Laser Q-switching with PtS2 microflakes saturable absorber

Ultrastrong Optical Harmonic Generations in Layered Platinum Disulfide in the Mid-Infrared

Nonlinear optical activities (e.g., harmonic generations) in two-dimensional (2D) layered materials have attracted much attention due to the great promise in diverse optoelectronic applications such as nonlinear optical modulators, nonreciprocal optical device, and nonlinear optical imaging. Exploration of nonlinear optical response (e.g., frequency conversion) in the infrared, especially the mid-infrared (MIR) region, is highly desirable for ultrafast MIR laser applications ranging from tunable MIR coherent sources, MIR supercontinuum generation, and MIR frequency-comb-based spectroscopy to high harmonic generation. However, nonlinear optical effects in 2D layered materials under MIR pump are rarely reported, mainly due to the lack of suitable 2D layered materials. Van der Waals layered platinum disulfide (PtS₂) with a sizable bandgap from the visible to the infrared region is a promising candidate for realizing MIR nonlinear optical devices. In this work, we investigate the nonlinear optical properties including third-and fifth-harmonic generation (THG and FHG) in thin layered PtS₂ under infrared pump (1550-2510 nm). Strikingly, the ultrastrong third-order nonlinear susceptibility χ⁽³⁾(-3ω;ω,ω,ω) of thin layered PtS₂ in the MIR region was estimated to be over 10^-18 m²/V², which is about one order of that in traditional transition metal chalcogenides. Such excellent performance makes air-stable PtS₂ a potential candidate for developing next-generation MIR nonlinear photonic devices.

Investigations of 2D PtS2’s Saturable Absorption Characteristic and Its Optimization to OPO’s Operation

A 6.2 nm-thickness platinum disulfide (PtS₂) film was prepared by electron beam evaporation with post vulcanization. The nonlinear transmittance was measured by power scanning method and the modulation depth is fitted to be 13%. Based on the transmittance curve, saturable absorption parameters of PtS₂ are calculated with inhomogeneously broadening mechanism, including 6.4298 × 10⁻¹⁹ cm⁻² ground-state absorption cross-section, 2.5927 × 10⁻¹⁹ cm⁻² excited-state absorption cross-section, and 1.043 ms excited-state lifetime. The PtS₂ film combined with active time management was implemented to modulate the fundamental light of optical parametric oscillator (OPO). Owing to the nonlinear absorption property of PtS₂, the operation of Q-switched OPO was optimized in both the experiment and dynamical theory. In particular, the conversion efficiency was experimentally improved by 13.2%. The pump-to-signal conversion efficiency went up to 3.29%, which is the highest conversion value reported so far. The theoretical values fit the experiment well, which are from the Gaussian rate equations with PtS₂’s saturable-absorption characteristic.

Fabrication of Large-Area Short-Wave Infrared Array Photodetectors under High Operating Temperature by High Quality PtS2 Continuous Films

A narrow bandgap of a few layers of platinic disulfide (PtS2) has shown great advantages in large-area array photodetectors for wide spectra photodetection, which is necessary for infrared imaging and infrared sensing under extreme conditions. The photodetection performance of two dimensional materials is highly dependent on the crystalline quality of the film, especially under high operating temperatures. Herein, we developed large area uniform array photodetectors using a chemical vapor deposition grown on PtS2 films for short-wave infrared photodetection at high operating temperature. Due to the high uniformity and crystalline quality of as-grown large area PtS2 films, as-fabricated PtS2 field effect transistors have shown a broadband photo-response from 532 to 2200 nm with a wide working temperature from room temperature to 373 K. The photo-responsivity (R) and specific detectivity (D*) of room temperature and 373 K are about 3.20 A/W and 1.24 × 107 Jones, and 839 mA/W and 6.1 × 106 Jones, at 1550 nm, respectively. Our studies pave the way to create an effective strategy for fabricating large-area short-wave infrared (SWIR) array photodetectors with high operating temperatures using chemical vapor deposition (CVD) grown PtS2 films.

PtS2 nanosheets as a peroxidase-mimicking nanozyme for colorimetric determination of hydrogen peroxide and glucose

Using an ultrasonication-assisted liquid exfoliation method, we have synthesized PtS2 nanosheets with good reproducibility. Herein, intrinsic peroxidase-like activity was for the first time demonstrated for PtS2 nanosheets, which can catalyze H2O2 oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to generate a colored solution. The catalytic mechanism of PtS2 nanosheets was investigated, which indicated that acceleration of the electron transfer between TMB and H2O2 was the main reason for the peroxidase-like activity of PtS2 nanosheets. Based on these observations, we exploited PtS2 nanosheets integrated into dopamine-functionalized hyaluronic acid (HA-DA) hydrogel microspheres by droplet microfluidics to construct PtS2 nanosheet- and PtS2@HA-DA microsphere-based sensors for highly sensitive determination of H2O2. When coupled with glucose oxidase, we further developed two glucose sensors based on the above two methods. Among them, the linearity of the PtS2 nanosheet-based spectrophotometry was in the range of 0.5 to 150 μM and the limit of detection as low as 0.20 μM. The linearity of the microsphere-based colorimetry was in the range 200 to 12,000 μM with a detection limit of 29.95 μM. Both of the glucose sensors can be applied to the determination of glucose in human serum with reliable results and reproducibility.

Synthesis and characterisation of thin-film platinum disulfide and platinum sulfide

Group-10 transition metal dichalcogenides (TMDs) are rising in prominence within the highly innovative field of 2D materials. While PtS₂ has been investigated for potential electronic applications, due to its high charge-carrier mobility and strongly layer-dependent bandgap, it has proven to be one of the more difficult TMDs to synthesise. In contrast to most TMDs, Pt has a significantly more stable monosulfide, the non-layered PtS. The existence of two stable platinum sulfides, sometimes within the same sample, has resulted in much confusion between the materials in the literature. Neither of these Pt sulfides have been thoroughly characterised as-of-yet. Here we utilise time-efficient, scalable methods to synthesise high-quality thin films of both Pt sulfides on a variety of substrates. The competing nature of the sulfides and limited thermal stability of these materials is demonstrated. We report peak-fitted X-ray photoelectron spectra, and Raman spectra using a variety of laser wavelengths, for both materials. This systematic characterisation provides a guide to differentiate between the sulfides using relatively simple methods which is essential to enable future work on these interesting materials.

Utilization of group 10 2D TMDs-PdSe2 as a nonlinear optical material for obtaining switchable laser pulse generation modes

In-plane anisotropic two-dimensional (2D) materials have gained considerable interest in the field of research, due to having the potential of being used in different device applications. Recently, among these 2D materials, group 10 transition metal dichalcogenides (TMDs) pentagonal Palladium diselenide (PdSe₂) is utilized in various sections of researches like nanoelectronics, thermoelectric, spintronics, optoelectronics, and ultrafast photonics, owing to its high air stability and broad absorption spectrum properties. In this paper, it is demonstrated that by utilizing this novel 2D layered PdSe₂ material as a saturable absorber (SA) in an EDF laser system, it is possible to obtain switchable laser pulse generation modes. At first, the Q-switching operation mode is attained at a threshold pump power of 56.8 mW at 1564 nm, where the modulation range of pulse duration and repetition rate is 18.5 μs-2.0 μs and 16.4 kHz-57.0 kHz, respectively. Afterward, the laser pulse generation mode is switched to the mode-locked state at a pump power of 63.1 mW (threshold value) by changing the polarization condition inside the laser cavity, and this phenomenon persists until the maximum pump power of 230.4 mW. For this mode-locking operation, the achieved pulse duration is 766 fs, corresponding to the central wavelength and 3 dB bandwidth of 1566 nm and 4.16 nm, respectively. Finally, it is illustrated that PdSe₂ exhibits a modulation depth of 7.01%, which substantiates the high nonlinearity of the material. To the best of the authors' knowledge, this is the first time of switchable modes for laser pulse generation are achieved by using this PdSe₂ SA. Therefore, this work will encourage the research community to carry out further studies with this PdSe₂ material in the future.

Passively Q-switched Ytterbium-doped fiber laser based on broadband multilayer Platinum Ditelluride (PtTe2) saturable absorber

Two-dimensional (2D) layered Platinum Ditelluride (PtTe₂), a novel candidate of group 10 transition-metal dichalcogenides (TMDs), which provides enormous potential for pulsed laser applications due to its highly stable and strong nonlinear optical absorption (NOA) properties. PtTe₂ saturable absorber (SA) is successfully fabricated with firstly demonstrated the passively Q-switched laser operation within a Yb-doped fiber laser cavity at 1066 nm. Few layered PtTe₂ is produced by uncomplicated and cost-efficient ultrasonic liquid exfoliation and follow by incorporating into polyvinyl alcohol (PVA) polymer to form a PtTe₂-PVA composite thin film saturable absorber. The highest achieved single pulse energy is 74.0 nJ corresponding to pulse duration, repetition rate and average output power of 5.2 μs, 33.5 kHz and 2.48 mW, respectively. This work has further exploited the immeasurable utilization potential of the air stable and broadband group 10 TMDs for ultrafast photonic applications.

8.8 GHz Q-switched mode-locked waveguide lasers modulated by PtSe2 saturable absorber

We demonstrate high-repetition-rate fundamentally Q-switched mode-locked Nd:YAG waveguide laser modulated by platinum diselenide (PtSe₂) saturable absorber. The laser operation platform is a femtosecond laser-written monolithic Nd:YAG waveguide, and the saturable absorber is large-area few-layer PtSe₂ that possesses relatively lower saturation intensity and higher modulation depth in comparison with graphene. With the superb ultrafast nonlinear saturable absorption properties of as-synthesized PtSe₂, the waveguide laser could operate at ~8.8 GHz repetition rate and ~27 ps pulse duration, while maintaining a relatively high slope efficiency of 26% and high stability with signal-to-noise ratio (SNR) up to 54 dB. Our work indicates the promising applications of laser-written Nd:YAG waveguides and atomically thin PtSe₂ for on-chip integration of GHz laser sources toward higher repetition rates and shorter pulse duration.

Strategy for Fabricating Wafer-Scale Platinum Disulfide

PtS₂ is a newly developed group 10 2D layered material with high carrier mobility, wide band gap tunability, strongly bound excitons, symmetrical metallic and magnetic edge states, and ambient stability, making it attractive in nanoelectronic, optoelectronic, and spintronic fields. To the aim of application, a large-scale synthesis is necessary. For transition-metal dichalcogenide (TMD) compounds, a thermally assisted conversion method has been widely used to fabricate wafer-scale thin films. However, PtS₂ cannot be easily synthesized using the method, as the tetragonal PtS phase is more stable. Here, we use a specified quartz part to locally increase the vapor pressure of sulfur in a chemical vapor deposition furnace and successfully extend this method for the synthesis of PtS₂ thin films in a scalable and controllable manner. Moreover, the PtS and PtS₂ phases can be interchangeably converted through a proposed strategy. Field-effect transistor characterization and photocurrent measurements suggest that PtS₂ is an ambipolar semiconductor with a narrow band gap. Moreover, PtS₂ also shows excellent gas-sensing performance with a detection limit of ∼0.4 ppb for NO₂. Our work presents a relatively simple way of synthesizing PtS₂ thin films and demonstrates their promise for high-performance ultrasensitive gas sensing, broadband optoelectronics, and nanoelectronics in a scalable manner. Furthermore, the proposed strategy is applicable for making other PtX₂ compounds and TMDs which are compatible with modern silicon technologies.

Emerging 2D materials beyond graphene for ultrashort pulse generation in fiber lasers

Ultrafast fiber lasers have significant applications in ultra-precision manufacturing, medical diagnostics, medical treatment, precision measurement and astronomical detection, owing to their ultra-short pulse width and ultra-high peak-power. Since graphene was first explored as an optical saturable absorber for passively mode-locked lasers in 2009, many other 2D materials beyond graphene, including phosphorene, antimonene, bismuthene, transition metal dichalcogenides (TMDs), topological insulators (TIs), metal-organic frameworks (MOFs) and MXenes, have been successively explored, resulting in rapid development of novel 2D materials-based saturable absorbers. Herein, we review the latest progress of the emerging 2D materials beyond graphene for passively mode-locked fiber laser application. These 2D materials are classified into mono-elemental, dual-elemental and multi-elemental 2D materials. The atomic structure, band structure, nonlinear optical properties, and preparation methods of 2D materials are summarized. Diverse integration strategies for applying 2D materials into fiber laser systems are introduced, and the mode-locking performance of the 2D materials-based fiber lasers working at 1-3 μm are discussed. Finally, the perspectives and challenges facing 2D materials-based mode-locked fiber lasers are highlighted.

Photoluminescence of PdS2 and PdSe2 quantum dots

PdS₂ and PdSe₂ QDs are fabricated via liquid exfoliation using NMP solvent. The PL behaviors of these QD solutions are studied. The obtained results suggest promising optoelectronic applications with group-10 TMD QDs in the future.