Reverse Saturable Absorption Research Articles

Nonlinear Absorption in Plasmonic Titanium Nitride Nanocrystals

AbstractTitanium nitride nanoparticles have become a research interest due to their distinguished optical and photothermal properties. Furthermore, the search for nanoparticle solutions with tunable nonlinear optical properties for laser‐based applications is critical. More specifically, third order optical nonlinearities such as reverse saturable absorption, optical liming, and self‐focusing are important in the biomedical and electronics fields. The optical nonlinearities of titanium nitride plasmonic nanoparticles are investigated as a function of material concentration in water solutions. Furthermore, the effect of nanoparticle clustering on optical nonlinearities is investigated by fabricating micrometer‐sized clusters of ≈50 nm titanium nitride particles. These studies demonstrate that the nonlinear absorption coefficient increases linearly with concentration. However, clusters require higher concentrations compared to the freestanding nanoparticles to exhibit similar nonlinear absorption coefficient and optical density. Similarly, the optical limiting threshold for titanium nitride nanoparticles appears to be lower compared to the cluster solutions, which is impacted by the collective scattering of nanoparticles and high reverse saturable absorption. In addition, self‐focusing is observed in the continuous resonant regime. This study provides an in‐depth analysis of the nonlinear optical properties of titanium nitride, with relevant consequences for applications such as sensor protection and photothermal therapy.

Third-order nonlinear optical responses of Cr3+ ions on La2(WO4)3 nanoparticles for optical limiting applications

In this article, we discuss the nonlinear optical limiting characteristics of pure and Cr3+ doped La2(WO4)3nanoparticles using soft chemical method. We studied the third-order nonlinear optical properties of nanoparticle using a continuous-wave (CW) laser system pumped by a diode laser at 785 nm. The results reveal that the materials possess reverse saturable absorption (RSA) and self-defocusing in nature. Due to the presence of near-resonant excitation state, the material exhibits sequential two-photon absorption (excited state induced thermally) process. We observe a higher non-linear absorption coefficient (β) and nonlinear refractive index (n2) for 0.7 % Cr3+ doped La2(WO4)3 systems which is higher than that of pure La2(WO4)3 nanoparticles. The transmittance decreases with increased input fluence for both pure and Cr3+ doped La2(WO4)3 samples exposing the optical limiting behavior of the prepared sample. The presence of larger concentrations of more polarizable Cr3+ ions, increased density of states, and higher oxygen defects resulted in enhanced OL behaviour for 0.7 % Cr3+ doped La2(WO4)3 sample. It is found that two photon absorption (β) is increased from 0.41 to 1.16 × 10-3 and third order nonlinear susceptibility (χ(3)) enhances from 3.909 x10-6 to 6.696 × 10-6 esu on Cr doping. The optical limiting threshold of pure and CrxLa1-xWO4 nanoparticles was also studied and found to be in the range of 91.2 to 86.2 W/cm2. As a consequence of the obtained results Cr3+ doped La2(WO4)3 is likely to be an appropriate candidate for CW low-power optical limiting (OL) applications.

Intensity-dependent transition from saturation absorption to reverse saturable absorption ways in TiSxSe2-x (0 ≤ x ≤ 1)

• Different atom ratios of TiS 2-x Se x were regulated by sulfur doping. • A laser intensity-dependent transition from SA to RSA in TiS x Se 2-x nanosheets was observed. • With the increase of S 2− contents in TiS x Se 2-x , the SA effect became weaker while the RSA effect became stronger. The third-order nonlinear effects in the TiS x Se 2-x (0 ≤ x ≤ 1) nanosheets were investigated via the open-aperture (OA) Z-scan technique. An input fluence dependent transition from saturation absorption (SA) to reverse saturable absorption (RSA) ways in TiS x Se 2-x was discovered. Under lower laser intensities, only SA existed in the TiS x Se 2-x . Higher incident laser intensities caused the transition from SA to RSA, due to the competition between ground state absorption and excited state absorption. This unique intensity-dependent absorption transition can be applied in all-optical logic gates, fast optical switch, optical limiter, mode storage.

Experimental observation of enhanced reverse saturable absorption in Bi 2 Se 3 nanoplates doped PMMA thin film

By employing the ultrafast Z-scan technique, we characterize the nonlinear absorption property of PMMA/Bismuth Selenide (Bi 2 Se 3) composite with varying concentrations. We report the fabrication of bismuth selenide (Bi 2 Se 3) nanoplate (topological insulator (TI)) doped poly methyl methacrylate (PMMA) thin film with varying doping concentrations. The effect of Bi 2 Se 3 on structural and linear properties of PMMA thin film has been investigated through UV-Vis spectroscopy, scanning electron microscope (SEM), and Energy dispersive x-ray spectroscopy (EDS) elemental mapping techniques. Furthermore, the nonlinear optical absorption property of PMMA and PMMA/Bi 2 Se 3 composites have been performed employing a single beam open aperture z-scan technique under femtosecond laser excitation at 750 nm. The z-scan results exhibit an enhancement of reverse saturable absorption (RSA) property with an increased nonlinear absorption coefficient (β) of the PMMA/Bi 2 Se 3 composites compared to pure PMMA measured with intensity at 320 GW cm−2. The RSA response gets enhanced with the increase in doping concentration also. Our experimental observations reveal that PMMA/Bi 2 Se 3 composite can provide a promising platform to realize photonic devices such as optical limiters, optical switches, and efficient protectors from high power sources.

Role of surface defects in the third order nonlinear optical properties of pristine NiO and Cr doped NiO nanostructures

Pristine NiO and 2% Cr doped NiO nanostructures are successfully synthesized by the modified auto–combustion method for the determination and improvement of linear and nonlinear optical behaviours, and for identifying them as suitable materials for optical limiting applications. Vibrational and linear optical properties of both nanostructures are investigated, and structural and morphological studies are carried out using XRD, FE-SEM, and HR-TEM. From the Kubelka-Munk model, the energy band gaps for pristine and doped samples are found to be 3.52 eV and 3.44 eV, respectively. Both pristine as well as Cr-doped NiO nanostructures reveal substantial nonlinear optical behaviour at the excitation wavelength of 532 nm, arising from the presence of strong reverse saturable absorption. The third order nonlinear absorption coefficients have values of the order of 10−10 m/W and 10−6 m/W, under pulsed (5 ns) and continuous wave laser excitations, respectively. These values confirm the suitability of these nanostructures for fabricating efficient optical limiting devices for safeguarding human eyes and optical sensors from hazardous laser radiation.

Two photon absorption induced optical limiting action of L-Aspartic acid monohydrate

The organic l-Aspartate Monohydrate (L-AspMH) crystal is grown by slow evaporation technique. Single crystal XRD analysis reveals that L-AspMH belongs to an orthorhombic system with P 21 21 21 space group. The inter-contacts in the crystal structure are analyzed using the Hirshfeld surface analysis. To support the experimental results, quantum chemical calculations using the density functional theory (DFT) are done. The molecular structure of L-AspMH crystal is optimized by DFT/B3LYP functional, 6–311G++(d,p) basis set. The FT-IR and FT-Raman spectra are also stimulated and validated experimentally. The blue-shift in the O–H stretching wavenumbers is due to the presence of O–H⋯O hydrogen bonding. The highest occupied molecular orbital (HOMO: −7.409 eV) energy, lowest unoccupied molecular orbital (LUMO: −0.927 eV) energy and energy gap (6.483 eV) of the AspMH crystal is calculated. The hyper conjugative and inter/intra molecular interactions have been investigated through the Natural Bond Orbital (NBO) analysis. UV–vis absorption studies shows the material exhibit absorbance maxima in the UV (204 nm) region and high transmittance in the Visible-NIR (340–900 nm) region. The predicted first order hyperpolarizability is found to be 13 times greater than that of urea. Third-order nonlinear optical property of the crystal is studied using Z-scan technique under nanopulsed Nd:YAG laser. L-AspMH exhibit intensity dependent nonlinear absorption behaviour was witnessed with M-type (2.46 × 1012 W/m2) at lower on-axis input intensity and reverse saturable absorption (4.98 × 1012 W/m2) at higher on-axis input intensity. The material demonstrates sequential two absorption induced optical limiting action. Higher two-photon absorption coefficient (0.56 × 10−10 m/W) and lower onset optical limiting threshold (5.41 × 1012 W/m2) makes AspMH a potential candidate for optical limiting devices.

Biosynthesis, characterization and nonlinear optical response of spherical flake-shaped copper oxide nanostructures

The copper oxide nanoparticles (CuO NPs) were synthesized via solution combustion approach with Bengal gram powder as a fuel. The XRD analysis confirms the monoclinic structure of CuO NPs. FT-IR spectrum reveals the formation of CuO NPs. SEM studies show that the NPs are nearly spherical, and the elemental composition was confirmed by EDAX. The absorption spectra revealed a direct optical band gap of 1.50[Formula: see text]eV. DFT calculations were performed to determine the HOMO–LUMO energy bandgap and found to be 1.72[Formula: see text]eV, which is in good agreement with the experimental value. The Z-scan technique was used to investigate the third-order nonlinear optical (NLO) characteristics using DPSS continuous wave laser (532[Formula: see text]nm, 200[Formula: see text]mW). A high reverse saturation absorption and negative nonlinear refractions were observed. Third-order NLO parameters [Formula: see text], [Formula: see text] and [Formula: see text] were found to be [Formula: see text][Formula: see text]cm/W, [Formula: see text][Formula: see text]cm2/W and [Formula: see text][Formula: see text]esu, respectively. The CuO NPs also displayed strong optical limiting behavior with a limiting threshold of 2.11[Formula: see text]kW/cm2.

Double transformation of the nonlinear absorption in silver nanoparticles.

The nonlinear absorption of 40 nm Ag nanoparticles (Ag NPs) was investigated using open aperture (OA) Z-scan technique at 532 nm. Experiments show that the nonlinear absorption behavior of Ag NPs is intensity dependent. Specifically, under low laser energy the Ag NPs shows saturable absorption (SA). At medium laser energy, the transformation of nonlinear absorption from SA to reverse saturable absorption (RSA) happens. While under stronger laser energy, double transformation (SA→RSA→SA) of nonlinear absorption occurs. The experimental results were analyzed theoretically using a model based on single-photon absorption and two-photon absorption saturation.

Nonlinear optical limiting property of the carboxyl-functionalized Ti3C2 MXene nanosheets.

Nonlinear optical limiting (OL) properties of carboxyl-functionalized Ti3C2 nanosheets (COOH-MXene) were studied using the nanosecond laser Z-scan technology. COOH-MXene showed excellent broadband OL properties with OL thresholds of 0.34 J/cm2 at 532nm and 0.58 J/cm2 at 1064nm, and the OL mechanism was mainly attributed to the reverse saturable absorption effect. Femtosecond time-resolved transient absorption measurements were used to clarify the ultrafast carrier dynamics in the OL process, and the results revealed that excited states absorption (ESA) in MXene was enhanced by introducing more carboxyl group terminations. When COOH-MXene was irradiated by laser pulses, excited electrons in the conduction band of MXene could transfer to the carboxyl groups and induce the ESA in the surface functional groups, resulting in the excellent OL property of COOH-MXene.

Nonlinear optical behaviour of bis (cytosinium) tartarate monohydrate single crystal

A nonlinear optical single crystal of bis (cytosinium) tartarate monohydrate (BCTM) was grown by slow evaporation method at room temperature. Single crystal X-ray diffraction study revealed their cell parameters and corresponding space group. Different functional groups were identified by using FTIR spectral analysis. Phase purity of the grown crystal was analysed by chemical etching and powder X-ray diffraction studies. The mechanical strength of the grown crystal was estimated using Vickers microhardness test. The thermal stability of the grown crystal was investigated by TGA-DTA studies. The optical absorption study was carried out in the wavelength range of 190–1100 nm. The dielectric response of the grown crystal was studied as a function of frequency at different temperatures. Second harmonic generation efficiency (SHG) was measured by Kurtz and Perry powder technique. The Z-scan pattern clearly evidenced that the BCTM exhibits sequential two photon absorption induced reverse saturable absorption.

Regulation of Third‐Order NLO Properties by Central Metal Exchange of Heterogeneous MOFs@CeO2

AbstractChanging the chemical composition and generating heterogeneous structures have a synergistic effect on the third‐order nonlinear optical (NLO) properties of metal–organic frameworks (MOFs) materials. In this work, it is demonstrated that the transformations from a parent‐MOF [Zn4(dcpp)2(DMF)3(H2O)2]n (1, dcpp = 3,4‐bis(4‐carboxyphenyl)phthalate) into two child‐MOFs, [Cu4(dcpp)2(DMF)3(H2O)2]n (2) or [Zn2.5Co1.5(dcpp)2(DMF)3(H2O)2]n (3), via central metal exchange can regulate the third‐order NLO properties of the parent‐MOF, especially its third‐order NLO absorption signal can change from the reverse saturable absorption (RSA) to the saturable absorption (SA) when Cu2+ are introduced. Heterogeneous 1@CeO2 materials are further engineered by depositing CeO2 nanospheres onto the whole surface of 1, and are surprisingly still able to be exchanged into 2@CeO2 or 3@CeO2. Analyses on these MOFs@CeO2 indicate that the interfacial interaction between metal oxide particles and MOFs surface can effectively tune the charge transfer efficiency of the material which leads to their third‐order NLO refraction signals. The interface inducement of CeO2‐shell to the MOF‐core also significantly changes their third‐order NLO properties compared to pure MOFs. This work provides new insights and efficient strategies for the development of new third‐order NLO materials with potential practical usage.

Low- and High-Order Optical Nonlinearities of Quantum Dots

Various potential applications of quantum dots (QDs) require knowledge of their optical nonlinearities. In this review, the third-order nonlinearities responsible for the saturable absorption, two-photon absorption, reverse saturable absorption, and nonlinear refraction in QDs, as well as the high-order harmonics generation in the laser-induced plasmas containing QDs, are analyzed. The methods of QD synthesis and preparation strongly affect their optical nonlinearities. Above-mentioned nonlinear optical studies in QDs are analyzed for various potential applications (sources of coherent extreme ultraviolet radiation, optical limiters, mode-lockers, etc.).

Quantum size-dependent luminescence and nonlinear optical properties of silicon quantum dots/SiO2 multilayer

The luminescence and nonlinear optical properties of silicon quantum dots (Si QDs)/SiO2 multilayers with different QDs diameters (2.5, 3 and 4 nm) were investigated by utilizing continue wave (325 nm) and picosecond laser (tp = 25 ps, λ = 1064 nm), respectively. It was found that both the linear and nonlinear optical properties of Si QDs/SiO2 multilayers strongly depended on the QDs size. The photoluminescence intensity could be enhanced by ∼32-fold, and about 17 times increase in the saturable absorption (SA) coefficient was achieved, which could be ascribed to the controllable density of interface-states as well as their coupling effect with the Si QDs core states. Moreover, a transformation from reverse saturable absorption (RSA) characteristic through two-step absorption process into the SA behavior due to the interface-state filling effect was observed when increasing the incident laser intensity. We proposed that the ultrafast free carries trapping process by the interface states would greatly influence the self-defocusing effect. In addition, the free carries absorption and SA effect should be considered in accounting for the variation of nonlinear parameters as changing the pump intensity. Our results suggest that the widely tunable SA feature through controlling the Si QDs size provides great potential to develop high-efficient Si QDs-based nonlinear optical devices such as passive mode-locking or Q-switching laser.

Experimental study of saturable and reverse saturable absorption of Zn nanoparticles photodeposited onto etched optical fibers

In this paper, the non-linear optical response of photodeposited zinc nanoparticles onto an etched optical fiber is reported. Through chemical etching, 20 mm of the cladding of a standard single-mode optical fiber was removed to expose its core and subsequently, photodeposit zinc nanoparticles on it at different times (1, 5 and 10 min) by using a continuous wave laser at 1550 nm. The non-linear optical response was obtained by the P-scan technique using a high-gain pulsed amplifier with a pulse duration of 10 ns at a wavelength of 1550 nm. The experimental results showed that it is possible to get the effects of reverse saturable absorption (RSA) at irradiances less than 380 MW/cm 2 and saturable absorption (SA) for higher values. Consequently, the analysis of the results obtained shows that the third-order non-linear susceptibility x3 of the RSA is 2.2130 × 10−06 (esu) for 10 min of photodeposition, which decreases for shorter photodeposition times; On the other hand, the third-order non-linear susceptibility x3 of the SA is −5.8955 × 10−07 (esu) for 10 min of photodeposition, which increases for shorter exposure times. Finally, the experimental results obtained show that it is possible to make a photonic device with desired non-linear absorption properties by the photodeposition of metallic nanoparticles onto etched fibers, which makes it ideal for applications in optical communications.

Investigation on nonlinear optical and optical limiting properties of Cd0.7Zn0.3Te quantum dots

Ternary alloyed Cd0.7Zn0.3Te colloidal quantum dots were synthesized under open atmosphere conditions. The Cd0.7Zn0.3Te quantum dots were characterized under XRD studies, DLS technique and optical absorption measurements. Using tauc and urbach relation the optical energy bandgap and urbach energy were obtained. The intensity depended nonlinear optical parameters of Cd0.7Zn0.3Te quantum dots were determined with Z-scan experimental setup using a green laser source working on continuous wave mode. The nonlinear absorption coefficient β, along with optical limiting capacity of Cd0.7Zn0.3Te quantum dot is investigated through the open aperture set up. The transmittance of Cd0.7Zn0.3Te quantum dot showed a sharp dip at the maximum intensity point of the laser which indicates reverse saturable absorption. The optical limiting threshold value for Cd0.7Zn0.3Te quantum dot was obtained around 4.6 KJ/cm2. The nonlinear refractive index of Cd0.7Zn0.3Te quantum dot is find out using closed aperture set up. The nonlinear refractive index with a negative sign was obtained for the Cd0.7Zn0.3Te quantum dot which is attributed to the self-defocusing phenomena. The nonlinear studies indicate that the sample exhibits good nonlinear properties and find applications in optical limiting materials.

Investigation of Intensity Dependent Nonlinear Absorption in Cerium Phosphate Nanorods

Cerium Phosphate (CePO4) is a material that has attracted attention because of its unique properties, redox capabilities, and a wide variety of applications. Cerium Phosphate nanoparticles with a nanorod structure were successfully synthesized by a hydrothermal synthesis procedure using Cerium Nitrate Hexahydrate (Ce (NO3)3.6H2O) and Diammonium Hydrogen Phosphate ((NH4)2HPO4) as the precursors without adding any surfactants. The synthesized CePO4 nanorods were characterized using X-ray Powder Diffraction (XRD) and Transmission Electron Microscopy (TEM) analysis which showed pure monoclinic nanorod structures. The linear absorption was analyzed by UV-visible absorption spectrometry. The nonlinear absorption was measured by the open aperture Z-scan technique using a Q switched Nd-YAG laser at 532nm. The Z-scan curve exhibited reverse saturable absorption. In this study, the dependence of nonlinear absorption of CePO4 on the intensity of incident light was investigated. The non-linear absorption coefficient was measured and it was found that the non-linear absorption decreased with the increasing intensity.

Defect-mediated carrier dynamics and third-order nonlinear optical response of WS2 quantum dots.

In this Letter, we report the third-order absorptive and refractive nonlinear optical response of highly luminescent WS2 quantum dots (QDs) in the off-resonant femtosecond and nanosecond pulses, which is beneficial for optical limiting and quantum information processing. For 800 nm femtosecond excitation, QDs show two-photon absorption (β = (107 ± 2)×10-3 cm/GW) with positive nonlinearity originating from bound carriers. This picture changes significantly for 532 nm nanosecond excitation, where it shows reverse saturable absorption with negative nonlinearity primarily originating from the sequential absorption of two single photons through the shallow defects, creating free carriers. Our results provide a promising route toward low-dimensional optoelectronic devices.

Nonlinear optical properties and photoexcited carrier dynamics of MnPS3 nanosheets.

Here, we systematically report on the preparation of high-quality few-layered MnPS3 nanosheets (NSs) by chemical vapor transport (CVT) and mechanical stripping method, and its carrier dynamics and third-order nonlinear optical properties were studied. Using the classical technique of open aperture Z-scan, a typical phenomenon of saturable absorption (SA) was observed at 475 nm, which indicates that the material is expected to be used as a saturable absorber in ultrafast lasers. The typical phenomenon of reverse saturation absorption (RSA) is observed at 800 and 1550 nm, which shows its potential in the field of broadband optical limiting. Compared with graphene, BP, MXene, MoS2 and other typical two-dimensional materials, MnPS3 NSs has a higher modulation depth. Using the non-degenerate transient absorption spectroscopy technology at room temperature, a slower cooling process of thermal carrier of MnPS3 was observed. Moreover, the carrier lifetime can be tuned according to the wavelength. This work is of great significance to the improvement of MnPS3 based devices, and lays a foundation for the application of MnPS3 in short-wavelength photovoltaic cell, photoelectric detection and other fields.

Tunable luminescence and nonlinear optical properties of nano colloidal Ge20Te75Bi5 chalcogenide glass

In this article, we report spectral studies and optical nonlinearities of optical grade thin films fabricated from nano colloidal solutions of Ge20Te75Bi5 chalcogenide glass. Emission peaks of varying concentrations of Ge20Te75Bi5 nanocomposites shift from 426 nm to 492 nm. Bandgap Eg also varies in the proportion tunable to emission peaks depending on the grain size of the films. The existence of reverse saturable absorption (RSA) is confirmed by the open aperture z-scan traces of nanocomposites with a valley-like pattern. Enhancement of third-order optical nonlinearities in Ge20Te75Bi5 chalcogenide nano colloids studied using the z-scan technique can be exploited to improve the desirable features for usage in nonlinear optical systems.

Optimization of Graphene on D-Fiber Saturable Absorbers

The graphene-light interaction in a waveguide can be optimized through the waveguide design. In the case of nonlinear optical devices, such as saturable absorbers, this optimization requires knowledge of the actual intensity that quantifies the nonlinear interaction with a waveguide mode. In this work we propose parameters that correctly quantify the strength of saturable absorption. We show that the graphene on D-fiber saturable absorber can be characterized through the absorption coefficient and a properly defined saturation power for each mode. We analyze the dependence of the graphene-light interaction on the geometrical parameters, chemical potential, number of graphene layers, and input power. The results show a wide variation of the graphene absorption with the design, which offers potential for polarizers with large polarization extinction ratios and saturable absorbers with low saturation powers. As a function of the number of layers, the interaction is maximized for five layers, and we predict a reverse saturable absorption effect for higher number of layers. The parameters introduced here to quantify the nonlinear graphene-light interaction can be applied to other waveguide structures and other 2D materials.