Third-order Harmonic Generation Research Articles

The nonlinear optical properties of a magneto-exciton in a strained Ga0.2In0.8As/GaAs quantum dot

The magnetic field-dependent heavy hole excitonic states in a strained Ga0.2In0.8As/GaAs quantum dot are investigated by taking into account the anisotropy, non-parabolicity of the conduction band, and the geometrical confinement. The strained quantum dot is considered as a parabolic dot of InAs embedded in a GaAs barrier material. The dependence of the effective excitonic g-factor as a function of dot radius and the magnetic field strength is numerically measured. The interband optical transition energy as a function of geometrical confinement is computed in the presence of a magnetic field. The magnetic field-dependent oscillator strength of interband transition under the geometrical confinement is studied. The exchange enhancements as a function of dot radius are observed for various magnetic field strengths in a strained Ga0.2In0.8As/GaAs quantum dot. Heavy hole excitonic absorption spectra, the changes in refractive index, and the third-order susceptibility of third-order harmonic generation are investigated in the Ga0.2In0.8As/GaAs quantum dot. The result shows that the effect of magnetic field strength is more strongly dependent on the nonlinear optical property in a low-dimensional semiconductor system.

Spectral characterization of third-order harmonic generation assisted by a two-dimensional plasma grating in air

A dramatic spectral modulation of third-order harmonic (TH) emission generated in a near-infrared femtosecond (fs) pulse filamentation, assisted by a two-dimensional plasma grating formed by two pump femtosecond pulses, is experimentally demonstrated when their spatiotemporal overlap is achieved. It is mainly attributed to strong cross-phase modulation induced by the fundamental wave of the probe pulse and two pump ones. The delay dynamic of TH spectra indicates the influence of two retarded nonlinear responses on the TH generation. The dependencies of TH generation on the energies of probe and pump pulses, relative field polarization angle are also studied.

Nonlinear Optical Properties of Halogenated Aniline Oligomers

High values of the first (b) and second (g) hyperpolarizabilities were obtained for the halogenated oligomers of the three neutral forms of polyaniline (pernigraniline, emeraldine, and leucoemeraldine). For enhancement of the b and g magnitudes, the t-butyl, t-butoxy, and dimethylamine electron donor groups were introduced into various halogenated oligomers. The effect of the oligomer chain size on the b and g magnitude was also investigated by considering the aniline trimers and hexamers. The highest value of the dynamic b hyperpolarizability (1060 nm) for the second-order harmonic generation (SHG) was found for a pernigraniline hexamer containing fluorine and dimethylamine substituents. The highest g hyperpolarizability magnitudes for the third-order harmonic generation (THG) were observed for all halogenated pernigraniline hexamers containing dimethylamine as a substituent. The AM1/TDHF results show that the halogenated aniline-based molecules are promising candidates for applications in nonlinear optics.

Linear and nonlinear light scattering and absorption in free-electron nanoclusters with diffuse surface: General considerations and linear response

Both linear and nonlinear scattering and absorption of a laser pulse by spherical nanoclusters with free electrons and with a diffuse surface are considered in the collisionless hydrodynamics approximation. The developed model of forced collective motion of electrons confined to a cluster permits one consistently to introduce into the theory all the sources of nonlinearity, as well as the inhomogeneity of the cluster near its boundary. Two different perturbation theories corresponding to different laser intensity ranges are developed in this context, and both cold metal clusters and hot laser-heated or -ionized clusters are considered within the same approach. In the present article, after developing the full nonlinear model, the linear response to the laser field of the free-electron cluster with diffuse surface is investigated in detail, especially the properties of the linear Mie resonance (width and position). Under certain conditions, depending on the various cluster parameters secondary resonances are found. The properties of resonance-enhanced third-order harmonic generation and nonlinear laser absorption and their dependence on the shape of the diffuse surface will be presented separately.

Stabilization of ferroelectricity in KNO 3 embedded into MCM-41 molecular sieves

Measurements of the linear permittivity and third-order harmonic generation were carried out for KNO 3 loaded molecular sieves MCM-41 with pores of 37 and 26 Å in comparison with bulk potassium nitrate. The samples were warmed up to 423 and 463 K from room temperature. The ferroelectric phase III was shown to occur upon cooling in both nanocomposites after warming till 463 K when it emerges also in bulk KNO 3. Nanoconfinement led to the pronounced broadening of the temperature range of ferroelectricity. While under the thermal conditions when phase III does not arise in bulk KNO 3, ferroelectricity was found only within pores of 26 Å.

Field localization and enhancement of phase-locked second- and third-order harmonic generation in absorbing semiconductor cavities

We predict and experimentally observe the enhancement by three orders of magnitude of phase mismatched second and third harmonic generation in a GaAs cavity at 650 and 433 nm, respectively, well above the absorption edge. Phase locking between the pump and the harmonics changes the effective dispersion of the medium and inhibits absorption. Despite hostile conditions the harmonics resonate inside the cavity and become amplified leading to relatively large conversion efficiencies. Field localization thus plays a pivotal role despite the presence of absorption, and ushers in a new class of semiconductor-based devices in the visible and uv ranges.

A Weakly Nonlinear Model for Kelvin–Helmholtz Instability in Incompressible Fluids

A weakly nonlinear model is proposed for the Kelvin–Helmholtz instability in two-dimensional incompressible fluids by expanding the perturbation velocity potential to third order. The third-order harmonic generation effects of single-mode perturbation are analyzed, as well as the nonlinear correction to the exponential growth of the fundamental modulation. The weakly nonlinear results are supported by numerical simulations. Density and resonance effects exist in the development of mode coupling.

Background-free third-order harmonic generation induced by dynamic gratings in dual filaments

Background-free third-order harmonic generation is observed from dynamic gratings induced by dual laser filaments in argon gas. The filaments were generated by focusing two intense 60 fs laser pulses noncollinearly into a gas cell. The optimal result is achieved with gas pressure of 2 atm and zero relative delay. It seems that the off-axis third-harmonic generation is mainly due to the interaction between the two interfering fundamental pulses and their filaments.

Third-Order Intermodulation Distortion and Harmonic Generation in Mismatched Weakly Nonlinear Transmission Lines

This paper describes a procedure to obtain analytical expressions for the spurious signals generated in nonlinear transmission lines with impedance mismatch when they are subject to small-signals. Using these expressions one can rapidly extract the nonlinear parameters describing the nonlinear effects due to the conductor, L(i) and R(i) , such as in superconductors, and/or the nonlinear parameters due to the dielectric, C(v) and G(v) , such as in ferroelectrics. The resulting closed-form expressions have been validated by equivalent circuit simulations. Spurious signal measurements on several coplanar waveguide superconducting and ferroelectric transmission lines have been explained by the use of the resulting closed-form expressions.

Spectral evolution of angularly resolved third-order harmonic generation by infrared femtosecond laser-pulse filamentation in air

We experimentally investigate the evolution of an angularly resolved spectrum of third harmonic generated by infrared femtosecond laser pulse filamentation in air. We show that at low pump intensity, phase matching between the fundamental and third-harmonic waves dominates the nonlinear optical effect and induces a ring structure of the third-harmonic beam, whereas at high pump intensity, the dispersion properties of air begin to affect the angular spectrum, leading to the formation of a nonlinear $\text{X}$ wave at third harmonic.

Multimode anharmonic third-order harmonic generation in a photonic-crystal fiber

While the third harmonic of a monochromatic pump field with a frequency omega0 is generated exactly at the frequency 3omega0, frequency tripling of broadband ultrashort pump pulses in extended nonlinear media tends to generate isolated spectral peaks substantially shifted from 3omega0. We demonstrate this phenomenon by studying nonlinear spectral transformations of femtosecond Cr:forsterite laser pulses in multimode photonic-crystal fibers. Third-harmonic generation is shown to map adjacent guided modes of the third harmonic onto a manifold of spectral peaks within a 150-THz range around 3omega0. The spectral shifts and the widths of these peaks are controlled by the phase and group-velocity mismatch between the pump field and third-harmonic modes, as well as the length of nonlinear-optical interaction and broadening of the pump spectrum, allowing the spectral content of the third-harmonic signal to be engineered by tailoring the fiber dispersion.

Low-threshold supercontinuum generation from an extruded SF6 PCF using a compact Cr4+:YAG laser

The modal properties of an extruded SF6 photonic crystal fiber (PCF) have been analyzed on the basis of a full-vector model. The favorable dispersion properties (the zero-dispersion wavelength for a PCF with 4.5-μm core size lies at approximately 1.5 μm) and the large nonlinearity figure of up to 280 W-1 km-1 may provide more than an octave of spectral broadening with launched pulse energies below 200 pJ. In agreement with simulations, experiments have demonstrated the low-energy spectral broadening under excitation by -–60 70fs pulses from a compact mode-locked Cr4+:YAG laser operating at a 100-MHz repetition rate. Besides the spectral broadening due to the soliton-fission mechanism, the rich mode structure of the fiber allows third-order harmonic generation and four-wave mixing, which extend the supercontinuum spectrum down to the visible-wavelength range.

Multiply subtractive Kramers–Krönig relations for arbitrary-order harmonic generation susceptibilities

Kramers–Krönig (K–K) analysis of harmonic generation optical data is usually greatly limited by the technical inability to measure data over a wide spectral range. Data inversion for real and imaginary part of χ n ( nω; ω,…, ω) can be more efficiently performed if the knowledge of one of the two parts of the susceptibility in a finite spectral range is supplemented with a single measurement of the other part for a given frequency. Then it is possible to perform data inversion using only measured data and subtractive K–K relations. In this paper multiply subtractive K–K relations are, for the first time, presented for the nonlinear harmonic generation susceptibilities. The applicability of the singly subtractive K–K relations are shown using data for third-order harmonic generation susceptibility of polysilane.

Third-order harmonic generation by self-guided femtosecond pulses in air.

Strong third-order harmonic (TH) emission is observed with a conversion efficiency higher than 10(-3) from a plasma channel formed by self-guided femtosecond laser pulses propagating in air. The main characteristics of TH emission in various conditions and the phase-matching condition between the fundamental and the TH wave are investigated. An optimized condition is found, under which the TH conversion efficiency is maximized. Our experimental results show that radiation of the emission in ultraviolet wavelength range makes a major attribution to TH emission, whereas the effects of self-phase modulation are not important when intense laser pulses interact with gaseous media.

Experimental and theoretical study of third-order harmonic generation in carbon nanotubes

Third-harmonic generation from solid samples of carbon nanotubes has been studied experimentally, using ultrashort pulses generated by a Cr:Forsterite laser, at a wavelength of 1250 nm. The results show an unusual nonperturbative behavior of the third-harmonic yield, for relatively low input laser fields, of ∼1010 W/cm2. This strong nonlinearity of the laser interaction with carbon nanoubes is also confirmed theoretically, in a full quantum-mechanical theory for harmonics generation from a single-walled carbon nanotube.

Third-Order Harmonic Generation in Atmospheric Air withFocused Intense Femtosecond Laser Pulses

Generation of third-order harmonics at 800 nm of femtosecond laser pulses isstudied in neutral atmospheric air and in plasma of optical breakdown in air. Itsefficiency is measured at different fundamental laser intensities. A maximumefficiency is observed at the intensity when optical breakdown in atmospheric airstarts. The factors that exhibit the main effects on the harmonic generation, includingself-focusing in a neutral air and self-focusing in plasma, are discussed. PACS: 42. 65. Jx, 42. 65. Ky

Phase matching and harmonic generation in Bessel Gauss–beams

Conversion efficiencies and far-field profiles for third-order harmonic generation in an atomic medium irradiated by an intense Bessel–Gauss beam are calculated with an integral method. The calculation takes into account the nonperturbative variation of the atomic polarizabilities, target depletion by photoionization, and the effect of the free electrons. Numerical results are presented for a pump beam of 355-nm wavelength and up to 3×1013 W/cm2 intensity incident on hydrogen. They are compared with equivalent results for a pure Gaussian pump beam. Significant differences are found that originate from the different phase-matching properties and intensity profile of Bessel–Gauss beams.

Third-order harmonic generation in high-temperature superconducting coplanar waveguides at microwave frequencies

Abstract We use third-harmonic measurements of coplanar waveguide (CPW) transmission lines to explore the behavior of nonlinearities in microwave devices fabricated from high-Tc superconductors. Our measurements focus on the effect of varying the CPW geometry, including center conductor linewidth, line length, and film thickness, on the nonlinearity of the transmission line circuit as measured by the third-order intercept. The third-order intercepts decrease (indicating more nonlinearity) with increasing line length for all geometries studied. Also, differences in the third-order intercepts between lines of different linewidth and film thickness can be explained quantitatively by appropriately scaling the incident microwave power. These observations demonstrate that the sources of nonlinearity in our CPW transmission lines are distributed along the line length, and depend on the detailed form of the current distribution within the superconductor.

Ultrafast response of third-order optical nonlinearity in glasses containing Bi_2O_3

We prepared nonresonant-type homogeneous glasses containing Bi(2)O(3) by the melting method. The thirdorder optical nonlinear susceptibility chi((3)) was found by third-order harmonic generation measurement to be 9.3 x 10(-12) esu. We attribute the nonlinearity of these glasses to the large molar refraction of glasses containing Bi(2)O(3). These glasses also exhibited an ultrafast response time below 200 fs by a degenerate fourwave mixing method using a femtosecond laser, indicating that the nonlinearity of these glasses originated mainly from pure electronic polarization.

Third-order nonlinear optical properties of new soluble poly 1,4-bis[2,4,6-tri(4-n-heptylphenyloxy)-3,5-difluorophenyl]butadiyne

A new soluble polydiacetylene with fluoro-aromatic rings directly attached to the π-conjugated main-chain backbone was synthesized by γ-radiation solid-state polymerization. The blue thin films of poly(fluorophenyl-diacetylene) could be only obtained from its red chloroform solution by a spin-coating technique. The third-order nonlinear optical susceptibilities of spin-coated amorphous thin films of poly (fluorophenyl-diacetylene) were measured by third-order harmonic generation. The third-order nonlinear optical coefficient susceptibility χ (3) calculated by comparing the 3ω signal intensity of sample with that of a standard fused silica plate, was about 6.4 × 10 −11 esu.