Nonlinear Saturable Absorption Research Articles

MnO2 nanosheets as saturable absorbers for a Q-switched fiber laser

Manganese oxide nanosheets (MnO2 NSs) with two-dimensional formation and typically ultrathin thickness have gained a great deal of attention due to their excellent physical and chemical properties. However, the potential capability of MnO2 NSs in laser application has been rarely explored. Here, we first report the MnO2 NSs as the saturable absorber (SA) for generating Q-switched pulsed laser. The MnO2 NSs–based SA not only shows a broadband absorption, but also possesses nonlinear saturable absorption feature. By integrating the MnO2 NSs-SA into an erbium-doped fiber laser cavity, a stable passively Q-switched operation at central wavelength of ∼1558 nm was realized with a threshold pump power of 220 mW, and 1.26 μs pulse width with a repetition rate of 92.35 kHz was obtained. Our results indicate that the MnO2 NSs can serve as promising candidates for constructing optical pulsed lasers.

Large-scale monolayer molybdenum disulfide (MoS2) for mid-infrared photonics

Abstract Mid-infrared (MIR) photonics has attracted tremendous interest because of its broad applications at atmospheric windows. In this work, we report high-performance MIR photonics based on large-scale and good-quality monolayer molybdenum disulfide (MoS2). The open-aperture Z-scan measurement on the nonlinear saturable absorption features shows that the as-grown monolayer MoS2 possesses a modulation depth of 26% and a low saturable intensity of 271 kW/cm2, enabling its application as an excellent saturable absorber for the MIR pulse generation. This is further evident by the measured high effective nonlinear absorption coefficient β eff (−16 cm/MW). In addition, the two-photon absorption coefficient and the nonlinear refractive index of monolayer MoS2 are also determined by the closed-aperture Z-scan technology. As an application, we demonstrate a passively Q-switched Tm,Ho:CaLu0.1Gd0.9AlO4 (Tm,Ho:CLGA) disordered crystal laser at 2.1 μm by using the monolayer MoS2 as the saturable absorber for the first time, producing a minimum pulse width of 765 ns and a pulse repetition rate of 36 kHz. Our results demonstrate that large-scale monolayer MoS2 is a promising candidate for the MIR photonic applications.

Controlled Production of MoS2 Full‐Scale Nanosheets and Their Strong Size Effects

AbstractThe production of 2D nanosheets (2D NSs) with all sizes (1–100 nm) and few (<10) layers is highly desired but remains great challenge. Herein, the top‐down production of molybdenum disulfide (MoS2) NSs with wide‐range (161–10 nm) controlled sizes is reported. Considering the recently achieved MoS2 quantum sheets (QSs) with sizes of ≈2 nm, full‐scale NSs of MoS2 are successfully produced. The top‐down method combines silica‐assisted ball‐milling and sonication‐assisted solvent exfoliation. Ball‐milling with controlled time enables the production of multiscale NSs with varying distributions, which are then precisely separated by cascade centrifugation. Multiple spectroscopic techniques reveal the dramatic size dependence, indicating prominent quantum confinement and edge effects of the MoS2 NSs. The NSs‐poly(methyl methacrylate) (PMMA) hybrid thin films demonstrate strong size effects in nonlinear saturation absorption (NSA). Both (absolute) modulation depths and saturation intensities can be broadly modulated by simple variation of the NS sizes. With the sizes down from 161 to 10 nm, the modulation depths are increased from 27.0% to 51.3% and the saturation intensities are decreased from 33 419 to 21.2 kW cm−2 (3341.9–2.12 nJ cm−2). The work greatly facilitates the mass production and full exploration of 2D NSs with all sizes.

Graphdiyne as a saturable absorber for 2-µm all-solid-state Q-switched laser

As a novel one-atom-thick carbon allotrope, graphdiyne (GDY) has attracted wide interest in two- dimensional materials owing to its unique feature with a planar layer comprising sp2- and sp-hybridized carbon atoms and a direct natural bandgap. A high-quality saturable absorber (SA) based on GDY was successfully fabricated, and the nonlinear saturable absorption properties were investigated. A compact diode-pumped solid-state passively Q-switched laser based on the as-prepared GDY-SA could be operated at 2 μm. The Q-switched laser delivered a maximum average output power of 1.29 W at a central wavelength of 1908.41 nm with up to 54.8% slope efficiency. A repetition rate of 91.58 kHz and single pulse energy of 23.08 μJ were obtained. This work is the first application of GDY as an SA to generate all-solid-state pulsed lasers. These results indicate that GDY is a promising SA for solid-state pulsed lasers and has further application potential for ultrafast photonic devices in the 2-μm region.

Tailoring Multi-Walled Carbon Nanotubes into Graphene Quantum Sheets.

Transformation of carbon nanotubes (CNTs) into sub-10 nm pieces is highly required but remains a great challenge. Herein, we report a robust strategy capable of mechanically tailoring pristine multi-walled carbon nanotubes (MWCNTs) into graphene quantum sheets (M-GQSs) with an extremely high yield of up to 44.6 wt %. The method combines silica-assisted ball-milling and sonication-assisted solvent exfoliation and therefore enables reproducible high-yield production of M-GQSs directly from MWCNTs. Remarkable solvent diversity and extraordinary solvability (up to 7 mg/mL) are demonstrated facilitating the solution processing of the M-GQSs. The M-GQSs are essentially monolayers with intrinsic curvature, which could be determinative to their outstanding performances in both dispersions and thin films. Besides the excitation wavelength-, concentration-, and solvent-dependent photoluminescence in dispersions, the solid-state fluorescence and exceptional nonlinear saturation absorption (NSA) in thin films are demonstrated. Particularly, NSA with relative modulation depth up to 46% and saturation intensity down to 1.53 MW/cm2 are achieved in M-GQS/poly(methyl methacrylate) hybrid thin films with a loading content of merely 0.2 wt %. Our method opens up a new avenue toward conversion and utilization of CNTs.

SnS nanosheets for harmonic pulses generation in near infrared region

Two-dimensional materials have attracted increasing attention because of their excellent mechanical, thermodynamic, magnetic, electrical and optical properties. Here, a new two-dimensional material of tin sulfide (SnS) is experimentally prepared. It is layered like black phosphorus and owns distinct optoelectronic properties, but eliminates the disadvantage of instability. The nonlinear saturable absorption characteristics of the SnS nanosheets is investigated at 1563.3 nm by the double-balanced detection method. The obtained modulation depth and saturation intensity are 5.4% and 66.3 MW/cm2, respectively. A passively harmonic mode-locked erbium-doped fiber laser based on the SnS saturable absorber (SA) has been demonstrated. The results show that mode-locking with fundamental frequency of 5.47 MHz is realized at pump power of 28.38 mW. With the increase of pump power, the laser can operate from fundamental frequency to high-order harmonic mode-locking. The maximum repetition rate of 412.73 MHz has been obtained, which is equivalent to the 76th harmonic mode-locking. This work reveals that SnS nanosheets is a novel and efficient SA with high damage threshold, which will find potential applications in optical communication, photoelectric detection, laser medicine, etc.

2.3 µm nanosecond passive Q-switching of an LD-pumped Tm:YLF laser using gold nanorods as a saturable absorber

Developing new saturable absorbers for use in the mid-infrared region has practical significance for short-pulsed lasers and related scientific and industrial applications. The performance of gold nanorods (GNRs) as saturable absorbers at novel mid-infrared wavelengths needs to be evaluated even though these benefit from ultrafast nonlinear responses and broadband saturable absorption. Passive Q-switching of an LD-pumped 2.3 µm Tm:YLF laser using GNRs was successfully realized in this study. Pulses with an 843 ns pulse width and a 6.67 kHz repetition rate were achieved using this Q-switched laser. Results showed that GNRs provide promising passive Q-switches for 2.3 µm Tm-doped lasers.

Watt-Level Continuous-Wave Mode-Locked Nd:YVO4 Laser With ReSe2 Saturable Absorber

We report a ReSe 2 passively mode-locked composite YVO 4 /Nd:YVO 4 laser at 1.06 μm, which can stably generate pure continuous-wave mode-locking (CWML) operation at watt-level output. ReSe 2 , as a new type of 2-D transition metal dichalcogenides (TMDs), has the features of weak-layered dependence, broadband saturable absorption, low modulation depth and saturation intensity, which is beneficial to initiate robust CWML mechanism via nonlinear saturable absorption. By employing few-layered ReSe 2 as saturable absorber, the nanosecond mode-locked pulses at fundamental repetition rate of 90.37 MHz was obtained experimentally in a composite YVO 4 /Nd:YVO 4 laser. The maximum output power in pure CWML operation was as high as 1.1 W. The high-power CWML laser source shows potential applications in time-resolved spectroscopy, telecommunication and detection.

NiS2 as a broadband saturable absorber for ultrafast pulse lasers

Nickel disulfide (NiS2) has recently been found to possess strong nonlinear saturable absorption properties. This feature is highly attractive for nonlinear photonics applications. Ultrafast pulse generation is successfully demonstrated in this article for both Ytterbium- and Erbium-doped fibre lasers using micro-fibre deposited nickel disulfide (NiS2) as a saturable absorber (SA). The fabricated SA device has a modulation depth of 23% at 1.06 μm and 30.8% at 1.55 μm. Stable dissipative soliton operation was achieved at 1064.5 nm with a pulse duration of 11.7 ps and another stable conventional soliton pulse train was also obtained at 1560.2 nm with a pulse duration of 524 fs. These results demonstrate that the microfibre-based NiS2 has a broadband nonlinear response and can function as an efficient SA, therefore it has significant potential for use in ultrafast laser pulse generation.

Stable passively Q-switched erbium-doped fiber laser based on CuCrO2 nanoparticles saturable absorber

We demonstrate metal oxides CuCrO2 exhibit considerable nonlinear saturable absorption property in the near-infrared region, and fabricate typical saturable absorber (SA) by wrapping the CuCrO2 nanoparticles(NPs) into a sodium carboxymethylcellulose (NaCMC) film or polyimide (PI) film separately. These SA films could keep stable exposed to air condition for several months. In the CuCrO2-NaCMC (CuCrO2-PI) Q-switched fiber laser, the pulse repetition rate increases from 10.6 kHz (48.5 kHz) to 24.6 kHz (88.7 kHz) and the pulse duration decreases from 19.08μs (3.85μs) to 3.91μs (1.18μs) by adjusting the pump power from 53 mW (82.6 mW) to 188.6 mW (184.6 mW). The results suggest that CuCrO2 could be a promising SA for ultrafast lasers generation.

The enhancement of nonlinear absorption of Ag thin film on laser induced defective MoOx buffer layer

Defect plays a key role in the optical properties of silver thin films. Herein, we introduced the oxygen vacancy defects by laser modification and fabricated the Ag/ir-MoOx thin film. The effects of ir-MoOx on the structure and optical properties of Ag thin films were investigated. We found that laser irradiation and effective silver trap will introduce numerous oxygen vacancy defects. The nonlinear absorption response of Ag/ir-MoOx was significantly improved compared with that of the single layer Ag. The increased concentration of oxygen vacancies in the composite film will promote the rate of charge transfer and enhance the nonlinear saturation absorption.

Phase segregation induced third order nonlinear saturable absorption behavior in Erbium doped ZnO nanoparticles synthesized by facile hydrothermal method

Abstract Here in this work, we present the dominance of rare earth dopant (Er) in association with the surfactant (Oleylamine) on the structural, surface morphology, optical, and nonlinear optical properties of hydrothermally grown ZnO nanoparticles. The polycrystalline nature of the prepared nanostructures is confirmed by the XRD diffractograms. The formation of erbium related compound (erbium oxide) in the highest Er doped ZnO nanoparticles is visible from the XRD diffractogram. The incorporation of Er at different doping concentrations (1 at. wt.%, 3 at. wt.%, and 5 at. wt.%) brings noticeable morphological changes in the FESEM images. The Raman spectra reveal the retention of wurtzite structure in undoped and Er doped nanoparticles. The disappearance of A1 (TO) mode in ZnEr3 and ZnEr5 nanoparticles shows the deteriorated polar lattice bond strength. The phase segregation observed from XRD spectrum of ZnEr5 nanoparticles is further confirmed by the detection of local vibrational mode (LVM). A severe decrement in the bandgap of the Er doped nanoparticles is noticed from UV–Vis spectroscopy. A continuous fall in the intensity in the NBE emission with increasing Er doping concentration is attributed to the formation of surface defects below the conduction band edge. The nonlinear optical parameters of the nanoparticles are quantified with the assistance of open aperture and closed aperture Z-scan curves. A remarkable switching from reverse saturable absorption (RSA) to saturable absorption (SA) and self-defocusing to self-focusing mechanisms in ZnEr5 shed light on the impact of phase segregation on the nonlinear response of the Er doped nanoparticles. The quantified values of nonlinear parameters look promising in the fabrication of photonic devices.

Photoluminescence characterizations and nonlinear optical of PM-355 nuclear track detector film by alpha-particles and laser irradiation

The imaging processing technique was used for studying a laser beam nature that transmitted through films of PM-355. The thermal nonlinearity of PM-355 films was studied using a 635 nm cw diode laser at 15 mW as the source of excitation. Third order nonlinear optical properties of PM-355 films irradiated with α-particles at different times and pristine sample has been studied using Z-scan technique. The samples showed a negative and large nonlinear refractive index and reverse saturable absorption (RSA) with high values of the nonlinear absorption coefficient. The fluorescence spectra of PM-355 films were investigated at room temperature and wavelength range of 250–500 nm for a pristine film and in different times of exposure to α-particles. The broad peaks were between 350, 420 and 465 nm. All-optical switching property of PM-355 samples irradiated with α-particles at 20 min was also studied using the standard pump-probe technique.

Passively Q-switched Tm:CaLu0.1Gd0.9AlO4 laser at 2 µm with hematite nanosheets as the saturable absorber.

We report the first passive Q-switching operation at 1.95 µm utilizing the disordered Tm:CaLu0.1Gd0.9AlO4 (Tm:CLGA) crystal and the hematite (α-Fe2O3) nanosheets as the saturable absorber. The nonlinear saturable absorption properties of the hematite nanosheets were investigated by the conventional Z-scan technology. The modulation depth of 14.3% with the low saturation intensity of 205 kW/cm2 was obtained, indicating that the hematite could be a suitable saturable absorber for the mid-infrared pulse generation. Using the disordered Tm:CLGA crystal as the gain medium, the passive Q-switching operation could be realized with the hematite nanosheets as the saturable absorber, producing the shortest pulse duration of 402 ns with a repetition rate of 76 kHz. The experimental results convinced us that the hematite nanosheets could be of great interest in the optical pulse generation in the mid-infrared region.

Tin selenide for high-power and ultrafast Q-switched fiber laser

Tin selenide (SnSe), as one of transition metal chalcogenides (TMCs), has aroused much attention due to the unique property of thickness-dependent. Here, the property of the nonlinear saturable absorption for SnSe is investigated. Using the SnSe saturable absorber (SA), the fiber laser is realized. The SnSe film is synthesized by the chemical vapor deposition method. In addition, a typical two-arm transmission measurement is used to investigate the power-dependent nonlinearity of the SnSe SA, and its modulation depth is 17.89%. Moreover, the pulse duration is 624.6 ns at 1561.8 nm. The output power is up to 31.6 mW. This is not only the first exploration of the application of SnSe in the field of optical nonlinearity, but also reveals its potential and great prospects in high-power and ultrafast Q-switched fiber laser.

Colloidal Au–CsPbBr3 for nonlinear saturable absorption effects

We demonstrate the nonlinear saturable absorption effects of colloidal Au–CsPbBr3 inorganic nanocrystals (INCs) that may useful as a saturable absorber in passively mode-locked pulse lasers. Femtosecond open-aperture Z-scan technique is responsible for measuring the nonlinear saturable absorption effects at 800 nm with a repetition rate of 76 MHz and a laser pulse duration of 130 fs. Compared to colloidal pure-CsPbBr3 INCs, the nonlinear saturable absorption coefficient β ~ 2.34 × 10–10 cm/W and the second-order absorption cross section σ2 ~ 2.13 × 104 GM of colloidal Au–CsPbBr3 INCs can be improved by up to one order of magnitude at the Au-doping concentration of 3.5 mmol/L, thanks to an obviously cocked tail absorption from visible to near-infrared spectral region through the localized surface plasmon-induced charge transition at Au–CsPbBr3 INCs interface rather than the light scattering of the deposited Au nanoparticles. And the deposited Au nanoparticles have not changed the crystalline structure, stability, and morphology of colloidal pure-CsPbBr3 INCs. As a result, colloidal Au–CsPbBr3 INCs are expected to become a potential saturable absorption candidate material used in passively mode-locked pulse lasers.

Graphene-dispersed polymer waveguide for efficient formation of mode-locked lasers at extremely low graphene concentration

Graphene-functioned mode-locked lasers have been the key elements in ultrafast optical data management. However, most conventional graphene mode-rely on deleterious transferred graphene that inefficiently interacts with the evanescent field of the propagating light. We demonstrate a polymer waveguide that contains reduced graphene oxide (rGO) particles to induce “direct” interaction with a significantly improved efficiency at an rGO concentration of 8 × 10−4 wt%. By confirming the nonlinear saturable absorption and dispersion stability of the rGO crystals hosted in a commercially available polymer matrix by only a solution process, we obtained a femtosecond fiber laser passively functioned by the waveguide. The resultant laser displays a center wavelength, spectral width, repetition rate, extinction ratio, and temporal pulse duration of 1561.8 nm, 9.5 nm, 2.35 MHz, 83.19 dB, and 690 fs, respectively.

Tin monoselenide based saturable absorbers for the generation of ultrashort pulses

The IV-VI semiconducting compounds, a family of two-dimensional material with attractive optical and electrical properties, have received extensive attention in recent years. Here, we demonstrate that tin monoselenide (SnSe) can be utilized as a saturable absorber (SA) for erbium-doped fiber laser (EDFL). By sandwiching the film of polyvinyl alcohol (PVA) and SnSe between two fiber connectors and depositing the SnSe nanoparticles onto the side-polished fiber (SPF), two types of SnSe based SAs are fabricated. The nonlinear optical properties of these two SAs are investigated, the modulation depth of the SnSe-SPF and SnSe-PVA SAs are 19.5% and 16.8%, respectively. Stable soliton mode-locking operations with center wavelength of 1556.6 (1558.2) nm and pulse width of less than 2 ps are obtained in the EDFL based on SnSe-SPF (SnSe-PVA) SA. Furthermore, the experimental results confirm that the damage threshold of the SnSe-SPF SA is much higher than that of the SnSe-PVA SA. Numerous photonics devices may benefit from the nonlinear saturable absorption properties of SnSe, such as near-infrared pulsed lasers, modulators, and so on.

Third-order optical nonlinearity in silicon oxycarbide films

We study the third-order nonlinear optical properties of amorphous silicon oxycarbide (SiOxCy) films prepared by magnetron sputtering at room temperature and annealed in oxygen atmosphere at the temperature ranging from 200 °C to 600 °C. The third-order optical nonlinearity of the films was measured by Z-scan method at a wavelength of 1064 nm and a pulse duration 25 ps? The closed-aperture measurements show that the as-deposited films exhibit self-defocusing effect, while the annealed films present self-focusing behavior. The nonlinear refractive index is determined about |n2|~10−15 m2/W, which is four orders of magnitude larger than that of SiC crystals. The open-aperture results show that the as-deposited SiOxCy films and films annealed at 200 °C exhibit strong three-photon absorption behavior, while the SiOxCy films annealed at 400 °C and 600 °C exhibits nonlinear saturable absorption. The nonlinear absorption coefficients of films dependent on laser intensity are determined, and show saturable tendency. The results indicate that the third-order optical nonlinearity in SiOxCy films can be sensitively affected and tuned by the atom composition and microstructure, thus be of great significance for integrated nonlinear photonic devices.

In2Se3 nanosheets for harmonic mode-locked fiber laser

Two-dimensional materials with a sheet structure have excellent optical, electrical and mechanical properties, and have attracted much attention in recent years, especially In2Se3 (the N-type semiconductor compound), which has a rapid development in the fields of materials science and optical communication. In this paper, the nonlinear saturation absorption characteristics of In2Se3 are studied. The In2Se3 nanosheet dispersion can be used in ultrafast photonics applications. The nonlinear absorption is measured by power dependent method, and the modulation depth and saturation intensity are 3.8% and 246.6 MW cm−2, respectively. More importantly, In2Se3 is used as a saturable absorber (SA) in a passively mode-locked erbium-doped fiber laser. The proposed mode-locked fiber laser is demenstrated with a center wavelength of 1529.4 nm, a fundamental frequency of 5.9 MHz, a spectral width of 3.96 nm, a pulse width of 1.38 ps, and a signal-to-noise ratio of 55 dB. For the first time, harmonic mode-locking with a high-repetition rate of 431 MHz is achieved when the pump power is 360 mW corresponding to 73rd-order harmonic mode locking. It can be seen that In2Se3 is indeed a new excellent photonic material, which can be used in fiber optic communication, SAs photonics, laser material processing and light modulators.