Optical Third Harmonic Generation Research Articles

Optical third-harmonic generation of spherical quantum dots under inversely quadratic Hellmann plus inversely quadratic potential

The third-harmonic generation (THG) coefficient for a spherical quantum dot system with inversely quadratic Hellmann plus inversely quadratic potential is investigated theoretically, considering the regulation of quantum size, confinement potential depth and the external environment. The numerical simulation results indicate that the THG coefficient can reach the order of 10−12 m2 V–2, which strongly relies on the tunable factor, with its resonant peak experiencing a redshift or blueshift. Interestingly, the effect of temperature on the THG coefficient in terms of peak location and size is consistent with the quantum dot radius but contrasts with the hydrostatic pressure. Thus, it is crucial to focus on the influence of internal and external parameters on nonlinear optical effects, and to implement the theory in practical experiments and the manufacture of optoelectronic devices.

Adaptive optical third-harmonic generation microscopy for in vivo imaging of tissues

Third-harmonic generation microscopy is a powerful label-free nonlinear imaging technique, providing essential information about structural characteristics of cells and tissues without requiring external labelling agents. In this work, we integrated a recently developed compact adaptive optics module into a third-harmonic generation microscope, to measure and correct for optical aberrations in complex tissues. Taking advantage of the high sensitivity of the third-harmonic generation process to material interfaces and thin membranes, along with the 1,300-nm excitation wavelength used here, our adaptive optical third-harmonic generation microscope enabled high-resolution in vivo imaging within highly scattering biological model systems. Examples include imaging of myelinated axons and vascular structures within the mouse spinal cord and deep cortical layers of the mouse brain, along with imaging of key anatomical features in the roots of the model plant Brachypodium distachyon. In all instances, aberration correction led to enhancements in image quality.

Strong coupling in an asymmetric two-dimensional guided mode resonance metasurface structure and enhancement for optical third-harmonic generation

A two-dimensional guided mode resonance structure supports a transverse magnetic (TM) resonant mode in the direction of incident polarization and a transverse electric (TE) resonant mode in the direction perpendicular to the polarization. In this work, the coupling between the transverse magnetic and the transverse electric resonant modes in an asymmetric two-dimensional dielectric metasurface structure is investigated. The asymmetric structure consists of a two-dimensional square nanohole array etched in a titanium dioxide thin film on a transparent silica substrate. With finite difference time domain simulations, anti-crossing of the resonant spectra of the TM and TE modes is observed by adjusting the asymmetry of the structure. The anti-crossing indicates that the interaction between TM and TE resonant modes results in a strong coupling state. A coupled harmonic oscillator model is used to explain the strong coupling effect. The results of the coupled harmonic oscillator modeling agree well with the results of numerical simulations. Furthermore, it is shown that the strong coupling can significantly enhance the third harmonic generation intensity compared with the uncoupled TM and TE resonant modes.

Enhanced optical third-harmonic generation in phase-engineered nanostructured Zn1−x Cd x S thin films for optoelectronic device applications

A polycrystalline nanostructured thin film of zinc cadmium sulfide was meticulously fabricated on a glass substrate using the thermal evaporation method physical vapor deposition within a vacuum chamber. Different doping concentrations were introduced by varying the cadmium (Cd) content, resulting in Zn1-x Cd x S films with Cd concentrations ranging from x = 0.00–0.20 wt %. The impact of Cd doping on the third-order nonlinear optical (TONLO) properties of these films was thoroughly studied using the Z-scan method, employing a diode-pumped solid-state continuous-wave laser. To gain insight into the structural characteristics, the Zn1-x Cd x S thin films underwent analysis through x-ray diffraction. Optical studies confirmed the tunability of the optical band gap (Eg) in the Zn1-x Cd x S films, ranging from 3.88 eV for undoped ZnS to 2.80 eV for the film fabricated with 20 wt. % of Cd-content. This significant reduction in ‘Eg’ renders the films highly suitable for use as absorbing layers in applications such as solar cells and optoelectronics. Surface morphology analysis, performed via field emission scanning electron microscopy, revealed noticeable alterations with increased Cd doping. Significantly, the doped films exhibited a substantial redshift in the band edge and an increase in transmittance within the visible and near-infrared regions. The investigation of TONLO properties, including the nonlinear absorption coefficient (β), nonlinear refractive index (n 2) and susceptibility χ(3), yielded values ranging from 3.15 × 10−3 to 8.16 × 10−3 (cm W−1), 1.65 × 10−8 to 7.45 x 10–8 (cm2 W−1), and 3.12 × 10−5 to 7.86 × 10−5 (esu), respectively. These results indicate the presence of self-defocusing nonlinearity in the films. Overall, the outcomes underscore the potential of Cd-doped ZnS nanostructures in modifying surface morphology and enhancing NLO characteristics. Zn1-x Cd x S thin films exhibit promise for applications in nonlinear optical devices, as evidenced by these encouraging findings.

Ultrafast Third-Order Nonlinear Optical Response Excited by fs Laser Pulses at 1550 nm in GaN Crystals.

The ultrafast third-order optical nonlinearity of c-plane GaN crystal, excited by ultrashort (fs) high-repetition-rate laser pulses at 1550 nm, wavelength important for optical communications, is investigated for the first time by optical third-harmonic generation in non-phase-matching conditions. As the thermo-optic effect that can arise in the sample by cumulative thermal effects induced by high-repetition-rate laser pulses cannot be responsible for the third-harmonic generation, the ultrafast nonlinear optical effect of solely electronic origin is the only one involved in this process. The third-order nonlinear optical susceptibility of GaN crystal responsible for the third-harmonic generation process, an important indicative parameter for the potential use of this material in ultrafast photonic functionalities, is determined.

Optical Third-Harmonic Generation in Hexagonal Boron Nitride Thin Films

Hexagonal boron nitride (hBN) is a layered material that exhibits remarkable optical features in the UV, visible, and IR ranges, attractive for applications in modern photonics. Being transparent in a wide spectral range, hBN is now considered an important building block for novel integrated photonic platforms, thus requiring the study of its optical properties. In this work, we report on the measurements of hBN optical cubic nonlinearity χ(3) equal to 8.4 × 10-21 m2/V2 by observing the third-harmonic generation for 1080 nm pump wavelength from mechanically exfoliated hBN flakes with thicknesses varying from 5 to 170 nm. The third-order susceptibility of hBN is close to that of Si3N4 highlighting the potential of hBN for nonlinear applications.

Magnetic Field Effects in Optical Harmonics Generation by Excitons

Mechanisms that are responsible for the optical harmonics generation at exciton transitions are analyzed in several classes of materials. In the cubic GaAs semiconductor, the magneto-induced optical second-harmonic generation second optical harmonic is observed in the region of orbital quantization of the valence and conduction bands. An unusually strong amplitude of the optical third-harmonic generation in an external magnetic field in the region of 1s exciton due to exciton–polariton resonance is found. The optical second-harmonic generation due to 1s, 2s, and 2p exciton resonances in a magnetic field is revealed in a hexagonal wide band-gap ZnO semiconductor. Depending on the symmetry of the exciton states, the mechanisms of the optical second-harmonic generation involve the spin and orbital Zeeman effects, and the magneto-Stark effect. The magneto-induced contribution to second harmonic generation (SHG) in the region of exciton transitions in the Cr2O3 antiferromagnet placed in an external magnetic field is studied.

Phase-matching and Peak Nonlinearity Enhanced Third-Harmonic Generation in Graphene Plasmonic Coupler

Optical third-harmonic generation (THG) is important for various applications in nanomedicine, photocatalysis, and biosensing, but advances are held back due to small third-order nonlinear susceptibility ${\ensuremath{\chi}}^{(3)}$ and phase mismatch between the fundamental and third-harmonic waves. This work uses a graphene plasmonic coupler to achieve tunable, highly efficient THG through combining phase matching with resonant three-photon transitions. The study not only offers understanding and guidance for the problem at hand, but also points to further exploration of tunable, subwavelength coherent sources and ultracompact signal processing in the midinfrared and terahertz spectral regimes.

Research on third-harmonic generation with position-dependent mass in a quantum well

In this paper, the energy levels and the wave functions of the Schrödinger equation with position-dependent mass are theoretically deduced, and they are brought into nonlinear optical third-harmonic generation. We find that the peak of the third-harmonic coefficient becomes larger and a blueshift occurs under the condition of variable mass. Moreover, with the increment of mass variable k, the energy interval Eij decreases, which makes the coefficients suffer a redshift, and the absolute value of the matrix elements product |M12M23M34M41| presents different monotonicity, which makes the peak value of the coefficient change regularly.

Linear and nonlinear properties of novel materials based on DNA containing [2.2]paracyclophane moiety

In this study, the synthesis and the characterization of new deoxyribonucleic acid (DNA) based compounds containing [2.2]paracyclophane moiety are reported. The DNA molecule was functionalized with hexadecyltrimethylammonium chloride (CTMA), [2.2]paracyclophane-4-methoxy-5-formyl [A] and [2.2]paracyclophane-4-hydroxy-5-formyl [B], respectively. These compounds were used for obtaining good optical quality thin films by spin coating method. The absorption and emission spectra of studied solutions and thin films showed that the new obtained materials are of good optical properties. The third-order nonlinear optical (NLO) properties of thin films were characterized by the optical third-harmonic generation technique at 1064.2 nm fundamental wavelength.

Nonlinear optical rectification, the second and third harmonic generation in asymmetric double quantum well under the intense laser field

Abstract . In this study, the effects of a non-resonant intense laser field and the Al-concentration on the optical rectification, second and third harmonic generation in asymmetric double quantum well are investigated within the compact density matrix approach theoretically. The results show that the intense laser field and the Al-concentration lead to significant changes in the coefficients of nonlinear optical rectification, second and third harmonic generations. Keywords: Asymmetric double quantum well, Nonlinear optical rectification, Second and third harmonic generations, Intense laser field Ozet. Bu calismada, asimetrik cift kuantum kuyusunun dogrusal olmayan optik duzeltme, ikinci ve ucuncu harmonikleri uzerine Al-konsantrasyonu ve rezonans olmayan yogun lazer alaninin etkisi kompakt yogunluk matris yaklasimi kullanilarak teorik olarak incelenmistir. Sonuclar, yogun lazer alani ve Al-konsantrasyonun dogrusal olmayan optik duzeltme, ikinci ve ucuncu harmonikler uzerine onemli degismelere neden oldugunu gostermektedir.

Fluorescence, optical absorption and third-order nonlinear optical properties of terbium (III) complex embedded into DNA-CTMA matrix

New DNA based materials, functionalized with hexadecyltrimethylammonium chloride (CTMA) and terbium – bis – (2.2′ – bipyridine) triazotate molecules [Tb(NO3)3(bpy)2], were prepared. The obtained complexes were processed into good optical quality thin films by spin coating method on commercial glass substrates and characterized for their spectroscopic, linear and nonlinear optical properties. The solution absorption and fluorescence measurements show incorporation of Tb(NO3)3(bpy)2 into DNA-CTMA backbones. Furthermore, the photoluminescent properties of the DNA-CTMA/Tb(NO3)3(bpy)2 thin films were superior to that of DNA-CTMA/Tb(NO3)3(bpy)2 solutions. The third-order nonlinear optical (NLO) properties of thin films were determined by the optical third-harmonic generation technique at 1 064.2nm fundamental wavelength. A large cubic susceptibility of Tb complex is observed.

Synthesis, linear and nonlinear optical properties of DNA-CTMA/europium (III) complex

Novel deoxyribonucleic acid (DNA) based materials, functionalized with hexadecyltrimethylammonium chloride (CTMA) and europium – (1.10 – phenanthroline) triazotate complex [Eu(NO3)3phen] were synthesized and characterized for their linear and nonlinear optical properties. The obtained complexes were processed into good optical quality thin films by spin coating method. The measured absorption spectra and fluorescence bands of studied solutions indicated the incorporation of Eu(NO3)3phen into DNA-CTMA matrix. The third-order nonlinear optical (NLO) properties of thin films were determined by the optical third-harmonic generation technique at 1 064.2nm fundamental wavelength. A large cubic susceptibility of Eu complex is observed.

Frequency dependence of optical third-harmonic generation from doped graphene

In connection with the controversial question about the frequency dependence of the optical third-harmonic generation (THG) from doped graphene, which has recently been discussed in the literature, we develop an analytical theory for the THG susceptibility of doped graphene by using the original Genkin–Mednis nonlinear-conductivity-theory formalism including mixed intra- and interband terms. The theory is free of any nonphysical divergences at zero frequency, and it predicts the main resonant peak in the THG spectrum to be located at the photon energy ħω equal to two thirds of the Fermi energy EF of charge carriers in doped graphene.

Synthesis of conducting azopolymers by electrochemical grafting of a diazonium salt at polypyrrole electrodes

In this paper we report a new strategy for obtaining conducting azopolymers having pendant azobenzene moieties via functionalization of polypyrrole by electrochemical reduction of 4-[(4′-nitrophenyl)azo]benzenediazonium tetrafluoroborate (NABDBF4−). The functionalization of polypyrrole films with 4′-nitroazobenzene (NAB) groups has been evaluated by cyclic voltammetry and by spectroscopic techniques such as XPS, Raman and UV–vis spectroscopy. Moreover, the third-order nonlinear optical response of NAB-functionalized polypyrrole has been investigated using the optical third-harmonic generation technique. All these investigations confirmed the presence at the polymeric films surface of the functional groups introduced by the electrochemical reduction of diazonium salt. The versatility of this methodology allows not only the functionalization of polypyrrole-type materials with chromophore groups, but can also be successfully applied to other conjugated polymer systems in order to create various photoresponsive materials.

Integrated optical auto-correlator based on third-harmonic generation in a silicon photonic crystal waveguide

The ability to use coherent light for material science and applications is linked to our ability to measure short optical pulses. While free-space optical methods are well established, achieving this on a chip would offer the greatest benefit in footprint, performance and cost, and allow the integration with complementary signal-processing devices. A key goal is to achieve operation at sub-watt peak power levels and on sub-picosecond timescales. Previous integrated demonstrations require either a temporally synchronized reference pulse, an off-chip spectrometer or long tunable delay lines. Here we report a device capable of achieving single-shot time-domain measurements of near-infrared picosecond pulses based on an ultra-compact integrated CMOS-compatible device, which could operate without any external instrumentation. It relies on optical third-harmonic generation in a slow-light silicon waveguide. Our method can also serve as an in situ diagnostic tool to map, at visible wavelengths, the propagation dynamics of near-infrared pulses in photonic crystals.

Third-Harmonic Generation in Ultrathin Films of MoS2

We observe optical third-harmonic generation in atomically thin films of MoS2 and deduce effective third-order nonlinear susceptibilities on the order of 10(-19) m(2)/V(2), which is comparable to that of commonly used semiconductors under resonant conditions. By measuring the susceptibility as a function of light wavelength, we find significant enhancements of the susceptibility by excitonic resonances. The demonstrated third-harmonic generation can be used for nonlinear optical identification of MoS2 atomic layers with high contrast, better distinguishing power of multilayers, and less restrictions to substrate selections. The size of the third-order nonlinear susceptibility suggests feasibility of exploring other types of third-order nonlinear optical effects of MoS2 two-dimensional crystals.

Influence of self-focusing of ultrashort laser pulses on optical third-harmonic generation at interfaces

We report on the third-harmonic generation of femtosecond laser pulses at interfaces. We measured slabs of different types of optical glasses and demonstrated that the asymmetric intensity profile observed for a tightly focused beam can be explained by self-focusing effects.

Optical Third-Harmonic Generation in Graphene

The optical properties of graphene previously used to probe its electronic structure are its optical dispersion and absorption coefficients. Now, scientists report the third-harmonic generation of light in graphene and demonstrate the promise of this nonlinear optical response as a technically versatile microscopic imaging approach of the physical structure of graphene.

Fluorescence, spectroscopic and NLO properties of green tea extract in deoxyribonucleic acid

Natural, purely biological deoxyribonucleic acid (DNA)–green tea extract (GTE) complexes at different concentrations were prepared and characterized for their spectroscopic, fluorescent, linear and nonlinear optical properties. The complexes can be processed into good optical quality thin films by solution casting. They fluoresce when excited in UV absorption band, with a significantly larger quantum yield for the DNA–GTE complex than for a pure GTE solution. The thin film refractive indices were determined by Fabry–Perot (FP) interference patterns. The third-order nonlinear optical (NLO) properties of thin films were determined by the optical third-harmonic generation technique at 1064.2nm fundamental wavelength. The phase of THG susceptibility was determined from the concentration variation of THG susceptibility. It reveals presence of a two-photon resonance with a band lying in the optical gap.