Harmonic Generation Efficiency Research Articles

Synthesis and characterization of a single crystalline exocyclic double-bonded NLO active chalcone derivative: (2E) -2-(2,4,6-trimethoxybenzylidene) -3,4-dihydro-2H-naphthalene -1-one

A novel polycyclic organic compound [2E]-2-(2, 4, 6-trimethoxybenzylidene)-3, 4-dihydro-2H-naphthalene-1-one [TBDN] with the chemical formula C20H20O4 was formed using the Claisen-Schmidt condensation reaction. A good-quality single crystal with the dimensions 25 mm ×12 mm ×6 mm is formed adopting a slow evaporation technique over the time of two weeks, and its characteristics are determined by UV–Vis, FT-IR, and NMR analytical methods. The single-crystal X-ray diffraction technique was used to analyse the grown crystal and determine its cell structure. The aforementioned chemical crystallises in a monoclinic system with the space group Cc and the following unit cell parameters: a = 26.6973(8) Å, b = 9.6336(3), c = 15.2791(4) Å, β= 118.4750(10), Z = 4, and V = 3454.26(18) Å3. The thermal analysis shows that the crystal has good thermal stability. The optical transmission and mechanical toughness of the formed crystals were evaluated. The crystals' second harmonic generation (SHG) efficiency was measured using the conventional powder approach and a Nd:YAG laser. It was worked out to be 4.29 times higher than that of KDP and 1.16 times higher than that of urea.

Enhanced second harmonic generation in laser-induced air plasma.

We report a systematic investigation into the processes behind a near hundred-fold enhanced second harmonic wave generated from a laser-induced air plasma, by examining the temporal dynamics of the frequency conversion processes, and the polarization of the emitted second harmonic beam. Contrary to typical nonlinear optical processes, the enhanced second harmonic generation efficiency is only observed within a sub-picosecond time window and found to be nearly constant across fundamental pulse durations spanning from 0.1 ps to over 2 ps. We further demonstrate that with the adopted orthogonal pump-probe configuration, the polarization of the second harmonic field exhibits a complex dependence on the polarization of both input fundamental beams, contrasting with most of the previous experiments with a single-beam geometry.

Efficient high harmonic generation in nonlinear photonic moiré superlattice

Photonic moir\'e superlattice as an emerging platform of flatbands can tightly confine the light inside the cavity and has important applications not only in linear optics but also in nonlinear optics. In this paper, we numerically investigate the third- and fifth-order harmonic generation (THG and FHG) in photonic moir\'e superlattices fabricated by the nonlinear material silicon. The high conversion efficiency of THG and FHG is obtained at a relatively low intensity of fundamental light, e.g., the maximum conversion efficiency of THG and FHG arrives even up to be $10^{-2}$ and $10^{-9}$ at the fundamental intensity of 30 kW/m2, respectively, in the moir\'e superlattice of near flat band formed by the twist angle 6.01o. The results indicate the photonic moir\'e superlattice of a high-quality factor and flatbands is a promising platform for efficient nonlinear processes and advanced photonic devices.

Sub-100-fs Kerr-lens mode-locked Yb:YAG ring-cavity thin-disk oscillator.

Ultrafast ring-cavity thin-disk oscillators combine high output power with the flexibility of generating output either unidirectionally or bidirectionally. Here, we report a Kerr-lens mode-locked ring-cavity Yb:YAG thin-disk oscillator delivering unidirectional 89-fs pulses by inducing additional spectral broadening with nonlinear plates. This is the shortest pulse duration for a ring-cavity mode-locked thin-disk oscillator. Bidirectional mode-locking was also realized. These results lay the foundation for the more efficient generation of high-order harmonics at MHz repetition rates and high-power dual frequency combs.

An investigation into the effects of electric field on the structural and optical properties of L-Cysteine doped KDP crystals

Nowadays, different methods to grow large-size crystals are gaining more interest compared to traditional crystal growth techniques. Based on the applications, crystals must be modified and for that new crystal growth techniques must be introduced to meet such demands. Potassium Dihydrogen Phosphate (KDP) crystal is a well-known non-linear optical (NLO) crystal which has numerous demands in various fields, for instance, electro-optic devices, lasers, modulators, etc and due to which its habit modification plays a significant role in research and development. A slow evaporation technique was used to grow transparent and good-quality L-Cysteine (1 mol% and 2 mol%) doped KDP crystals; however, the crystals were grown in presence of a constant electric field at room temperature. With powder x-ray Diffraction (XRD) analysis and utilising FullProf Suite software, the crystal structure of the crystal was confirmed. The inclusion of L-Cysteine into KDP lattice was confirmed with fourier transform infrared (FTIR) spectroscopy. Optical transmittance spectra were recorded in the range of 200 and 800 nm. Photoluminescence (PL) studies were conducted in the range of 300–600 nm in order to detect lattice defects and intrinsic impurities. The value of relative second harmonic generation (SHG) efficiency was observed to be enhanced for crystals grown in presence of an electric field.

Nonlinear resonant magnetoelectric effect in a circumferentially magnetized ferromagnetic–piezoelectric ring heterostructure

The nonlinear magnetoelectric (ME) effect of voltage harmonic generation in a ring heterostructure, comprising a magnetostrictive layer of an amorphous ferromagnet and a piezoelectric layer of lead zirconate titanate is investigated. The structure was circumferentially magnetized with a permanent field H = 0–40 Oe and excited by a circular alternating magnetic field h = 0–3.6 Oe. At the radial acoustic resonance frequency of the structure of ∼54.2 kHz, the first voltage harmonic generation efficiency was 2.9 V/(Oe cm), the second was 0.95 V/(Oe2 cm), and the third was 0.21 V/(Oe3 cm). The absence of demagnetization effects in the ring structure, in comparison with a planar one, leads to a decrease in the optimal biasing magnetic field as well as to a change in the dependence of the second and third ME voltage harmonics on the magnetic field. The discovered nonlinear effect can be used to create frequency doublers.

Enhance high harmonic generation (HHG) efficiency via compact multi-plate continuum post-compression for time-resolved angle-resolved photoemission spectroscopy.

Time-resolved angle-resolved photoemission spectroscopy (Tr-APRES) gives direct insight into electron dynamics by providing temporal-, energy-, and momentum-resolved information in one experiment. A major obstacle to using high harmonic generation (HHG) probe pulses for photoemission spectroscopy is the low conversion efficiency, that is, the low flux of probe photons. We use a Yb-KGW based duo-laser source with an oscillator to pump two separate amplifiers and generate two synchronized pulsed laser sources with average energies of 7.5 and 6W. By using the multiplate continuum method and chirped mirrors, the resulting flux of HHG photons at 33-70eV can be increased 50-fold (up to 1011 photons/s) by using post-compressed 30fs pulses compared with the photon flux generated by the fundamental 190fs pulses. Moreover, pulses from the 6W amplifier are used to pump an optical parametric amplifier that can vary the wavelengths for photoexcitation. The system performance is demonstrated by applying Tr-ARPES to single-crystal graphite. The front tilt broadening is significantly suppressed by the off-plane mounted conical grating, leading to a 184fs temporal resolution that is mainly limited by the pump pulse. The energy resolution is 176meV.

Growth and characterization of Oxalic acid doped Guanidine carbonate (OGC) single crystal

Oxalic acid doped Guanidine carbonate, an organic nonlinear optical single crystal is developed successfully by slow evaporation solution growth method using deionized water as a solvent. The crystal structure and lattice parameters of grown crystals are determined by single crystal X – ray diffraction of the grown crystal. The presence of expected functional groups of the grown crystal is identified by Fourier Transform Infrared spectroscopy. The optical transmittance spectrum of the crystals has been recorded by UV –Vis-NIR spectral analysis. The calculated large bandgap of the grown crystals attests them for optoelectronic applications. The Thermo Gravimetric and Differential Thermal analyses have been carried out to understand the thermal responses of the crystals. Second harmonic generation efficiency of the grown crystals have been calculated by Kurtz powder method. Nd – YAG laser (1064 nm) was used to find out the laser damage threshold of the grown crystal. The inspiring results confirms that the grown crystal serve as a potential candidate for photonic devices.

Nonlinear propagation of quasiplanar shear wave beams in soft elastic media with transverse isotropy.

Model equations are developed for shear wave propagation in a soft elastic material that include effects of nonlinearity, diffraction, and transverse isotropy. A theory for plane wave propagation by Cormack [J. Acoust. Soc. Am. 150, 2566 (2021)] is extended to include leading order effects of wavefront curvature by assuming that the motion is quasiplanar, which is consistent with other paraxial model equations in nonlinear acoustics. The material is modeled using a general expansion of the strain energy density to fourth order in strain that comprises thirteen terms defining the elastic moduli. Equations of motion for the transverse displacement components are obtained using Hamilton's principle. The coupled equations of motion describe diffraction, anisotropy of the wave speeds, quadratic and cubic plane wave nonlinearity, and quadratic nonlinearity associated with wavefront curvature. Two illustrative special cases are investigated. Spatially varying shear vertical wave motion in the fiber direction excites a quadratic nonlinear interaction unique to transversely isotropic soft solids that results in axial second harmonic motion with longitudinal polarization. Shear horizontal wave motion in the fiber plane reveals effects of anisotropy on third harmonic generation, such as beam steering and dependence of harmonic generation efficiency on the propagation and fiber directions.

Effect of cycloalkanone ring size on second and third order nonlinear optical properties of bischalcones

With the objective of establishing the effect of cycloalkanone ring size on the NLO properties of bischalcones para-substituted diarylideneacetone and substituted diarylidenecycloalkanone derivatives were synthesized by the Claisen–Schmidt condensation reaction and characterized by using UV–Vis, FT-IR, 1H NMR, 13C NMR and mass spectrometry. The second harmonic generation (SHG) efficiencies and third-order nonlinear optical (NLO) properties of the synthesized compounds were studied using the Kurtz-Perry method and the Degenerate Four Wave Mixing (DFWM) technique respectively. Among all the synthesized compounds that we have reported here, 2,6-bis-(4-methoxydibenzylidene) acetone showed the highest SHG efficiency (12.96 times that of urea) and 2, 6-bis-(4-methylthiobenzylidene) cyclopentanone showed the highest third order NLO property with χ (3) value of 2.650 ± 0.023 × 10−13 esu. Though diarylideneacetones exhibited the highest SHG efficiency, among the diarylidenecycloalkanones SHG efficiency decreased with an increase in the cycloalkanone ring size. Diarylidenecyclopentanone series showed better third order NLO activity followed by diarylideneacetone, diarylidenecycloheptanone and diarylidenecyclohexanone series. The results indicate that the cycloalkanone ring size as well as the presence of substituents on the aryl rings affect the NLO properties. The experimental findings correlated well with the results of in silico studies with a correlation factor, R2 = 0.9285.

Frequency-doubled Q-switched 4 × 4 multicore fiber laser system.

Frequency doubling of a Q-switched Yb-doped rod-type 4 × 4 multicore fiber (MCF) laser system is reported. A second harmonic generation (SHG) efficiency of up to 52% was achieved with type I non-critically phase-matched lithium triborate (LBO), with a total SHG pulse energy of up to 17 mJ obtained at 1 kHz repetition rate. The dense parallel arrangement of amplifying cores into a shared pump cladding enables a significant increase in the energy capacity of active fibers. The frequency-doubled MCF architecture is compatible with high-repetition-rate and high-average-power operation and may provide an efficient alternative to bulk solid-state systems as pump sources for high-energy titanium-doped sapphire lasers.

Doubly-resonant enhanced second-harmonic generation and its wide-band tunability

The second-harmonic generation (SHG) from the doubly-resonant metasurfaces composed of the U-shaped and the rectangular apertures on an optically opaque gold film is investigated theoretically. By engineering the fundamental plasmonic resonances of the composite metasurfaces to match the excitation and the second-harmonic wavelengths, respectively, the doubly-resonant enhanced SHG intensity of almost an order of magnitude is obtained, compared with the singly-resonant U-apertures. In addition, the satisfaction of doubly-resonant condition can be extended to a wide wavelength range by changing the refractive index of the surrounding medium, which benefits from the two fundamental plasmonic resonances oscillating at frequencies of a two-fold relationship. Our work provides a new way to enhance the efficiency of nonlinear harmonic generation.

Doubly resonant photonic crystal cavity using merged bound states in the continuum

In this work, a doubly resonant photonic crystal (PhC) cavity using the merged bound states in the continuum (BICs) is proposed to obtain a higher second harmonic generation (SHG) efficiency. Firstly by scanning geometry parameters the accidental BICs and a band-edge mode outside the light cone can be obtained. Then as the lattice constant or the thickness of the slab is adjusted the accidental BICs will merge. A supercell with large and small holes is constructed and the band-edge mode outside the light cone can be mode-matched with the merged BICs mode. Finally the heterostructure PhC cavity is designed. The merged BICs show a high quality factor for the photonic crystal with finite size. Consequently, the SHG efficiency of the lattice constant near merged BICs of ~6000% W-1 is higher than the one of the isolated BIC.

High-power continuous-wave optical waveguiding in a silica micro/nanofibre

As miniature fibre-optic platforms, micro/nanofibres (MNFs) taper-drawn from silica fibres have been widely studied for applications from optical sensing, nonlinear optics to optomechanics and atom optics. While continuous-wave (CW) optical waveguiding is frequently adopted, so far almost all MNFs are operated in low-power region (e.g., <0.1 W). Here, we demonstrate high-power low-loss CW optical waveguiding in MNFs around 1550-nm wavelength. We show that a pristine MNF, even with a diameter down to 410 nm, can waveguide an optical power higher than 10 W, which is about 30 times higher than demonstrated previously. Also, we predict an optical damage threshold of 70 W. In high-power CW waveguiding MNFs, we demonstrate high-speed optomechanical driving of microparticles in air, and second harmonic generation efficiency higher than those pumped by short pulses. Our results may pave a way towards high-power MNF optics, for both scientific research and technological applications.

Highly efficient harmonic vortex generation from a laser irradiated hollow-cone target.

It has been recently reported that ultraviolet harmonic vortices can be produced when a high-power circular-polarized laser pulse travels through a micro-scale waveguide. However, the harmonic generation quenches typically after a few tens of microns of propagation, due to the buildup of electrostatic potential that suppresses the amplitude of the surface wave. Here we propose to use a hollow-cone channel to overcome this obstacle. When traveling in a cone target, the laser intensity at the entrance is relatively low to avoid extracting too many electrons, while the slow focusing by the cone channel subsequently counters the established electrostatic potential, allowing the surface wave to maintain a high amplitude for a much longer distance. According to three-dimensional particle-in-cell simulations, the harmonic vortices can be produced with very high efficiency >20%. The proposed scheme paves the way for the development of powerful optical vortices sources in the extreme ultraviolet regime-an area of significant fundamental and applied physics potential.

Local Field Enhancement Due to the Edge States of Nanoplasmonic Crystal

In this paper, we describe the effect of local electric field enhancement due to the existence of photonic edge states in a nanoplasmonic crystal. These states can be excited by a normal incident wave and are localized along the continuous line defect, where translational symmetry is broken. The nanoplasmonic crystal is formed by a triangular lattice of SiO2 cylinders on top of SiO2 and Ag thin films. Numerical simulations demonstrated that edge modes that are concentrated around a defect in a nanophotonic crystal may result in 12 field enhancements of the electric field for the incident plane wave of wavelength 545 nm. This effect can be employed for improving the sensitivity of surface-enhanced Raman scattering (SERS) spectroscopy, increasing the Purcell factor of quantum systems and improving the efficiency of higher harmonic generation.

Investigation on the growth, characterization and computational analysis of 2-Amino-2-thiazoline single crystals

By adapting the slow evaporation techniquethe titled compound 2-Amino-2-thiazoline (AMTZ) has been synthesized. The structural parameters of the crystal was studied by using single crystal X-ray diffraction method.Without the deposition of secondary phases, crystallite nature of the sample has been confirmed by analyzing powder X-ray diffraction method. From UV–visible spectrum study, the cut off wavelength was perceived at 285 nm & its optical constants has been calculated.Up to 128 °C, the thermal constancy of the sample was maintained & it reveals the durability of the crystal. The scanning electron microscope investigation has been carried out to decisive the surface morphology of the synthesized crystal. The mechanical roughness of the crystal has been characterized by Vickers's micro hardness test. It has been reported, that the variations in dielectric constant and loss for frequencies and temperature were observed for AMTZ crystals. By adapting Kurtz Perry Powder technique the second harmonic generation (SHG) efficiency was confirmed. By utilizing09W program package, B3LYP/6–311++G(d, p) method was adopted &the optimization of the structure was carried outto calculate the donor accepter interaction energy.The Time-Dependent Density Functional Theory (TD-DFT) was used to compute the electronic level of transition.

Design, synthesis and characterization of organic second-order nonlinear optical crystal materials DOBS

Recent advance of the organic nonlinear optical (NLO) crystals on the design, synthesis and characterization of 2-(3,4-Dimethoxystyryl)-3-methylbenzothiazolium-benzenesulfonate (DOBS) is reported. It is found that crystal belongs to the triclinic system, with the space group P1. The second harmonic generation efficiency is 1.8 times higher than the standard KDP. Based on density functional theory (DFT), the maximum first-order hyperpolarizability of DOBS molecule is obtained by Gaussian calculation βmax is 107.7 × 10− 30 esu. The molecular surface electrostatic potential, HOMO-LUMO orbital, ELF/LOL, Hole-electron, Hirshfeld surface and 2-D fingerprint were analyzed. The thermal stability analysis shows that DOBS crystal has a high melting point of 251 °C. In addition, UV-Vis-NIR spectra, dielectric properties and fluorescence were investigated.

Polarization multiplexing multichannel high-Q terahertz sensing system

Terahertz functional devices with high-Q factor play an important role in spectral sensing, security imaging, and wireless communication. The reported terahertz devices based on the electromagnetic induction transparency (EIT) effect cannot meet the needs of high-Q in practical applications due to the low-Q factor. Therefore, to increase the Q-factor of resonance, researchers introduced the concept of bound state in the continuum (BIC). In the quasi-BIC state, the metasurface can be excited by the incident wave and provide resonance with a high-Q factor because the condition that the resonant state of the BIC state is orthogonal is not satisfied. The split ring resonator (SRR) is one of the most representative artificial microstructures in the metasurface field, and it shows great potential in BIC. In this paper, based on the classical single-SRR array structure, we combine the large and small SRR and change the resonance mode of the inner and outer SRR by changing the outer radius of the inner SRR. The metasurface based on parameter-tuned BIC verified that the continuous modulation of parameters in a system could make a pair of resonant states strongly coupled, and the coherent cancellation of the resonant states will cause the linewidth of one of the resonant states to disappear, thus forming BIC. Compared with the single-SRR array metasurface based on symmetry-protected BIC, the dual-SRR array metasurface designed in this paper has multiple accidental BICs and realizes multichannel multiplexing of X-polarization and Y-polarization. It provides a brilliant platform for high-sensitivity optical sensor array, low threshold laser and efficient optical harmonic generation.

Versatile, compact chirped pulse amplifier pump system for ultrafast optical parametric amplifiers.

We report on the development of a pump system for ultrafast optical parametric amplifiers (uOPA) as an upgrade for the existing uOPA at the Petawatt High Energy Laser for heavy Ion eXperiments (PHELIX) and the new Petawatt ENergy-Efficient Laser for Optical Plasma Experiments (PEnELOPE). The system consists of a two-stage chirped pulse amplifier, centered around a high energy Yb:YAG regenerative amplifier that delivers 108 mJ uncompressed output energy, resulting in 92 mJ at 1030 nm after compression, pulse durations of 1.4 ps, a high beam quality of Mx/y2 = 1.02 / 1.16 and a relative energy stability of 0.35 %. A second harmonic generation (SHG) efficiency of up to 70 % is achievable and a maximum pulse energy of 43 mJ at 515 nm has been obtained, which is only limited by the damage threshold of the SHG crystal. A self-phase modulation stage makes this system a widely applicable, self-seedable pump module for uOPA without placing strong requirements on its seed oscillator.