Optical Crystals Research Articles

Crystal Growth, Characterization, and Properties of Nonlinear Optical Crystals of Li0.5Ag0.5GaTe2 for Mid-Infrared Applications.

LiGaTe2 is a promising nonlinear optical crystal with a large figure of merit (d362/n3), but it is difficult to grow the LiGaTe2 single crystal due to its extreme instability. In this work, we used Ag to replace Li and successfully grew a Li0.5Ag0.5GaTe2 crystal by the modified Bridgman method for the first time. We found it has thermal stability below 200 °C in an atmospheric environment, and the thermal expansion coefficient is positive. This is different from LiGaTe2 and AgGaTe2 which have a negative thermal expansion coefficient along the c-axis. When the temperature exceeds 200 °C, Li0.5Ag0.5GaTe2 is easily decomposed and oxidized. Under closed vacuum conditions, the melting and solidifying points of Li0.5Ag0.5GaTe2 are measured to be 719 and 694 °C. XPS spectra show that the binding energies of Li, Ga, and Te are higher than LiGaTe2, and the surface is easily oxidized. The A1 vibration modes are found at 117.72 and 135.44 cm-1 by the Raman spectrum which is related to the Te and Ga-Te bond in [GaTe4]5- tetrahedra. Li0.5Ag0.5GaTe2 has a wide transmittance range from 0.94 to 20 μm, and there was two-photon absorption near 16 μm. The phonon spectrum and PDOS were simulated by the DFT calculation to study the phonon vibration modes in the lattice, which shows that the density of the Raman vibration is higher than those of AgGaTe2 and LiGaTe2. The SHG test results showed that the SHG response intensity of Li0.5Ag0.5GaTe2 is 1.5 times that of AgGaS2, which shows its excellent nonlinear optical properties for mid-IR applications.

Exploiting Deep‐Ultraviolet Nonlinear Optical Material Rb2ScB3O6F2 Originated from Congruously Oriented [B3O6] Groups

AbstractThe exploration and research for deep‐ultraviolet (UV) nonlinear optical (NLO) crystals are of great significance for all‐solid‐state lasers. This work is based on the excellent structural [B3O6] units which manipulate the excellent performances of famous commercial NLO crystal β‐BaB2O4 (β‐BBO) to explore new alternatives of deep‐UV NLO materials. A deep‐UV rare‐earth metal borate fluoride Rb2ScB3O6F2 (RSBF) is successfully designed by combining the heterovalent ions substitution strategy, and fluorination strategy. Expectedly, RSBF exhibits an extremely short cutoff edge below 175 nm (189 nm for β‐BBO), and a moderate birefringence of 0.088 at 1064 nm. The shortest phase‐matching (PM) wavelength of RSBF (λPM=182 nm) is shortened by 23 nm compared with β‐BBO (λPM=205 nm) due to the improvements in the chromatic dispersion and cutoff edge, and an experimental frequency‐doubling effect 1.4×KH2PO4 (KDP) further suggests that RSBF can output a deep‐UV harmonic laser. This work provides new sights from the original influencing factors for the rational and purposeful design of deep‐UV NLO materials.

Exploiting Deep-Ultraviolet Nonlinear OpticalMaterial Rb2ScB3O6F2 Originated from Congruously Oriented [B3O6] Groups.

The exploration and research for deep-ultraviolet (UV) nonlinear optical (NLO) crystals are of great significance for all-solid-state lasers. This work is based on the excellent structural [B3O6] units which manipulate the excellent performances of famous commercial NLO crystal β-BaB2O4 (β-BBO) to explore new alternatives of deep-UV NLO materials. A deep-UV rare-earth metal borate fluoride Rb2ScB3O6F2 (RSBF) is successfully designed by combining the heterovalent ions substitution strategy, and fluorination strategy. Expectedly, RSBF exhibits an extremely short cutoff edge below 175 nm (189 nm for β-BBO), and a moderate birefringence of 0.088 at 1064 nm. The shortest phase-matching (PM) wavelength of RSBF (λPM=182 nm) is shortened by 23 nm compared with β-BBO (λPM=205 nm) due to the improvements in the chromatic dispersion and cutoff edge, and an experimental frequency-doubling effect 1.4×KH2PO4 (KDP) further suggests that RSBF can output a deep-UV harmonic laser. This work provides new sights from the original influencing factors for the rational and purposeful design of deep-UV NLO materials.

Investigating novel optical soliton solutions for a generalized (3+1)-dimensional q-deformed equation

In this study, we investigate the (3+1) q-deformed tanh-Gordon equation due to its importance in the context of mathematical physics. It describes solitonic solutions in quantum field theory; it can sometimes be used in condensed matter physics to describe interactions between particles in magnetic materials or superconductors; it can model light propagation in nonlinear optical fibers or photonic crystals where the refractive index has a q-deformed structure; and it also can be applied in studying shock waves, turbulence and rogue waves where the deformation introduces corrections to classical wave phenomena. Utilizing the (G′ωG′+G+r)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(\\frac{{\\mathfrak {G}}^{\\prime }}{\\omega {\\mathfrak {G}}^{\\prime }+{\\mathfrak {G}}+r})$$\\end{document}-expansion technique, we derive novel analytical solutions that enhance our understanding of the underlying dynamics. Additionally, we employ a finite element method (extended cubic B-spline method) to validate our analytical findings and explore the behavior of the q-deformed equation under different parameter regimes. Our results demonstrate the versatility of the q-deformed framework in generating rich optical phenomena, paving the way for future research in both theoretical and applied physics.

Improvement of angle measurement sensitivity using second harmonic wave interference

This paper presents the angular displacement measurement based on second harmonic generation (SHG). In our previous study, the angular resolution of sub-arcsecond was achieved. In this paper, three kinds of sensors based on SHG are reported. In these three sensors, the angular displacement is determined from the intensity of the SHG signal since the SHG is sensitive to the angle of the incident light. Two of these sensors in this study utilize the interference of SHG to improve the sensitivity performance. Comparing with the sensors which have been studied before, interference type sensors in this study allow the femtosecond laser to pass through the nonlinear optical crystal twice, which leads to a significant sensitivity improvement. The principles were verified by both simulation and experiment. In the simulation part, the sensitivities of these three kinds of sensors are compared. In the experiment, the sensitivities were confirmed to be consistent with the simulation. Additionally, the resolution of the presented systems is evaluated and sub-0.1-arcsecond is achieved.

Development of crystal optics for X-ray multi-projection imaging for synchrotron and XFEL sources.

X-ray multi-projection imaging (XMPI) is an emerging experimental technique for the acquisition of rotation-free, time-resolved, volumetric information on stochastic processes. The technique is developed for high-brilliance light-source facilities, aiming to address known limitations of state-of-the-art imaging methods in the acquisition of 4D sample information, linked to their need for sample rotation. XMPI relies on a beam-splitting scheme, that illuminates a sample from multiple, angularly spaced viewpoints, and employs fast, indirect, X-ray imaging detectors for the collection of the data. This approach enables studies of previously inaccessible phenomena of industrial and societal relevance such as fractures in solids, propagation of shock waves, laser-based 3D printing, or even fast processes in the biological domain. In this work, we discuss in detail the beam-splitting scheme of XMPI. More specifically, we explore the relevant properties of X-ray splitter optics for their use in XMPI schemes, both at synchrotron insertion devices and XFEL facilities. Furthermore, we describe two distinct XMPI schemes, designed to faciliate large samples and complex sample environments. Finally, we present experimental proof of the feasibility of MHz-rate XMPI at the European XFEL. This detailed overview aims to state the challenges and the potential of XMPI and act as a stepping stone for future development of the technique.

Anisotropic Laser Performance in an Optically Isotropic Crystal by Phonon Engineering

Symmetry is an eternal motif in understanding the characteristics of nearly all the laws and courses of science. The symmetry‐breaking in the optical crystal will generate a rich variety of unprecedented physical phenomena and create new functional properties. Herein, the symmetry‐breaking in a photon–phonon collaboratively pumped laser, dominated by the anisotropic lattice vibrations is investigated. Using an optically isotropic Nd:YAG crystal as an example, the phonon‐assisted electronic transitions accompanied by anisotropic fluorescence emission are observed, beyond the intrinsic structural symmetry ruled by Neumann's principle. For the first time, the phonon‐assisted new‐wavelength lasers at 1151 and 1166 nm are achieved in Nd:YAG with divergent light polarization, determined by the vibrational direction of involved phonons. These results provide a flexible degree of freedom for photonics by phonon engineering and pave the way to new frontiers in the field of laser generation and manipulation.

Structure and optical properties of alkali rare-earth double phosphates of M3RE(PO4)2 (M = K, Rb; RE = Y, La, and Lu)

Designing and synthesizing phosphate nonlinear optical materials with novel structures and excellent properties remains challenging. In this work, the electronic structure and optical properties (second harmonic generation (SHG) response or birefringence) of alkali rare-earth double phosphates M3RE(PO4)2 (M = K, Rb; RE = Y, La, and Lu) are systematically investigated. It is worth mentioning that P31m-Rb3Lu(PO4)2 was successfully synthesized by a flux-method, and the UV–vis–NIR diffuse reflectance spectroscopy showed that Rb3Lu(PO4)2 exhibits a short absorption edge at 207 nm and a high transmittance of 77.9 %. Based on first-principles calculations, the results show that the birefringence of the M3RE(PO4)2 series of crystals exhibits significant differences (0.009-0.028@1064 nm). Subsequently, analysis of the electronic structure and the real-space atom cutting method reveals that rare-earth polyhedra play a major role in enhanced birefringence. Overall, this work enriches the study of nonlinear optical crystals of rare earth phosphates and provides a case for further exploration.

Structural design and characterization of a new type of organic nonlinear optical flavanone crystal

Two new crystals were designed and obtained: the chalcone derivative HMMP (1-(2‑hydroxy-4-methoxyphenyl)-3-(4-(methylthio)phenyl)prop‑2-en-1-one) and the flavanone derivative 7M4MC (7‑methoxy-2-(4-(methylthio)phenyl)chroman-4-one). Yellow bulk 7M4MC single crystal with dimensions of 3 × 2 × 1 mm3 and orange-yellow needle-like HMMP single crystal were grown by solution evaporation. 7M4MC crystal belongs to the P21 space group of the monoclinic structure, which has a non-centrosymmetric structure. HMMP crystal monoclinic, belongs to the P21/m space group with a centrosymmetric structure. In the 7M4MC molecule, the methoxy and methylthio groups act as electron donors (D) and the carbonyl group acts as an electron acceptor (A), forming a d-π-A-π-D structure with an electron gradient. 7M4MC exhibits a high degree of second-harmonic generation intensity (11 × KDP), a broad transmission range (600–1600 nm, >88 %), an elevated optical energy bandgap (Eg = 2.57 eV), high thermal stability (Tm = 105 °C) and excellent dielectric properties (εr ≈ 2.1). This work not only provides two new crystals but also offers a viable molecular design option by changing the degree of intramolecular distortion by altering the backbone structure.

Nonlinear optical cyanurate crystals

The exploration of ultraviolet (UV) nonlinear optical (NLO) crystals is of great significance in various fields, such as optical communication, medical diagnosis, deep space exploration and optical digital signal processing. Accordingly, cyanurates attracted widespread attention due to their strong second-harmonic-generation (SHG) effects, large birefringence for phase-matching, short UV cutoffs, high solar blind transmittances and easy crystal preparations. This article reviews the optical properties of so far reported cyanurate NLO crystals, describes the preparation approaches of cyanurates, compares their structures to further analyze the source of their large SHG effect, and provides some insights for designing and synthesizing new UV cyanurates in the future.

Constructing Broadband THz Optical Crystals by Extending the Length of the Alkyl Chain

Constructing Broadband THz Optical Crystals by Extending the Length of the Alkyl Chain

Investigations on the growth, spectral, optical, electrical, thermal and nonlinear optical properties of L-valine itaconic acid single crystal

A nonlinear optical single crystal of L-Valine Itaconic Acid (LVIA) was grown at room temperature from an aqueous solution by using the slow evaporation method. The grown crystal was undergone X-ray diffraction investigation, which confirm that the crystal belongs to orthorhombic system with the non-centro symmetric Pbca space group. This single crystal contains several functional groups, according to FTIR spectroscopic analysis there were identified. By analyzing the crystal's UV–visible spectrum, based on its optical transparency this crystal may use for optoelectronic device manufacturing. The emission happens at 553 nm wavelength, according to the photoluminescence spectrum. Thermo gravimetric and differential thermal analytical studies helps us to measure title crystal melting point and thermal stability. At various temperatures, the dielectric property of the crystal was found out. The Kurtz-powder method has been used to study the phenomenon of Second Harmonic Generation (SHG) in the crystal.

Optical Activities of Organic Crystals: Crystal Orbital Formulation of Anisotropic Gyration.

To describe the optical activities of crystals, gyration tensors are necessary for all wavelengths of incident light. To date, few studies on direct calculations of gyration tensors from Bloch states have been conducted. Herein, a practical procedure to obtain gyration tensors of organic crystals is presented using the crystal orbital method. The extended Hückel method was adopted to evaluate the gyration tensors, epitomizing the one-electron formulation. To confirm the validity of the formulation, the optical rotatory power of alanine and γ-glycine was examined. The reproduced profiles of the optical rotatory power were consistent with the results of recent experiments. This is a general formulation of the one-electron theory of optical activities for three-dimensional crystals. In principle, the optical rotatory strength tensor is not invariant with translation. For systems with small unit cells, however, the formalism is quasi-invariant with respect to translation. The quasi origin-independent formalism is sufficiently substantial to be applicable to modern crystal optics.

Study of Characteristics of Fluorescent Optical Crystals of Multi-Leaf Collimator of Linear Electron Accelerator By Electa Synergy for the Purpose of the Possible Import Substitution

Study of Characteristics of Fluorescent Optical Crystals of Multi-Leaf Collimator of Linear Electron Accelerator By Electa Synergy for the Purpose of the Possible Import Substitution

Extending mid-infrared wavelength to 6.84 μm in oxide nonlinear optical crystal via birefringence dispersion management.

Extending lasing wavelengths to the mid-infrared (MIR) spectrum is vital for both civilian and military applications; however, it remains challenging when employing oxide nonlinear optical crystals. In this study, we report the generation of MIR nanosecond pulses via difference frequency generation (DFG) with a near-IR pump using a newly designed langasite (LGS) crystal, La3(Nb0.6Ta0.4)0.5Ga5.5O14 (LGNT0.4), which incorporates birefringence dispersion management techniques with La3Ga5.5Nb0.5O14 (LGN) as a template. Due to the improved effective nonlinear coefficients and the maintained IR cutoff relative to LGN, the tunable DFG laser in LGNT0.4 extended from 4.24 to 6.84 μm, delivering a maximum pulse energy of 16.3 μJ at 5.02 μm. To the best of our knowledge, this is the first known oxide material capable of generating tunable nanosecond pulsed lasers beyond 6 μm at μJ-level energies, demonstrating promising potential for high-intensity MIR laser systems owing to its high laser damage threshold.

Constructing Ultraviolet Nonlinear Optical Crystals with Superior Thermal Stability Based on Organic π-Conjugated [HCOO] Groups.

In recent years, more and more organic π-conjugated moieties have been screened out to create excellent ultraviolet (UV) and deep-UV nonlinear optical (NLO) crystal materials. However, NLO crystals with organic groups usually exhibit poor thermal stability compared with those of traditional inorganic NLO materials. Herein, the organic group [HCOO], which is similar to traditional planar trigonal π-conjugated anionic groups, was employed to successfully build three UV NLO crystals RE(HCOO)3 (RE = Eu, Gd, and Dy) and two centrosymmetric compounds RE(HCOO)2(OH) (RE = Eu, and Gd) with superior thermal stability. Their structures and properties were further studied and characterized, especially the structure evolutions between noncentrosymmetric RE(HCOO)3 (RE = Eu, Gd, and Dy) and centrosymmetric RE(HCOO)2(OH) (RE = Eu, and Gd), as well as the NLO properties of the three crystals RE(HCOO)3 (RE = Eu, Gd, and Dy).

Polar Thiazole Derivative-Induced Second Harmonic Response in Hybrid Bismuth Chlorate with Reversible Photochromism.

Inorganic-organic hybrid bismuth halides demonstrate great prospect in the field of second-order nonlinear optical (NLO) crystals because the ns2 electron on Bi(III) could lead to large molecular polarization and high second harmonic generation (SHG) coefficient on a noncentrosymmetric structure. However, researchers cannot yet control the effective arrangements of the bismuth halide functional motif, which results in SHG-active hybrid bismuth halides being rare. Herein, thiazole derivatives with a polar donor-π-acceptor system are designed to explore hybrid bismuth halide NLO crystals. The protonated 2-(4-hydroxyphenyl) thiazole (denoted as hpt) interacts with the (BiCl6) motif via H···Cl hydrogen bonds to prevent antiparallel arrangements, which therefore enhance the NLO property. (Hhpt)3[BiCl6] crystallizes in the monoclinic polar P21 space group, which exhibits a strong SHG response and reversible photochromic behavior. Structural analysis and theory calculations reveal that the synergistic effect between the polar thiazole derivative and the distorted inorganic [BiCl6]3- motif is responsible for the SHG response. This is the first report of polar thiazole derivative-induced SHG-active hybrid bismuth halide coupled with reversible photochromism.

Estimation of the Uncertainty in Daytime Cirrus Cloud Radiative Forcing and Heating Rates Due to Ice Crystal Optics

Abstract The uncertainties in absolute daytime top-of-the-atmosphere (TOA) net cirrus cloud radiative forcing (CRF) and radiative heating rates are estimated at five Micro-Pulse Lidar Network (MPLNET) sites spanning the tropics to high-latitudes. One year of semi-transparent cirrus cloud (optical depth < 3.0 and cloud top temperature < −37 °C) measurements are subject to spectrally-consistent optical properties for nine different ice crystal habits, thus providing a range of possible forcing values. The annual average absolute daytime TOA net CRF is positive at Barbados, Kanpur, and, Singapore (0.59–0.67, 0.61–0.65, and 1.94–2.09 W∙m−2, respectively), negative at Fairbanks (−0.67 to −0.28 W∙m−2), and can regularly become positive or negative at Goddard Space Flight Center (GSFC) (−0.06 to 0.32 W∙m−2). The TOA CRF depends on ice crystal shape; in particular, plates lead to relatively large absolute values that decreases for bullet rosettes and columns. Uncertainties in daytime cirrus cloud radiative properties are estimated as the standard deviation of all possible outcomes when considering the different particle habits individually. Annually, the average uncertainty of the absolute daytime TOA net CRF ranges from 0.50–1.80 W∙m−2. In-cloud daytime net radiative heating rates are positive, on average, at all five sites (0.25–3.84 K/day) and have an estimated uncertainty of less than 0.30 K/day. The uncertainties in cirrus radiative forcing and heating that are characterized by assumptions regarding the ice crystal optical properties must be considered in downstream applications, including satellite retrievals and numerical weather prediction.

Broadband THz Wave Generation and Detection in Organic Crystal PNPA at MHz Repetition Rates

AbstractOrganic nonlinear optical (NLO) crystals have emerged as efficient room‐temperature emitters of broadband THz radiation with high electric field strengths. Although initially confined to high‐pulse‐energy excitation in the millijoule range with kHz rates, recent efforts have focused on tailoring the physical properties of organic NLO materials for compatibility with popular MHz‐rate telecommunication wavelength lasers emitting nanojoule energy pulses. This is motivated by the large potential of such crystals for more portable and user‐safe spectroscopic systems, additionally complemented by their room‐temperature field‐sensitive THz detection capabilities. In this work, the MHz‐rate operation of the organic crystal PNPA ((E)‐4‐((4‐nitrobenzylidene)amino)‐N‐phenylaniline), which was recently discovered through data mining algorithms and reported to surpass the conversion efficiency of rivaling NLO crystals at 1 kHz repetition rate is demonstrated. Using a compact 200 mW Er:fiber laser producing 18 fs pulses at 50 MHz repetition rate, the THz field generation and detection capabilities of PNPA via performing gas phase spectroscopy in the 1.3–8.5 THz range are demonstrated. A dynamic range of 40 dB over 3.6 s and 70 dB over 2 h is obtained. The work extends the family of organic crystals compatible with telecommunication‐wavelength excitation using nJ pulses for spectroscopy beyond 5 THz.

Achieving the Birefringence Optimization by Methyl Modulation in Organic Nonlinear Optical Crystals

AbstractNon‐centrosymmetric organics are promising nonlinear optical (NLO) candidates, which always exhibit a short UV absorption cutoff edge, and a strong second harmonic generation (SHG) response, but an overlarge birefringence. Here, in order to optimize the birefringence, the methyl modulation of π‐conjugated organic planar units is proposed and implemented with the urea structure as a template. Thus, N‐methylurea and N,N'‐dimethylurea crystals are obtained by partially replacing hydrogen atoms with methyl groups. This replacement reduces hydrogen donors and weakens interchain hydrogen bonds, which facilitates the decreasing density and the parallel arrangement of π‐conjugated planar units. Hence, both N‐methylurea and N,N'‐dimethylurea crystals exhibit not only an optimized birefringence (N‐methylurea ≈0.099 and N,N'‐dimethylurea ≈0.072 at 546 nm) but also an enhanced SHG response (N‐methylurea ≈1.2 × β‐BaB2O4 and N,N'‐dimethylurea ≈1.9 × β‐BaB2O4), while maintaining a short UV absorption cutoff edge. Therefore, this work provides a novel strategy for the structural design and performance modulation of organic NLO crystals.