Nonlinear Absorption Effect Research Articles

Study on Nonlinear Absorption Effect of Nanosecond Pulse Laser Irradiation for GaAs.

In order to research nonlinear absorption effect of pulse laser irradiation for GaAs, a physical model of Gaussian distribution pulse laser irradiation for semiconductor material was established by software COMSOL Multiphysics. The thermal effects of semiconductor material GaAs was analyzed under irradiation of nanosecond pulse laser with wavelength of 1064 nm. The radial and transverse temperature distribution of semiconductor material GaAs was calculated under irradiation of nanosecond pulse laser with different power density by solving the thermal conduction equations. The contribution of one-photon absorption, two-photon absorption and free carrier absorption to temperature of GaAs material were discussed. The results show that when the pulse laser power density rises to 10(10) W/cm2, free carrier absorption played a leading role and it was more than that of one-photon absorption of material. The temperature contribution of two-photon absorption and free carrier absorption could be ignored at laser power density lower than 10(8) W/cm2. The result is basically consistent with relevant experiments, which shows that physical model constructed is valid.

Effect of size and indium-composition on linear and nonlinear optical absorption of InGaN/GaN lens-shaped quantum dot**Project supported by the Ministry of Higher Education and Scientific Research in Iraq, Ibnu Sina Institute and Physics Department of Universiti Teknologi Malaysia (UTM RUG Vote No. 06-H14).

Based on the Schrödinger equation for envelope function in the effective mass approximation, linear and nonlinear optical absorption coefficients in a multi-subband lens quantum dot are investigated. The effects of quantum dot size on the interband and intraband transitions energy are also analyzed. The finite element method is used to calculate the eigenvalues and eigenfunctions. Strain and In-mole-fraction effects are also studied, and the results reveal that with the decrease of the In-mole fraction, the amplitudes of linear and nonlinear absorption coefficients increase. The present computed results show that the absorption coefficients of transitions between the first excited states are stronger than those of the ground states. In addition, it has been found that the quantum dot size affects the amplitudes and peak positions of linear and nonlinear absorption coefficients while the incident optical intensity strongly affects the nonlinear absorption coefficients.

Second harmonic generation of q-Gaussian laser beam in preformed collisional plasma channel with nonlinear absorption

This paper presents a scheme for second harmonic generation of an intense q-Gaussian laser beam in a preformed parabolic plasma channel, where collisional nonlinearity is operative with nonlinear absorption. Due to nonuniform irradiance of intensity along the wavefront of the laser beam, nonuniform Ohmic heating of plasma electrons takes place. Due to this nonuniform heating of plasma, the laser beam gets self-focused and produces strong density gradients in the transverse direction. The generated density gradients excite an electron plasma wave at pump frequency that interacts with the pump beam to produce its second harmonics. The formulation is based on a numerical solution of the nonlinear Schrodinger wave equation in WKB approximation followed by moment theory approach. A second order nonlinear differential equation governing the propagation dynamics of the laser beam with distance of propagation has been obtained and is solved numerically by Runge Kutta fourth order technique. The effect of nonlinear absorption on self-focusing of the laser beam and conversion efficiency of its second harmonics has been investigated.

Donor–acceptor molecules based on benzothiadiazole: Synthesis, X-ray crystal structures, linear and third-order nonlinear optical properties

Three π-conjugated donor–acceptor molecules containing either N,N-dimethylaniline or carbazole as the electron donor and 2,1,3-benzothiadiazole as the electron acceptor were synthesized through either Suzuki or Sonogashira cross-coupling reactions. Their X-ray crystal structural, optical, electrochemical properties were investigated. These compounds showed blue-shifted emission in the solid state compared with those in organic solvents. HOMO–LUMO gaps of these compounds estimated from cyclic voltammetry experiments correlated well with those obtained from theoretical calculation results. The nonlinear optical properties of the three D–A molecules were studied using the top-hat Z-scan technique with 21 ps laser pulses at 532 nm. The compound with N,N-dimethylaniline as the donor featuring a more planar configuration makes π-electrons more delocalized, which exhibited large third-order nonlinear absorption and refraction effect.

Principles and applications of trans-wafer processing using a 2-μm thulium fiber laser

A self-developed nanosecond-pulsed thulium fiber laser operating at the wavelength λ = 2 μm was used to selectively modify the front and the back surfaces of various uncoated and metal-coated silicon and gallium arsenide wafers utilizing transparency of semiconductors at this wavelength. This novel processing regime was studied in terms of the process parameter variations, i.e., pulse energy and pulse duration, and the corresponding modification fluence thresholds were determined. The results revealed nearly debris-free back surface processing of wafers, in which modifications could be induced without affecting the front surfaces. The back surface modification threshold of Si was significantly higher than at the front surface due to non-linear absorption and aberration effects observed in experiments. A qualitative study of the underlying physical mechanisms responsible for material modification was performed, including basic analytical modeling and z-scan measurements. Multi-photon absorption, surface-enhanced absorption at nano- and microscopic defect sites, and damage accumulation effects are considered the main physical mechanisms accountable for consistent surface modifications. Applications of trans-wafer processing in removal of thin single- and multi-material layers from the back surface of Si wafers, both in single tracks and large areas, are presented.

Stability properties of a delayed HIV model with nonlinear functional response and absorption effect

The Journal of the National Science Foundation of Sri Lanka publishes the results of research in all aspects of Science and Technology. The journal also has a website at http://www.nsf.gov.lk/. 2021 Impact Factor: 0.682The JNSF provides immediate open access to its content on the principle that making research freely available to the public supports a greater global exchange of knowledge.

Linear and nonlinear characterization of low-stress high-confinement silicon-rich nitride waveguides.

In this paper we introduce a low-stress silicon enriched nitride platform that has potential for nonlinear and highly integrated optics. The manufacturing process of this platform is CMOS compatible and the increased silicon content allows tensile stress reduction and crack free layer growth of 700 nm. Additional benefits of the silicon enriched nitride is a measured nonlinear Kerr coefficient n(2) of 1.4·10(-18) m(2)/W (5 times higher than stoichiometric silicon nitride) and a refractive index of 2.1 at 1550 nm that enables high optical field confinement allowing high intensity nonlinear optics and light guidance even with small bending radii. We analyze the waveguide loss (∼1 dB/cm) in a spectrally resolved fashion and include scattering loss simulations based on waveguide surface roughness measurements. Detailed simulations show the possibility for fine dispersion and nonlinear engineering. In nonlinear experiments we present continuous-wave wavelength conversion and demonstrate that the material does not show nonlinear absorption effects. Finally, we demonstrate microfabrication of resonators with high Q-factors (∼10(5)).

Nonlinear absorption, optical limiting behavior and structural study of a new chalcone derivative-1-(3, 4-dimethylphenyl)-3-[4(methylsulfanyl) phenyl] prop-2-en-1-one

A new third order nonlinear optical (NLO) organic material-1-(3, 4-dimethylphenyl)-3-[4(methylsulfanyl) phenyl] prop-2-en-1-one (4DPMS) belonging to chalcone family has been crystallized in acetone solution. The 4DPMS crystals are characterized by CHNS analysis, FTIR, UV–visible spectral and thermal techniques. The single crystal X-ray diffraction study reveals that 4DPMS crystallizes in monoclinic system with P21/n space group. The linear optical absorption spectrum revealed that the 4DPMS crystals are transparent in the entire visible region. Thermogravimetric data shows absence of phase transition before melting point and from differential scanning calorimetry analysis the melting point of the crystal is found to be 106°C. Third order nonlinear absorption and optical limiting experiment on 4DPMS was carried out using open aperture Z-scan technique with Nd: YAG laser operating at 532nm. It was found that the calculated values of excited state absorption cross section for 4DPMS molecules is much greater than the ground state absorption cross section. A decrease in effective nonlinear absorption coefficient was observed with increase in the input irradiance of laser. The observed optical limiting property in 4DPMS is attributed to reverse saturable absorption.

Synchronous-asynchronous laser mode-locking transition

Synchronous-asynchronous mode-locking transition in a hybrid active and passive mode-locked laser is investigated theoretically. Three distinct mode-locking states are found and their transition diagram under varying detuning frequency and modulation strength is determined. By examining the steady-state lasing gain as a function of the detuning modulation frequency, we also clarify why the laser will become unstable near the transition points and why the nonlinear saturable absorption effect is crucial for the stable asynchronous mode-locking operation.

Plasma absorption evidence via chirped pulse spectral transmission measurements

This work aims at highlighting the plasma generation dynamics and absorption when a Bessel beam propagates in glass. We developed a simple diagnostics allowing us to retrieve clear indications of the formation of the plasma in the material, thanks to transmission measurements in the angular and wavelength domains. This technique featured by the use of a single chirped pulse having the role of pump and probe simultaneously leads to results showing the plasma nonlinear absorption effect on the trailing part of the pulse, thanks to the spectral-temporal correspondence in the measured signal, which is also confirmed by numerical simulations.

Direct detection of the transient superresolution effect of nonlinear saturation absorption thin films

Using a strong nonlinear saturation absorption effect is one technique for breaking through the diffraction limit. In this technique, formation of a dynamic and reversible optical pinhole channel and transient superresolution is critical. In this work, a pump–probe transient detection and observation–experimental setup is constructed to explore the formation process directly. A Ge2Sb2Te5 thin film with strong nonlinear saturation absorption is investigated. The dynamic evolution of the optical pinhole channel is detected and imaged, and the transient superresolution spot is directly captured experimentally. Results verify that the superresolution effect originates from the generation of an optical pinhole channel and that the formation of the optical pinhole channel is dynamic and reversible. A good method is provided for direct detection and observation of the transient process of the superresolution effect of nonlinear thin films.

Rapid assessment of nonlinear optical propagation effects in dielectrics.

Ultrafast laser processing applications need fast approaches to assess the nonlinear propagation of the laser beam in order to predict the optimal range of processing parameters in a wide variety of cases. We develop here a method based on the simple monitoring of the nonlinear beam shaping against numerical prediction. The numerical code solves the nonlinear Schrödinger equation with nonlinear absorption under simplified conditions by employing a state-of-the art computationally efficient approach. By comparing with experimental results we can rapidly estimate the nonlinear refractive index and nonlinear absorption coefficients of the material. The validity of this approach has been tested in a variety of experiments where nonlinearities play a key role, like spatial soliton shaping or fs-laser waveguide writing. The approach provides excellent results for propagated power densities for which free carrier generation effects can be neglected. Above such a threshold, the peculiarities of the nonlinear propagation of elliptical beams enable acquiring an instantaneous picture of the deposition of energy inside the material realistic enough to estimate the effective nonlinear refractive index and nonlinear absorption coefficients that can be used for predicting the spatial distribution of energy deposition inside the material and controlling the beam in the writing process.

Fabrication and optical nonlinearities of composite films derived from the water-soluble Keplerate-type polyoxometalate and chloroform-soluble porphyrin.

Composite films derived from the water-soluble Keplerate-type polyoxometalate (NH4)42[Mo132O372(CH3COO)30(H2O)72]·ca. 300H2O·ca. 10CH3COONH4 (denoted (NH4)42{Mo132}) and chloroform-soluble tetraphenylporphyrin perchlorate [H2TPP](ClO4)2 are successfully fabricated by a layer-by-layer self-assembly method and characterized by UV-vis spectroscopy and X-ray photoelectron spectroscopy (XPS). The structure of the {Mo132} and [H2TPP](2+) in the films remain intact in light of the results of UV-vis spectroscopy and XPS. UV-vis spectra measurements reveal that the amounts of deposition of {Mo132} and [H2TPP](2+) remain constant in every adsorption cycle in the composite films assembly process. Nonlinear optical properties of the composite films have been investigated by using the Z-scan technique at a wavelength of 532 nm and pulse width of 7 ns. The results show that the composite films have notable nonlinear saturated absorption and self-defocusing effects. The combination of {Mo132} with [H2TPP](2+) can result in composite films with remarkably enhanced optical nonlinearities. The interfacial charge transfer induced by laser from porphyrin to POM in the films is thought to play a key role in the enhancement of NLO response. The third-order NLO susceptibility χ((3)) of the composite films increases with the increase of film thickness.

Optical limiting properties and mechanisms of single-layer graphene dispersions in heavy-atom solvents.

The optical limiting (OL) properties of single-layer graphene dispersions in different solvents were studied using a nanosecond pulse laser. The graphene dispersions, especially in heavy-atom solvents, showed much better OL properties compared with referenced C60-toluene solution. The dependences of OL thresholds and nonlinear scattering (NLS) intensities on the solvent surface tensions indicated that, NLS effect played an important role in the OL process of graphene dispersions, while nonlinear absorption (NLA) effect might also contribute in solvents with heavy atoms. The NLA measurements further demonstrated the contribution of NLA effect to the excellent OL property of graphene dispersions in heavy-atom solvents.

Nonlinear Scattering and Absorption Effects in Size-Selected Diphenylpolyynes

The nonlinear optical properties of monodispersed diphenylpolyynes with different chain length were studied by using a nanosecond pulsed laser excitation. A strong optical limiting response was detected at laser fluences above 0.35 J/cm2. The nature of the nonlinear effect as a function of the number of carbon atoms in the linear chain was investigated by the Z-scan technique, determining the molecular second-order hyperpolarizability γ. An interesting coupling was found between the decrease of scattering phenomena and the alignment of longer carbon chains in the focus region. The effect of an external highly intense electric field, combined with a detailed density functional theory (DFT) investigation, has been invoked to explain molecular arrangement, polarizability, isomery, and scattering of diphenylpolyynes. The interesting findings derived from our investigations demonstrate that phenyl-end-capped polyynes could be very interesting for various optoelectronic applications.

Structures and third-order nonlinear optical properties of two cobalt(II) coordination polymers constructed from bis(imidazol-l-yl-methyl)benzene and aromatic dicarboxylic ligands

Two new cobalt(II) coordination polymers, {[Co(OBA)(1,3-bib)]2}n·H2O (1) and [Co(OBA)(1,2-bib)]n·H2O (2), (H2OBA=4,4′-oxydibenzoic acid; 1, 3-bib=1,3-bis(imidazol-l-yl-methyl)benzene; 1, 2-bib=1,2-bis(imidazol-l-yl-methyl)benzene), have been obtained by the hydrothermal reactions. Compound 1 displays a two-dimensional grid net. Compound 2 exhibits a three-dimensional porous network with 12.5% porosity. Their third-order nonlinear optical (NLO) properties were determined by Z-scan technique in DMSO solution. Two compounds show strong third-order nonlinear optical absorption and self-focusing effects with absorptive coefficients β(MKS) 8.29×10−11m·W−1 for 1 and 6.89×10−11m·W−1 for 2, and the refractive indexes γ(MKS) 4.37×10−18m2·W−1 for 1 and 5.22×10−18m2·W−1 for 2. The third-order NLO susceptibility χ(3) are calculated to be 1.86×10−11 for 1, 1.58×10−11esu for 2. These values are larger than those of C60, phthalocyanine derivatives and semiconductor materials.

Microfiber-based few-layer MoS2 saturable absorber for 2.5 GHz passively harmonic mode-locked fiber laser.

We reported on the generation of high-order harmonic mode-locking in a fiber laser using a microfiber-based molybdenum disulfide (MoS(2)) saturable absorber (SA). Taking advantage of both the saturable absorption and large third-order nonlinear susceptibilities of the few-layer MoS(2), up to 2.5 GHz repetition rate HML pulse could be obtained at a pump power of 181 mW, corresponding to 369th harmonic of fundamental repetition frequency. The results provide the first demonstration of the simultaneous applications of both highly nonlinear and saturable absorption effects of the MoS(2), indicating that the microfiber-based MoS(2) photonic device could serve as high-performance SA and highly nonlinear optical component for application fields such as ultrafast nonlinear optics.

Enhanced optical limiting performance in phthalocyanine-quantum dot nanocomposites by free-carrier absorption mechanism

Enhanced nonlinear optical properties (in dimethyl sulphoxide) is observed for 2(3),9(10),16(17),23(24)-tetrakis-(4-aminophenoxy)phthalocyaninato indium(III) chloride (InPc) when covalently linked to CdSe/ZnS or CdSe quantum dots (QDs). The experimental nonlinear optical parameters were obtained from Z-Scan measurements. Contributions from two-photon absorption (2PA) due to the InPc, and free-carrier absorption (FCA) by QDS have been identified as the main factors responsible for the enhanced optical limiting. The effective nonlinear absorption coefficient for InPc-CdSe/ZnS was found to be 700.0cm/GW. The FCA cross-sections for InPc-CdSe/ZnS and InPc-CdSe composites were found to be 1.52×10−19 and 6.00×10−20cm2 respectively. A much lower limiting threshold of 92mJcm−2 was observed for InPc-CdSe/ZnS nanocomposite, hence, making it suitable for use as optical limiting material. Density Functional Theory (DFT) calculations on similar phthalocyanine-quantum dots system was modeled in order to explain the enhancement in the observed nonlinear optical properties of the Pc in the presence of the QDs. The experimentally determined nonlinear optical properties are well within the range of the DFT calculated properties.

ChemInform Abstract: Application of W‐Cu‐S‐Based Secondary Building Units in Functional Metal‐Organic Frameworks

AbstractReview: 57 refs.

Nonlinear Optical Properties of Conjugated Platinum(II) Acetylides with Multibranched Donor–Acceptor Structures

AbstractSix conjugated platinum(II) acetylides with multibranched donor‐acceptor structures (1–6) were synthesized. The absorption maxima of triazine‐centered complexes 1–3 are red‐shifted by 36–43 nm compared with those of triphenylamine‐centered complexes 4–6. The luminescence spectra of 4–6 in air‐saturated chloroform showed one fluorescence peak and one phosphorescence peak. However, only one fluorescence peak was detected for 1–3 in air‐saturated chloroform. The transient absorption spectra of the compounds indicate the effective intersystem crossing from S1 to T1. The nonlinear optical properties of 1–6 in N,N‐dimethylformamide were studied using open Z‐scan method. The results indicate that complexes 1 and 6 exhibit good nonlinear optical performance. The ratios of the effective nonlinear absorption cross section to ground‐state absorption cross section σeff/σ0 of complexes 1–6 are in the range of 4–22.