Complex Third-order Nonlinear Susceptibility Research Articles

Nonlinear optical properties of gold with intense femtosecond laser excitations above the damage threshold

The nonlinear optical properties of gold thin films have been studied under the irradiation of destructive laser pluses. The transmissivity and the reflectivity of a 100-nm-thick gold film are measured with femtosecond laser irradiations up to 106 J/m2 fluence, which is much higher than the damage threshold of gold. The nonlinearity is calculated with Fresnel loss equations. The real part of the complex refractive index is calculated to have a peak at ∼10 kJ/m2, which is close to the damage threshold. The complex third-order nonlinear susceptibility χ3 is estimated to be (4.95 − 2.02i) × 10−21 m2/V2, which agrees with the trend in previous reports that it decreases as the pulse duration decreases. This nonlinearity is further studied with a plasmon-photon exchange (PPE) model, where laser induced plasmons and absorbed photons are strongly correlated. The result of the simulation with the PPE model is in good agreement with the experimental transmissivity above the damage threshold. The model predicted an interaction time between photons and plasmons to be about 500 fs. This model is found to be essential in understanding such nonlinear optical processes under both extremely high and conventionally low laser irradiations.

Complex third-order nonlinear susceptibility of single-layer graphene governing third-harmonic generation

Complex third-order nonlinear susceptibility of single-layer graphene governing third-harmonic generation

Synthesis of selenium nanoparticles and their nonlinear optical properties

Selenium nanoparticles were fabricated using a physical deposition method based on heterogeneous condensation. The Selenium nanoparticles were deposited on a quartz substrate and the ultrafast nonlinear optical responses were investigated by using the [Formula: see text]-scan technique. The nanosize films showed two-photon absorption and a large positive nonlinear refractive index at 800 nm excitation wavelength. The obtained real and imaginary parts of the intensity-dependent complex third-order nonlinear susceptibility of the Selenium nanoparticles ranged from [Formula: see text] to [Formula: see text] (esu) for different irradiance levels.

Large enhancement of third-order nonlinear effects with a resonant all-dielectric metasurface

A novel low-profile nonlinear metasurface, consisting of a single-layer of all-dielectric material, is proposed and numerically investigated by a nonlinear full-wave finite-difference time-domain (FDTD) method. The proposed metasurface is transparent for low, and opaque for high values of incident light intensity. The metasurface design is broadly applicable to enhancement of intrinsic nonlinearities of any material with a sufficiently high refractive index contrast. We illustrate the ability of this design to enhance intrinsic nonlinear absorption of a transition metal oxide, vanadium pentoxide (V2O5), with resonant metasurface elements. The complex third-order nonlinear susceptibility (χ(3)) for V2O5, representing both nonlinear refraction and absorption is considered in FDTD simulations. Our design achieves high initial transparency (>90%) for low incident light intensity. An order of magnitude decrease in the required input light intensity threshold for nonlinear response of the metasurface is observed in comparison with an unpatterend film. The proposed all-dielectric metasurface in this work is ultrathin and easy to fabricate. We envision a number of applications of this design for thin film coatings that offer protection against high-power laser radiation.

Low power optical limiting and thermal lensing in Mn doped ZnO nanoparticles

In the present work, third order optical nonlinearity of chemically synthesized ZnO nanoparticles with different concentrations of Mn (0–20 at %) has been investigated. All the prepared samples exhibit good crystallinity with hexagonal wurtzite phase. A blue shift in the excitonic absorption peak of ZnO (365–350 nm) due to Mn addition is identified from the optical absorption study. Further, emissions at 410 and 465 nm authenticate the presence of zinc vacancy in undoped ZnO and its enhancement in Mn doped samples. Nonlinear optical study carried out by Z-scan method using a 532 nm continuous wave laser excitation reveals the self-defocusing effect with negative sign of the nonlinear refractive index n2. The complex third-order nonlinear susceptibility (χ(3)) is estimated in the range (0.39–1.02) × 10−5 esu. In addition, optical power limiting is also found in Mn: ZnO nanoparticles with low threshold of 20.7 mW. The origin behind the observed nonlinearity and the limiting behavior are discussed in detail.

Complex third-order nonlinear optical susceptibility spectrum of a CdS film coat on a silver nanoparticle

We have fabricated a CdS-coated Ag nanoparticle using the reverse micelle method and observed the nonlinear optical response of the scattered light intensity caused by an individual particle. In addition, we succeeded in obtaining the complex third-order nonlinear susceptibility χ(3) spectrum near the energy band edge of the CdS film by comparing the experimental result and the result of the Mie calculation that considered the optical Kerr effect of the CdS. At ħωi = 2.43 eV, the χ(3) of the CdS was (1.1 + i0.6) × 10−17m2/V2. We conjecture that an increase in the carriers in the interband transition of the CdS originates from the increase in the χ(3) of the CdS at ħωi > 2.4eV.

Determining the cubic susceptibility (3) of films or glasses by the Maker fringe method: a representative study of spin-coated films of copper phthalocyanine derivation

An experimental analysis technique is described for accurate extraction of the coherence length and the complex third-order nonlinear susceptibility χ(3) in films or bulk optical glasses from the Maker fringes obtained by third-harmonic generation measurements. This method permits calculation of the third-order susceptibility of a sample without the need for assumptions as to the magnitude or the phase of the nonlinearity relative to a reference material such as the substrate. To illustrate the utility of the method we study spin-coated films of copper 2,3,9,10,16,17,23,24-octa(1,4,7,10-tetraoxaundecyl)phthalocyanine.