Strong Nonlinear Absorption Research Articles

Combination of graphene plasmons and surface plasmons in a crystalline Ge2Sb1.5Bi0.5Te5 metasurface structure for laser mode-locking

Owing to the dynamic tunability and strong confinement, graphene plasmons (GPs) have emerged as an excellent candidate for the manipulation of light–matter interaction. Surface plasmons (SPs) have been admitted as another effective way allowing strong confinement of light at the nanoscale. The combination of GPs and SPs like localized surface plasmons (LSPs) and propagating surface plasmon polaritons (SPPs) will lead to a synergistic effect that could remarkably improve light–matter interactions, showing great potential for many applications for the improvement of solar cell efficiency, biosensor sensitivity, and the performance of photonic devices. In this study, the GPs were activated by placing graphene film onto a two-dimensional (2D) phase-changing crystalline Ge2Sb1.5Bi0.5Te5 (cGSBT) nanograting structure, which also acts as an original source generating LSPs. The SPPs originated by laying the above structure onto an Au mirror. The combined effects of GPs, LSPs, and SPPs are epitomized in such a simple Gr/2D cGSBT gratings/Au heterostructure, which allows easy realization of an ultrafast mode-locked laser quite stable working at 1550 nm range due to the strong nonlinear optical absorption capability. This approach overcomes the heat and energy loss in metallic gratings or a Gr-based heterostructure, exhibiting great potential for applications in the design and fabrication of photonic devices.

Lead‐Sulfide‐Based Hybrid Inorganic‐Organic Superlattice Particles for Prominent Nonlinear Optical Absorption

AbstractSimultaneously optimizing nonlinear absorption coefficient and modulation depth is a considerable challenge for nonlinear optical materials. Here we present an effective solution through constructing PbS2‐based inorganic‐organic superlattice. PbS2/Cn superlattice particles are synthesized, where n (4, 6, and 8) denotes the number of carbon atoms in the organic component. First‐principles simulations indicate the formation of covalent bonds and van der Waals interaction between PbS2 unit and interlayer organic molecules. All samples exhibit strong nonlinear absorption under femtosecond laser excitation with a wavelength range between 515 nm and 900 nm, and the nonlinear absorption coefficient increases with interlayer distance. The optimized sample, PbS2/C8, demonstrates outstanding nonlinear absorption and substantial modulation depth under 800 nm (the third‐order nonlinear absorption coefficient βeff, 10449 ± 609 cm GW−1; modulation depth, 39.1%) and 900 nm (the fifth‐order nonlinear absorption coefficient γeff, 6465 ± 68 cm3 GW−2; modulation depth, 88.1%), which exhibits saturable absorption under 515 nm (βeff, ‐4932 ± 818 cm GW−1; modulation depth, 48.1%). It exhibits a small optical limiting threshold of 1.23 mJ cm−2. These performances surpass those of typical single‐/few‐layer metal chalcogenides. Structural and spectral analyses elucidate that the remarkable optical nonlinearity can be attributed to quantum confinement in the inorganic layer and the dielectric enhancement of the superlattice.

Watt‐Level Second‐Order Topological Charge Ultrafast Green Vortex Laser with Quasi ‐2D PEA2(CsPbBr3)n‐1PbBr4 Perovskite Films Saturable Absorber

AbstractUltrafast vortex beams have significant scientific and practical value because of their unique phase properties in both the longitudinal and transverse modes, enabling multi‐dimensional quantum control of light fields. Directly generating watt‐level ultrafast vortex beams with large angular momentum has remained a major challenge due to the limitations of mode‐locked materials and existing spatiotemporal mode‐locking generation methods. In this study, quasi‐2D PEA2(CsPbBr3)n‐1PbBr4 perovskite films are prepared by an anti‐solvent method and employed for the first time in a mode‐locked resonator operating in free space. Utilizing the angle‐based non‐collinear pumping and frequency doubling techniques, the second‐order ultrafast green vortex beams with a power of up to 1.05 W and a duration of 373 ps are generated. Experimental findings demonstrate the strong nonlinear saturable absorption properties of quasi‐2D PEA2(CsPbBr3)n‐1PbBr4 perovskite films at high power levels, highlighting their considerable potential in ultrafast laser technology and nonlinear optics.

Two-photon absorption induced optical limiting action of Ag-doped lanthanum molybdate decorated reduced graphene oxide nanocomposites

In this research, we aimed to investigate the linear and non-linear optical properties of Ag-La2(MoO4)3@RGO nanocomposites. For this purpose, Graphene Oxide (GO) was synthesized by Modified Hummer’s method after which GO was chemically reduced to Reduced graphene oxide (RGO). The nanocomposite Ag-doped La2(MoO4)3 is prepared by a simple and facile co-precipitation method. The prepared nanocomposite was characterized by Fourier transform infrared (FTIR), Ultraviolet-Visible (UV-Vis) absorption, X-ray diffraction (XRD), Scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDX). XRD and EDX analysis indicated the reduction of GO and successful synthesis of Ag-doped La2(MoO4)3 nanocomposite. FESEM images portray the presence of thin layers of graphene sheets and Ag-doped La2(MoO4)3 on the sheets of reduced graphene oxide. Ground state absorption studies show that the reduction of graphene oxide causes a hypsochromic shift in the absorption maxima of the graphene layers. The photoluminescence of Ag- La2(MoO4)3@RGO demonstrates the utmost emission in the UV range caused by the valence band and conduction band's direct transitions in the band gap region. Z-scan method using Nd: YAG laser exposes that both nanocomposite and specific counterparts hold reverse saturable absorption behaviour. The source of optical limiting action is attributed to the excited state absorption process, emerging from the influence of the plasmon resonance state of Ag nanoparticles. Strong nonlinear absorption and lower onset limiting threshold make the Ag-La2(MoO4)3@RGO nanocomposite desirable material for laser safety devices.

Nonlinear Responses and Optical Limitation of Copper Nanoparticles by Z-scan Method

Recently, copper particles in nano dimensions have been gaining attention because they have advanced features and potential applications in various fields. This work studies the nonlinear optical performance of copper nanoparticles. We utilized laser ablation to create copper nanoparticles. In this technique, a piece of copper in distilled water is irradiated using the laser beam. Laser ablation was done for 30 min. The optical nonlinearities are measured by means of the Z-scan technology. The open-aperture Z-scan experiments showed that Cu nanoparticles have strong nonlinear absorption. Through a closed aperture Z-scan experiment, we could analyze the nonlinear refraction of sample. We analyze the optical limiting effect of copper nanoparticles. A theoretical model is presented and shows that at high laser light intensity, nonlinear light scattering occurs. By analyzing the experimental data with the presented model, the values of optical nonlinearities of copper particles were found to be n2=0.8×10-19m2w-1 and γ=1.46×10-13m/W, respectively. Our work confirmed that Cu nanoparticles show outstanding nonlinear optical features, which can cause the development of nonlinear optics. Received: 8 September 2023 | Revised: 2 January 2024 | Accepted: 3 January 2024 Conflicts of InterestThe authors declare that they have no conflicts of interest to this work. Data Availability Statement Data sharing is not applicable to this article as no new data were created or analyzed in this study.

120 nm wide band tunable pulsed laser generation employing vanadium carbide MXene/polyvinyl alcohol (V2C-PVA) film

MXene, a group of 2D materials, has garnered significant attention from researchers due to its impressive characteristics, such as large surface area, high metallic conductivity, and strong nonlinear saturable absorption. These properties make MXene an excellent material for exploring new possibilities in ultrafast photonics technology. The present study has demonstrated that vanadium carbide (V2C) MXene can function as a saturable absorber (SA) and effectively generate Q-switching pulses in the 1.9 μm wavelength region. The molten salt synthesis method was used to synthesize V2C MXene, which involved the selective etching of aluminum (Al) layers from the V2AlC MAX Phase precursor. The V2C MXene was transformed into a thin film by mixing it with polyvinyl alcohol (PVA) using a solution casting technique. The resulting V2C-PVA film was found to have saturable absorption properties, with a modulation depth of 8% and saturation intensity of 1.6 MW cm −2. Upon integrating the V2C-PVA film into the Thulium/Holmium-doped fiber laser (THDFL) cavity, stable Q-switching pulses were realized at a central wavelength of 1896.9 nm with 13.9 nm of 3-dB spectral bandwidth. At the maximum pump power of 448.7 mW, the 2.2 μs of pulse duration, 58.26 kHz of repetition rate, and 31 nJ of pulse energy were achieved. By adjusting the tunable bandpass filter (TBPF) integrated within the THDFL cavity, the system has a tunable spectral range of approximately 120.75 nm, from 1889.75 nm to 2010.5 nm. The exceptional performance of V2C-based SA for Q-switching operation showcases the immense potential of other MXene materials in the future of photonics applications.

Phase Transitions, Dielectric Response, and Nonlinear Optical Properties of Aziridinium Lead Halide Perovskites.

Hybrid organic-inorganic lead halide perovskites are promising candidates for next-generation solar cells, light-emitting diodes, photodetectors, and lasers. The structural, dynamic, and phase-transition properties play a key role in the performance of these materials. In this work, we use a multitechnique experimental (thermal, X-ray diffraction, Raman scattering, dielectric, nonlinear optical) and theoretical (machine-learning force field) approach to map the phase diagrams and obtain information on molecular dynamics and mechanism of the structural phase transitions in novel 3D AZRPbX3 perovskites (AZR = aziridinium; X = Cl, Br, I). Our work reveals that all perovskites undergo order-disorder phase transitions at low temperatures, which significantly affect the structural, dielectric, phonon, and nonlinear optical properties of these compounds. The desirable cubic phases of AZRPbX3 remain stable at lower temperatures (132, 145, and 162 K for I, Br, and Cl) compared to the methylammonium and formamidinium analogues. Similar to other 3D-connected hybrid perovskites, the dielectric response reveals a rather high dielectric permittivity, an important feature for defect tolerance. We further show that AZRPbBr3 and AZRPbI3 exhibit strong nonlinear optical absorption. The high two-photon brightness of AZRPbI3 emission stands out among lead perovskites emitting in the near-infrared region.

2D Non-van der Waals Nanoplatelets of Hematene and Magnetene: Nonlinear Optical Response and Optical Limiting Performance from UV to NIR.

Recently, the preparation of some hematene and magnetene ultrathin non van der Waals (non-vdW) 2D nanoplatelets was reported starting from hematite and magnetite natural iron ores. The present work reports on the determination and evaluation of the nonlinear optical response and the optical limiting (OL) action of these 2D nanoplatelets dispersed in water under ns laser excitation. The obtained results show that both hematene and magnetene exhibit strong nonlinear absorption and refraction, comparable and even larger than those of other van der Waals (vdW) 2D counterpart materials. In addition, due to their strong nonlinear absorption, both hematene and magnetene show exceptional OL performance from the UV to visible, attaining very low values of optical limiting onset (OLon ), comparable and even lower than that of vdW 2D nanomaterials, such as graphene, graphene oxide, other transition metal dichalcogenides like MoS2 , WS2 and MoSe2 , black phosphorous and antimonene. Moreover, hematene was found to exhibit more efficient OL action than magnetene for all the excitation wavelengths studied, attributed to more efficient ligand to metal charge transfer. The present findings open new possibilities for the potential use of these non-vdW 2D materials in photonics and optoelectronics, e. g., as optical limiters and optical switchers.

Improved Haacke's quality factor, third order nonlinear susceptibility and specific capacitance realized for PbS thin films through La3+ doping

The present study examines the third order NLO and electrochemical properties of spray deposited lanthanum doped PbS (PbS:La) thin films. FCC crystallization was confirmed by XRD patterns along the plane (2 0 0). PbS crystallites vary in size between 27 and 36 nm with La doping concentration. Surface morphology improved with La doping. La doping increases the band gap from 1.97 to 2.18 eV. Near band edge (NBE) emissions in PL spectra originates from electron-hole recombination. A low resistivity of 0.23 x10−3 Ω-m was realized for PbS film doped with 4 wt% La concentration. Figure of merit of pure PbS improves from 1.32 x 10−3 Ω−1 to 1.607 x 10−2 Ω−1 with La doping. La doping modifies the energy states and band gap of PbS favouring strong nonlinear optical absorption. PbS:La thin films demonstrate self-defocusing due to temperature effects caused by absorption of single photons or free carriers. As a result of the low cationic field strength and high polarizability of La3+ ions, PbS exhibits a higher nonlinear refractive index. The nonlinear susceptibility and refractive index were found to be in the range 3.23–5.33 x 10−6 esu and 2.74 to 3.64 x 10−9 cm2/W, respectively. From the electrochemical studies, increased specific capacitance (256.46 F/g) and decreased charge transfer resistance (12 x 103 Ω) was observed for the 4 wt% La doped film.

Q-switched fiber laser operating at 1560 nm modulated by Cr3C2 film

Chromium carbide (Cr3C2), as a kind of transition metal carbides, has exhibited extraordinary optoelectronic properties and aroused enormous attention. However, few reports have been focused on the nonlinear properties and relevant devices. In this study, we first demonstrated a novel Cr3C2 saturable absorber (SA). Cr3C2 with an average size of 200 nm was prepared through a low temperature salt flux synthetic method. The Cr3C2-film SA exhibited high robustness and strong linear and nonlinear saturable absorption response at 1560 nm. As the Cr3C2 SA was inserted into the Er3+-doped fiber laser cavity, Q-switched pulses were generated with a central wavelength of 1560 nm. To the best of our knowledge, this was the first report on the optical nonlinearity of Cr3C2 as a Q-switcher for the near-infrared fiber laser. Our experimental results verified that the integrated Cr3C2-based device possessed great potential as a nonlinear optical medium for high-performance optical applications.

Ultrashort pulsed laser ablation of zirconia toughened alumina: Material removal mechanism and surface characteristics

Zirconia toughened alumina (ZTA) is commonly used in hip joint implants and cutting tools. The difference in material properties of the zirconia and alumina phases makes the composite inhomogeneous at the grain size level. Due to the strong nonlinear laser absorption mechanisms of wide band gap materials under intense laser field, the smaller band gap zirconia phase can absorb a significantly larger amount of laser energy than the alumina phase. The nonuniform energy deposition and lattice heating takes place at a comparable timescale as the laser pulse duration, which is too short for thermal diffusion to play a role. As a result, the temperature in the zirconia phase can be significantly higher than in the alumina phase, leading to a unique selective phase melting phenomenon, i.e. localized melting of the higher melting point zirconia phase (2715 °C) surrounded by a lower melting point alumina phase (2072 °C) which remains solid. This phenomenon makes the material removal mechanism of the nanocomposite significantly different from that of single-phase materials under ultrashort pulsed laser processing. On the basis of experimental analysis and theoretical modelling, material ablation by the disintegration of alumina grains due to the localized melting of the zirconia phase was identified.

Broadband Nonlinear Response and Ultrafast Photonics Applications in Few-Layer MBene

2D MBenes, the latest derivatives of bulk ternary or quaternary transition metal boride (MAB) phases, have gradually attracted increasing research attention as novae in the flatland. However, the fabrication of MBenes is still a great challenge at present, leading to the lack of reported MBene applications in the photonic field (e.g., ultrafast lasers). Hence, we successfully fabricated few-layer Mo4/3B2–xTz MBenes by selectively etching nanolaminated 3D parent boride (Mo2/3Y1/3)2AlB2. Density functional theory calculations were used to theoretically analyze its electronic and optical properties. By employing the Z-scan technique, the nonlinear absorption characteristics of Mo4/3B2–xTz MBenes from the visible to mid-infrared regime were revealed for the first time. Compared with mainstream 2D materials and common MXenes, Mo4/3B2–xTz has more potential as a nonlinear optical (NLO) material, such as stronger nonlinear absorption (about 100 times of graphene) and lower saturation intensity (about 1% of black phosphorus). Furthermore, by integrating Mo4/3B2–xTz as a saturable absorber (SA) into three similar gain fiber-based laser resonators, broadband stable ultrafast pulses were obtained with pulse durations of 358.7 ps (1 μm), 582.3 fs (1.5 μm), and 2.31 ps (2 μm). Innovation in MBenes as SA will allow the design of novel photonic systems and devices with broadband functionality, opening a promising paradigm for the conscious design of high-performance NLO materials.

Molecular structure and third-order non-linear optical properties of two novel tetralone-based chalcone derivatives: Promising materials for optical limiting applications

Two novel tetralone-based chalcone derivatives (2E)-2-(3,4-dimethoxybenzylidene]-3,4-dihydro-2H-napthalen-1-one (DMDN) and (2E)-2-(3,4-dimethoxybenzylidene]-6-methoxy-3,4-dihydro-2H-napthalen-1-one (DM6MDN) have been synthesized via a Claisen–Schmidt condensation reaction. Single crystals were obtained using a slow evaporation solution growth method. Structural characterization was carried out using single crystal X-ray diffraction study. Non-centrosymmetric DMDN crystallized in the orthorhombic system with a P212121 space group. Centrosymmetric DM6MDN crystallized in the monoclinic system with a P21/c space group. Hirshfield analysis of both crystals revealed the existence of C–H···π and π···π interactions, which play an important role in creating supramolecular structures. Our TG-DSC study revealed that DM6MDN has higher thermal stability than DMDN. The linear absorption coefficient of DMDN and DM6MDN were calculated from our UV spectral analysis and their respective optical band gaps were calculated to be 2.88 and 3.05 eV, respectively. The photoluminescence spectra show emission peaks in the blue region. DMDN exhibits SHG activity and a large β value when compared to DM6MDN. The third-order NLO properties of the chalcone derivatives was investigated using the Z-scan technique. The obtained crystals show strong non-linear absorption (NLA) and negative non-linear refraction (NLR) for DMDN and a positive NLR for DM6MDN. The third-order non-linear susceptibility (χ(3)) was of the order 10−7 esu. DMDN and DM6MDN also exhibit optical limiting (OL) and optical switching behavior under continuous wave excitation. The static NLO parameters, such as dipole moment (μ), polarizability (α) and first order hyperpolarizability (β), were computed using the B3LYP/6–31++G(d,p) level of theory. The Donor-π-Acceptor-π-Donor (D-π-A-π -D) system of DMDN and DM6MDN also makes them promising materials for NLO applications.

Crystalline Phase Effects on the Nonlinear Optical Response of MoS2 and WS2 Nanosheets: Implications for Photonic and Optoelectronic Applications

In the present work, some MoS2 and WS2 nanosheets were prepared and characterized. Depending on the preparation procedures, trigonal prismatic (2H) or octahedral (1T) coordination of the metal atoms was obtained, exhibiting metallic (1T) or semiconducting (2H) character. Both MoS2 and WS2 nanosheets were found exhibiting large nonlinear optical (NLO) responses, strongly dependent on their metallic (1T) or semiconducting (2H) character. Therefore, the semiconducting character of MoS2 and WS2 exhibits positive nonlinear absorption and strong self-focusing behavior, while their metallic character counterparts exhibit strong negative nonlinear absorption and important self-defocusing behavior. In addition, the semiconducting MoS2 and WS2 were found exhibiting important and very broadband optical limiting (OL) action extending from 450 to 1750 nm. Therefore, by selecting the crystalline phase of the nanosheets, that is, their semiconduction/metallic character, their NLO response can be greatly modulated. The results of the present work demonstrate unambiguously that the control of the crystalline phase of MoS2 and WS2 provides an efficient strategy for 2D nanostructures with custom-made NLO properties for specific optoelectronic and photonic applications such as OL, saturable absorption, and optical switching.

Prediction Model for Liquid-Assisted Femtosecond Laser Micro Milling of Quartz without Taper.

The strong nonlinear absorption effect and “cold” processing characteristics of femtosecond lasers make them uniquely advantageous and promising for the micro- and nanoprocessing of hard and brittle materials, such as quartz. Traditional methods for studying the effects of femtosecond laser parameters on the quality of the processed structure mainly use univariate analysis methods, which require large mounts of experiments to predict and achieve the desired experimental results. The method of design of experiments (DOE) provides a way to predict desirable experimental results through smaller experimental scales, shorter experimental periods and lower experimental costs. In this study, a DOE program was designed to investigate the effects of a serious of parameters (laser repetition frequency, pulse energy, scan speed, scan distance, scan mode, scan times and laser focus position) on the depth and roughness (Ra) of the fabricated structure through the liquid-assisted femtosecond laser processing of quartz. A prediction model between the response variables and the main parameters was defined and validated. Finally, several blind holes with a size of 50 × and a depth of 200 were fabricated by the prediction model, which demonstrated the good consistency of the prediction model.

The valorisation of grass waste for the green synthesis of graphene quantum dots for nonlinear optical applications

The recent years have seen an increase in efforts to develop a simple and less complex method of converting waste materials into graphene nanomaterials. Herein, we present the valorisation of grass waste for the green synthesis of graphene quantum dots (GQDs) using hydrothermal technique. The efficacy of using three different precursors that had been sourced from green waste materials to produce GQDs was investigated; namely, grass waste, and grass waste-derived cellulose, and cellulose nanocrystals. The resulting GQDs were characterised using UV–Vis spectroscopy, fluorescence spectroscopy, Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The UV–Vis analysis revealed the existence of π-π* transition of the CC bond of the GQDs samples while the FTIR results showed the samples contained typical functional groups; such as O–H, CO, and C–O. The surface functionalisation of the GQDs was further corroborated by the XPS analysis. The Raman analysis indicated that the structure of the GQDs was highly functionalised, with a more prominent D-band than G-band indicating a high ID/IG ratio. The morphological analyses, which were conducted using TEM and AFM, showed that the particles of the samples were uniform in size and circular in shape. The AFM analysis found that the thickness of the GQDs samples ranged between 0.5 and 2.6 nm, implying that the samples contained 1–3 layers of GQDs. Further analysis using the Z-scan technique indicated that the GQDs exhibited strong nonlinear refraction and nonlinear absorption which holds great promise for nonlinear integrated applications such as optical limiting, optical switching, image transmission, logic devices and mode-locked laser system, and so on.

Understanding the linear and nonlinear optical responses of few-layer exfoliated MoS2 and WS2 nanoflakes: experimental and simulation studies

Understanding the linear and nonlinear optical (NLO) responses of two-dimensional nanomaterials is essential to effectively utilize them in various optoelectronic applications. Here, few-layer MoS2 and WS2 nanoflakes with lateral size less than 200 nm were prepared by liquid-phase exfoliation, and their linear and NLO responses were studied simultaneously using experimental measurements and theoretical simulations. Finite-difference time-domain (FDTD) simulations confirmed the redshift in the excitonic transitions when the thickness was increased above 10 nm indicating the layer-number dependent bandgap of nanoflakes. WS2 nanoflakes exhibited around 5 times higher absorption to scattering cross-section ratio than MoS2 nanoflakes at various wavelengths. Open aperture Z scan analysis of both the MoS2 and WS2 nanoflakes using 532 nm nanosecond laser pulses reveals strong nonlinear absorption activity with effective nonlinear absorption coefficient (β eff) of 120 cm GW−1 and 180 cm GW−1, respectively, which was attributed to the combined contributions of ground, singlet excited and triplet excited state absorption. FDTD simulation results also showed the signature of strong absorption density of few layer nanoflakes which may be account for their excellent NLO characteristics. Optical limiting threshold values of MoS2 and WS2 nanoflakes were obtained as ∼1.96 J cm−2 and 0.88 J cm−2, respectively, which are better than many of the reported values. Intensity dependent switching from saturable absorption (SA) to reverse SA was also observed for MoS2 nanoflakes when the laser intensity increased from 0.14 to 0.27 GW cm−2. The present study provides valuable information to improve the selection of two-dimensional nanomaterials for the design of highly efficient linear and nonlinear optoelectronic devices.

Heptazine‐Based TADF Materials for Nanoparticle‐Based Nonlinear Optical Bioimaging

Abstracts‐Heptazines are emerging as strong electron acceptors for efficient thermally activated delayed fluorescent (TADF) materials, yet the difficulties in synthesizing them have limited their practical use. Here, three novel s‐heptazine TADF materials with green to deep‐red emission (λmax = 525–664 nm) and high photoluminescence quantum yields, synthesized by either pseudoelectrophilic substitution or Negishi coupling routes, are described. These materials also demonstrate strong nonlinear optical absorption, with two‐photon cross sections up to 1260 GM. With deep‐red fluorescence, strong two‐photon absorption, high quantum yield, and delayed fluorescence, the emitter HAP‐3MeOTPA is ideally suited for use in nanoparticle‐based bioimaging experiments. The two kinds of luminescent nanoparticle are prepared, namely hostless, aggregate‐based organic dots (a‐Odots) and rigid, glassy Odots (g‐Odots) as biocompatible and water‐dispersible TADF probes. The g‐Odots are shown to retain the nonlinear optical properties, high photoluminescence quantum yield, and TADF observed in the constituent heptazine dye. These g‐Odots are then used as biological imaging probes with immortalized human kidney cancer (HEK293) cells, and single and multi‐photon‐excited microscopy coupled with time‐gated luminescence measurements are demonstrated. This work not only describes new routes to efficient heptazine‐based TADF materials, but also demonstrates their potential as nanoparticle‐based bioimaging probes combining several advanced optical functions.

Facile Synthesis of Monodispersed Titanium Nitride Quantum Dots for Harmonic Mode-Locking Generation in an Ultrafast Fiber Laser.

As a member of the transition metal nitride material family, titanium nitride (TiN) quantum dots (QDs) have attracted great attention in optical and electronic fields because of their excellent optoelectronic properties and favorable stability. Herein, TiN QDs were synthesized and served as a saturable absorber (SA) for an ultrafast fiber laser. Due to the strong nonlinear optical absorption characteristics with a modulation depth of ~33%, the typical fundamental mode-locked pulses and harmonics mode-locked pulses can be easily obtained in an ultrafast erbium-doped fiber laser with a TiN-QD SA. In addition, at the maximum pump power, harmonic mode-locked pulses with a repetition rate of ~1 GHz (164th order) and a pulse duration of ~1.45 ps are achieved. As far as we know, the repetition rate is the highest in the ultrafast fiber laser using TiN QDs as an SA. Thus, these experimental results indicate that TiN QDs can be considered a promising material, showing more potential in the category of ultrafast laser and nonlinear optics.

Nanosecond mid-infrared pulse generation modulated by platinum ditelluride nanosheets

We demonstrated the generation of nanosecond mid-infrared (MIR) pulse from an Er3+-doped ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber laser modulated by platinum ditelluride nanosheets experimentally. The platinum ditelluride nanosheets exhibit strong nonlinear absorption with the saturation intensity 46.5 GW cm−2 and modulation depth 27.8% at 2.8 μm wavelength, respectively. With the saturable absorber mirror fabricated by depositing the platinum ditelluride nanosheets on a gold mirror, we have obtained the stable Q-switched pulses with repetition rate of 173.4 kHz and pulse duration of 600 ns at 2.8 μm wavelength under the pump power of 5.6 W. In addition, the maximum average output power and pulse energy reach 591 mW and 3.41 μJ, respectively. The experimental results confirm that the platinum ditelluride nanosheets exhibit excellent nonlinear optical behavior towards the MIR spectral range, and may make inroads towards MIR photonics with group-10 transition-metal dichalcogenides.