Nonlinear Optical Dispersion Research Articles

Dependence of Structure Variation, Pyrolysis, and Nonlinear Optical Dispersion on the Chemical Etching of Poly Allyl Diglycol Carbonate (PADC) Irradiated with $${\alpha}$$-Particles

Dependence of Structure Variation, Pyrolysis, and Nonlinear Optical Dispersion on the Chemical Etching of Poly Allyl Diglycol Carbonate (PADC) Irradiated with $${\alpha}$$-Particles

Spin coated La2CuO4 thin film: An extensive study on optical dispersion parameters

In this paper, a layered perovskite-type La2CuO4 thin film was deposited on quartz substrate using sol-gel spin coating technique. Though it is a well-studied material, the novelty of the proposed work is the technology adopted for the preparation of this thin film and extensive studies on optical dispersion parameters. The structural characterizations revealed the formation of pure phase ternary La2CuO4 compound with orthorhombic structure. The chemical state analysis detects the valance state of the constituent elements, La, Cu, and O as + 3, (+2,+1) and − 2 respectively. The average grain size was found to be nearly 115 nm from the FESEM images. The surface topography was studied using Atomic Force Microscopy and the root mean square roughness of the film was estimated as 20 nm. The optical studies indicated the semiconducting nature of the compound with a bandgap of 1.6 eV. The refractive index and extinction coefficient have been evaluated from the reflectance data. The linear and non-linear optical dispersion parameters are thoroughly studied using the Wemple and DiDomenico (WDD) single oscillator model. The linear dispersion parameters like the effective single oscillator energy, zero frequency refractive index, optical oscillator strength, and zero frequency dielectric constant have been estimated. Moreover, the nonlinear refractive index, optical susceptibility and optical moments were evaluated. The refractive index and third-order nonlinear susceptibility of La2CuO4 thin film were observed to be higher than some other materials reported in the literature. Thus, this study may be useful in designing La2CuO4-based high-performance devices for optical communications and integrated circuits.

Nonlinear optical dispersion and higher-order effects in bulk and wavelength-ordered photonic materials

The dispersion of the nonlinear optical coefficients and the optical nonlinearities in bulk and wavelength-ordered materials are investigated using numerical simulations and compared with the experimental evidence. The dispersion of nonlinear absorption over a wide spectral region is investigated for materials such as Cadmium Sulfide (CdS) and Reduced Graphene Oxide (rGO) using Kramers-Kronig (KK) integral, invoking two-parabolic model which demonstrates the dominant mechanism for broadband ultrafast optical limiting behavior due to the strong two- and multi-photon absorption processes. The optical nonlinearity in the wavelength-ordered photonic structures ( metal-dielectric and dielectric-dielectric) are investigated by the transfer matrix method (TMM) incorporating the Gaussian single beam nonlinear pulse propagation technique. The optical field is deposited differently at different penetration depths inside the structure. Thus, the nonlinear contributions from individual layers also vary accordingly. In such photonic structures, the nonlinearities are considered to be layer-by-layer contributions and/or an average of the dominant nonlinear layers. The present study can be more effective as compared to the usual analysis of optical nonlinearities in practical applications.

Mechanisms for nonlinear refractive index in organic cavity polaritons

The nonlinear optical response of organic polaritonic matter has received increasing attention due to their enhanced and controllable nonlinear response and their potential for novel optical devices such as compact photon sources and optical and quantum information devices. Using $z$ scans at different wavelengths and incident powers we have studied the nonlinear optical dispersion of ultrastrongly coupled organic cavity polaritons near the lower polariton band. We show that the up to 150-fold enhancement of the nonlinear response compared to a cavityless organic film arises from an intensity-dependent polaritonic resonant frequency shift (``blueshift''). Consequently, we find that these $z$-scan data can only be described by several terms of a power series expansion in intensity whose respective contributions depend on power broadening and detuning from the lower polariton band. We further show that the nonlinear response can be quantitatively described by a semiclassical three-level molecular model coupled to the cavity in which saturation reduces the Rabi splitting, thus accounting for the lower polariton band's observed blueshift.

Nonlinear Lorentz model for the description of nonlinear optical dispersion in nanophotonics simulations [Invited

The Lorentz model provides a simple and intuitive approach to linear optical dispersion. In this paper, we present a nonlinear formulation of the Lorentz model based on an analytical solution of a quantum-mechanical two-level model atom in the under-resonant limit and show how multiple nonlinear Lorentz equations can be combined to describe nonlinear optical dispersion in both time and frequency domain nanophotonics simulations.

Multiphoton Absorption Order of CsPbBr3 As Determined by Wavelength-Dependent Nonlinear Optical Spectroscopy

CsPbBr3 is a direct-gap semiconductor where optical absorption takes place across the fundamental bandgap, but this all-inorganic halide perovskite typically exhibits above-bandgap emission when excited over an energy level, lying above the conduction-band minimum. We probe this bandgap anomaly using wavelength-dependent multiphoton absorption spectroscopy and find that the fundamental gap is strictly two-photon forbidden, rendering it three-photon absorption (3PA) active. Instead, two-photon absorption (2PA) commences when the two-photon energy is resonant with the optical gap, associated with the level causing the anomaly. We determine absolute nonlinear optical dispersion over this 3PA-2PA region, which can be explained by two-band models in terms of the optical gap. The polarization dependence of 3PA and 2PA is also measured and explained by the relevant selection rules. CsPbBr3 is highly luminescent under multiphoton absorption at room temperature with marked polarization and wavelength dependence at the 3PA-2PA crossover and therefore has potential for nonlinear optical applications.

Three‐Dimensional, Time‐Resolved Profiling of Ferroelectric Domain Wall Dynamics by Spectral‐Domain Optical Coherence Tomography

We apply here spectral‐domain optical coherence tomography (SD‐OCT) for the precise detection and temporal tracking of ferroelectric domain walls (DWs) in magnesium‐doped periodically poled lithium niobate (Mg:PPLN). We reproducibly map static DWs at an axial (depth) resolution down to ∼ 0.6 μm, being located up to 0.5 mm well inside the single crystalline Mg:PPLN sample. We show that a full 3‐dimensional (3D) reconstruction of the DW geometry is possible from the collected data, when applying a special algorithm that accounts for the nonlinear optical dispersion of the material. Our OCT investigation provides valuable reference information on the DWs’ polarization charge distribution, which is known to be the key to the electrical conductivity of ferroelectric DWs in such systems. Hence, we carefully analyze the SD‐OCT signal dependence both when varying the direction of incident polarization, and when applying electrical fields along the polar axis. Surprisingly, the large backreflection intensities recorded under extraordinary polarization are not affected by any electrical field, at least for field strengths below the switching threshold, while no significant signals above noise floor are detected under ordinary polarization. Finally, we employed the high‐speed SD‐OCT setup for the real‐time DW tracking upon ferroelectric domain switching under high external fields.

Polarization-selective three-photon absorption and subsequent photoluminescence inCsPbBr3single crystal at room temperature

We report on highly polarization-selective three-photon absorption (3PA) in a Bridgman-grown single crystal of ${\mathrm{CsPbBr}}_{3}$ oriented along the (112) direction, which is an inorganic counterpart to emerging organic-inorganic hybrid halide perovskites for solar-cell and optoelectronic applications. The crystal exhibits strong photoluminescence (PL) at room temperature as a direct consequence of 3PA of fundamental radiation. Interestingly, 3PA disappears when the input polarization is parallel to the $(\ensuremath{-}110)$ direction. This 3PA effect is strongest when orthogonal to $(\ensuremath{-}110)$ and the corresponding 3PA coefficient was measured to be $\ensuremath{\gamma}=0.14\ifmmode\pm\else\textpm\fi{}0.03\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{3}/{\mathrm{GW}}^{2}$ under picosecond-pulse excitation at the fundamental wavelength of $\ensuremath{\lambda}=1200$ nm. The laser-induced damage threshold was also determined to be about 20 GW/${\mathrm{cm}}^{2}$ at the same wavelength. Based on relative PL intensities upon $\ensuremath{\lambda}$ tuning over the entire 3PA range ($1100\text{--}1700$ nm), we determined the nonlinear optical dispersion of the 3PA coefficient for ${\mathrm{CsPbBr}}_{3}$, which is consistent with a theoretical prediction. Experimentally observed significant polarization dependence of $\ensuremath{\gamma}$ was explained by relevant selection rules. The perovskite is potentially important for nonlinear optical applications owing to its highly efficient 3PA-induced PL response with a sharp on/off ratio by active polarization control.

Strong second harmonic generation in LiInX2 (X=Se, Te) chalcopyrite crystals as explored by first-principles methods

Complex first-order linear optical dispersion and complex second-order non-linear optical dispersion of LiInX2 (X = Se, Te) chalcopyrite single crystals were calculated in the framework of the density functional theory using the local density approximation (LDA), general gradient approximation (GGA) and modified Becke-Johnson potential The performed calculations show that these materials posses direct energy band gap (–Γ) of about 1.58 eV (LDA), 1.85 eV (GGA) and 2.04 eV (mBJ) for LiInSe2 and 1.76 eV (LDA), 1.92 eV (GGA) and 2.40 eV (mBJ) for LiInTe2. Comparison with the experimental data unambiguously indicates that the mBJ succeeds by bringing the calculated gaps in close agreement with the measured ones (2.05 eV -LiInSe2 and 2.41 eV -LiInTe2). It has been found that both compounds exhibit negative uniaxial anisotropy and positive birefringence at the static limit. In addition, LiInTe2 exhibits a higher second harmonic generation (SHG) signal than LiInSe2. Moreover, LiInSe2 (LiInTe2) exhibits a SHG signal of about seven (nine) times greater than the corresponding experimental value for the well known KTiOPO4 (KTP) single crystals.

Lead nitrate hydroxide: A strong second-order optical nonlinearity acentric crystal with high laser damage thresholds

A comprehensive theoretical calculation for the complex first-order linear and the second-order non-linear optical dispersion of acentric lead nitrate hydroxide (Pb16(OH)16(NO3)16) single crystals was performed based on the experimental crystallographic data obtained by Chang et al. [Inorg. Chem. 53, 3320–3325 (2014)]. Calculations show an energy band gap of about 3.70 eV, in close agreement to the measured one (3.78 eV). The energy gap value confirms that the Pb16(OH)16(NO3)16 single crystal exhibits an exceptional laser damage threshold. The complex first-order linear optical dispersion helps to get deep insight into the electronic structure and reveals the existence of considerable anisotropy, negative uniaxial anisotropy, and positive birefringence. The calculated second harmonic generation of Pb16(OH)16(NO3)16 at wavelength (λ = 1064 nm) shows a good agreement with the reported measured value. In addition, the microscopic first hyperpolarizability was obtained at the static limit and at the wavelength 1064 nm.

Strong optical nonlinearity of CVD-grownMoS2monolayer as probed by wavelength-dependent second-harmonic generation

While noncentrosymmetric ${\mathrm{MoS}}_{2}$ monolayer is known to exhibit efficient second-harmonic generation (SHG), there is currently no agreement on its absolute nonlinear susceptibility ${\ensuremath{\chi}}^{(2)}$, varying over three orders of magnitude according to recent experiments. In order to resolve this conflicting issue, we have studied the nonlinear optical properties of ${\mathrm{MoS}}_{2}$ monolayer grown by chemical vapor deposition. The polycrystalline nature of the monolayer was directly probed by the SHG polarization dependence across the grain boundaries using femtosecond pulses. Broadband wavelength-dependent SHG response $(\ensuremath{\lambda}=1.1--2.0\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m})$ using picosecond pulses was studied by comparing the relative SHG counts of ${\mathrm{MoS}}_{2}$ to quartz and incorporating the structural and optical characteristics of the monolayer. Significant nonlinear optical dispersion gives rise to ${\ensuremath{\chi}}^{(2)}\ensuremath{\sim}430$ pm/V at 580 nm, where SHG is neither affected by any excitonic absorption/resonance nor by fundamental absorption. We also show that ${\ensuremath{\chi}}^{(2)}$ must be derived from a thin bulk (sheet) optical nonlinearity and that the previous measurements are in fact all consistent, together with our measurements and first-principle calculations.

Photonic time-stretched analog-to-digital converter: fundamental concepts and practical considerations

Ultra-wide-band analog-to-digital (A/D) conversion is one of the most critical problems faced in communication, instrumentation, and radar systems. This paper presents a comprehensive analysis of the recently proposed time-stretched A/D converter. By reducing the signal bandwidth prior to digitization, this technique offers revolutionary enhancements in the performance of electronic converters. The paper starts with a fundamental-physics analysis of the time-wavelength transformation and the implication of time dilation on the signal-to-noise ratio. A detailed mathematical description of the time-stretch process is then constructed. It elucidates the influence of linear and nonlinear optical dispersion on the fidelity of the electrical signal. Design issues of a single-sideband time-stretch system, as they relate to broad-band operation, are examined. Problems arising from the nonuniform optical power spectral density are explained, and two methods for overcoming them are described. As proof of the concept, 120 GSa/s real-time digitization of a 20-GHz signal is demonstrated. Finally, design issues and performance features of a continuous-time time-stretch system are discussed.

非線形自由電子モデルによる有色金属の分光放射率の推定式

The spectral emissivity of metals has been analyzed by the linear equation governing motion of electrons. Such analysis is sufficient if we discuss the spectral emissivity for relatively wide wavelength range from macroscopic viewpoint.When we determine the true temperature from a measured color temperature, we need the accurate spectral emissivity in the narrow wavelength range in the vicinity of the visible ray. But the spectral emissivity of color metals, such as gold and copper, varies roughly depending on wavelength in that range. Therefore the spectral emissivity obtained by the linear dissipation theory does not agree enough to be measured due to the nonlinear characteristic of this phenomenon.In this paper, we take into account the nonlinearity in the equation governing free electrons motion, and using the solution of this equation we derive the nonlinear optical dispersion formula which estimates dependency of the wavelength on spectral emissivity. As the result, by using this formula we have succeeded to describe more accurately the spectral emissivity of color metals which varies roughly with wavelength.