symmetry points of an undistorted BIC metasurface, acting as a coupler to the radiation continuum. This approach is validated by adding a ≈100 nm diameter cylinder between two reflection‐symmetry points separated by a 300 nm gap in an elliptical disk metasurface unit cell, using gallium phosphide as the dielectric. It is found that high‐Q resonances emerge when the cylindrical coupler is placed at any position between such symmetry points. This metasurface's second harmonic generation capability in the optical range is further explored. Displacing the coupler as much as a full diameter from a BIC condition produces record‐breaking normalized conversion efficiencies >102 W−1. The strategy of enclosing a disruptive element between multiple high‐symmetry points in a BIC metasurface can be applied to construct robust high‐Q quasi‐BICs in many geometrical designs.

A double guidance mechanism, nitroaniline based microstructured optical fiber

A new type of all-solid, photonic bandgap fiber exhibiting a wavelength dependent guidance mechanism and second harmonic generation capabilities is presented. A silica glass microstructured optical fiber was infiltrated with 2-methyl 4-nitroaniline for creating the composite material optical fiber. This optical fiber was characterized over a broad wavelength range, revealing that a transition from photonic bandgap guidance to modified total internal reflection propagation occurs from short to longer wavelengths, attributed to the dispersion characteristics of the low Abbe number nitroaniline. Annealing post-processing was used for tuning the morphology of the solidified nitroaniline inside the capillaries of the silica glass microstructured optical fiber which increased the extinction ratio of the transmission bandgaps. This composite material optical fiber also exhibits second harmonic generation capabilities under 1064 nm laser excitation, with conversion characteristics dependent upon the packing of the nitroaniline inside the optical fiber capillaries. As the pump and generated light fall into different guidance regimes of the optical fiber, such a device could be potentially used as an all optical gate or light conversion device.

Demonstration of dimensional control and stabilization of second harmonic electro-optical response in chalcogenide glasses

Second-order optical susceptibility, χ(2), has been induced in thermally poled chalcogenide glasses, doped with varying levels of sodium. Using alkali-doped chalcogenide glasses, the second harmonic generation (SHG) capability is retained for over a year whereas in alkali-free glasses it disappears in days. The enhanced stability is attributed to a stabilization of the space charge through structural re-arrangements. Polarization-resolved SHG shows that the induced electric field has components in three spatial directions, all with varying extents of stability. Using structured electrodes, we demonstrate the ability to control the various electric field components’ geometry, location and stability to realize a long-lived, nonlinear grating in an alkali-doped chalcogenide glass.

ChemInform Abstract: First‐Principles Design of a Deep‐Ultraviolet Nonlinear‐Optical Crystal from KBe2BO3F2 to NH4Be2BO3F2.

AbstractA computer‐assisted material design system based on first‐principles DFT calculations is employed to predict that NH4Be2BO3F2 possesses nonlinear optical properties, such as deep‐UV second harmonic generation capability, very close to those of KBe2BO3F2.

Homogenous smooth sol gel films doped with organic compounds for nonlinear optics

The demand for protection of various types of optical sensors from laser-beam pulses has resulted in the search for optical limiting devices that have the property of being transparent at low intensity of light (normal light), but no transparent towards high intensity (laser) light. Organic material with nonlinear optical (NLO) properties as reverse saturable absorption and two-photon absorption can be used for optical limiting with the advantage of a very fast response and self-activation. A promising approach in the fabrication of thin films by low cost/easy use deposition methods for second-order nonlinear optics is sol–gel technique. The present paper reports on the sol–gel synthesis of some pyrazolone derivative doped SiO2–P2O5 smooth and homogenous films (Root mean square roughness (Rq)=1.1nm) using as precursors tetraethylorthosilicate (TEOS) and phosphoric acid (H3PO4). The structure of the deposited azo-derivatives doped thin films was examined by Fourier transform infrared spectroscopy and atomic force microscopy, while their optical properties of the films by UV–VIS spectroscopy. The nonlinear optical efficiencies due to the interaction of the NLO-active chromophores with the inorganic matrix have a significant influence on the second harmonic generation capabilities that was measured using a femtosecond Ti:Sapphire laser. The properties of the films were investigated and correlated with the concentration of the organic dopant and the thermal treatment temperature.

Pb2Ba3(BO3)3Cl: A Material with Large SHG Enhancement Activated by Pb-Chelated BO3 Groups.

Pb(II) has long been associated with lone pair activity and is often substituted in alkali earth metal borates to create new nonlinear optical (NLO) materials with enhanced second harmonic generation (SHG) capabilities. However, large enhancement in isomorphic Pb-free analogues is rare. Here we report a new NLO material Pb2Ba3(BO3)3Cl with a phase-matching SHG response approximately 3.2× that of KDP and 6× higher than its isomorphic compound Ba5(BO3)3Cl. We show that the enhanced SHG response originates from a unique edge-sharing connection between lead-oxygen polyhedra and boron-oxygen groups, making the dielectric susceptibility more easily affected by the external electric field of an incident photon. This understanding provides a route to identify systems that would benefit from SHG-active cation substitution in isomorphic structures that exhibit weak or null SHG responses.

Octahydroacridine thin films grown by matrix-assisted pulsed laser evaporation for non linear optical applications

We report on the thin film growth of 1,2,3,4,5,6,7,8-octahydroacridine (OHA) by matrix-assisted pulsed laser evaporation (MAPLE), starting from a frozen solution of 1% OHA dissolved in methanol and using a Nd:YAG laser emitting at 266nm wavelength with fluences in the range 0.1–1J/cm2. The optical properties were studied by spectroscopic-ellipsometry (SE), while Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), and scanning electron microscopy (SEM) were performed for structure and surface morphology investigation. Second harmonic generation (SHG) capabilities of the thin films were investigated by using a tunable Ti:sapphire laser with maximum emission centred in near infra-red. The peak of emitted photons is located at 388nm, therefore half the wavelength of the initial photons (776nm). The semi logarithmic dependence of SHG intensity on incident power is almost linear, except the value obtained at highest power of incident photons. This value indicates a local changing of sample due to the heating produced by the high-power incident beam.

Superstructure studies in hydrothermal-grown RbBe2BO3F2 crystals

Deep-UV nonlinear optical crystal RbBe2BO3F2 (RBBF) grown by the hydrothermal method was found to have a centrosymmetric structure of R3¯c by powder X-ray diffraction. The structure of R3¯c has cell parameters of a=4.44223(11)Å and c=39.6696(12)Å in the lattice where the (BO3)3− groups turn 60° along each (Be2BO3F2)∞ layer in the a–b plane and it is double size along the c-axis compared with standard R32 structure. As the examined RBBF shows a very low second harmonic generation capability, a stacking fault model was proposed that the hydrothermal RBBF is nonuniform with a mixture of both R32 and R3¯c structures using the DIFFaX program.

Silicophosphate films doped with organic compounds for nonlinear optical applications

Doped organic compounds are of great interest for optical communications and high-density optical data storage due to their large second-order nonlinearity and high-speed response. A promising approach in the fabrication of new materials for second-order nonlinear optics is sol–gel technique. The present paper reports on the sol–gel synthesis of some pyrazolone derivative doped SiO2–P2O5 films. The precursors used for sol gel synthesis were tetraethylorthosilicate and phosphoric acid (H3PO4). The organic compound was added under continuous stirring in the precursors’ mixture. The structure of the deposited azo-derivatives doped thin films was examined by Fourier transform infrared spectroscopy, and atomic force microscopy and their optical properties by UV–VIS spectroscopy. The nonlinear optical efficiencies due to the interaction of the NLO-active chromophores with the inorganic matrix has a significant influence on the second harmonic generation capabilities that was measured using a femtosecond Ti:sapphire laser. The properties of the films were investigated and correlated with the concentration of the organic dopant and the thermal treatment temperature.

Azo-derivatives thin films grown by matrix-assisted pulsed laser evaporation for non-linear optical applications

Azo-dye compounds, in bulk or as thin films, are extensively studied due to their particular optical properties. These properties include non-linear interaction, e.g. two-photon absorption, optical limiting and all-optical poling, with potential applications in optoelectronics and sensors development. Herein, we report on the deposition of pyrazolone derivatives, namely 1-phenyl-3-methyl-4-(1′-azo-2′-sodium carboxylate)-pyrazole-5-one thin films, for applications in second harmonic generation. Matrix-assisted pulsed laser evaporation was employed for layers growth, using a Nd:YAG device operating at 266nm (4ω). The structure and surface morphology of the deposited films were examined by Fourier transform infrared spectroscopy, atomic force microscopy, and scanning electron microscopy. Spectroscopic-ellipsometry was employed to investigate thin film optical properties. Significant second harmonic generation capabilities of the compound were pointed out by using a femtosecond Ti:sapphire laser.

Ferrocene carboxaldehyde thin films grown by matrix-assisted pulsed laser evaporation for non linear optical applications

Thin films of ferrocene carboxaldehyde, also known as cyclopentadienyl(formylcyclopentadienyl)iron, were grown on silicon and glass substrates by matrix-assisted pulsed laser evaporation technique, using a Nd:YAG device operating at 266nm(4ω). Spectroscopic-ellipsometry, Fourier transform infrared spectroscopy, scanning electron microscopy and atomic force microscopy investigations revealed that the films are homogeneous in thickness, with dense morphology and without cracks, low surface roughness (∼11nm), and no significant chemical damage. Second harmonic generation capabilities of the thin films were evidenced by using a femtosecond Ti:sapphire laser.

Ferrocene, an old molecule with a bright future: Thin films grown by matrix-assisted pulsed laser evaporation for nonlinear optical applications

Ferrocene – Fe(C5H5)2, the prototypical metallocene, is a type of organometallic chemical compound consisting of two cyclopentadienyl rings bound on opposite sides of a central iron atom. We discuss here on the growth of high quality, nanometric-sized ferrocene thin films by a non-conventional technique, i.e. matrix-assisted pulsed laser evaporation (MAPLE), on silicon and ITO coated glass substrates, by using a Nd:YAG pulsed laser device emitting at 266 nm (4ω). Spectroscopic-ellipsometry, Fourier transform infrared spectroscopy, scanning electron microscopy and atomic force microscopy techniques were used to investigate the structure, morphology and optical properties of the films. Low-to-medium second harmonic generation capabilities of the films were evidenced, when irradiated by a femtosecond Ti:sapphire pulsed laser.

Chiral Vicinal Bis(amide) Molecules: Polar/Helical Assemblies in Crystals and Second Harmonic Generation

A family of organic and metal−organic materials based on chiral vicinal bis(amide) structures are developed. Subtle molecular structure variations give rise to polar and helical organizations in crystals of the two basic compounds N,N‘-bis(benzoyl)-(1R,2R)-diaminocyclohexane and N,N‘-bis(isonicotinoyl)-(1R,2R)-diaminocyclohexane; they exhibit the unusual syn and normal anti conformations of the bis(amide) group, respectively. The new materials exhibit appreciable thermal stability and optical transparency. Trends in their second harmonic generation capability are analyzed.

Remote Functionalized Nonlinear Optical Chromophore: Optimal Assembly in Crystals for Second Harmonic Generation

Structural investigations of salts of 4-nitroaniline (pNA) and N-(2-aminoethyl)-4-nitroaniline (AENA) with S-10-camphorsulfonic acid reveal that the introduction of the remote amino functionality in AENA facilitates intermolecular interactions that lead to molecular orientations optimally suited for second harmonic generation. The salt of AENA shows appreciable solid-state second harmonic generation whereas the control case of the pNA salt shows no measurable effect. This study highlights the utility of a remote functionality in steering the molecular assembly and achieving nearly the maximum second harmonic generation capability for the given nonlinear optical chromophore.

Laser‐Induced Second Harmonic Generation Decay in a Langmuir– Blodgett Film: Arresting by Polyelectrolyte Templating

Stabilizing Langmuir–Blodgett (LB) films: Laser irradiation accelerates π dimerization of hemicyanine nonlinear optical chromophores in monolayer LB films and causes degradation of their second harmonic generation capability. The metastability of the film is overcome effectively by polyelectrolyte templating. Nanoscopic characterization (see Figure) of the ultrathin films reveals the impact of the polyelectrolyte.

Modulation of SHG responses via supramolecular association/dissociation between two complementary cryptands

Two sets of complementary cryptands are investigated for supramolecular nitro–amino H-bonding interactions in solutions. The D-π-A cryptand and the unsubstituted cryptand forms 1:1 H-bonded structure. Its second harmonic generation capabilities in solution are explored by HRS titration experiments. Supramolecular assembly leads to spontaneous increase of the SHG intensity, which undergoes steady decrease on addition of MeOH due to the breakdown of the H-bonded structure. Thus, NLO responses can be reversibly modulated by applying such supramolecular principles.

Coordination Polymers of Cu(I) with a Chiral Push−Pull Ligand: Hierarchical Network Structures and Second Harmonic Generation

Hierarchical structures of chiral coordination polymers based on Cu(I) and the C2-symmetric ligand, N,N‘-bis(4-cyanophenyl)-(1R,2R)-diaminocyclohexane are presented. The polymer topologies, two-dimensional network in one case and three-dimensional architecture built up of three interwoven diamondoid structures in the other, arise from significant differences in the ligand conformations and modes of ligation. The impact of the structural motifs on the solid-state optical second harmonic generation capability is discussed.

A new self-doubling material: RbTiOPO4:(Nb,Ln)

Abstract Concentrations of Er 3+ and Yb 3+ of 0.65 × 10 20 and 1.95 × 10 20 atoms cm −3 , respectively, have been obtained in RbTiOPO 4 :Nb (RTP:Nb) crystals. Some of the Er 3+ and Yb 3+ spectroscopic properties in RTP:Nb crystals are discussed to illustrate the contribution of different centres to the optical absorption and photoluminescence properties. The second harmonic generation capability of crystals containing Nb slightly increase with respect to RTP and a strong dependence was observed with the ratio between the concentration of Nb and lanthanide in them. All these results open the possibility of obtaining a new self-doubling material.

Synthesis and characterization of chiral main chain polyesters with polar segments tailored for second harmonic generation

The synthesis, characterization and solvatochromic behavior of a new series of chiral polyesters are reported. These polymers with π-conjugated donor-acceptor segments were synthesized with a view to be suitable for second harmonic generation. The polyesters were prepared by the reaction of diacid chlorides with biphenolic azo chromophores with Λ-conformation and optically active dihydroxy compound (isosorbide). The polymers containing isosorbide units are optically active. They showed Tg between 100°C to 160°C and are stable up to 400°C. A red shift in the longer wavelength absorption band of these polymers in UV-Vis. absorption spectra (positive solvatochromism) shows that the dipole moment of excited state is higher than that of the ground state. Therefore these polyesters are expected to have good second harmonic generation capability.