Nonlinear Optical Absorption Research Articles

Third-order nonlinear optical responses of CuO nanosheets for ultrafast pulse generation

As a representative transition metal oxide, cupric oxide (CuO) has attracted a lot of interest in miscellaneous fields. In the present work, the prominent third-order nonlinear optical (NLO) features of CuO nanosheets were demonstrated via the typical Z-scan technique at 1 μm. The open-aperture (OA) Z-scan measurements at different intensities clearly showed that CuO nanosheets possessed the saturable absorption (SA), reverse saturable absorption (RSA) and optical limiting behaviors. The closed-aperture (CA) Z-scan technology was implanted to investigate the nonlinear refractive index and the third-order nonlinear susceptibility. In virtue of the strong nonlinear optical absorption properties of CuO nanosheets, a stable all-solid-state mode-locked laser with the as-prepared CuO nanosheets as saturable absorber at 1.06 μm was realized for the first time. Our work confirmed that CuO nanosheets exhibited outstanding NLO properties, which might stimulate the development in ultrafast photonics and nonlinear optics.

Tunable nonlinear optical properties in magnetic nanoparticles suspension under picosecond laser excitation

In this paper, the intensity-dependent nonlinear optical absorption and nonlinear refraction behaviors of the Fe3O4 nanoparticles suspension exposed to the 1064 nm picosecond laser pulses (25 ps) were investigated by applying the Z-scan technique. A new type of saturation absorption curve of the magnetic fluids was obtained at lower excitation power levels. As the exciting energy increased, the nonlinear absorption changed from saturable absorption to reverse-saturable absorption, while the nonlinear refraction correspondingly reversed from self-defocusing to self-focusing. These interesting tunable nonlinear optical properties were attributed to the inter-valence charge transfer.

Nonlinear optical properties in AlGaAs/GaAs symmetric coupled quantum wells

Based on the density matrix approach and iterative method, we calculated the analytic forms of linear and third-order nonlinear optical absorption coefficients and refractive index changes for symmetric coupled quantum wells (SCQWs) considering a two-level system, and gave the corresponding numerical results. The calculated results show that the optical properties of SCQWs are significantly better than those of asymmetrically coupled quantum wells, and the optical absorption coefficient and refractive index change are affected by the structure parameters of the SCQWs and the incident optical intensity. Their physical mechanisms are elucidated.

Enhancement of optical limiting performance in nanocrystalline La3+ doped ZnO film

Zn1-xLaxO nanofilms were prepared on the glass substrate at 723K using the chemical spray pyrolysis technique. All deposits are hexagonal wurtzite structures with intense plane along the (101) plane. The films doped with 3% La3+ ion showed the least crystalline size with maximum dislocation density. The surface morphology of the deposits changed from fibrous to needles like structure with increased dopant concentration. Both red and blue shifts of absorption edge were noticed as a function of dopant in highly transparent deposited films. A systematic variation of the extinction coefficient and the refractive index was noticed with the incorporation of La3+ in the deposits. Various defects oriented in the films were confirmed by photoluminescence spectra. However, white light emission was found for 4% doped film. Third-order nonlinear optical absorption coefficient (β), susceptibility (χ3) and refractive index (n2) values are 15 × 10−1cm/W, 6.11 × 10−4esu, and −0.34 × 10−5cm2/W, respectively for 3% doped film. It was noticed that Zn0.97La0.03O nanofilm is a more suitable optical limiter application.

Enhanced nonlinear optical properties of RGO via Au modification: application for Q-switched waveguide laser

Both reduced graphene oxide (RGO) and gold (Au) nanoparticles have shown distinct nonlinear optical characteristics, such as saturable absorption, that are appropriate for generating ultrashort pulse lasers. Unfortunately, there are no studies of Q-switched waveguide lasers using RGO and RGO modified with Au nanoparticles (Au-RGO) as saturable absorbers. Here we perform the pump-probe experiments to investigate the nonlinear optical absorption properties of RGO and Au-RGO. Our results show that, compared with RGO, Au-RGO has advantages of a higher modulation depth, faster optical response and wavelength-independent nonlinear absorption, which demonstrates that nonlinear optical properties of Au-RGO have been enhanced owing to the Au nanoparticles. Moreover, the laser emission of Q-switched Nd:YAG channel waveguidewith Au-RGO as a saturable absorber has been obtained. In comparison with the waveguide laser system utilizing RGO, the Q-switched laser observed with Au-RGO exhibits a shorter pulse duration and a higher repetition frequency, indicating the potential application of Au-RGO as a cost-effective saturable absorber in the pulsed waveguide laser systems.

The nonlinear optical absorption in $$\hbox {Al}_{{x}}\hbox {Ga}_{1-x}$$As/GaAs double-graded quantum wells: magnetic field effect and the position-dependent effective mass effect

The nonlinear optical absorption in $$\hbox {Al}_{{x}}\hbox {Ga}_{1-x}$$As/GaAs double-graded quantum wells: magnetic field effect and the position-dependent effective mass effect

Nonlinear Optical Studies of Conjugated Organic Dyes for Optical Limiting Applications

D-π-A conjugated organic dyes made of different donor/acceptor moieties namely Hexylcarbazole (HC), 4,7- Dithiophene-2-yl) benzo[c][1,2,5]thiadiazole (DTBT) and Poly-4-(5-(9-Hexyl-9H-carbazol-2-yl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole (PCTB) were prepared by coupling reactions. FTIR, NMR, and mass spectrometry were used to determine the molecular structure of synthesized compounds. Both HC and DTBT show a wide optical transmittance window (400-600 nm) with absorption maxima in the UV region. However, PCTB shows an altered band structure with a broad absorption in the visible domain (448 nm). Density functional theory (DFT) calculations expose that the bandgap between HOMO and LUMO decreases as the conjugation extends, and redshift occurs in UV-Vis absorption spectra. The emission spectrum of PCBT shows strong emission maxima at 541 nm with the corresponding large Stokes shift 3837 cm−1 due to its enhanced charge transfer property in the excited state. Nonlinear optical absorption was studied by open-aperture Z-scan technique using Nd:YAG laser (532 nm, 10 Hz, 9 ns). Here HC, DTBT exhibit a genuine two-photon absorption (TPA) process while PCTB possesses sequential TPA involving excited-state absorption. All dyes exhibit energy-absorbing optical limiting behaviour ascribed due to the two-photon absorption process. Among the investigated dyes, PCTB polymer shows a higher TPA coefficient (1.22 × 10−10 m/W) and a lower onset optical limiting threshold (1.06 × 1012 W/m2). Thus, the tunability of band structure and nonlinearity with a change in the molecular arrangement was successfully demonstrated in thiophene-benzothiadiazole-based organic dyes.

Principles to tailor the saturable and reverse saturable absorption of epsilon-near-zero material

Indium tin oxide (ITO) films have recently emerged as a new class of functional materials for nonlinear optical (NLO) devices due to their exotic properties around epsilon-near-zero (ENZ) wavelength. Here, we experimentally investigated and tailored the NLO absorption properties of ITO films. The NLO absorption response of ITO films is investigated by using the femtosecond Z-scan measurement technique at two different wavelengths of 1030 nm (out of ENZ region) and 1440 nm (within ENZ region). Interestingly, we observed conversion behavior from saturable absorption (SA) to reverse saturable absorption (RSA) at 1030 nm with the increasing incident laser intensity, whereas only SA behavior was observed at 1440 nm. We demonstrate that SA behavior was ascribed to ground-state free electrons bleaching in the conduction band, and RSA was attributed to three-photon absorption. Moreover, results reveal that ITO film shows more excellent SA performance at 1440 nm with a nonlinear absorption coefficient of ∼ − 23.2 cm / GW and a figure of merit of ∼ 1.2 2 × 10 − 1 6 esu · cm . Furthermore, we tailored the SA and RSA behaviors of ITO films at 1030 and 1440 nm wavelengths via post-annealing treatment. The modulatable NLO absorption was ascribed to the changing of free-carrier concentration in ITO films via annealing treatment. The experimental findings offered an inroad for researchers to tailor its NLO absorption properties by changing the free-carrier concentration through chemical modification such as annealing, oxidation, or defect implantation. The superior and tunable nonlinear optical response suggests that ITO film might be employed as a new class material with potential applications in novel optical switches or optical limiters to realize the all-optical information process.

Enhancement of Nonlinear Absorption in Defect Controlled ZnO Polycrystalline Thin Films by Means of Co‐Doping

The structural, optical, and nonlinear optical absorption properties of ZnO polycrystalline thin films are investigated. Energy bandgap values are obtained with linear absorption spectrum and depending on either sole doping of Al or co‐doping, bandgap energies shift toward higher or lower energies. With Al‐only doping, bandgap of the ZnO thin film shifts toward higher energies which can be attributed to Moss–Burstein effect, and with co‐doping (Al–Cu or Al–Co) bandgap energies shift toward lower energies due to defect states residing within the bandgap. Urbach energies and grain sizes are calculated to study the effect of defect states on the nonlinear absorption, and these calculations indicate that co‐doping drastically reduces the grain size thereby increasing the contribution to the defect density by means of boundary defects. To analyze the transmission in open aperture Z‐scan data, a theoretical model incorporating one‐photon, two‐photon, and free‐carrier absorptions as well as their saturations is used. By this modeling, saturation intensity thresholds and effective nonlinear absorption coefficients are extracted from fitting of the experimental data. Highest saturation intensity threshold and effective nonlinear absorption coefficient are found for ZnO:(Al, Co) and ascribed to having the smallest bandgap energy and highest Urbach energy.

Metal-organic hybrids of tin(IV): Synthesis, crystal structure, third-order nonlinear optical properties and Hirshfeld surface analysis of bis(1,2,3,4-tetrahydroquinolinium) hexahalostannate(IV)

The self-assembled organic-inorganic hybrid materials such as bis(1,2,3,4-tetrahydroquinolinium) hexachlorostannate(IV) (1) and bis(1,2,3,4-tetrahydroquinolinium) hexabromostannate(IV) (2) have been synthesized for their huge applications in opto-non-linear devices. The hybrid materials (1) and (2) have been synthesized and their single crystals were grown by slow evaporation of solution technique (SEST) at room temperature. The presence of protonated NH2 group at 3396 cm–1 in both compounds are confirmed by FT-IR spectral analysis. Diffuse reflectance spectral measurements imply that the tunability of band gap is easily achieved by altering the halide ion. TG-DTA analysis reveals the thermal stability of the compounds is up to 205 °C. Bond valence sum (BVS) calculations performed on SnCl62− and SnBr62− anions (1) and (2), prove the formal oxidation state of tin in the compounds as 4+. The closed and open aperture Z-scan studies ascertained the nature of third order nonlinear optical refraction and absorption of the hybrids. The third-order nonlinear optical susceptibilities χ(3) for the two compounds (1) and (2) are found to be 1.57 × 10−7 esu and 1.46 × 10−7 esu respectively. Investigation of the intermolecular interactions and crystal packing using Hirshfeld surface analysis, derived by single-crystal XRD data, reveals the closer contacts associated with strong interactions.

Characterisation of passively Q-switched Yb:Lu2O3 ceramic laser based on graphdiyne absorber

A stable pulsed Yb:Lu2O3 ceramic laser using graphdiyne (GDY) as a saturable absorber has been successfully demonstrated for the first time. The nonlinear optical absorption of GDY was obtained by a homemade picosecond pulsed solid-state laser at ~1064 nm as the source, which indicate the feasibility of GDY in laser modulation. The passively Q-switched Yb:Lu2O3/GDY laser was carried out. A 288 mW maximum average output power was achieved. The obtained repetition rate, pulse energy and peak power were 46.20 kHz, 6.23 μJ and 3.85 W, respectively, when the absorbed pump power of Yb:Lu2O3 ceramics was 2.3 W. These results indicate that GDY is a promising saturable absorption material and is expected to be widely used in ceramic laser.

C60 nanorods as a promising infrared nonlinear optical material for ultrafast photonics

As a typical one dimensional (1D) crystals, C60 nanorods has attracted widely attention in ultrafast optical field due to its excellent photoelectric properties, including broadened and extended optical absorption, high photosensitivity as well as photogenerated charge carriers mobility. Here, C60 nanorods are synthesized by a liquid-liquid interfacial precipitation method of m-xylene and isopropyl alcohol (IPA) solution. By tuning the solvent amount ratio, a hexagonal close-packed polycrystalline nanorod structure with a broadband absorbance spectrum is achieved. Its’ nonlinear optical absorption characteristics are studied through a balanced twin-detector measurement system. Experimental results show that C60 nanorods has excellent nonlinear absorption with a high modulation depth of ∼16% and a low nonsaturable absorption of ∼4%. Besides, a high optical-to-optical slope efficiency of 7.8% mode-locking all fiber laser is achieved in the optical communication region. The C60 nanorods has great prospect on high effective fiber laser mode locking and open a new way for the development of ultrafast optical devices.

The effect of impurity position and doping concentration on the binding energies and total optical absorption coefficients in a $${\delta }$$-doped quantum well

In this present work, for different impurity position and ionized doping concentrations, we have theoretically investigated the linear, third-order nonlinear, and total optical absorption coefficients corresponding to the $$(1\rightarrow 2)$$ intersubband transitions between the ground and first-excited conduction band states in a single $$\delta $$ -doped GaAs well, with and without the presence of a donor impurity. Impurity binding energies were calculated using the effective-mass and parabolic band approximations within a variational scheme. The linear, third-order nonlinear, and total optical absorption coefficients for the intersubband transitions are calculated within the compact density matrix approach. The obtained results show that adding an impurity positioned at the symmetry center of the well, as well as the increase in the ionized donor concentrations, shifts the total optical absorption coefficients to higher photon energies. However, the off-center positions of impurities together with the varying ionized donor concentrations lead to blue or red shifts in relation to the values of binding energies. The results in this study may be useful for the design and applications of the devices based on the $$\delta $$ -doped structures.

Fabrication of Silver-Decorated Graphene Oxide Nanohybrids via Pulsed Laser Ablation with Excellent Antimicrobial and Optical Limiting Performance.

The demand for metallic nanoparticle ornamented nanohybrid materials of graphene oxide (GO) finds copious recognition by virtue of its advanced high-tech applications. Far apart from the long-established synthesis protocols, a novel laser-induced generation of silver nanoparticles (Ag NPs) that are anchored onto the GO layers by a single-step green method named pulsed laser ablation has been exemplified in this work. The second and third harmonic wavelengths (532 nm and 355 nm) of an Nd:YAG pulsed laser is used for the production of Ag NPs from a bulk solid silver target ablated in an aqueous solution of GO to fabricate colloidal Ag-GO nanohybrid materials. UV-Vis absorption spectroscopy, Raman spectroscopy, and TEM validate the optical, structural, and morphological features of the hybrid nanomaterials. The results revealed that the laser-assisted in-situ deposition of Ag NPs on the few-layered GO surface improved its antibacterial properties, in which the hybrid nanostructure synthesized at a longer wavelength exhibited higher antibacterial action resistance to Escherichia coli (E. coli) than Staphylococcus aureus (S. aureus) bacteria. Moreover, nonlinear optical absorption (NLA) of Ag-GO nanohybrid was measured using the open aperture Z-scan technique. The Z-scan results signify the NLA properties of the Ag-GO hybrid material and have a large decline in transmittance of more than 60%, which can be employed as a promising optical limiting (OL) material.

Wavelength-Dependent Optical Nonlinear Absorption of Au-Ag Nanoparticles

The nonlinear optical absorption properties of Au-Ag nanoparticles (NPs) were studied using an open-aperture Z-scan under a nanosecond pulsed laser with wavelengths of 450 nm, 510 nm, 550 nm, and 600 nm. The experimental results demonstrated that, when the laser intensity was 1.04 × 1013 W/m2, the Au-Ag NPs showed saturated absorption (SA). When the laser intensity was increased to 3.03 × 1013 W/m2, the switch from SA to reverse saturation absorption (RSA) occurred. The nonlinear absorption and its transformation were analyzed by using local surface plasmon resonance (LSPR) effect, bleaching of ground state plasmon, and free carrier absorption theory.

Unlocking the ultrafast potential of gold nanowires for mode-locking in the mid-infrared region.

In this Letter, we present the mode-locking operation of a 2.87 µm Ho3+/Pr3+ codoped fluoride fiber laser, helped by the ultrafast nonlinear optical absorption behavior of gold nanowires (GNWs). The mode locker is fabricated by depositing the GNW solution onto a silver mirror. It has a modulation depth of 14.2%, a saturation intensity of 26.2MW/cm2, and a non-saturation loss of 29.9% at 2.87 µm. With an increased pump power, the laser operates in Q-switched mode-locking, fundamental mode-locking, and harmonic mode-locking (HML) states. This represents the first, to our knowledge, mid-infrared mode-locked laser using gold nanomaterials. Additionally, the HML is also the first observation in a laser in this band using material saturable absorbers, implying the capability of GNWs for high repetition rate generation.

Saturable Absorption Dynamics of Highly Stacked 2D Materials for Ultrafast Pulsed Laser Production

This review summarizes recent developments of saturable absorbers (SAs) based on 2D materials for nonlinear optical absorption and ultrafast pulsed laser generation. Apart from graphene, various 2D materials such as topological insulators and transition metal dichalcogenides are investigated for SA applications and their important potential as passive mode-lockers for femtosecond laser production are extensively investigated. By selecting appropriate 2D materials, a wide spectral range of passively mode-locked pulsed lasers are obtained, covering visible, midinfrared and a terahertz region. A set of different approaches is used for fabricating SA modules of fiber laser photonics, which include sandwiching, side-polishing and tapering methods. Noticeably, through systematic studies, it is demonstrated that layer-stacking seldom deteriorates the SA performance of 2D materials in the evanescent regime, although their ultrathin nature may improve the efficiency in a transmission mode like sandwich-type SAs. The direction for designing new SAs is presented based on material characterization.

Optical properties of spherical quantum dot in the presence of donor impurity under the magnetic field

In this study, the binding energies of an on-center and off-center hydrogenic donor impurity in a spherical quantum dot with finite confinement potential under an applied external magnetic field are investigated in detail by using the matrix diagonalization method in the effective mass approximation. Depending on the calculated energies and wave functions, the linear, third-order nonlinear and total optical absorption coefficients between the ground and several excited states are examined by the iterative method in the compact density matrix approximation for the two-level system. The combined effect of donor position, magnetic field and dot size on binding energies and optical absorption coefficients is observed. The results show that these effects cause significant changes on donor binding energy and optical absorption coefficients.

Gold Nanocluster‐Modified Titanium Nitride for Ultrafast Photonics Applications

AbstractTransition metal nitride materials exhibit unique optical characteristics and have attracted much interest for various applications, including waveguiding, photovoltaics, and nonlinear optical devices. Herein, titanium nitride (TiN), as a typical representative of biocompatible transition metal nitrides, is prepared and modified with gold nanoclusters (Au NCs) for promoting the carrier mobility, and the corresponding physical characteristics are systematically characterized. The TiN‐based saturable absorber (SA) on microfiber is fabricated and its nonlinear optical absorption property is also studied experimentally. Furthermore, the TiN‐decorated SA is applied in an ultrafast fiber laser at the communication bands. The fiber laser can generate the stable ultrashort pulses with a pulse width of 1.66 ps, a fundamental repetition rate of 7.49 MHz, and a spectral bandwidth of 2.61 nm. More importantly, the chaotic multiple pulses can be obtained, which is reported for the first time in the fiber laser based on the TiN SA on microfiber as far as it is known. The chaotic multiple pulses show many interesting characteristics, including high average pulse energy, varying pulse separations, and pulse intensities. These results have proved that the TiN shows great potential in many fields, such as advanced optical‐intensity modulator, ultrafast pulse dynamics, and optical fiber communications.

Regulation and enhancement of the nonlinear optical properties of reduced graphene oxide through Au nanospheres and Au@CdS core-shells.

Regulating nonlinear optical (NLO) absorption and refraction properties of graphene is significant in nonlinear photonics. In this work, the functionalizing strategy of quantum dots (QDs) was used for the regulation of the NLO properties of reduced graphene oxide (rGO) with Au nanospheres and Au@CdS core-shells. The third-order NLO properties of rGO-Au and rGO-Au@CdS nanocomposites were investigated by Z-scan technique with 38 ps laser pulses at 532 nm wavelength. The saturation absorption (SA) of rGO was weakened when it was combined with Au nanospheres and switched to reverse saturation absorption (RSA) when combined with Au@CdS core-shells as irradiance intensity increased. The strength of RSA was tunable with the size of Au@CdS core-shells. Meanwhile, the nonlinear susceptibility of rGO was weakened with the complex Au but was tunable with the complex Au@CdS and realized two times enhancement. The effect of charge transfer mechanism was proposed to explain the regulated effect.