Third Harmonic Generation Studies Research Articles

Wavelength Dependent Nonlinear Spectroscopic Study of Third Harmonic Generation Probed by Rotational Maker Fringes Method

Wavelength Dependent Nonlinear Spectroscopic Study of Third Harmonic Generation Probed by Rotational Maker Fringes Method

Study of third harmonic generation in InxGa1−xAs semi-parabolic 2-D quantum dot under the influence of Rashba spin-orbit interactions (SOI): Role of magnetic field, confining potential, temperature & hydrostatic pressure

Study of third harmonic generation in InxGa1−xAs semi-parabolic 2-D quantum dot under the influence of Rashba spin-orbit interactions (SOI): Role of magnetic field, confining potential, temperature & hydrostatic pressure

Influence of tunnel ionization to third-harmonic generation of infrared femtosecond laser pulses in air

Here we present an experimental as well as theoretical study of third-harmonic generation in tightly focused femtosecond filaments in air at the wavelength of 1.5 ,upmu hbox {m}. At low intensities, longitudinal phase matching is dominating in the formation of 3rd harmonics, whereas at higher intensities locked X-waves are formed. We provide the arguments that the X-wave formation is governed mainly by the tunnel-like ionization dynamics rather than by the multiphoton one. Despite of this fact, the impact of the ionization-induced nonlinearity is lower than the one from bound–bound transitions at all intensities.

Microscopic study of resonant third-harmonic generation from amorphous silicon nanodisk arrays.

A detailed microscopic study of third-harmonic generation (THG) from two-dimensional arrays of sub-wavelength spaced amorphous silicon nanodisks is reported. The arrays are designed to support broadband, minimally angle-sensitive resonances for the fundamental excitation wavelength in the 1500nm region. This results in resonantly enhanced visible THG in the green spectral range with ∼500-fold enhancement on-resonance, compared to the unpatterned a-Si thin-film. THG multispectral microscopic imaging reveals individual nanodisks with enhanced nonlinear signal on-resonance. For increasing pump intensities, spatially dependent saturation effects are observed for the first time, to the best of our knowledge, in such dielectric nanostructure arrays with THG images showing a reversal of contrast.

Density-Matrix Renormalization Group Study of Third Harmonic Generation in One-Dimensional Mott Insulator Coupled with Phonon

We examine the third-order non-linear optical response of a one-dimensional Mott insulator coupled with phonons. The Mott insulator is described by an extended Hubbard-Holstein model. The third harmonic generation (THG) of the model is calculated by dynamical density-matrix renormalization group. We find that the electron-phonon interaction enhances the intensity of THG if the on-site Coulomb interaction is comparable to the band width, but the enhancement is small for a realistic parameter value of a typical Mott insulator Sr$_2$CuO$_3$. The low-energy spin excitation does not contribute to the optical response if the electron-phonon coupling is neglected. We find that the THG spectrum can detect the spin excitations even for no electron-phonon coupling. The introduction of the electron-phonon coupling leads to a slight increase of low-energy weight in THG without peak structure through phonon-assisted spin excitation. To fully understand the phonon-assisted spin excitation, we additionally calculate the linear susceptibility of a doped Hubbard-Holstein model, showing a spectral distribution different from that at half filling.

Third-harmonic generation in the presence of classical nonlocal effects in gap-plasmon nanostructures

Classical nonlocality in conducting nanostructures has been shown to dramatically alter the linear optical response by placing a fundamental limit on the maximum field enhancement that can be achieved. This limit directly extends to all nonlinear processes, which depend on field amplitudes. A numerical study of third-harmonic generation in metal film-coupled nanowires reveals that for subnanometer vacuum gaps, the nonlocality may boost the effective nonlinearity by 5 orders of magnitude as the field penetrates deeper inside the metal than that predicted assuming a purely local electronic response. We also study the impact of a nonlinear dielectric placed in the gap region. In this case the effect of nonlocality could be masked by the third-harmonic signal generated by the spacer. By etching the dielectric underneath the nanowire, however, it is possible to muffle such contributions. Calculations are performed for both silver and gold nanowire.

Optimization study of third harmonic generation in quantum cascade lasers.

A systematic optimization study of quantum cascade lasers with integrated nonlinearity for third-harmonic generation is performed. To model current transport the Pauli master equation is solved using a Monte Carlo approach. A multi-objective particle swarm optimization algorithm is applied to obtain the Pareto front. Our theoretical analysis indicates an optimized structure with five orders of magnitude increase in the generated third-harmonic power with respect to the reference design. This striking performance comes with a low threshold current density of about 1.6 kA/cm2 and is attributed to double resonant phonon scattering assisted extraction and injection scheme of the laser.

A theoretical study of third-harmonic generation in semi-parabolic plus semi-inverse squared quantum wells

A theoretical study of third-harmonic generation is performed by using the compact-density-matrix method. An electron is confined in semi-parabolic potential plus semi-inverse squared potential quantum wells. Our calculations show that the absolute value, the imaginary part and the real part of third-harmonic generation coefficients are greatly influenced by the parabolic confinement frequency and the characteristic parameter of the inverse squared potential. The relationship between the absolute value and the imaginary part as well as the relationship between the absolute value and the real part is discussed. It is found that the resonant peaks of the absolute value originate from the imaginary part and are not related to the real part.

Study of third-harmonic generation in zigzag carbon nanotubes using the Green function approach

We study the frequency behavior of third-order nonlinear optical harmonic of metallic and semiconductor zigzag carbon nanotubes. The tight binding model Hamiltonian is considered for electrons on the rolled honeycomb lattice. Based on the relation between nonlinear optical susceptibility and four current correlation function, the third harmonic can be obtained using Green’s function. The effect of the radius of the nanotube on the susceptibility has been investigated. Furthermore, the role of temperature on the behavior of third-order harmonic is studied. The contribution of interband transitions due to the quantum aspects has been brought within the nonlinear response theory as a generalization of the Kubo formalism.

空气中双色场激光诱导三次谐波随时间延迟变化特性的理论研究

空气中双色场激光诱导三次谐波随时间延迟变化特性的理论研究

Green's function formulation for third-harmonic generation microscopy

We report a theoretical study of third-harmonic generation (THG) microscopy by use of a Green’s function formulation. The third-harmonic signal under a tight-focusing condition is calculated for samples with various shapes and sizes. Our results show that THG signals can be efficiently generated at a sizable interface perpendicular or parallel to the optical axis or from a small object with a size comparable to the width of the axial excitation intensity profile. The signal-generation mechanism of THG microscopy is explained by a modified phase-matching condition, |k3-3(k1+Δkg)|l≪π, where Δkg is the wave vector mismatch induced by the Gouy phase shift of the focused excitation field. The relation of the THG power and radiation pattern to the orientation of an interface is investigated. A comparison between signal generation in THG microscopy and that in coherent anti-Stokes Raman scattering microscopy is given.

Third-harmonic generation at atmospheric pressure in methane by use of intense femtosecond pulses in the tight-focusing limit

An experimental study of third-harmonic generation in methane with a 100-fs, 820-nm, Ti:sapphire laser in a tight focusing geometry is presented. The harmonic intensity and bandwidth were measured in a range of intensities extending from below to far above the first ionization threshold and at pressures as high as 10 atm (1 atm=760 Torr). The harmonic signal follows a power-law dependence on the laser intensity with an exponent of ∼7 and saturates at an intensity Is∼4×1014 W/cm2. The conversion efficiency was found to increase with the pressure for laser intensities smaller than the saturation intensity Is and to decrease with the pressure at larger intensities. At laser intensities larger than the saturation intensity a substantial modification in the third-harmonic bandwidth and structure was observed.

Second-Order Nonlinear Eulerian Analysis of a Travelling-Wave Tube Amplifier

A solution of the nonlinear Eulerian fluid-dynamical equation of a helix traveling-wave tube was developed by the method of successive approximation. The nonlinearity was restricted to the second order that could account for the second harmonic generation in the device and could estimate the sensitivity of the second harmonic to the beam and circuit parameters. The second harmonic RF output power relative to the fundamental was found to be controlled by the beam voltage and current; was less for a negative than for a positive dispersion helical slow-wave structure of the device; and could be minimized by optimizing the distributed loss put along the structure. Unlike the Lagrangian approach, the present Eulerian approach gives a closed-form solution, avoiding a large-scale numerical integration of the problem. Hence the present approach is less encumbered and takes less computertime than the Lagrangian approach. Also, the present analysis, though it is exemplified in this paper with particular reference to the second-order nonlinearity for second harmonic generation, is rather general. One can easily extend the analysis to a higher-order nonlinearity, say, to the third order for the study of third harmonic generation, intermodulation distortion etc. The method however has the limitation in that it cannot account for the saturation that is caused by the defocussing of the electron bunch from the RF phase. However, it can be extended to account for the saturation of the fundamental that is caused by the third-order nonlinearity.

Three-photon reststrahl bands near exciton resonances.

Excitation of a KI crystal by a high-power laser in the visible (around 6930 nm) leads to «reflected» light at the third harmonic (around 210 nm). There is a pronounced structure in the spectrum between the longitudinal and the transverse excitons, which is interpreted as a nonlinear reststrahl band. Study of third-harmonic generation in transmission also reveals pronounced structure. An analysis according to Maxwell boundary conditions leads to a good fit to the experimental results