Optical Crystals Research Articles

Infrared nonlinear optical materials with multiple strongly ionic cations

Infrared nonlinear optical (IR-NLO) crystals with excellent properties are in extensive demand due to their important role in IR laser technology. Currently, it remains a great challenge to obtain IR-NLO materials with both high second harmonic generation (SHG) response and large laser-induced damage thresholds (LIDTs). Some structural design strategies such as ‘structural/functional regions’ have been adopted to develop new high-performance NLO materials. The covalent structural region producing SHG signals has been extensively investigated, whereas the hard cations (alkali, alkaline-earth, and rare-earth metal ions) which are responsible for improving LIDTs, have been relatively neglected. Utilizing the concept of structural/functional regions, we focus on the relation between structural regions and SHG properties in chalcogenides. Combining different kinds of hard cations can change the dimension of structures and affect the stacking of NLO-active groups. Introducing more hard cations and constructing more complex ion regions help to increase the laser damage threshold. Based on the mentioned structural strategies, guidance will be provided for developing high-performance multiple-cation materials for IR NLO applications.

A New Criterion for Determining Optical Damage of Nonlinear Optical Crystals, Based on the Use of an RF Oscillator Circuit

A New Criterion for Determining Optical Damage of Nonlinear Optical Crystals, Based on the Use of an RF Oscillator Circuit

A perspective on deep-ultraviolet nonlinear optical materials

Deep ultraviolet (DUV) nonlinear optical (NLO) crystals have important applications in lithography, microfabrication, and high-resolution photoelectric spectrometer. In recent years, significant progress has been made in both the theoretical design and experimental research of DUV NLO crystals. This review aims to offer a comprehensive perspective on exploring a new generation of DUV NLO materials. First, we summarize various computer-aided strategies for crystal structure design and emphasize their significant role in advancing the discovery of DUV NLO materials. Then, we outline several representative DUV crystals of experimental synthesis. Finally, we discuss the future prospects for exploring new generations of DUV NLO materials. We believe that employing data-driven, computer-aided methods to explore DUV NLO materials will help address the current challenges in the field of DUV NLO materials research. The close integration of calculation and experimentation will unlock new opportunities.

Giant enhancement of second harmonic generation via merging bound states in the continuum for vacuum ultraviolet radiation

Vacuum ultraviolet (VUV) light plays a crucial role in various scientific and technological fields, such as nanolithography and biomedical treatments. However, the inherent nonlinear optical coefficient of nonlinear optical crystals is typically very low, and increasing the action length is often necessary to improve the nonlinear conversion efficiency. This makes it challenging for these materials to achieve high-density optoelectronic integration at the micro-/nano-scale. In this study, we propose a design for generating coherent VUV radiation close to 175 nm using second harmonic generation (SHG) with an absolute efficiency exceeding 1.2‰ mW−1. This is achieved by merging multiple bound state in the continuum modes in a free-standing photonic crystal slab. Even with fabrication imperfections at a level lower than 10% disorder, the SHG efficiency of the samples remains robust, maintaining an efficiency of at least 2‰. This research provides a beneficial platform for generating efficient VUV light in the nanoscale.

A comparative study of second order Non-linear optical crystals derived from chloro- and dichloro- aniline

Followed by one-pot mechanism Schiff base products derived from the substituted anilines are crystallized by the slow-evaporation technique. Both crystals are characterized by FT-IR, 1H NMR and 13C NMR spectral studies. Single crystal XRD analysis provides data of both crystals and it is well fitted with NMR and IR spectral results. The obtained results of IR frequencies and NMR chemical shifts are compared with theoretical predicted results obtained from DFT method. The energy gap Eg was calculated by HOMO and LUMO and other theoretical parameters are determined by using DFT method with B3LYP/6–311++ G (d,p) basis set and the energy gap is very small 3.59, 3.52 eV for PCA and DCA crystals. The supramolecular investigation of crystal structure explained by Hirshfeld analysis. Using quantum computations techniques, the topological parameters LOL and ELF, scatter graph and diagram of the crystals was the further characterization. The first order hyperpolarizability (β0) was calculated by B3LYP/6–311++ G (d,p) basis set. Using the Kurtz-Powder technique, the second order Non-linear optical activity of the crystal was obtained. Based upon these crystals, which are outstanding Nonlinear optical activity material and best for the laser safety devices.

Crystal growth, structure, spectral and thermal properties of ScxY1-xCOB single crystals

Yttrium calcium oxyborate (YCOB) crystals are excellent nonlinear optical crystals. To enhance the thermal properties of YCOB crystal, Sc-doped YCOB crystals, denoted as ScxY1-xCa4O(BO3)3 (x = 0.1 and 0.2) were grown using the Czochralski method along the b-direction. Various measurements, including X-ray powder diffraction, rocking curve analysis, inductively coupled plasma-optical emission spectroscopy (ICP-OES), transmission spectroscopy, density measurements, and thermal property assessments, were conducted to evaluate the characteristics of the ScxY1-xCOB crystals. The results indicated that ScxY1-xCOB crystals have an isostructural arrangement like YCOB, with segregation coefficients of approximately 0.2. The full width at half maximum (FWHM) values of the rocking curves of the ScxY1-xCOB (x = 0.1 and 0.2) crystals are 33.9″ and 29.3″, respectively. Furthermore, the specific heat, thermal diffusion coefficients and thermal conductivity of the ScxY1-xCOB crystals were examined in the temperature range of 298–573 K, which were found to be higher than those of pure YCOB. These high-quality ScxY1-xCOB crystals are expected to serve as suitable nonlinear optical crystals media for optical parametric chirped pulse amplification (OPCPA) applications.

An inorganic liquid crystalline dispersion with 2D ferroelectric moieties.

Electro-optical effect-based liquid crystal devices have been extensively used in optical modulation techniques, in which the Kerr coefficient reflects the sensitivity of the liquid crystals and determines the strength of the device's operational electric field. The Peterlin-Stuart theory and the O'Konski model jointly indicate that a giant Kerr coefficient could be obtained in a material with both a large geometrical anisotropy and an intrinsic polarization, but such a material is not yet reported. Here we reveal a ferroelectric effect in a monolayer two-dimensional mineral vermiculite. A large geometrical anisotropy factor and a large inherent electric dipole together raise the record value of Kerr coefficient by an order of magnitude, till 3.0×10-4mV-2. This finding enables an ultra-low operational electric field of 102-104Vm-1 and the fabrication of electro-optical devices with an inch-level electrode separation, which has not previously been practical. Because of its high ultraviolet stability (decay <1% under ultraviolet exposure for 1000 hours), large-scale production, and energy efficiency, prototypical displayable billboards have been fabricated for outdoor interactive scenes. This work provides new insights for both liquid crystal optics and two-dimensional ferroelectrics.

Soaking the Rare-Earth Carbonates for a Change: An Alternative Approach to Explore Carbonate Nonlinear Optical Crystals.

Alkali-metal rare-earth carbonates (ARECs) find great potential in nonlinear optical applications. As the most common method, the hydrothermal reaction is widely used in synthesizing ARECs. The black-box nature of the hydrothermal reaction makes it difficult for understanding the formation processes and therefore may slow down the pace of structural discovery. Here, by simply soaking the rare-earth carbonates in Na2CO3 solutions, we successfully obtain a series of noncentrosymmetric Na3RE(CO3)3·6H2O (RE = Tb 1, Sm 2, Eu 3, Gd 4, Dy 5, Ho 6, and Er 7) compounds without using the high-temperature hydrothermal method. The transformation process, investigated by powder X-ray diffraction and scanning electron microscopy, is governed by the concentration of the soaking solutions. Na3Tb(CO3)3·6H2O, as an example, is studied structurally, and its physical properties are characterized. It exhibits a second harmonic generation effect of 0.5 × KDP and a short UV cutoff edge of 222 nm (5.8 eV). Our study provides insights for exploring new AREC structures, which may further advance the development of carbonate nonlinear optical crystals.

Vison crystal in quantum spin ice on the breathing pyrochlore lattice

Recent excitement in the quantum spin ice (QSI) community has come from the experimental discovery of pseudospin-12 breathing pyrochlores, including Ba3Yb2Zn5O11, in which inversion symmetry is broken by the “up” and “down” tetrahedra taking different physical sizes. We show here that the often-neglected Jz± coupling between Kramers ions, in combination with the breathing nature of the lattice, can produce an imaginary ring flip term. This can lead to an unconventional “U(1)π/2 phase”, corresponding to a maximally dense packing of visons on the lattice. The coherent, emergent QED dynamics of conventional QSI persist in this phase, in a manner reminiscent of fragmentation in spinon crystals. We characterize the excitations of the system within the enlarged QSI phase diagram, showing that the imaginary ring flip acts both as a chemical potential for visons and as an effective three-photon vertex akin to strong light-matter coupling. The coupling causes a structured high-energy continuum to emerge above the photon dispersion, which is naturally interpreted as three photon up-conversion in a nonlinear optical crystal. Published by the American Physical Society 2024

Theoretical Understanding of Nonlinear Optical Properties in Solids: A Perspective.

Nonlinear optical (NLO) crystals have become a hot topic in chemical science and material physics, due to their essential role in laser technology, optical information, optoelectronics, and precision measurements. In this Perspective, we provide an overview of recent advances in second-order nonlinear optics, with a focus on two critical topics: second harmonic generation (SHG) and the bulk photovoltaic effect (BPVE). For SHG, we discuss recent progress in deep-ultraviolet (DUV) materials, highlighting their structural characteristics and nonlinear groups that contribute to their exceptional performance. For BPVE, we concentrate on the emerging field of low-dimensional materials, emphasizing their potential in a shift current. Additionally, we discuss the development of regulation approaches for NLO materials, which is vital for their practical application. Finally, we address the outlook for the field, including the challenges that must be overcome to further advance NLO materials research.

High-repetition-rate injection-seeded terahertz-wave parametric generation pumped by a 1.5 μm sub-nanosecond laser

Injection-seeded terahertz (THz)-wave parametric generation (is-TPG) using a nonlinear optical crystal of MgO-doped lithium niobate (MgO:LiNbO3) has made it possible to obtain THz waves with high peak powers and narrow linewidths. To achieve stable THz-wave generation from the MgO:LiNbO3 crystal under strong excitation, the photorefractive effect in the MgO:LiNbO3 crystal would be crucial, which could be eliminated by using a longer pump wavelength than the conventional 1-μm spectral band. Here, we propose to use a 1.5-μm near-infrared (NIR), high-repetition-rate, sub-nanosecond laser source based on a unique Er,Yb:glass planar waveguide amplifier (PWA) as the pump source for the is-TPG using the MgO:LiNbO3 crystal. At a repetition rate of 25 kHz, the frequency tunability from 1.3 to 2.5 THz was obtained with a maximum THz-wave average output power of 0.14 mW at 1.77 THz.

A2Pb3[H2N(CH2COO)2]3Cl5 (A = K, Rb): Porous Crystals Constructed on [Pb3Cl5O6] Clusters with Comprehensive Nonlinear Optical Performance

AbstractNonlinear optical (NLO) crystals that can extend the frequency range of coherent light have significant applications in laser technology, semiconductor manufacturing, and lithography. Herein, two interesting NLO crystals, A2Pb3[H2N(CH2COO)2]3Cl5 (A = K, Rb), are rationally obtained. Their porous structures are constructed on [Pb3Cl5O6] clusters that possess large hyperpolarizability and polarizability anisotropy, and are arranged in a parallel manner. Remarkably, A2Pb3[H2N(CH2COO)2]3Cl5 (A = K, Rb) exhibits comprehensive NLO performance, including strong phase‐matching second‐harmonic generation (SHG) response, the widest bandgap among lead oxychloride NLO crystals, larger laser damage threshold than 127 MW cm−2, suitable birefringence of 0.11@1064 nm, high thermal stability, non‐deliquescence, as well as facile crystal growth. Theoretical calculations and structural analysis demonstrate that their strong SHG response is predominantly originated from the [Pb3Cl5O6] cluster. This study will provide a unique method for the discovery of new interesting NLO crystals in future.

(C8H6BrN2O)NO3: A Hybrid Nonlinear Optical Crystal With an Appropriate Birefringence

AbstractOrganic planar groups have recently been used to construct nonlinear optical materials because of their large hyperpolarizability, and then most of the products have birefringence which is unfavorable to phase matching. Here, a new organic–inorganic hybrid nonlinear optical crystal (C8H6BrN2O)NO3 is synthesized by combining the π‐conjugated organic [C8H6BrN₂O]+ cation and inorganic [NO3]− anion as the fundamental building blocks. Surprisingly, it not only shows a large second‐harmonic generation response of 3.8 times that of the commercial K2HPO4 crystals, but also has a moderate birefringence of 0.08 at 550 nm. Furthermore, it demonstrates high thermal stability up to 220 °C despite its hybrid material characteristics. Single crystal structure analysis and theoretical calculations confirm that the specific arrangement of NLO‐active [C8H6BrN₂O]+ groups with halogen branch chains and strong hydrogen bonding between two π‐conjugated groups leads to moderate birefringence and large frequency‐doubling effect. These findings provide a method to explore hybrid nonlinear optical crystals.

Rational Combination of π-Conjugated and Non-π-Conjugated Groups Achieving Strong Nonlinear Optical Response, Large Optical Anisotropy, and UV Light-Switchable Fluorescence.

Combining π-conjugated and non-π-conjugated groups is an important strategy for synthesizing new nonlinear optical (NLO) crystals. However, the second harmonic generation (SHG) response and optical anisotropy can be limited by improper spatial alignment of these functional groups in the crystal structure. In this work, it is revealed that non-π-conjugated [NH2SO3] group acts as both hydrogen bond donor and acceptor, effectively regulating the 2D planar structure formed by π-conjugated [C4N3H6] groups. The resulting organic-inorganic hybrid crystal C4N3H6SO3NH2 exhibits a strong SHG response (2.5 × KDP), large optical anisotropy (0.233@546nm), and blue-violet and green fluorescence near 360 and 520nm, respectively. This work expands the methodology for creating new NLO crystals through organic-inorganic hybridization, while also showcasing the potential of C4N3H6SO3NH2 as a multifunctional optical material.

Growth, mechanical, thermal, electrical, linear, and nonlinear optical studies of urea resorcinol single crystals for NLO applications

Urea Resorcinol (UR) was synthesized and grown using the slow cooling technique to form a possible organic nonlinear optical crystal. Single crystal X-ray diffraction analysis was used to determine the shape and lattice characteristics of the generated UR crystals. The crystallinity was verified using a high-resolution X-ray diffraction examination. The emission and transparency of the formed crystal were revealed by optical studies including photoluminescence and UV–visible-NIR spectrum analyses. Through the use of an optical microscope and the Vickers microhardness tester, its mechanical behavior was investigated and the density of its etch pits was estimated. The investigations were also conducted on the UR crystal's microphysical properties, including its dielectric tensor, dielectric loss, and thermal analysis. An Nd:YAG laser was used to quantify the laser-induced surface damage and the results were connected to the grown crystal's specific heat capacity. By using the Kurtz and Perry technique, the efficiency of second harmonic generation was determined for different UR crystal particle sizes that have good phase matchability, and its SHG output was compared to urea.

Anisotropic Strain-Tailoring Nonlinear Optical Response in van der Waals NbOI2.

Two-dimensional (2D) NbOI2 demonstrates significant second-harmonic generation (SHG) with a high conversion efficiency. To unlock its full potential in practical applications, it is desirable to modulate the SHG behavior while utilizing the intrinsic lattice anisotropy. Here, we demonstrate direction-specific modulation of the SHG response in NbOI2 by applying anisotropic strain with respect to the intrinsic lattice orientations, where more than 2-fold enhancement in the SHG intensity is achieved under strain along the polar axis. The strain-driven SHG evolution is attributed to the strengthened built-in piezoelectric field (polar axis) and the enlarged Peierls distortions (nonpolar axis). Moreover, we provide quantifications of the correlation between strain and SHG intensity in terms of the susceptibility tensor. Our results demonstrate the effective coupling of orientation-specific strain to the anisotropic SHG response through the intrinsic polar order in 2D nonlinear optical crystals, opening a new paradigm toward the development of functional devices.

Crystal growth and characterization of glycine chlorzoxazone nonlinear optical crystal for energy storage capacitor applications

This research presents the synthesis of a glycine chlorzoxazone (GC) organic single crystal through a slow evaporation process using a mixed solvent of water and ethanol at room temperature. The crystal's functional group coordination is examined via fourier-transform infrared (FTIR) spectroscopy. The study delves into the linear optical properties through UV–visible spectroscopy, and thermal analyses provide insights into the material's thermal behavior. Optical nonlinearity is confirmed using the Kurtz-Perry powder technique. The investigation extends to the electrical properties of prepared crystals, incorporating a combination of AC and DC electrical studies. This comprehensive approach enhances our understanding of the multifaceted characteristics of synthesized crystal, positioning it as a promising candidate for different electronic and optical applications.

Growth, DFT, spectroscopic analysis, third-order NLO properties and optical limiting behavior of Bis(p-aminobenzoic acid-N) dichloro cadmium (II) (BPANDC) crystal

A new organic nonlinear optical crystal, Bis(p-aminobenzoic acid-N) dichloro cadmium (II) (BPANDC) has been grown by Slow Evaporation Solution Technique (SEST). The experiments were carried out to study the structural, optical, DFT and nonlinear optical properties of the grown crystals. The BPANDC crystal belongs to triclinic system with space group Pī with lattice parameters a = 6.359(4)Å, b = 7.509(11)Å, c = 17.263(7)Å, α= 94.50(2)˚, β=104.56(2)˚, γ=96.79(4)˚, and volume V = 787.20Å3. Using the TD-DFT method, the electronic absorption spectra of BPANDC was calculated in gas phase. The calculated FT-IR, FT-Raman spectrum, Molecular geometrical analysis, TD-DFT, HOMO–LUMO energy gap and Molecular electrostatic potential surface of BPANDC were calculated by DFT/ LANL2DZ basis set. The Z-scan analysis evidenced that the BPANDC exhibits sequential two-photon absorption induced reverse saturable absorption.

First-principles screening of metal–organic frameworks for entangled photon pair generation

The transmission of strong laser light in nonlinear optical materials can generate output photons sources that carry quantum entanglement in multiple degrees of freedom, making this process a fundamentally important tool in optical quantum technology. However, the availability of efficient optical crystals for entangled light generation is severely limited in terms of diversity, thus reducing the prospects for the implementation of next-generation protocols in quantum sensing, communication and computing. To overcome this, we developed and implemented a multi-scale first-principles modeling technique for the computational discovery of novel nonlinear optical devices based on metal–organic framework (MOF) materials that can efficiently generate entangled light via spontaneous parametric down-conversion (SPDC). Using collinear degenerate type-I SPDC as a case study, we computationally screen a database of 114 373 synthesized MOF materials to establish correlations between the structure and chemical composition of MOFs with the brightness and coherence properties of entangled photon pairs. We identify a subset of 49 non-centrosymmetric mono-ligand MOF crystals with high chemical and optical stability that produce entangled photon pairs with intrinsic G(2) correlation times τc∼10−30 fs and pair generation rates in the range 104−1010s−1mW−1mm−1 at 1064 nm. Conditions for optimal type-I phase matching are given for each MOF and relationships between pair brightness, crystal band gap and optical birefringence are discussed. Correlations between the optical properties of crystals and their constituent molecular ligands are also given. Our work paves the way for the computational design of MOF-based devices for optical quantum technology.

Experimental and theoretical interpretations of structural, optical, mechanical and thermal properties of 2-aminopyridinium phthalate single crystals

Nonlinear optical good quality single crystals of 2-aminopyridinium phthalate single crystals are synthesized by solution growth technique. Structural parameters are elucidated by Single Crystal X-ray diffraction method which reveals that the material crystallizes in non-centrosymmetric crystalline framework. Vibrational assignments are interpreted by Fourier Transform Infrared spectral analysis. The thermal, mechanical and laser stability are explored by TG/DTA, microhardness and Laser Damage threshold analysis. The material has good emission nature in the violet emission region. The linear optical properties are elucidated with the help of UV–visible spectral analysis. The intermolecular charge transfer interactions are analyzed by HOMO-LUMO and MESP maps by using Gaussian ’09 software program. The second harmonic generation efficiency of the synthesized material are predicted by Kurtz Perry powder technique.