Reverse Saturable Absorption Research Articles

Third-order optical nonlinearities of zinc porphyrins accommodated in the cavity of a doughnut-like molybdenum crown cluster

As compared with the pristine ZnTCPP, the hybrid 1 showed quenched fluorescence, greater nonlinear reverse saturated absorption and self-defocusing effect, smaller nonlinear optical limiting threshold, indicating its high potential in optical limiting applications.

Enhanced nonlinear optical absorption in defect enriched graphene oxide and reduced graphene oxide using continuous wave laser z-scan technique

This work pertains to the investigation of the nonlinear optical (NLO) properties of defect enriched graphene oxide (GO) and reduced graphene oxide (rGO). The modified Hummers method approach was adopted to synthesize GO. The rGO was obtained by reducing GO using L-ascorbic acid. The X-ray diffraction patterns have confirmed the structure of GO and rGO. Optical phonons of the samples, excited by the visible laser light, are studied using Raman spectroscopy. After reduction, the optical band gap energy is decreased from 4.43 eV to 3.56 eV. The third-order NLO properties of defect enriched GO and rGO have been investigated by performing a single beam z-scan experiment. The nonlinear absorption coefficient of the samples is obtained from open aperture (OA) z-scan study by using a continuous-wave (CW) laser at 532 nm. Reverse saturable absorption behaviour is observed in both samples. The self-defocusing of the laser beam and negative nonlinear refractive index is determined from the closed aperture data. NLO behaviour is found to increase with the increase in defects/disorder. The optical limiting property of GO and rGO was investigated by using OA data and both samples have shown improved optical limiting values. Thus thr defect enriched GO and rGO may be strong contenders for optical limiting applications.

Saturable Absorption and Reverse Saturable Absorption of Cdga2se4 Nanoparticles Determined by Bond Strength

Saturable Absorption and Reverse Saturable Absorption of Cdga2se4 Nanoparticles Determined by Bond Strength

Fullerene superlattices containing charge transfer complexes for an improved nonlinear optical performance.

To improve the nonlinear optical (NLO) properties of fullerene C60, chemical modifications are normally needed to construct a donor-π-acceptor (D-π-A) system, which requires tedious and time-consuming synthesis procedures. In addition, the conjugated structure of C60 will inevitably be destroyed, which is disadvantageous for other applications. Here, we use solvent-based nanoarchitectonics to obtain highly ordered, three-dimensional (3D) C60 supramolecular structures. For this purpose, a liquid-liquid interfacial precipitation (LLIP) method was employed using quinoline as the good solvent. Hollow polyhedra (HPH) and multilayer flowers (MFs) were obtained when methanol and ethanol were selected as the poor solvents, respectively. While quinoline failed to enter the HPH, it was found to be successfully intercalated with the MFs, which induced a transition of the C60 organization from a pristine face-centered-cubic (fcc) phase to a hexagonal close packed (hcp) lattice. When embedded in a poly(methyl methacrylate) (PMMA) matrix, the HPH and MFs both show reverse saturable absorption (RSA) and optical limiting (OL) properties. The MFs-based film showed a third-order nonlinear absorption coefficient (β) of 1.25 × 105 cm·GW-1 and an optical limiting threshold (Fol) of 0.00625 J·cm-2. Comparatively, the HPH-based film exhibited a lower β value of 9.80 × 104 cm GW-1 and a higher Fol value of 0.00834 J cm-2. The better NLO performance of the MFs was mainly ascribed to the formation of the charge transfer complexes between quinoline and C60, proven by UV-vis and electrochemical measurements. The fine tuning of the NLO properties of C60 without chemical modification provides new opportunities for C60 to be applied in nonlinear optics.

Study on the third-order nonlinear optical properties of Cd2+ ion doped ZnS/PVP nanocomposite films

Cd2+ ion doped ZnS/PVP nanocomposite films have been prepared using in-situ chemical method. XRD studies confirm the cubic structure of ZnS for all the films. The SEM micrograph shows the mono dispersion of ZnS nanoparticles in PVP matrix. FTIR spectra confirm the formation of nanocomposites containing ZnS nanoparticles and PVP polymer. Optical absorption spectra reveal the blue shift on the absorbance onset with the comparison of bulk ZnS. Photoluminescence spectra show a blue emission peak for all the films. The Z-scan results of all the films show a reverse saturation absorption process in open Z-scan experiment and self-focusing behavior in closed Z-scan experiment. Both ZnS/PVP and Cd2+ ion doped ZnS/PVP films exhibited the large optical nonlinearity and the value of nonlinear refractive index (n2), nonlinear absorption coefficient (β), third-order nonlinear optical susceptibility (χ(3)) and figure of merit (FOM) increase with Cd doping. The estimated n2, β, χ(3) and FOM values are found to be 1.771 × 10−10 m2 W−1, 4.148 × 10−3 mW−1, 1.603 × 10−4 esu and 9.576 × 10−6 esu m 6 mol% Cd doped ZnS/PVP nanocomposite film. The experimental results clearly showed that the Cd2+ ion doped ZnS/PVP nanocomposite film is a worthy candidate for the future nonlinear optical device fabrication.

Doubly 1,3-butadiyne-bridged ditwistacene with enhanced ultrafast broadband reverse saturable absorption

The introduction of a double 1,3-butadiyne bridge greatly enhances the ultrafast broadband reverse saturable absorption of twistacene.

Layer-Dependent Nonlinear Optical Properties of WS2, MoS2, and Bi2S3 Films Synthesized by Chemical Vapor Deposition.

Two-dimensional (2D) layered materials have shown layer-dependent optical properties in both linear optical and nonlinear optical (NLO) regimes due to prominent interlayer coupling and quantum confinement in an atomic scale. However, the NLO properties become more complicated as both saturable absorption (SA) and reverse saturable absorption (RSA) easily happen in 2D materials, which results in a significant challenge to understand the evolution of nonlinear absorption with layers. Motivated by this, chemical vapor-deposited chalcogenide compounds (WS2, MoS2, and Bi2S3) are used to investigate the pump intensity and layer number-dependent NLO properties. The values of nonlinear absorption coefficients of these chalcogenide compounds increase with the pump intensity by an 800 nm femtosecond laser, which can be described by an empirical power law function. The SA process due to the large transition probability of the ground state readily takes place in thick samples, while RSA occurs easily in thin samples due to the two-photon absorption (TPA). The transition from TPA to SA is deduced to occur at 13L-WS2, 15L-MoS2, and 5L-Bi2S3, which is related to the layer-dependent band gaps. Our results provide an efficient way to tune optical nonlinearities with a controlled layer number and to design corresponding NLO devices such as optical switches and saturable absorbers.

Preparation and third order nonlinear optical properties of corrole functionalized GO nanohybrids

Three novel corroles, 5,15-bis(phenyl)-10-(3-methoxy-4-hydroxylphenyl)- corrole PC, 5,15-bis(naphthyl)-10-(3-methoxy-4-hydroxylphenyl)-corrole NAPC and 5,15-bis(pyrenyl)-10-(3-methoxy-4-hydroxylphenyl)-corrole PYPC, were designed and synthesized. Their graphene oxide (GO) nanohybrids, PC-GO, NAPC-GO and PYPC-GO, were prepared by a covalent functionalization method and characterized by various spectroscopic techniques. The third order nonlinear optical (NLO) behavior of the corroles and their corresponding nanohybrids was investigated using open aperture Z-scan technique at 532 nm with 4 ns laser pulses. The nanohybrids showed enhanced NLO properties in comparison to the corresponding corroles. In addition, the NLO properties of nanohybrids increase in the order of NAPC-GO < PC-GO < PYPC-GO, while the corrole molecules exhibit NLO performance in the same order of NAPC < PC < PYPC, implying the NLO response originating from the corrole moiety play a more important role in the NLO properties of the nanohybrids than that arising from the photo-induced electron or energy transfer process between GO and corrole molecules. Importantly, at same transmission intensity, all the corroles showed typical nonlinear reverse saturation absorption (RSA) behavior, while all the nanohybrids exhibited a flip over behavior from saturation absorption (SA) to RSA. The different NLO response between the corrole molecules and their nanohybrids implies their promising applications as NLO materials.

Investigation of ultrafast broadband optical nonlinearity and intensity-dependent nonlinear absorption in novel hydrazone derivatives

Two novel hydrazone derivatives (BTH-1 and BTH-2) were designed and synthesized to investigate the modulation of intramolecular charge transfer (ICT) and planar π conjugation on optical nonlinearities. Femtosecond Z-scan measurements show that trithiophene-substituted BTH-2 exhibits stronger broadband (600–900 nm) reverse saturable absorption (RSA) resulting from two-photon absorption (TPA)-induced excited state absorption (ESA). Combined with quantum chemical calculations, the results indicate that the local excitation and spatial delocalization enhanced by planarized trithiophene are more conducive to promoting the nonlinear optical (NLO) response of hydrazone molecules than the ICT introduced by twisted triphenylamine. In addition, the intensity-dependent transition from saturable absorption to RSA of BTH-2 at 532 nm under multiple pulse widths (fs, ps, ns) was explored. Transient absorption spectroscopy provided information on the excited state dynamics of the compounds. This work extends NLO research on hydrazone derivatives and provides a reference for the design of hydrazone molecules with high nonlinearity. The results also suggest that BTH-2 is a promising candidate for optical limiting applications.

Impact of different auxochromes hydroxyl and methyl on two photon absorption coefficients and ultrafast dynamics of near-infrared hemicyanine dyes

There is immense interest in the design of organic nonlinear optical (NLO) chromophores for optical limiting and bioimaging applications. In this work, two near-infrared hemicyanine compounds which are named 2-(2-(3-Hydroxy-8,9-dihydro-7H-pyrido[1,2-a]quinazolin-10-yl)vinyl)-1,1-dimethyl-3-propy l-1H-benzo[e]indol-3-ium iodide (Hemicyanine1) and 1,1-Dimethyl-2-(2-(3-methyl-8,9-dihydro-7Hpyrido[1,2-a]quinazolin-10-yl)vinyl)-3-propyl-1H-benzo[e]indol-3-ium iodide (Hemicyanine2) were synthesized. The difference between Hemicyanine1 and Hemicyanine2 is that one of the auxochrome is hydroxyl and the other is methyl. The third-order nonlinear optical absorption properties of Hemicyanine1 and Hemicyanine2 were investigated using broadband Z-scan measurements at nanosecond time regime. The Z-scan results demonstrate that both chromophores have reverse-saturable absorption (RSA), while the NLO response of Hemicyanine2 is significantly stronger than Hemicyanine1. The corresponding physical mechanism were studied via femtosecond transient absorption (TA) spectroscopy. The results of femtosecond TA measurement demonstrate that the lifetime of excited state of Hemicyanine2 is considerably longer than that of Hemicyanine1. Our study indicated that the auxochrome is critically important in optimizing the NLO response and excited-state lifetime of hemicyanine chromophores for photonic applications.

Nonlinear absorption of CsPbBr3/antimonene blend materials prepared by laser ablation in liquid

Recently, through the continuous research on perovskite materials, the excellent nonlinear optical properties of perovskite have been shown to the world. Nevertheless, people still try their best to improve its optical nonlinearity to make it better applied to nonlinear optical devices. In this work, the nonlinear optical performance of the perovskite quantum dot (PQD) has been studied and tested, and its reverse-saturable absorption property and optical limiting potential have been discovered. On this basis, we tried to further improve the nonlinearity of the PQD by compounding other materials that has excellent optical properties especially highly nonlinearity. It is found that the new two-dimensional (2D) Group-VA material antimonene He meets our needs. Although antimonene has excellent nonlinear optical performance, its dispersibility is poor and not easy to store. Here, we tried to incorporate PQD and antimonene to further improve its nonlinear optical performance. With the method of laser ablation in liquid (LAL), CsPbBr3/antimonene blend materials (CPBAB) with stronger nonlinear absorption and higher dispersibility were successfully prepared. The nonlinear absorption properties of CPBAB with different ablation time were studied by Z-scan technology. It was found that by adjusting the laser ablation time parameters, CPBAB with higher optical limiting ability could be prepared. In addition, this CPBAB can be encapsulated in a polymer for curing, which improves its practical application to protect human eyes and optical equipment from high-power laser damage.

Impact of reverse saturable absorption on pulse dynamics in the ultrafast fiber laser

In this work, we present a numerical investigation of the pulse dynamics in an all-normal dispersion fiber laser mode-locked by a physical saturable absorber. We erected a theoretical model including the reverse saturable absorption (RSA) and spectral filtering effects. Utilizing the double-parameter scanning method, the pulse state distribution is mapped in the two-dimensional parameter space. The simulation results emphasize that the RSA greatly affects the transitions of pulse states and pulse properties. Moreover, we explore the multipulse region in detail and then demonstrate two completely different multipulse evolution dynamics. Based on this, we offer an analysis of dissipative soliton resonance multipulse generating in the physical saturable absorber-based ultrafast fiber laser.

Nanoarchitectonics of heterometallic compound Al4Bi4 for optical limiting

Presented herein are the synthesis, structure, and optical properties of a novel aluminum-bismuth heterometallic coordination compound. [Al4Bi4(L)10(μ4-O)2(sal)4(Hsal)2] (L = benzyl alcohol, H2sal = salicylic acid) represents the highest nuclearity of AlBi based cluster compound. This compound is fully characterized. In addition, the optical limiting mechanism was investigated using the open-aperture and closed-aperture techniques. The results show it exhibits obvious reverse saturation absorption (RSA) response.

Investigation on optical switching behaviour of regenerated and non-regenerated silk by nanosecond Z-scan technique

The nonlinear optical behaviour of silk, a natural fibre, is investigated in this study. We have considered silk in the cocoon, fibre and film forms of bivoltine and multivoltine breeds. The nonlinear absorption and optical limiting studies were performed using the open aperture Z-scan technique at 1064 nm. Interestingly, silk in cocoon and fibre form possess saturable absorption (SA), whereas silk in the film form exhibits reverse saturable absorption (RSA). This shift is attributed to the removal of sericin during the regeneration of silk into a film. Further, silk films exhibit optical limiting behaviour, whose limiting thresholds are in the order of 1012 W cm−2. Functional data analysis (FDA), a statistical approach, is employed to draw correlations amongst physical parameters. FDA offers good insight into the dependencies between silk varieties and their optical parameters. This helps in identifying the sample possessing the best properties.

Ultrafast nonlinear absorption properties of Ag/Sb2Se3 composite films in the near-infrared region

To explore the nonlinear absorption(NLA) properties of the Sb2Se3 composite system, Ag/Sb2Se3 composite films were prepared by magnetron sputtering at room temperature, and part of the films were annealed under 300 °C. The NLA properties were investigated using femtosecond(fs) Z-scan technology under 800 nm. The results showed that Ag/Sb2Se3 and annealed-Ag/Sb2Se3 composite films exhibited reverse saturated absorption(RSA) and saturated absorption(SA), respectively. The results indicated that annealing could tunable the NLA types of composite films. Furthermore, Ag can strengthen the NLA properties of the Ag/Sb2Se3 composite films compared with the single Sb2Se3. By increasing Ag sputtering power and incident laser energy, the NLA properties of composite films are enhanced. This study provides a new perspective for the application of Ag/Sb2Se3 composite films in optoelectronic devices.

Synthesis, characterization and nonlinear optical properties of polylactide and PMMA based azophloxine nanocomposites for optical limiting applications

The widespread usage of harmful pulsed laser sources emitting brief but intense radiations implies to search for appropriate and convenient forms of protection. Nonlinear optical nanomaterials can serve this purpose when properly embedded in a solid medium, resulting in nanocomposite passive optical limiting filters.This article focuses on the optical limiting behavior of a series of polymer-dye nonlinear nanocomposites, for which we combined azophloxine, a red azo dye, with two polymer hosts, namely polymethyl methacrylate (PMMA) and polylactide (PLA). In this work, optical filters were produced by chemical synthesis from the bulk. Their linear absorption and transmittance were measured by UV–VIS-NIR spectrophotometry and their thermal examination was done via TGA measurements. The optical limiting properties were characterized using an appropriate custom-made optical setup and the nonlinear absorption coefficients and refractive indices were measured by the Z-scan method. Optical measurements in the nonlinear regime were performed at the wavelength of 1064 nm with nanosecond pulses at a low pulse repetition rate. The nonlinear optical properties resulting from energy dependent transmittance assessments reveal that the dye concentration is of major relevance regarding the PMMA nanocomposites, and to a lesser extend for the PLA based systems. The PLA synthesis concept described in this study offers an easy way to directly attach the dye covalently to the polymer chain. The originality and novelty of this synthesis technique is to be pointed out since it has never been mentioned elsewhere to date. For the various types of nanocomposites investigated, significant differences in the optical limiting response were observed. For instance, it is averred that a significantly higher optical limiting effect results in the systems with the less azo dye concentration and the best optical limiting performance corresponding to a laser protection level of OD = 3.3 was measured for the PLA based system. Besides, the PMMA nanocomposite system exhibits an optical limiting level of OD = 1.9. A molecular model claiming for the dye aggregation in the PMMA nanocomposites is discussed. Two different absorption regimes responsible for the optical limiting action have been identified to be reverse saturable (RSA) – excited state absorption (ESA) on the one hand and multi-photons absorption (MPA) on the other hand. By means of transmittance investigations in an open Z-scan configuration, one could observe the sudden and remarkable changeover from a saturable absorption (SA) regime to a reverse saturable absorption one for high azo dye loads in PMMA. Such transition from SA to RSA has been basically revealed for materials and experimental conditions close to or centered on the resonance of absorption (i.e. around 532 nm). To the author’s knowledge, a study in off-resonant conditions (i.e. 1064 nm) was never reported elsewhere to date. Also tracked out by open Z-scan measurements, significantly higher nonlinear absorption coefficients βresulted for the PLA based systems. Similar experiments in a close aperture Z-scan scheme revealed nonlinear refractive indexes in the order of n2=-2.0X10-15cm2/W for the PMMA nanocomposites and n2=-3.0X10-15cm2/W for the PLA nanocomposites.

Nonlinear optical properties of single-walled carbon nanotubes/water dispersed media exposed to laser radiation with nano- and femtosecond pulse durations

The constant increase in the power of laser systems and the growth of potential fields for the application of lasers make the problem of protecting sensitive elements of electro-optical systems and visual organs from high-intensity radiation an urgent issue. Modern systems are capable of generating laser radiation in a wide range of wavelengths, durations, and pulse repetition rates. High-quality protection requires the use of a universal limiter capable of attenuating laser radiation, not causing colour distortion, and having a high transmission value when exposed to low-power radiation. For this, dispersed media based on carbon nanotubes with unique physicochemical properties can be used. Such media have constant valuesof their absorption coefficient and refractive index when exposed to low-intensity laser radiation and change their properties only when the threshold value is reached.The aim of this work was the study of the nonlinear optical properties of an aqueous dispersion of single-walled carbon nanotubes exposed to nano- and femtosecond radiation. For the characterization of the studied medium, Z-scan and fixed sample location experiments were used. The optical parameters were calculated using a threshold model based on the radiation transfer equation.As a result of the experiments, it was shown that the aqueous dispersion of single-walled carbon nanotubes is capable of limiting radiation with wavelengths from the visible and near-IR ranges: nano- (532, 1064 nm) and femtosecond (810 nm). A description of nonlinear optical effects was proposed for when a medium is exposed to radiation with a nanosecond duration due to reverse saturable absorption and two-photon absorption. When the sample exposed for a femtosecond duration the main limiting effect is spatial self-phase modulation. The calculated optical parameters can be used to describe the behaviour of dispersions of carbon nanotubes when exposed to radiation with different intensities. The demonstrated effects allow us to conclude that it is promising to use the investigated media as limiters of high-intensity laser radiationin optical systems to protect light-sensitive elements.

Third-order optical nonlinearity of DSR13/THF solutions under CW He–Ne laser irradiation using Z-scan method

The Z-scan technique was employed to explore the third-order nonlinear optical properties of disperse red 13 organic chromophore solutions in tetrahydrofuran. A continuous-wave He–Ne laser (632.8 nm) was used as a source of irradiation. The nonlinear absorption and nonlinear refractive index coefficients of this dye were investigated. The results showed that this dye has a good nonlinear response with its real and imaginary quantities of third-order susceptibility. The solutions showed negative nonlinear refraction. The best obtained value of the third-order susceptibility was 6.37 × 10–3 esu at a dye concentration of 3.15 × 10–4 mol/L. Moreover, the nonlinear optical properties were enhanced with higher dye concentrations, and an elevated trend in nonlinear absorption and nonlinear refractive index coefficients was observed. Also, it was found that the reverse saturable absorption was the main mechanism responsible for the two-photon absorption effect in DSR13/THF samples.

Improved near‒infrared nonlinear optical properties of Sm3+ containing borate glasses: Effect of silver nanoparticles concentration

Efficacy of silver nanoparticles on tuning the optical nonlinear characteristics of Sm3+ doped borate‒based glasses has been investigated comprehensively and the outcomes are provided. The nonlinear optical (NLO) attributes were retrieved using the Z‒scan technique under an ultrafast pulse excitation with the wavelength ranging from 700 nm to 1000 nm. Reverse saturable absorption (RSA), ascribed to two‒photon absorption, was realized in open aperture Z‒scan profiles whereas refraction nonlinearity of positive type due to the self‒focusing was observed in closed aperture Z‒scan data. Based on the Z‒scan results along with the figure of merit condition (higher than unity), it was identified that the silver nanoparticles embedded Sm3+ containing glass hosts are competing materials for NLO device applications to function in near‒infrared region.

Nonlinear optical properties of LLDPE composites with titanium dioxide anatase phase

In this research work, the linear and nonlinear optical properties of linear low-density polyethylene (LLDPE) composites with anatase phase of titanium dioxide nanoparticles in different weight percentages are investigated. Solvent casting method have been used to synthesize the thin film of LLDPE/anatase nanocomposites. Thin films are characterized via XRD technique and field emission scanning electron microscope (FESEM). Wrinkles formed on the surface of thin films by adding the titanium dioxide. Linear optical and electrical parameters such as linear absorption coefficient, extinction coefficient, refractive indices, optical conductivity, and dielectric constants at various wavelengths from 190 nm to 2700 nm are determined for different weight percentages of nanoparticles in polymer nanocomposites. Z-scan technique has been employed to explore the nonlinear optical properties using CW laser at 532 nm wavelength. The nonlinearity is examined at various irradiance of laser to study the effect of irradiance on nonlinear optical properties. Pure LLDPE has saturable absorption (SA) at low laser irradiance. As the laser irradiance increases, the nonlinearity behavior turns from SA to reverse saturable absorption (RSA). The results show the suitability of the thin films for the applications in optical devices that involve the use of optical limiting properties of materials.