Reverse Saturable Absorption Research Articles

Study of femtosecond nonlinear optical coefficients for Bi doped Se85-xTe15Bix chalcogenide thin films

The present work reports the influence of selenium replacement by bismuth on the nonlinear optical parameters of ternary Se85-xTe15Bix (x=0, 1, 2, 3, 4, 5 atomic %) chalcogenide thin films. Calculation of nonlinear refractive index (n2), two-photon absorption coefficient (β2) and third-order susceptibility (χ (3)) by well known Z-scan technique with femtosecond laser pulses were done. The Z-scan spectra for Se85-xTe15Bix upto Bi= 4 atomic % results in self- focusing behavior of n2 is positive while for Bi=5 atomic % n2 is negative. The behavior of n2 by using different physical parameters are exlpained. The comparison of experimental and theoretical values of n2 with pure silica are also studied. The presence of the valley at focus in open aperture Z-scan graph demonstrates strong reverse saturable absorption. The figure of merit (FOM) for the SeTe-Bi chalcogenide thin films is found to be less than 1 and are beneficial for all-optical switch devices.

Minimized thermal effects and strong two-photon absorption of aluminum, silver doped platinum bi-metal nanoparticles

Herein, for the first time, we have investigated the strong nonlinear optical (NLO) properties aided with minimal thermo-optical effects in silver-platinum (Ag-Pt) nanoparticles (NPs) using Z-scan technique with high repetition rate femtosecond pulses at 700 nm. The NPs were synthesized using ultrafast laser ablation of Ag/Al targets immersed in the Pt colloidal solutions in isopropyl alcohol (IPA). We observed reverse saturable absorption (RSA)/two-photon absorption (2PA) behavior in Ag-Pt NPs (with 0.5 mM concentration of Pt), W-shaped switching behavior in Ag-Pt NPs (with 1 mM concentration of Pt), and RSA/2PA behavior in Ag-Pt NPs (with 3 mM concentration of Pt). The multiple-stage nonlinear absorption phenomenon is attributed to the interchange of pure 2PA or excited-state absorption, and 2PA saturation effects. Additionally, the broadband third-order NLO properties of aluminum-doped Pt (Al-Pt) bi-metallic NPs were obtained using spectral-dependent Z-scan studies at 700 nm, 800 nm, and 900 nm. The results revealed that Al-Pt bi-metallic NPs exhibited strong saturable absorption (SA), 2PA, and switching from SA to RSA. It is also revealed from the closed aperture Z-scan data that Ag-Pt and Al-Pt bi-metallic NPS exceed thermal contribution with strong 2PA coefficients unprecedentedfor single metal NPs. In the case of Ag-Pt NPs, strong 2PA saturation effects are attributed to the filling of Ag-O anti-bonding states by the photo-excited electrons and then charge transfer to the Pt plane. In the case of Al-Pt NPs, strong 2PA phenomena are ascribed to the enhancement of charge carriers in the conduction band and, hence, the strong surface plasmon resonances. The 2PA coefficients were evaluated to be ∼10−7 cm/W. The superior and switching NLO effects indicate that these materials might be utilized for potential applications, including optical modulators, and all-optical switching devices.

Fine-Tuning Tridentate Ligands for the Construction of Nanotube-Based Boron Imidazolate Frameworks with High Chemical Stability

Two unusual nanotube-based boron imidazolate frameworks (BIF-134 and BIF-135) were synthesized by a dual-ligand synthetic strategy under solvothermal conditions. In the structure of BIF-134 ([Co(BH(2-mim)3)(BTC)1/3](HBH(2-mim)3)1/3(NMA); 2-mim = 2-methylimidazole, NMA = N-methylacetamide, and BTC = 1,3,5-benzene tricarboxylate), one part of boron imidazolate ligands participate in the structural skeleton coordination, while another part of boron imidazolate ligands act as guest molecules that are located between adjacent nanotubes, which enhance the stability of the framework by the host-guest interaction and the pore space partition effects. It was found to be highly stable in air, water, organic solvents, and a wide pH range (pH 0-12). However, in the structure of BIF-135 ([Zn(BH(2-mim)3)(CHTC)1/3]; CHTC = 1,3,5-cyclohexanetricarboxylate), all boron imidazolate ligands participate in the structural skeleton coordination; there is no boron imidazolate guest molecule in the pores. The topology of BIF-135 is similar to that of BIF-134 by replacing BTC with CHTC and replacing Co with Zn. Furthermore, the obtained BIFs exhibited third-order nonlinear optical properties and potential optical limiting applications demonstrated by reverse saturable absorption.

Impact of defects on the χ(3) optical nonlinearity of sputtered WSe2 thin films in the optical communication band

We present an experimental investigation on third-order nonlinear optical properties of RF-sputtered WSe2 thin films using a single-beam Z-scan technique around the optical communication window in a near-infrared spectral band. The nonlinear absorption coefficient was obtained from the open-aperture Z-scan transmission using ultrashort pulses centered at 1520nm excitation wavelength. The results show a reverse saturable absorption signature for all the WSe2 films due to two-photon absorption (TPA) mediated electronic transitions. The dependency of the TPA coefficient on film thickness is analyzed through the modification in an electronic band structure essentially caused due to defects induced in the samples. In addition, we also explored the impact of high laser intensity on the TPA process, which essentially pointed toward a significant contribution of free-carrier absorption at small laser intensities in WSe2 thin films. This investigation provides a basis for optimally tailoring the nonlinear optical properties of transition-metal-dichalcogenides via bandgap engineering for improving photonic device functionality.

Crossover from Reverse Saturable to Saturable Absorptions in Two-Dimensional Tungsten Disulfide

The Tungsten disulfide atomic layer has enormous scientific merits that play a key role in the nonlinear absorption process. Four distinct excitonic peaks in the absorption spectra are crucial for identifying the polarity of nonlinear absorption by virtue of the resonant or non-resonant excitation process. The excitation source of 532 nm is enough for the one-photon optical transition at both low-energy excitonic peaks and two-photon transition at both higher-energy excitonic peaks. The Tungsten disulfide atomic layer exhibited the reverse saturable (or positive nonlinear) absorption through the two-step excitation process which could be possible due to the optical transition at the higher energy excitonic peaks. In addition, the polarity of the nonlinear absorption coefficient and its interchange have been analytically studied with the aid of a magnitude of excited-state absorption cross-section and Ground-state absorption cross-section. Besides, the various possible factors affecting the Z-scan results are discussed.

Enhanced Ultrafast Broadband Reverse Saturable Absorption in Twistacenes with Enlarged π-Conjugated Central Bridge.

Optical nonlinearities of two all-carbon twistacenes, DPyA and DPyN, with the different π-conjugated central bridges were investigated. The nonlinear absorption properties of these compounds were measured using the femtosecond Z-scan with wavelengths between 650 and 900 nm. It has been found that the nonlinear absorption originated from two-photon absorption (TPA) and TPA-induced excited state absorption (ESA), wherein DPyA demonstrates higher performance than DPyN. The TPA cross section of DPyA (4300 GM) is nearly 4.3 times larger than that of DPyN at 650 nm. Moreover, the different central structures modulate the intensity of ESA at 532 nm, and DPyA exhibits an excellent ESA at 532 nm with multi-pulse excitation. Meanwhile, the result of data fitting and quantum chemistry calculation shows that the enhancement of nonlinear absorption in DPyA is due to the extended π- conjugated bridge and improved delocalization of π-electrons. These all-carbon twistacenes could yield potential applications in optical power limiting (OPL) technology.

Gold-nanoparticles induced transition in YVO4 crystal: From saturable to reverse saturable absorption

The embedded gold (Au) nanoparticles (NPs) are synthesized inside the yttrium vanadate (YVO4) crystal by direct Au ion implantation. The formed Au nanospheres are with average diameter of ∼5 nm, generating a clear optical absorption band centered at 595 nm due to the localized surface plasmon resonance (LSPR). With the doping of Au NPs, the nonlinear optical properties of YVO4 crystal are also modified, endowing the substrate with new features. Using femtosecond open-aperture Z-scan investigation under variable laser intensities, the Au NPs-modified YVO4 exhibits saturable absorption (SA) property at moderate excitation irradiances due to the plasmonic effect of embedded Au NPs, whilst transits to reverse saturable absorption (RSA) under higher pump irradiances. As an example for practical applications, we demonstrate a 1-μm pulse laser generation utilizing Au NPs-embedded YVO4 crystal as the saturable absorber. This work suggests that ion beam synthesis of metallic NPs may be a suitable way to tailor properties of functional crystals to achieve diverse applications in optics.

Ultrafast nonlinear absorption with multiple transformations and transient dynamics of gold nanobipyramids.

The process and condition of saturable absorption (SA) and reverse saturable absorption (RSA) of ultrafast nonlinear optics in metal nanoparticles are essential for applications including light generation, amplification, modulation, and switching. Here, we first discover and explore the multiple transformations (SA-RSA-SA) of ultrafast nonlinear absorption behavior of metal nanoparticles in femtosecond pulses. Correspondingly, the energy level model and fitting formula of multiple transformations are established to illustrate the process of optical response. The femtosecond transient absorption spectra provide information about their ultrafast dynamics process and vibrational mode, which further reveals the multiple transformation mechanisms of nonlinear absorption in gold nanobipyramids (Au-NBPs). Furthermore, Au-NBPs exhibit a significantly higher SA modulation depth up to 42% in the femtosecond, which is much higher than the reported values of other nanomaterials. Our results indicate that Au-NBPs can be used as broadband ultrafast Q-switching and mode-locking, and the conversion offers new opportunities for metal nanostructures in applications of optical switching.

Optical Nonlinearity of Emerging ZrS2 and HfS2 Semiconductors

AbstractCompatible with existing processing technology, chemical vapor deposition method is used to synthesize ZrS2 and HfS2 films a a large scale. The nonlinear optical properties are characterized by Z‐scan measurement with femtosecond pulses at 800 nm. The results show that saturable absorption happens in ZrS2 owing to the larger ground state absorption than the excited state absorption, while reverse saturable absorption appears in HfS2 due to the two‐photon absorption. The figure of merit values of ZrS2 (≈4.30 ± 0.12 × 10−15 esu cm) and HfS2 (≈6.0 ± 1.4 × 10−15 esu cm) are much larger than those of MoS2 and graphene in ultrafast nonlinear optical performance at the wavelength of 800 nm.

Reverse saturation absorption of CaWO4 and Ce3+ substituted CaWO4 growth on rGO sheets an 2D/3D nanocomposite for smart filtering optical radiation

The CaWO4, CaWO4/rGO and Ce3+:CaWO4/rGO nanocomposites are synthesized and subjected to hydrothermal treatment. The optical filtering behavior of materials was explored using reliable Z-scan analysis. It utilizes the focused Gaussian beam of He:Ne laser (632.8 nm) in a continuous wave regime. Closed aperture Z-scan analysis of the synthesized samples exhibits negative refraction evident from the pre-focal peak to post-focal valley. The explicit third order nonlinear parameters such as kerr nonlinearityΔn = 5.6 x10-7 (W/cm2), two photon absorption β = 2.3 x10-4 (W/cm) and optical susceptibility χ3 = 10.5 x10-8 esu were obtained for the Ce3+:CaWO4/rGO (5 wt%) nanocomposites. Ce3+:CaWO4 micro dumbbells grown on the sheets of rGO is observed using HRSEM and HRTEM images. The C 1 s spectra recorded from XPS displays the area of sp2 hybridized (CC) graphitic like structure increases which enhances the optical nonlinearities. Id/Ig ratio increases by increasing the addition of rGO signifies the reduction of oxygenated functional groups in the nanocomposite evidenced by Raman spectra analysis. The bandgap calculated from the Tauc-plot relation is found to be around 3.0 eV and it decreases to 2.9 eV when the wt.% of rGO is increased.

A comparative analysis of power-dependent nonlinear optical traits in unique ‘star-type’ triphenylmethane chromophores via facile Z-scan measurement

This study reports the nonlinear optical (NLO) attributes of both nonlinear refraction (NLR) and nonlinear absorption (NLA) for the “star-type” chromophores known as Malachite green (MG) and Light green SF yellowish (LGSF). In this research, a Z-scan technique was utilized to carry out the nonlinear procedure. The presence of linear absorptions at 532 nm for both chromophores are the prerequisite for the emergence of NLA phenomenon. The vital intermolecular charge transfer of the π-bonds were evidenced by the vibrational bonds of FTIR analysis spectrum for both chromophores. These bonds were responsible for the appearance of the functional attributes of nonlinearities under the utilized laser power, P. The output signals from open and closed-apertures recorded that MG and LGSF chromophores possesses reverse saturable absorption (RSA) and self-defocusing effect (-n2) in the order of 10−4 cmW−1 and 10−9 cm2W−1, respectively. This indicates a good property of nonlinearity to developed into various optical applications.

Effect of Cerium dopant on third-order nonlinear optical properties of CdS/PEG self-standing nanocomposite films

CdS/PEG, 4 and 7 mol% Ce doped CdS/PEG nanocomposite films were synthesized by in situ method. The XRD pattern confirmed the cubic structure of the CdS and the size of the CdS nanocrystallite is found to be smaller than the Bohr exciton radius for all the samples. SEM analysis shows that CdS and Ce doped CdS nanoparticles are well mono-dispersed in PEG polymer. FTIR spectra confirm the interaction of Ce-doped CdS nanoparticles with PEG polymer. UV–Vis optical absorption studies exhibit a red-shift of CdS nanoparticle with Ce doping. The photoluminescence spectra of all the films show a red emission due to the surface defects. The third-order nonlinear optical properties of all the films have been studied using the Z-scan technique. Closed and open aperture Z-scan plots show self-focusing optical nonlinearity and reverse saturable absorption with positive nonlinear coefficients. The 7 mol% Ce doped CdS/PEG nanocomposite film exhibits the highest value of nonlinear refractive index and nonlinear absorption coefficient which are about 1.649 × 10−9 m2/W and 7.149 × 10−3 m/W. The third-order nonlinear optical susceptibility and figure of merit have also been estimated for all the films and also increase with increase in Ce dopant concentrations. The maximum value of third-order nonlinear optical susceptibility and figure merit are found for 7 mol% Ce doped CdS/PEG nanocomposite film and are about 9.882 × 10−4 esu and 5.902 × 10−8 esu m. The present study strongly recommends that the Ce doped CdS/PEG nanocomposite films are worthy candidates for fabricating the future optical limiting devices.

Nonlinear Optical Properties of Zinc Oxide Nanoparticle Colloids Prepared by Pulsed Laser Ablation in Distilled Water

The nonlinear optical properties of zinc oxide nanoparticles (ZnONPs) in distilled water were measured using a femtosecond laser and the Z-scan technique. The ZnONPs colloids were created by the ablation of zinc bulk in distilled water with a 532 nm Nd: YAG laser. Transmission electron microscopy, an ultraviolet-visible spectrophotometer, and atomic absorption spectrophotometry were used to determine the size, shape, absorption spectra, and concentration of the ZnONPs colloids. The nonlinear absorption coefficient and nonlinear refractive index were measured at different excitation wavelengths and intensities. The nonlinear absorption coefficient of the ZnONPs colloids was found to be positive, caused by reverse saturable absorption, whereas the nonlinear refractive index was found to be negative due to self-defocusing in the ZnONPs. Both laser parameters, such as excitation wavelength and input intensity, and nanoparticle features, such as concentration and size, were found to influence the nonlinear optical properties of the ZnONPs.

Extraction of Natural Pigment from Ocimum tenuiflorum Using Different Polar Solvents and Their Nonlinear Optical Characteristics.

Herein, we report the extraction, characterization, linear and third-order nonlinear optical (TONLO) features of the natural pigment from Ocimum tenuiflorum leaves using different polar solvents. The polar solvents such as, ethanol, acetone, methanol and dimethyl sulfonate (DMSO) were used to extract the natural pigment from Ocimum tenuiflorum leaves. The effect of solvent on linear and TONLO properties of the natural pigment was studied and multi- parameter scale known as Kamlet-Abboud-Taft was used to analyse the solvent characteristics on solute molecule. The functional groups of the extracted natural pigments were examined via Fourier transform infrared (FT-IR) spectrometer. TONLO characteristics of the natural pigment was scrutinised by a continuous wave (CW) diode laser working at 650nm wavelength. The nonlinear refractive index (n2) and nonlinear coefficient of absorption (β) of the natural pigment was ascribed to the behavior of self-defocusing, saturable absorption (SA) and reverse saturable absorption (RSA). The TONLO susceptibility (χ(3)) of the natural pigment in polar solvents was found to be the order of 10-6 esu. The natural pigment extracted from Ocimum tenuiflorum leaves is a potential material for applications in nonlinear optical.

Size dependence of nonlinear optical properties of PbS QDs, passivated with thioglycolic acid

The size dependence of the nonlinear optical response of hydrophilic colloidal PbS quantum dots, passivated with thioglycolic acid (PbS/TGA QDs) with an average size of 3.0, 3.5, 4.5 nm in the field of 10 ns laser pulses at 532 nm has been analyzed. It is shown that the key mechanism of nonlinear absorption is the reverse saturable absorption, which occurs with involvement of QDs defect trap states. The formation of SiO2 monolayer on the PbS/TGA QDs surface, using MPTMS makes it possible to significantly increase in the luminescence intensity from 4 to 4.5 times. In this case, the nonlinear absorption coefficient and nonlinear refraction index do not change. The facts indicate the implementation of a nonlinear optical response in the nanosecond probe pulse range on trap states that are not luminescence centers.

Implications of morphology on excited state absorption of α-MnO2 nanostructures

Nanoclusters, nanorods and nanowires of α-MnO2 were synthesized by reduction method at different annealing temperature (100 °C–500 °C). X-ray diffraction and Raman studies confirms the formation of pure tetragonal phase of α-MnO2. Surface morphology using SEM and HRTEM reveals the gradual transformation of α-MnO2 nanoclusters (100 °C–300 °C) to nanorods (400 °C) to well defined nanowires (500 °C). While increasing the annealing temperature, Ostwald ripening process initially withholds the agglomerated clusters and its size get reduced and fused that leads to orientation along particular direction. HRTEM clearly displays the influence of temperature on favoured growth plane where (411) of nanoclusters changed to (211) plane of nanorods and nanowires. Optical band edge absorption at 268 nm arising from d–d transitions of Mn4+ in MnO2 got blue shifted due to variations in morphology. Here with increase in temperature, aspect ratio increases which alters the number of surface atoms and consequently the cohesive energy put on effect in the widening of bandgap of the material from 4.31 eV (nanoclusters) to 4.63 eV (nanowires). Open aperture Z-scan technique using Nd: YAG laser (532 nm, 10 Hz & 9 ns) revealed all MnO2 nanostructures involve reverse saturable absorption ascribed due to excited state absorption and its strength varies with morphology. Significant absorption in the visible region (532 nm) provoked excited state absorption and intensity dependent variation of nonlinear absorption coefficient confirms the existence of sequential two photon absorption process. α-MnO2 nanowires with extended interconnected network and larger aspect ratio exhibits wider excited state cross-section (6.64 × 10−2 GM), higher two-photon absorption coefficient (2.01 × 10−10 m/W) and lower onset optical limiting threshold (2.13 × 1012 W/m2). This stronger optical limiting performance of α-MnO2 nanowires symbolizes the scope of utilizing optimal α-MnO2 nanostructure for optical limiting applications.

Panchromatic Excited-State Absorption in Bis-Cyclometalated Iridium Isocyanide Complexes.

In this work, we introduce a series of cyclometalated iridium complexes and evaluate the suitability of this class of compounds in nonlinear optical (NLO) applications, with an emphasis on long-lived, panchromatic reverse-saturable absorption (RSA). The investigated complexes are represented by the general formula [Ir(C^N)2(CNArdmp)2]+, (C^N = cyclometalating ligand, CNArdmp = 2,6-dimethylphenyl isocyanide). Seven such complexes were synthesized and characterized, including in-depth analysis of their photophysical properties (UV-vis absorption, photoluminescence, and transient absorption). This series of compounds contains seven different cyclometalating ligands (2-phenylbenzothiazole (bt) (Ir1), 5-nitro-2-phenylpyridine (ppyNO2) (Ir2), 5-nitro-2-(9-phenanthryl)pyridine (phenNO2) (Ir3), 2-(benzo[b]thiophen-2-yl)quinoline (btq) (Ir4), 6-(benzo[b]thiophen-2'-yl)phenanthridine (btph) (Ir5), 2,4-diphenylquinoline (dpq) (Ir6), and 6-nitro-2,4-diphenylquinoline (NO2dpq) (Ir7)), which have profound effects on their ground-state and excited-state absorption spectra. To evaluate the effects of the isocyanide ancillary ligands, some heteroleptic bis-cyclometalated iridium(III) acetylacetonate (acac) analogue complexes are included as points of comparison. In the ground state, the bis-isocyanide complexes display UV-vis absorption with the characteristic 1LC (π → π*) band at λ < 350 nm and 1MLCT bands at 350-500 nm. Five of the complexes (Ir1, Ir2, Ir4, Ir5, and Ir6) display broad, intense triplet excited-state absorption with no ground-state bleach (GSB) over the spectral window of 400-900 nm, with excited-state lifetimes spanning three orders of magnitude from ∼32 ns to 12 μs. The photophysical data suggests that the isocyanide ancillary ligand blue-shifts the GSB transient into the UV, which is normally found in the middle of the visible region for cyclometalated iridium complexes. This study demonstrates the applicability of cationic cyclometalated iridium(III) bis-isocyanide complexes as candidate RSA materials.

Optical limiting and nonlinear optical properties of Cr2O3 and WO3 based polymer nanocomposites

The optical limiting behavior of templated transition metal nanoparticles Cr2O3 and WO3 in a PMMA host at the wavelength of 1064 nm in the nanosecond regime is discussed. Optical filters were produced by chemical synthesis from the bulk. The optical limiting properties were characterized using an adequate custom-made optical setup and the third order nonlinear parameters, namely the nonlinear absorption coefficients and refractive indices were measured by the Z-scan method. The optical limiting performance improvement is clearly demonstrated for the PMMA/Cr2O3 filter bearing out a laser protection level of OD = 1.2, a factor of 4 larger than the pure PMMA filter. A significant blue shift in the nonlinear activation threshold energy occurs when WO3 or Cr2O3 are embedded in a PMMA host as the values have been subsequently pulled down from 500 µJ (pure PMMA) to 65 µJ and 23µJ, respectively. Z-scan measurements highlighted a self-defocusing effect as a result of a negative nonlinearity. Nonlinear refractive indexes in the order of n2 = −1.0X10−15cm2/Wwere calculated for the PMMA/Cr2O3 and PMMA/ WO3 systems. A nonlinear absorption coefficient as high as β = 163cm/GW was measured for the PMMA/Cr2O3 optical limiting filter while the one for PMMA/ WO3 lies 1 order of magnitude behind. It is suggested that the PMMA/Cr2O3 optical system undergoes reverse saturable absorption enhanced by excited state absorption (ESA/RSA). Besides, it is believed that multi-photons absorption (MPA) occurs in PMMA/WO3 or pure PMMA.

Hot-carrier tunable abnormal nonlinear absorption conversion in quasi-2D perovskite

Controlling the high-power laser transmittance is built on the diverse manipulation of multiple nonlinear absorption (NLA) processes in the nonlinear optical (NLO) materials. According to standard saturable absorption (SA) and reverse saturable absorption (RSA) model adapted for traditional semiconductor materials, the coexistence of SA and RSA will result in SA induced transparency at low laser intensity, yet switch to RSA with pump fluence increasing. Here, we observed, in contrast, an unusual RSA to SA conversion in quasi-two-dimensional (2D) perovskite film with a low threshold around 2.6 GW cm−2. With ultrafast transient absorption (TA) spectra measurement, such abnormal NLA is attributed to the competition between excitonic absorption enhancement and non-thermalized carrier induced bleaching. TA singularity from non-thermalized “Fermi Sea” is observed in quasi-2D perovskite film, indicating an ultrafast carrier thermalization within 100 fs. Moreover, the comparative study between the 2D and 3D perovskites uncovers the crucial role of hot-carrier effect to tune the NLA response. The ultrafast carrier cooling of quasi-2D perovskite is pointed out as an important factor to realize such abnormal NLA conversion process. These results provide fresh insights into the NLA mechanisms in low-dimensional perovskites, which may pave a promising way to diversify the NLO material applications.

Porphyrin covalently functionalized MoS2 nanosheets: “Click” synthesis and tunable nonlinear absorption

Functionalized MoS2 nanosheets are of significant academic and commercial interest due to their use in electronic and photonic applications as transistors, electrocatalysts, electrodes, and nonlinear optical materials. However, MoS2 nanosheets exhibit low reactivity and poor dispersibility in common solvents, which significantly hinders their functionalization with optoelectronic groups and their downstream applications. Herein, a porphyrin covalently functionalized MoS2 nanohybrid (MoS2-Por) is synthesized by a mild thiol−ene “click” reaction. Optical studies demonstrate that a dispersion of the MoS2-Por nanohybrid in N,N-dimethylformamide (DMF) exhibits reverse saturable absorption (RSA) behavior to femtosecond pulsed laser irradiation at 800 nm, in contrast to the saturable absorption (SA) displayed by MoS2 nanosheets. This significant switch likely stems from enhanced two-photon absorption (TPA) in the MoS2 nanosheets, which may be ascribed to efficient charge transfer in the excited-state of the MoS2-Por nanohybrid. Polymethyl methacrylate (PMMA) films MoS2-Por/PMMA exhibit a low optical limiting threshold of 1.2 mJ cm-2 (18.3 GW cm-2), indicating great potential as an optical limiter. The MoS2-Por nanohybrid also exhibits stronger self-focusing than MoS2 nanosheets towards femtosecond pulses at 800 nm due to the increased free-carries concentration arising from the improved TPA. These observations demonstrate that the MoS2-Por nanohybrid is an excellent candidate for optical limiting in the infrared region towards femtosecond pulses, and shed new light on the construction of covalently functionalized MoS2 nanohybrids for tuning nonlinear optical properties and broadening application scope.