Controllable transitions among phase-matching conditions in a single nonlinear crystal

Entangled photon pairs are crucial resources for quantum information processing protocols.Via the process of spontaneous parametric downconversion(SPDC),we can generate these photon pairs using bulk nonlinear crystals.Traditionally,the crystal is designed to satisfy a specific type of phase-matching condition.Here,we report controllable transitions among different types of phase matching in a single periodically poled potassium titanyl phosphate crystal.By carefully selecting pump conditions,we can satisfy different phase-matching conditions.This allows us to observe first-order Type-II,fifth-order Type-I,third-order Type-0,and fifth-order Type-II SPDCs.The temperature-dependent spectra of our source were also analyzed in detail.Finally,we discussed the possibility of observing more than nine SPDCs in this crystal.Our work not only deepens the understanding of the physics behind phase-matching conditions,but also offers the potential for a highly versatile entangled biphoton source for quantum information research.

Inverse design of nonlinear phononic crystal configurations based on multi-label classification learning neural networks

Phononic crystals,as artificial composite materials,have sparked significant interest due to their novel characteristics that emerge upon the introduction of nonlinearity.Among these properties,second-harmonic features exhibit potential applications in acoustic frequency conversion,non-reciprocal wave propagation,and non-destructive testing.Precisely manipulating the harmonic band structure presents a major challenge in the design of nonlinear phononic crystals.Traditional design approaches based on parameter adjustments to meet specific application requirements are inefficient and often yield suboptimal performance.Therefore,this paper develops a design methodology using Softmax logistic regression and multi-label classification learning to inversely design the material distribution of nonlinear phononic crystals by exploiting information from harmonic transmission spectra.The results demonstrate that the neural network-based inverse design method can effectively tailor nonlinear phononic crystals with desired functionalities.This work establishes a mapping relationship between the band structure and the material distribution within phononic crystals,providing valuable insights into the inverse design of metamaterials.

Compact generation scheme of path–frequency hyperentangled photons using 2D periodical nonlinear photonic crystal

Hyperentanglement is a promising resource for achieving high capacity quantum communication.Here,we propose a compact scheme for the generation of path-frequency hyperentangled photon pairs via spontaneous parametric down-conversion(SPDC)processes,where six different paths and two different frequencies are covered.A two-dimensional periodicalχ^((2))nonlinear photonic crystal(NPC)is designed to satisfy type-Ⅰquasi-phase-matching conditions in the plane perpendicular to the incident pump beam,and a perfect phase match is achieved along the pump beam's direction to ensure high conversion efficiency,with theoretically estimated photon flux up to 2.068×10^(5) pairs·s^(-1)·mm^(-2).We theoretically calculate the joint-spectral amplitude(JSA)of the generated photon pair and perform Schmidt decomposition on it,where the resulting entropy S of entanglement and effective Schmidt rank K reach 3.2789 and 6.4675,respectively.Our hyperentangled photon source scheme could provide new avenues for high-dimensional quantum communication and high-speed quantum information processing.

Ultra-broadband near-infrared NOPAs based on the nonlinear crystals Bi BO and YCOB

We evaluate and demonstrate ultra-broadband near-infrared noncollinear optical parametric amplification in two nonlinear crystals,bismuth borate(Bi BO)and yttrium calcium oxyborate(YCOB),which are not commonly used for this application.The spectral bandwidth is of the microjoule level;the amplified signal is≥200 nm,capable of supporting sub-10 fs pulses.These results,supported by numerical simulations,show that these crystals have a great potential as nonlinear media in both low-energy,few-cycle systems and high peak power amplifiers for terawatt to petawatt systems based on noncollinear optical parametric chirped pulse amplification(NOPCPA)or a hybrid.

Surface second-harmonic generation based on periodically poled LiNbO_3 nonlinear optical crystal

We have generated a second-harmonic generation （SHG） of a Q-switched microchip Nd：YAG laser on the surface of a periodically poled LiNbO3 （PPLN） nonlinear crystal near the grazing incidence angle. Three individual SHC waves as transmitted homogeneous, kthomogeneous and reflected radiations have been generated and their intensities are measured and characterized within a desirable range of about 10 different incidence angles of the Nd：YAG laser as pump source on the PPLN surface. The basic of surface nonlinear radiation is also investigated and similar results are calculated and extracted from the theory. Comparison between calculated and measured data shows that they are in good agreement with each other.

Synthesis and Properties of New Infrared Nonlinear Optical Li_2Ga_2GeS_6 Crystal

IR Li2Ga2GeS6 nonlinear crystals were directly obtained with the composition of 40GeS2- 30Ga2Ss-30LieS, by the conventional melt-quenching method. The high depth digital image indicated that the obtained LizGa2GeS6 crystals showed a big size of 0.3 × 0.25 × 0.3 mm3. It was shown that the compound was very suscepfive to H20 with second harmonic observation. Besides, the glass-forming region of GeS2-Ga2S3- Li2S system was further studied by the conventional melt-quenching method.GeS2-Ga2S3-Li2S glass-ceramics containing IR Li2Ga2GeS6 nonlinear nanocrystals were obtained at a more carefully controlled heating rate.

Crystal Growth and Structure of Novel Tolane Nonlinear Optical Materials

A novel tolane 4-methoxy-4'-nitro-diphenyl-acetylene (MONA) has been prepared quantitatively by reacting cuprous p-methoxy phenyl-acetylene with p-iodonitrobenzene. A single crystal of the Moan was grown by solution growth method. The crystal was then characterized by X-ray diffraction structure analysis and second-harmonic generation(SHG)investigation. Polymorphous crystal forms of the MONA were grown from different solvents having different nonlinear optical properties depending on their different crystal structures. The relationship between the crystal growth and crystal structure is discusse.

Thermal and Transmission Properties of UV Nonlinear Optical Material——ZnCd(SCN)_4 Crystal

zinc cadmium thiocyanate (ZCTC), ZnCd(SCN)_4, has been discoveredas a UV second-order nonlinear optical coordination crystal. Titsthermal and transmission Properties are reported. The thermaldecomposition is characterized by using the X-ray Powder diffraction(XRPD) and infrared (IR) spectroscopy at room temperature. TheAbsorptions of intrinsic ions and ZCTC in a solution state arediscussed as well as Transmission properties of the ZCTC crystal. Aneffective method of reducing the surface Reflection loss of ZCTCcrystal is introduced.

Chemical Bond and Nonlinear Optical Effects of Crystals

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Design of photonic crystal fiber with elliptical air-holes to achieve simultaneous high birefringence and nonlinearity

A new type of V-shaped photonic crystal fiber with elliptical air-holes is proposed to realize simultaneous high bire- fringence and nonlinearity at a wavelength of 1.55 μm. The full vector finite element method was adopted to investigate its characteristics, including birefringence, nonlinearity, and dispersion. The PCF exhibited a very high birefringence of 2.89x10-2 and very high nonlinear coefficient of 102.69 W-1 .km 1. In particular, there were two zero-dispersion wave- lengths （ZDWs） in the visible （X： 640-720 nm and Y： 730-760 nm） and near-infrared regions （X： 1050-1606 nm and Y： 850-1500 nm）. The combination of high birefringence and nonlinearity allowed the PCF to maintain the polarization state and generate a broadband super continuum, with potential applications in nonlinear optics.

Growth and Characterization of a New Semi-Organic Nonlinear Optical Crystal: Thiosemicarbazide Cadmium Acetate

A new semi-organic nonlinear optical thiosemicarbazide cadmium acetate (TSCA) material has been synthesized. TSCA single crystals were grown from aqueous solution by slow evaporation method. The solubility of TSCA has been determined for various temperatures. The grown crystals were characterized by single crystal X-ray diffraction (XRD), FTIR, UV-Vis., thermal and second harmonic generation (SHG) analysis. Single crystal XRD study has been carried out to identify the lattice parameters. FTIR studies confirm the functional groups present in the grown crystal. Optical transmission studies have confirmed that the grown crystal is highly transparent. Thermogravimetric and differential thermal analyses reveal the good thermal stability of the material. The SHG conversion efficiency of TSCA was determined using Kurtz powder technique and found two times that of potassium dihydrogen orthophosphate (KDP).

ORGANIC NONLINEAR OPTICAL CRYSTAL:N-(4-NITROPHENYL)-(s)-(+)-2-PYRROLIDINEMETHYLENE TOSYLATE(NPP-OTs)

Large crystal NPP-OTs has been obtained by growth from solution,its powder SHG efficiency is 1/3 of urea.It shows it is a new convenient approach to obtain organic second-order NLO crystal:the dipole-dipole interaction is oppos- ed by introducing a large side group.

New Complex Nonlinear optical Crystal-Bis(4-methoxybenzaldehyde thiosemicarbazone) Zinc Chloride(ZnL_2Cl_2)

The structure of ZnL2Cl2 (L=4-methoxybenzaldehyde thiosemicarbazone) has beenobtained by x-ray diffraction. The compound crystallized in space group Cc with Z=4, in a unit cellof dimensions, a=9.08909(10), b=22. l420(10), c=11 .7890(l0)A,β=90.050(10)°, v=2374.6(12)A3,Dc=1 .552gcm-3. H=1 .463mm-1. R=0.0338. and Rw=0.0418. The structure contains individualZnL2Cl2 distorted tetrahedral units in which L molecules are S-bonded as monodentate to the metalions; chloride ions are also coordinated. The nonlinear optical properties of the zinc complex arealso presented in this letter.

Synthesis, Growth and Characterization of Organic Nonlinear Optical Single Crystals of 4-Bromo-4’-Methyl Benzylidene Aniline

Organic nonlinear optical material of 4-bromo-4’-methyl benzylidene aniline (BMBA) was synthesized and single crystal of BMBA was grown by solvent evaporation method at room temperature using ethanol as solvent. The crystalline nature of the grown crystals was confirmed using powder X-ray diffraction studies. The crystals were also characterized by single crystal X-ray diffraction method and their lattice parameters were determined. Thermal properties of BMBA were evaluated with thermogravimetric, differential thermal and differential scanning calorimetric analyses. Fourier transform infrared and FT-Raman spectral studies were carried out on the BMBA material to confirm the synthesized compound. 1H and 13C-nuclear magnetic resonance spectral studies were recorded to elucidate the structure of the grown crystals. Fluorescence spectrum recorded shows a peak at 485 nm. UV-Vis-NIR spectral analysis shows transmittance of ~92% in the visible region. The mechanical stability was analyzed by Vickers microhardness tester and the work hardening coefficient of the grown crystal was calculated. Second harmonic generation efficiency of the grown crystal measured by Kurtz powder technique is ~1.8 times that of potassium dihydrogen orthophosphate.

Crystal Structure and the Third-order Nonlinear Optical Property of a Cadmium(Ⅱ) Complex Based on a D-π-A Structural Organic Ligand

A triphenylamine-containing Schiff base ligand(L), namely, N-(4-(1 H-imidazol-1-yl)benzylidene)-N,N-diphenylbenzene-1,4-diamine, was synthesized and characterized. By coordination of the ligand with CdI2, a complex CdI2 L2 was obtained. The structure of the complex was analyzed through single-crystal X-ray diffraction. It crystallizes in monoclinic, space group P21/c with a = 25.277(5), b = 11.176(5), c = 17.912(5) ?, β = 106.056(5)°, V = 4863(3) ?3, Z = 4, Dc =1.633 Mg/m3, F(000) = 2360, Μr = 1195.19, μ = 1.766 mm-1, the final R = 0.0323 and wR = 0.0758 for 33414 observed reflections with I > 2?(I). The linear absorption spectra of the complex were experimentally and theoretically studied. And the third-order nonlinear optical(NLO) property of the complex was also measured through Z-scan technique.

Nonlinear dynamic analysis of a photonic crystal nanocavity resonator

A nonlinear dynamic model of a one-dimensional photonic crystal nanocavity resonator is presented. It considers the internal tensile stress and the geometric characteristics of a photonic crystal with rectangular(and circular) holes. The solution of the dynamic model shows that the internal tensile stress can suppress the hardening and softening behaviors of the resonator. However, the stress can reduce the amplitude, which is not conducive to an improvement of the sensitivity of the sensor. It is demonstrated that with an optimized beam length, the normalized frequency drift of the beam can be stabilized within 1% when the optical power increases from 2 mW to 6 mW. When the hole size of the resonator beam is close to the beam width, its increase can lead to a sharp rise of the resonant frequency and the promotion of hardening behavior. Moreover,the increase in the optical power initially leads to the softening behavior of the resonator followed by an intensification of the hardening behavior. These theoretical and numerical results are helpful in understanding the intrinsic mechanism of the nonlinear response of an optomechanical resonator, with the objective of avoiding the nonlinear phenomena by optimizing key parameters.

Acousto-Resonance Spectroscopy of Nonlinear-Optical Crystals in Process of Laser Frequency Conversion

Dependence of the periodically poled nonlinear-optical lithium niobate (PPLN) crystal temperature on laser power in the course of laser frequency conversion was measured using piezoelectric resonance. Crystal’s temperature tuning curves are precisely measured using concept of the equivalent temperature. Both optical absorption and heat transfer coefficients of the crystal are measured employing kinetics of the crystal equivalent temperature.

The interaction of nonlinear waves in two-dimensional dust crystals

This paper investigates the collision between two nonlinear waves with different propagation directions in two- dimensional dust crystals. Using the extended Poincare-Lighthill-Kuo perturbation method, two Korteweg-de Vries equations for nonlinear waves in both the ξ and η directions are obtained, respectively, and the analytical phase shifts and trajectories after the collision of two nonlinear waves are derived. Finally, the effects of parameters of the lattice constant a, the arbitrary constant u0η, the forces f（r）, and the colliding angle θ on the phase shifts of both colliding nonlinear waves are examined.

First-principles study of structure and nonlinear optical properties of CdHg(SCN)_4 crystal

The geometric structure,electronic structure,and optical properties of CdHg（SCN）4 crystal are calculated by using the density functional perturbation theory and Green function screening Coulomb interaction approximation.The band gap of CdHg（SCN）4 crystal is calculated to be 3.198 eV,which is in good agreement with the experimental value 3.265 eV.The calculated second-order nonlinear optical coefficients are d14 = 1.2906 pm/V and d15 = 5.0928 pm/V,which are in agreement with the experimental results（d14=（1.4 ±0.6） pm/V and d15=（6.0 ±0.9） pm/V）.Moreover,it is found that the contribution to the valence band mainly comes from Cd-4d,Hg-5d states,and the contributions to the valence band top and the conduction band bottom predominantly come from C-2p,N-2p,and S-3p states.The second-order nonlinear optical effect of CdHg（SCN）_4 crystal results mainly from the internal electronic transition of（SCN）^-.

Crystal Structure,Electrochemical Properties and Third-order Nonlinear Optical Response of 4-Methyloxy benzaldehyde Thiosemicarbazone and Its Copper(Ⅱ)Complex

The crystal structUre of the title ligand and its copper (Ⅱ) complex was determined bysingle crystal X-ray diffraction. The electrochendcal properties and the third-order nonlinearoptical response of the ligand and its copper (Ⅱ) complex were also studied.