Reverse Saturable Absorption Effect Research Articles

Nonlinear optical properties of methyl green investigated by the femtosecond Z-scan technique

The third-order optical nonlinearities of methyl green in aqueous solution are studied by the Z-scan technique using a femtosecond laser at 800 nm. The valley shape in the open aperture measurements reveals the presence of reverse saturable absorption effect, which is ascribed to the three-photon absorption process. The closed aperture Z-scan traces demonstrate a negative sign for the nonlinear refractive coefficient, indicating the self-defocusing optical nonlinearity. Furthermore, the magnitudes of the nonlinear refractive index n 2, the three-photon absorption coefficient α 3, and the real part of the third-order nonlinear optical susceptibility Re χ (3) are determined and found to be linearly proportional to the dye concentration within the investigated range. Our results suggest that methyl green may be a hopeful candidate for applications in nonlinear optics.

Femtosecond nonlinear optical investigations of nitro chalcones-doped PMMA thin films for optical limiting and photonic applications

Herein we present the linear and third-order nonlinear optical properties of two nitro substituted chalcone derivatives [3-(4-fluorophenyl)− 1-(3-nitrophenyl) prop-2-en-1-one and (2E,4E)− 1-(3-nitrophenyl)− 5-phenylpenta-2,4-dien-1-one; abbreviated as F3NC and Ci3NC, respectively] doped PMMA polymer thin films. The chemical spray pyrolysis method was adopted to prepare the films at three different doping concentrations (5 wt%, 10 wt%, 15 wt%). The linear optical studies were performed using UV-Visible-NIR spectra, and surface roughness using AFM technique. Hirshfeld surface analysis was adopted to understand the intermolecular interactions. The third-order nonlinear optical properties were investigated using Z-scan method under Ti:Sapphire femtosecond (fs) laser pulses (∼150 fs, 80 MHz, 800 nm). Open and closed aperture Z-scan curves indicated the presence of two-photon assisted reverse saturable absorption and self-defocusing effect, respectively. The calculated nonlinear refraction (n2), nonlinear absorption (β) coefficients and third-order susceptibility [χ(3)] were found to be in the order ∼10−12 cm2 W−1, ∼10−8 cm W−1 and ∼10−11 e.s.u., respectively. We observed increase in nonlinearity of the films with increased chalcone doping concentration. Among the doped chalcones, F3NC doped films exhibit a higher nonlinearity than Ci3NC doped films. The observed results reveal that chalcone-doped PMMA thin films are possible materials for optical limiting and photonic applications.

Bi/Ti3C2Tx composites: Synthesis and enhanced nonlinear optical and electrochemical properties

The Bi/Ti3C2Tx composites were synthesized by a hydrothermal method. Then the Bi/Ti3C2Tx powder was dispersed into methyl methacrylate (MMA) to fabricate the (Bi/Ti3C2Tx)2–6/polymethyl methacrylate (PMMA) organic glasses. The crystalline structure and phase of the Bi/Ti3C2Tx were measured by the X-ray diffraction. The photoluminescence (PL) spectra and the electrochemical impedance spectra (EIS) of the Bi/Ti3C2Tx were measured to prove the enhanced optical and electrical properties. The nonlinear optical (NLO) properties of the (Bi/Ti3C2Tx)2–6/PMMA organic glasses were investigated by the Z-scan technique. The (Bi/Ti3C2Tx)2–6/PMMA organic glasses exhibit the reverse saturable absorption (RSA) and self-defocusing effects. Compared to the (Bi)2/PMMA and (Ti3C2Tx)2/PMMA organic glasses, the (Bi/Ti3C2Tx)2–6/PMMA organic glasses exhibit the enhanced NLO properties. Among three different amount Bi/Ti3C2Tx/PMMA organic glasses, (Bi/Ti3C2Tx)4/PMMA organic glass exhibits the strongest RSA and self-defocusing effects with βeff = (6.34 ± 1.90)× 102 cm·GW−1 and γ = (–3.52 ± 0.07)× 10−4 cm2·GW−1. The enhanced RSA and self-defocusing effect of the (Bi/Ti3C2Tx)2–6/PMMA organic glasses make them exhibit the excellent optical limiting (OL) performance. In addition, the Bi/Ti3C2Tx composites show excellent electrochemical performance as an electrode material for energy storage systems. The resultant Bi/Ti3C2Tx electrode yields a high specific capacity of 68.5 mAh·g−1 at a current density of 1 A·g−1, which is approximately 4.2 and 6.1 times than those of the Bi and Ti3C2Tx electrodes, respectively. The experimental results exhibit the Bi/Ti3C2Tx is highly promising for energy storage and OL devices.

Adjusting the nonlinear optical and optical limiting properties of MAPbBr3/PMMA by doping with Zn

Third-order nonlinear optical and optical limiting properties of MAPbBr3/polymethyl methacrylate (PMMA) are adjusted by doping with Zn. X-ray diffraction and photoluminescence are performed to confirm the effective doping of Zn. Typical reverse saturable absorption and self-focusing effects are observed in the undoped MAPbBr3/PMMA and Zn-doped MAPbBr3/PMMA. After Zn doping, the nonlinear absorption coefficient becomes larger but nonlinear refraction coefficient becomes smaller. This may be related to the decreased defect states after Zn doping. Besides, both values of the optical limiting threshold and the clamping normalized transmittance for the Zn-doped MAPbBr3/PMMA are obviously smaller than those of the undoped sample, indicating that its optical limiting property enhances. The reverse saturable absorption properties are caused by one photon absorption-induced excited-state absorption processes, which have been explained by using three-energy-level diagrams. The nonlinear optical and optical limiting properties of the Zn-doped MAPbBr3/PMMA make it show great potentials for application in optical limiter.

Spatiotemporal dissipative soliton resonances in multimode fiber lasers

Spatiotemporal mode-locking in multimode fiber lasers is intriguing for the complex nonlinear dynamics and the increase of theoretical energy limit. In this paper, we enrich spatiotemporal mode-locking with dissipative soliton resonances, a kind of solitons which is characterized by large pulse energy in single mode fiber lasers, and demonstrate their emergence in multimode fiber lasers by employing the reverse saturable absorption effect from real saturable absorbers. The spatiotemporal dissipative soliton resonances are expected to raise the energy limit further by the locking of dissipative soliton resonances in different transverse modes, whose energy is about twice the maximum single-mode energy in our results. Moreover, properties of spatiotemporal dissipative soliton resonances are investigated by tailoring parameters of the multimode fiber laser, where evolution and transformation of the proposed pulses including shaping and broadening are disclosed. The spatiotemporal dissipative soliton resonances in multimode fiber lasers may open up new avenue for high-power and spatiotemporally engineered coherent light fields in laser dynamics and nonlinear optics.

Fabrication, Characterization of Basic Blue 7 Dye-Doped PVA Films and Their Third-Order Nonlinear Optical Properties.

In this work, we report on the fabrication, characterization and the third-order nonlinear optical (NLO) properties of basic blue 7 (BB 7) dye‒doped polyvinyl alcohol (PVA) polymer thin films. The absorption spectra of BB 7 dye‒PVA films were measured by UV‒visible absorption studies. The functional groups of BB 7‒PVA films have been identified by FT‒IR spectroscopic analysis. The surface morphology was examined by AFM and SEM analysis which shows that the BB 7 dye‒doped PVA films have a homogenous and smooth surface. The nonlinear absorption and refraction of BB 7‒PVA films were respectively explored by open aperture and closed aperture Z‒scan technique using a 5 mW semiconductor diode laser of 635nm wavelengths. The BB 7‒PVA films exhibit the reverse saturable absorption (RSA) and self-defocusing effect and the measured third‒order nonlinear susceptibility χ(3) values of these films were found to be of the order of 10- 5 esu. The present experimental results show that BB 7‒PVA films may have potential applications in future photonic and NLO devices.

Dissipative pure-quartic soliton resonance in an Er-doped fiber laser

Dissipative pure-quartic soliton (DPQS) that arises from the balance of positive fourth-order dispersion (FOD), nonlinearity, gain and loss has been proposed to generate high-energy pulse. Herein, we numerically investigate the generation of dissipative pure-quartic soliton resonance (DPQSR) in an Er-doped mode-locked fiber laser with all positive FOD. Our findings indicate that the formation of DPQSR depends on the reverse saturable absorption (RSA) effect of real saturable absorber. Then, the impacts of pump power, RSA coefficient and positive FOD in generating DPQSR pulse are investigated. With the increase of pulse energy, the asymmetrical temporal profile of DPQS transforms into a rectangular one. This work can be utilized to comprehend the dissipative pure-quartic soliton resonance as well as the development of an all positive FOD Er-doped fiber laser. In addition, it lays the way for the development of highly stable, high-energy pulsed lasers.

Nonlinear absorption and refraction of Cs3Cu2Br5 perovskite

Halide perovskite (Cs3Cu2Br5) is synthesized by a thermal injection method. The X-ray diffraction (XRD) proves that the Cs3Cu2Br5 crystal phase is an intersection phase. The Cs3Cu2Br5 organic glasses are fabricated by dispersing Cs3Cu2Br5 materials in methyl methacrylate (MMA). The nonlinear absorption (NLA) and the nonlinear refraction (NLR) performances of Cs3Cu2Br5/PMMA organic glasses are measured via the open-aperture (OA) and the closed-aperture (CA) Z-scan technique, respectively. The samples show typical reverse saturable absorption (RSA) and self-focusing effect with the change of input energy (40–72 μJ). Meanwhile, the room-temperature photo-luminescence (PL) measurement reveals light emission for Cs3Cu2Br5. The effects on nonlinear optical (NLO) properties are investigated by controlling the input energy and the amount of the sample. The Cs3Cu2Br5/PMMA organic glasses exhibit excellent NLA and NLR properties. The NLA coefficient of (Cs3Cu2Br5)18/PMMA organic glass is much higher than those of lead-containing perovskite such as CsPbCl3 and CsPbBr3 nanosheets. This results in Cs3Cu2Br5/PMMA organic glasses show superior optical limiting (OL) performance. The Cs3Cu2Br5 perovskite materials show great potential in devices such as light-emitting diodes and optical switches.

Reverse saturable absorption in Ti3C2 MXene nanosheets for dissipative soliton resonance mode-locking operation in Er-doped fiber laser

In this paper, Ti3C2Tx MXene nanosheets were prepared using a low-power ultrasonic-assisted liquid phase exfoliation method. The Ti3C2Tx nanosheets based saturable absorber deposited on the tapered microfiber possessed the typical saturable absorption and reverse saturable absorption with the surface evanescent field. With a home-made femtosecond excitation source at 1550 nm, the modulation depth was determined as 4.8% with a saturation intensity of 18.7 MW/cm2. By inserting our as-prepared saturable absorber into an Erbium-doped fiber laser (EDFL), two types of mode-locked pulses operating in the stable conventional soliton (CS) and dissipative soliton resonance (DSR) regimes were realized at the fundamental repetition frequency of 7.39 MHz, respectively. The pulse width of the CS pulse was 1.185 ps with a central wavelength of 1560.6 nm. While the pulse width of the DSR pulses varied from 2.07 ns to a maximum of 8.13 ns with the increase of the pump power. Our work reveals the reverse saturable absorption effect of Ti3C2Tx could play a key role in the DSR pulse generation, which may benefit the application of the pulse modulation and optical communication with the two-dimensional materials.

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.

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.

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.

Dissipative-soliton-resonance and evolution in an all-normal dispersion Er-doped fiber laser

The generation of dissipative soliton resonance (DSR) in an all-normal dispersion erbium-doped fiber laser based on a real saturable absorber is amazing in both experiment and theory. However, it’s rarely to realize DSR in an all-normal Er-doped fiber laser in experiments to our knowledge. In this work, we analyze the principle of DSR generated in an all-normal dispersion erbium-doped fiber laser based on a real saturable absorber, and prove that the key reason is the reverse saturable absorption (RSA) effect of the real saturable absorber (SA). Then, we investigate the impacts of pump power, filter, and RSA coefficient in generating DSR pulse. In addition, when the saturable power of SA is above 25 W and the modulation depth of SA above 50%, a novel soliton explosion phenomenon based on RSA in DSR region is obtained for the first time to our knowledge. The work can be used for understanding the dissipative soliton resonance as well as the evolution in an all-normal dispersion Er-doped fiber laser. Furthermore, it also paves a way to realize high stable and high energy pulsed lasers in telecommunication region.

Synthesis, characterization, and investigation of nonlinear property of fly ash-red mud-Ag: A low-cost sustainable nanocomposite

The silver-coated fly ash-red mud nanocomposite (FARM-Ag) is synthesized through the environment-friendly facile chemical method. Scanning electron microscopy (SEM), Energy dispersive x-ray analysis (EDAX), X-ray diffraction (XRD), and UV–Visible absorption spectroscopy techniques are used to characterize the nanocomposite. A sensitive single-beam Z-scan technique is used to study its nonlinear properties under continuous-wave (CW) laser excitation as a function of sample concentration and laser power. It is observed that FARM-Ag exhibits negative refractive and positive absorptive nonlinearity due to the self-defocusing and reverse saturable absorption (RSA) effect, respectively. Here, the origin of the nonlinearity is attributed to the thermal lensing effect and the larger magnitude of the nonlinear refractive index (n2), nonlinear absorption coefficient (β), third-order nonlinear susceptibility (|χ(3)|), and thermo-optical coefficient (dn/dT) are obtained as – 2.978 × 10−12 m2W−1, 1.424 × 10−5 mW−1, 3.477 × 10−14 m2V−2, and - 3.903 × 10−5 K−1, respectively. The results suggest that this newly synthesized nanocomposite from industrial waste might have a possible use for nonlinear optical devices.

Nonlinear absorption, refraction and optical limiting properties of cobalt molybdate microcrystals

Cobalt molybdate (CoMoO4) microcrystal was synthesized by a hydrothermal method. The CoMoO4 microcrystal was dispersed in methyl methacrylate (MMA) that was polymerized to polymethyl methacrylate (PMMA) to prepare CoMoO4/PMMA organic glass. The successful synthesis of CoMoO4 was verified by Raman spectroscopy. The CoMoO4 microcrystal was characterized by scanning electron microscopy (SEM). The results indicate that the CoMoO4 microcrystal is microrod. The diameter and length of the sample are about 0.5–3 μm and 2–20 μm. The band gap of CoMoO4/PMMA is about 3.5 eV. The nonlinear absorption (NLA) and refraction properties of CoMoO4/PMMA organic glasses were investigated for the first time by a Z-scan technique. The laser pulse energy is 7–20 μJ. The results indicate that CoMoO4/PMMA organic glasses exhibit good reverse saturable absorption (RSA) and self-defocusing effects. NLA and refraction coefficients are β = 68 cm GW−1 and γ = −1.4 × 10−4 cm2 GW−1 at the laser pulse energy of 20 μJ, respectively. The enhanced RSA and self-defocusing effects make the CoMoO4/PMMA organic glasses exhibit excellent optical limiting (OL) performance. The nonlinear absorption, refraction and OL properties of CoMoO4/PMMA organic glasses can be controlled by adjusting the laser pulse energy and the amount of CoMoO4 in PMMA.

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.

Large Optical Nonlinearity of the Activated Carbon Nanoparticles Prepared by Laser Ablation.

Carbon nanoparticles (CNPs) with high porosity and great optical features can be used as a luminescent material. One year later, the same group investigated the NLO properties CNPs and boron-doped CNPs by 532 nm and 1064 nm laser excitations to uncover the underlying physical mechanisms in their NLO response. Hence, a facile approach, laser ablation technique, was employed for carbon nanoparticles (CNPs) synthesis from suspended activated carbon (AC). Morphological properties of the prepared CNPs were studied by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). UV-Vis and fluorescence (FL) spectra were used to optical properties investigation of CNPs. The size distribution of nanoparticles was evaluated using dynamic light scattering (DLS). The nonlinear optical (NLO) coefficients of the synthesized CNPs were determined by the Z-scan method. As a result, strong reverse saturable absorption and self-defocusing effects were observed at the excitation wavelength of 442 nm laser irradiation. These effects were ascribed to the presence of delocalized π-electrons in AC CNPs. To the best of our knowledge, this is the first study investigating the NLO properties of the AC CNPs.

Influence of reverse saturable absorption effect on conventional and dissipative solitons fiber lasers

We numerically investigate the influence of the reverse saturable absorption effect of real saturable absorbers on conventional and dissipative solitons. The results show that the reverse saturable absorption effect leads to more loss and clamps peak power of both conventional and dissipative solitons, but plays different roles on their properties. When the cavity operates at conventional solitons state, the reverse saturable absorption effect restricts the maximum pulse energy to less than 0.1 nJ, facilitates the formation of multiple solitons, but maintains the time-bandwidth product close to 0.315, indicating the pulses maintain the sech2 shape. While the cavity operates at dissipative solitons state, the reverse saturable absorption effect increases the maximum pulse energy from 11 to 13 nJ and plays a key role in transforming the pulse states, which further facilitates the generation of dissipative soliton resonance pulses. In addition, the reason of the different influences on pulses in two mode-locked regimes is also discussed. Our results reveal the role and promote the rational use of the reverse saturable absorption effect in different mode-locked regimes.

Polarization‐Dependent and Wavelength‐Tunable Optical Limiting and Transparency of Multilayer Selenium‐Doped Black Phosphorus

AbstractAs one of the hottest 2D materials, black phosphorus (BP) exhibits a narrow band gap, high carrier mobility, exceptional photoelectric and thermoelectric properties. Nevertheless, easy oxidation in air limits its practical application. Here, versatile optical properties of multilayer selenium‐doped BP (Se‐BP) with air stability are reported. Based on polarization‐resolved Raman spectroscopy, which clarifies the sample structure and doping content, the optical absorption information of Se‐BP is investigated by employing polarized linear absorption spectra and femtosecond (fs) laser intensity scanning (I‐scan). Importantly, wavelength‐changed I‐scan results demonstrate a distinct maximum of 5.9% saturable absorption (SA) and 14.2% reverse saturable absorption (RSA) effect whose modulation depths act out polarization dependence. Through the results of I‐scan and fs transient absorption spectroscopy, not only is the origin of RSA proven to be the excited state absorption (ESA), but also the correlation between SA‐induced optical transparency and RSA‐induced optical limiting is discussed and confirmed. This work sheds new light on multifunctional optical applications based on doped BP materials.

Generation of mode-locked square-shaped and chair-like pulse based on reverse saturable absorption effect of nonlinear multimode interference.

In this paper, the phenomenon of reverse saturable absorption of offset-spliced graded index multimode fibers (OS-GIMF) is revealed. And based on that, the stable square-shaped and chair-like mode-locked pulses are demonstrated with the maximum pulse energy of 0.14 µJ and 23.8 nJ respectively, while the OS-GIMF acts as a saturable absorber (SA) in fiber laser. By adjusting polarization controller (PC) and the pump power, square-shaped and chair-like pulse can be switched to each other. This multimode SA could sever as high power light source owing to its high damage threshold, compact structure and low cost.