Nonlinear Absorption Effect Research Articles

A compliant helical structure to amplify inertia for nonlinear vibration absorption

The vibration absorption is a passive approach for vibration control by attaching a secondary vibration system to realize the energy transfer and dissipation. To generate a sufficient inertial force, vibration absorbers need to introduce large additional mass, and thus the engineering applications are limited. In this study, a novel compliant structure is proposed with the inertial amplified through a helical movement, and the structure is adopted for nonlinear vibration absorption. The dynamic equations of the absorber are established based on the Lagrange equation, characterizing the nonlinear characteristics arising from the large deformation of the structure and the nonlinear kinetic relationship between the translation and the rotation. Amplitude-frequency responses of the absorber under different excitations are solved using the harmonic balance method and the arc-length continuation method. A rotation-inertial dominant absorber (RIDA) and a translation-inertial dominant absorber (TIDA) are fabricated with the same helical structure while different mass distributions and experiments are performed to validate the nonlinear characteristics and vibration absorption effects. It is observed that both RIDA and TIDA demonstrate effective vibration absorption performances., RIDA introduces smaller additional mass than TIDA. The proposed helical structure absorbers exhibit combined nonlinearities of softening stiffness and displacement-dependent inertia and damping, demonstrating resonance shifting and jump phenomena. With an increasing excitation amplitude, the vibration absorption efficiency decreases and then increases.

Surface plasmonic Au nanoparticles assisted CuO nanorods for broadband diverse ultrafast pulse generation

In virtue of the local surface plasmon resonance (LSPR) properties of metal nanoparticles to enhance the nonlinear optical response of the material, we successfully embed small-size Au nanoparticles into CuO nanorods. Then, theoretical and experimental methods verify that the assistance of ultrafast plasma response enhances the light-matter interaction. The LSPR characteristics and evanescent field distribution of the Au-CuO saturable absorber on the tapered fiber are studied by the finite element simulation method (FEM). By utilizing the Z-scan technology and twin-balanced detector system, excellent nonlinear optical (NLO) properties of the Au-CuO nanorods are demonstrated. Subsequently, depending on the remarkable nonlinear saturable absorption effect of Au-CuO, multiple operating states such as Q-switched, conventional soliton, double-subpulse soliton cluster, and noise-like pulse mode-locking are achieved in the erbium-doped fiber ring cavity at 1.5 μm. In addition, dual-wavelength mode-locking pulses with the center wavelengths of 1031 nm and 1035 nm are realized in the ytterbium-doped fiber ring cavity. This work describes an effective strategy to improve the NLO properties of CuO nanorods and indicates the great potential of Au-CuO in pulsed fiber lasers, opening a path for its application in ultrafast photonics and optoelectronics.

Design of Holographic Condenser Lens for Visible Light Lithography

Photolithography with visible light at λ = 405 nm utilizing the concept of nonlinear saturable absorption effect where the size of the spot is diminished to the nanometer scale as proposed by several researchers is an alluring proposition for cost-effective projection lithography. Costly conventional condenser lenses can be replaced by monochromatic aberration-free and cost-effective volume phase holographic lenses for visible light photolithography with enhanced resolution utilizing the concept of off-axis illumination. However, the diffraction efficiency of holographic lenses depends on the wavelength of illuminating light and the angle of illumination. Angular and spectral characteristics of volume phase holograms can be controlled by optimizing processing parameters. The results on the theoretical optimization of three important processing parameters, namely fringe spacing ( ∧ ), thickness of the film ( d ), and refractive index modulation ( Δ n ) in the light of coupled wave theory for recording holographic lenses of high diffraction efficiency at λ = 405 nm are presented. It is pointed out that a properly designed single holographic lens can be used for off-axis illumination of a photomask with a parallel beam of light, whereas a system of two identical holographic lenses cemented together has to be used to realize a condenser lens similar to a converging lens.

Self action effects of q-Gaussian laser beam in preformed parabolic plasma channels: effect of nonlinear absorption

Self action effects of q-Gaussian laser beam in preformed parabolic plasma channels: effect of nonlinear absorption

Porous nano-grained cuprous selenide (Cu2Se) for mid-infrared photonics

Recently, mid-infrared photonics has attracted tremendous attention for various applications. To address the dilemma of the limited variety of materials for mid-infrared photonics, the mid-infrared optical modulation characteristics of the porous nano-grained cuprous selenide (Cu2Se) were investigated for the first time. The large effective nonlinear absorption coefficient, large modulation depth, and low saturation absorption intensity at 2.3 μm indicate that the porous nano-grained Cu2Se were promising saturable absorbers for the generation of Q-switched pulsed laser in the mid-infrared regime. As an application, the Tm:GdVO4 passively Q-switched laser operating on the 3H4 → 3H5 Tm3+ transition was achieved for the first time by using the prepared porous nano-grained Cu2Se as the saturable absorber. The minimum pulse duration and the maximum repetition rate of the stable Q-switched pulse train were 440 ns and 76.9 kHz, respectively. Our results demonstrated that the porous nano-grained Cu2Se was a promising candidate for the mid-infrared photonic applications.

Ge-polymer bridge waveguide for mode-locked laser pulse generation.

A Ge-polymer hybrid waveguide is sandwiched between an indium phosphide (InP) reflective gain chip and a fiber Bragg grating (FBG) to construct a laser system. The hybrid waveguide serves as a bridge between the gain chip and the fiber with tailored mode-field matching at both facets. The 50-nm amorphous Ge (α-Ge) layer shows a nonlinear absorption effect at 1550 nm. The hybrid waveguide is further verified by a femtosecond laser transmission experiment to show the pulse width compression effect. Such waveguide is then integrated inside the laser cavity as a passive saturable absorber to modulate the longitudinal modes for a pulsed output. This polymer-bridged mode-locked laser adopts an InP gain chip for compact assembly and also a FBG with a flexible length to adjust the pulse repetition rate. The mode-locked laser output around the designed 50 MHz repetition rate is demonstrated. The pulse width is measured as 147 ps, and the signal-to-noise ratio is larger than 50 dB. This work introduces a "ternary" mode-locked laser system, taking advantage of discrete photonic components bridged by a polymer-based waveguide. It also proves the feasibility of applying α-Ge films as practical and low-cost saturable absorbers in photonic devices.

Quadruple Gaussian laser beam in cubic-quintic nonlinear media: effect of nonlinear absorption

Quadruple Gaussian laser beam in cubic-quintic nonlinear media: effect of nonlinear absorption

Modifying optical nonlinearities of ionic liquid crystal glass by adding gold and carbon nanoparticles

Future disruptive photonics technologies depend on the development of new types of nonlinear-optical glass composites containing nanoparticles. In this paper, we report the synthesis, structural characterization, spectral and nonlinear-optical properties of overlooked yet very promising glass nanocomposites made of glass forming ionic liquid crystals (cadmium caprylate) and two types of nanoparticles (gold and carbon). Nonlinear-optical properties of the prepared nanocomposites are studied by means of a standard Z-scan method and using visible (532 nm) nanosecond laser pulses. By exciting glass nanocomposites within their absorption band, an interplay between several nonlinear-optical mechanisms can be revealed. A simultaneous use of two types of nanoparticles (i.e. carbon and gold) enables a better control over effective optical nonlinearities of nanocomposites. More specifically, by changing an intensity of a laser beam, it is possible to vary the magnitude of the effective nonlinear refractive index and of the effective nonlinear absorption coefficient. In addition, even the sign of the effective nonlinear absorption coefficient can be changed. The proposed strategy to create novel nonlinear-optical materials using metal-alkanoates based glass-forming ionic liquid crystals and several types of nanoparticles will benefit rapidly growing nanophotonics and plasmonics technologies.

Enhanced Femtosecond Nonlinearities and Multiphoton Absorptions in Discrete Bands of Porphyrins.

Optical nonlinearities of discrete absorption energy levels of one of the typical heterocyclic aromatic molecules, free-base porphyrins, have been probed over a broad spectral region (400-1600 nm) utilizing intense femtosecond pulses. A wide range of strong one- and multiphoton-induced nonlinear absorptions of both the blue-end Soret (B) band (au → b1g) and red-end orbital mixing split quasi-allowed Q-bands (Qx(0,0; 0,1), Qy(0,0; 0,1), au → eg) are critically probed and reported. During the resonant excitation within B- (400 nm) and Q-bands (600-750 nm), the nonlinear absorption has become predominant by the saturation of absorption (SA) of the one-photon absorption (1PA) process due to ground-state bleaching. At nonresonant wavelengths, it is dominated by the reverse saturation of absorption (RSA), involving various nonlinear processes of two-, three-, and four-photon (2PA, 3PA, and 4PA) absorptions, either to B- or Q-bands (1100-1600 nm). The laser intensity-dependent nonresonant (2PA, 800 nm) excitations for the prominent B-band show a distinct cross-over from SA to RSA, contributed by the excited-state absorption (ESA) utilizing a three-photon induced (3PA) process, whereas resonant (1PA, 400 nm) excitation reveals a systematic strong SA process. Both wavelength- and intensity-dependent nonlinear refractive index studies exhibit positive electronic Kerr-based self-focusing effects, with prominent contributions of nonlinear absorption and higher-order effects. The spectrally discrete, highly intense laser probing of individual energy bands and the consequent variety of nonlinearities can be broadly generalized for many free-base porphyrins and metalloporphyrins. The present studies provide a strong foundation and new insight into the broad categories of macrocycles, such as porphyrins and phthalocyanines, for myriad applications in nonlinear optics and bio/optophotonics.

一种逐级超分子组装策略用于显著提高簇合物的三阶非线性光学响应

Developing practical optical materials with strong third-order nonlinear optical (NLO) responses attracts increasing attention. Efforts in this area extend to the activation of appropriate materials and the magnification of their low NLO responses. Herein, we propose a stepwise assembly-amplification strategy to enhance the NLO responses of low NLO-active metal sulfide clusters. Through a self-assembly process, W/Cu/S cluster-based tetrahedral and octahedral cages are successfully obtained, both exhibiting weak NLO responses in solution that are not apparent for the unassembled components. Their incorporation into polyvinyl alcohol (PVA), followed by spin-coating, results in the formation of cluster@PVA composite membranes with controlled thicknesses. Remarkably, the effective nonlinear absorption coefficients β for 12-layered membranes are 104 times higher than those of the respective cage solutions. The octahedral cage delivers a stronger response than the tetrahedral cage, which likely reflects the higher degree of aggregation of the clusters. This work showcases a new approach for amplifying NLO responses, greatly facilitating the development of integrated photonic devices.

Gold Nanomaterial‐Based Optical Modulators for Wideband Pulse Laser Generation

Pulsed lasers have wide applications in several fields, such as basic research, telecommunications, and industrial materials processing. A saturable absorber (SA) is a key component for pulse laser generation. However, the current SAs exhibit certain limitations. Hence, developing new nonlinear optical materials as SAs for pulse lasers generation is significantly important in ultrafast photonics and related applications. Metallic nanomaterials have attracted considerable attention because of their higher nonlinearity coefficients and wideband nonlinear response, which are induced by the surface plasmon resonance (SPR) effect. The SPR effect depends on the size and morphology of materials. Thus, the nonlinear optical absorption effect of gold nanomaterials for pulse laser generation must be explored. In this review, the optical properties of gold nanomaterials are introduced, including SPR absorption, photoluminescence properties, and surface‐enhanced Raman scattering effect. Then, the synthesis and characterization of different gold nanomaterials are reviewed. Subsequently, the nonlinear optical characteristics and devices based on gold nanomaterials are also introduced. Furthermore, the generation of different types of lasers using gold nanomaterial‐based devices is also reviewed. A comparison between gold nanomaterials and other SA materials is presented. Finally, the conclusion and outlook on gold nanomaterial‐based nonlinear optical devices are presented.

Linear and nonlinear characterization of a broadband integrated Si-rich silicon nitride racetrack ring resonator for on-chip applications.

We demonstrate the linear and nonlinear characterization of a plasma-enhanced chemical vapor deposited silicon-rich silicon nitride (SRSN) racetrack ring resonator for on-chip applications within the telecommunication wavelength range. The SRSN waveguide parameters are optimized by employing the refractive index profile measured by ellipsometry to achieve flat dispersion in the telecom band. Furthermore, we measure the thermo-optic coefficient of the micro-resonator by analyzing the temperature-dependent transmission spectra and assess it to be 3.2825×10-5 ∘ C -1. Additionally, we study power-dependent transmission spectra to investigate the effect of local heating and nonlinear absorption. The power-dependent transmission spectra exhibit a blueshifting of the resonance peak in the visible and near-IR regions, which indicates the presence of nonlinear losses in that range. The power-dependent transmission spectra almost remain unchanged in the telecom band, revealing the absence of nonlinear losses and excellent thermal stability in that wavelength range. Our experimental results reveal that the SRSN-based structure can be employed potentially to realize linear and nonlinear applications in the telecom band.

Investigation on the saturable absorption characteristics of GeNS and its application to harmonic mode‐locked modulation

AbstractThe high‐quality germanene nanosheets (GeNS) were fabricated by a liquid‐phase exfoliated technique and used as the saturable absorber (SA) to generate the harmonic mode‐locked (HML) pulses in an Er‐doped fiber laser. The investigation on the nonlinear absorption effect of the GeNS was carried out systemically in this work. On the basis of the GeNS SA, the third‐ and fourth‐order HML pulses with repetition rates of 5.275 and 7.031 MHz were achieved, corresponding to the minimum pulse width of 3.04 and 3.21 ps, respectively. The research reveals that the GeNS has great capability for ultrafast pulses modulation and can be used as an outstanding nonlinear optical device to expand its applications in nonlinear optics.

Au–WS2 Nanohybrids with Enhanced Optical Nonlinearity for Optical Limiting Applications

Utilizing plasmonic effects of metal nanostructures on tailoring the properties of semiconducting materials has gained substantial research attention in the past 10 years. Here, we report the plasmon resonance-induced enhanced optical nonlinearity of Au–WS2 nanohybrids prepared via the blending of liquid phase exfoliated few-layer WS2 nanosheets with chemically synthesized spherical gold nanoparticles (NPs). Nonlinear optical properties were studied using the open aperture Z-scan technique with nanosecond laser pulses of wavelength 532 nm, which lie in the plasmonic band of Au NPs (480–550 nm) and B-excitonic transition range of WS2 nanosheets (520–535 nm). Au–WS2 nanohybrids exhibited an enhanced nonlinear absorption and optical limiting activity with an effective nonlinear absorption coefficient of 182 cm/GW at an on-axis input intensity of 0.14 GW/cm2, which is 3.87 times higher than that of bare WS2 nanosheets. The improved NLO response of nanohybrids is due to the plasmon resonance-induced local field effects, which significantly enhance B-excitonic transitions in WS2 nanosheets. The simulated field intensity enhancement profile also confirmed the effect of formation, where a strong interaction of plasmonic fields with WS2 nanosheets is clearly visible. The enhancement observed in simulated absorption density profiles indicated improved B-excitonic transitions in WS2 nanosheets due to the resonant plasmonic field. Au–WS2 nanohybrids exhibited a low limiting threshold of 0.55 J/cm2, which is better than that of many eminent nanohybrids reported so far. The strategy followed in this work for attaining superior nonlinear optical responses in Au–WS2 nanohybrids will be useful to develop novel nonlinear optical materials for photonic device applications.

Third-order optical nonlinearity and passively Q-switching operation with BiOCl nanosheets at 1.3 µm.

In this contribution, we measured the third-order nonlinear optical response of bismuth oxychloride (BiOCl) nanosheets with the open-aperture (OA) and the closed-aperture (CA) Z-scan techniques with a variable excitation intensity at 1.34 µm. The effective nonlinear absorption coefficient βeff and the nonlinear refractive index n2 of the prepared BiOCl nanosheets with abundant oxygen vacancies were obtained under the excitation intensity. The third-order nonlinear optical susceptibility |χ(3)| was 1.64 × 10-9 esu. The nonlinear optical features of BiOCl enabled it as a superb saturable absorber for pulse laser generation. As a consequence, we demonstrated the first passively Q-switched Nd:GdVO4 laser with the BiOCl saturable absorber, producing a shortest pulse duration of 543 ns and a highest repetition rate of 227 kHz, leading to a maximum pulse energy of 74 nJ. Our findings show that BiOCl nanosheets with oxygen vacancies have large nonlinear optical sensitivities and can be exploited to generate optical pulses.

Modulating the nonlinear absorption response of SnOx thin films via phase engineering.

Phase (composition) is known to play a key role in determining the electronic and optical properties of amorphous oxide semiconductors. In this work, modulating the ultrafast nonlinear optical (NLO) response of SnO2 and SnO thin films by tuning oxygen partial pressure during film sputtering is explored. Femtosecond Z-scan results demonstrate that intermediate phases have no profound impact on the two-photon absorption (TPA) response of SnO2 and SnO films. Interestingly, the magnitude of the effective nonlinear absorption coefficient (βeff) of both intermediate SnO2-x and SnOx are enhanced after the change of Sn2+/Sn4+ composition ratio, as measured by picosecond Z-scan technique. Femtosecond degenerate pump-probe measurements show that intermediate phases accelerate the carrier trapping and improve the defect-related carrier absorption in SnOx (SnO-rich) film, while intermediate phase suppress the TPA response of SnO2-x (SnO2-rich) films, therefore carrier-induced absorption dominates the NLO behavior of SnO2-x film on picosecond regime. Our results indicate a simple and effective way to modulate the NLO response of transparent conductive oxide SnO2 and SnO.

Second-harmonic generation of intense Laguerre Gaussian Beam in collisional plasma: Effect of nonlinear absorption

Second-harmonic generation of intense Laguerre Gaussian Beam in collisional plasma: Effect of nonlinear absorption

MXene-Nanoflakes-Enabled All-Optical Nonlinear Activation Function for On-Chip Photonic Deep Neural Networks.

2D metal carbides and nitrides (MXene) are promising material platforms for on-chip neural networks owing to their nonlinear saturable absorption effect. The localized surface plasmon resonances in metallic MXene nanoflakes may play an important role in enhancing the electromagnetic absorption; however, their contribution is not determined due to the lack of a precise understanding of its localized surface plasmon behavior. Here, a saturable absorber made of MXene thin film and a silicon waveguide with MXene flakes overlayer are developed to perform neuromorphic tasks. The proposed configurations are reconfigurable and can therefore be adjusted for various applications without the need to modify the physical structure of the proposed MXene-based activator configurations via tuning the wavelength of operation. The capability and feasibility of the obtained results of machine-learning applications are confirmed via handwritten digit classification task, with near 99% accuracy. These findings can guide the design of advanced ultrathin saturable absorption materials on a chip for a broad range of applications.

Nonlinear optical limiting effect and charge transfer dynamics in a Fe-porphyrin metal-organic framework

The nonlinear absorption effect in a Fe-porphyrin metal-organic framework (Co-TCPP(Fe) MOF) was studied using the nanosecond Z-scan technique, which showed an enhanced reverse saturation absorption (RSA) compared with TCPP(Fe) ligand. By femtosecond transient absorption (fs-TA) measurements, the charge transfer dynamics of MOF are unveiled. Compared with TCPP(Fe) ligand, the ultrafast formation of charge separation states (CSSs) with extra-long lifetime (> 3.5 ns) detracts the recombination of electron-hole pairs, resulting in an enhanced excited state absorption (ESA). Based on the strong ESA caused by CSSs absorption, the MOF nanosheets showed an excellent optical limiting (OL) effect with the OL threshold of 0.89 J/cm2.

Crack-free high-aspect ratio holes in glasses by top–down percussion drilling with infrared femtosecond laser GHz-bursts

We report novel results on top-down percussion drilling in different glasses with femtosecond laser GHz-bursts. Thanks to this particular regime of light–matter interaction, combining non-linear absorption and thermal cumulative effects, we obtained crack-free holes of aspect ratios exceeding 30 in sodalime and 70 in fused silica. The results are discussed in terms of inner wall morphology, aspect ratio and drilling speed.