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Platinum diselenide (PtSe2), classified as a noble metal dichalcogenide, has garnered substantial interest owing to its layer-dependent band structure, remarkable air-stability, and high charge-carrier mobilities. These properties make it highly promising for a wide array of applications in next-generation electronic and optoelectronic devices, as well as sensors. Additionally, two-dimensional (2D) PtSe2 demonstrates significant potential as a saturable absorber due to its exceptional nonlinear optical response across an ultrabroad spectra range, presenting exciting opportunities in ultrafast and nonlinear photonics. In this work, we explore the second-order nonlinear optical characteristics of 2D PtSe2 by analyzing its second-harmonic generation (SHG) excited by a pulsed laser at 1064 nm. Our investigation unveils a layer-dependent SHG response in PtSe2, with prominent SHG intensity observed in few-layer PtSe2. The distinct six-fold polarization dependence pattern observed in the SHG intensity reflects the inherent threefold rotational symmetry inherent to the PtSe2 crystal structure. Remarkably, the SHG intensity of 4-layer PtSe2 surpasses that of mechanically exfoliated monolayer molybdenum disulfide (MoS2) by approximately two orders of magnitude (60-fold), underscoring its exceptional second-order nonlinear optical response. Combined with its ultrahigh air-stability, these distinctive nonlinear optical characteristics position two-dimensional PtSe2 as a promising candidate for ultrathin nonlinear nanophotonic devices.

Plasmonic nanoparticles enable manipulation and enhancement of light fields at deep subwavelength scales, leading to structures and devices for diverse applications in optics. Despite hybrid plasmonic materials display remarkable optical properties due to interactions between components in nanoproximity, scalable production of plasmonic nanostructures within a single‐crystalline matrix to achieve an ideal plasmon–crystal interface remains challenging. Here, a novel approach is presented to realize efficient manipulation of in‐lattice plasmonic nanoparticles. Employing ultrafast‐laser‐driven plasmonic nanolithography, metallic nanoparticles with controllable morphology are precisely defined in the crystalline lattice of yttrium aluminum garnet (YAG) crystal. Through direct ion implantation, hybrid plasmonic material composed of nanoparticles embedded in a sub‐surface amorphous YAG layer is created. Subsequently, femtosecond laser pulses guide formation and reshaping of plasmonic nanoparticles from the amorphous layer into the single‐crystalline matrix along direction of light propagation, facilitated by a plasmon‐mediated evolution of laser energy deposition. By tailoring resonance modes and optimizing the coupling between structured particle assemblies, a range of applications including polarization‐dependent absorption and nonlinearity, controllable photoluminescence, and structural color generation is demonstrated. This research introduces a new approach for fabricating advanced optical materials featuring in‐lattice plasmonic nanostructures, paving the way for the development of diverse functional photonic devices. [ABSTRACT FROM AUTHOR]

Platinum diselenide (PtSe2), classified as a noble metal dichalcogenide, has garnered substantial interest owing to its layer-dependent band structure, remarkable air-stability, and high charge-carrier mobilities. These properties make it highly promising for a wide array of applications in next-generation electronic and optoelectronic devices, as well as sensors. Additionally, two-dimensional (2D) PtSe2 demonstrates significant potential as a saturable absorber due to its exceptional nonlinear optical response across an ultrabroad spectra range, presenting exciting opportunities in ultrafast and nonlinear photonics. In this work, we explore the second-order nonlinear optical characteristics of 2D PtSe2 by analyzing its second-harmonic generation (SHG) excited by a pulsed laser at 1064 nm. Our investigation unveils a layer-dependent SHG response in PtSe2, with prominent SHG intensity observed in few-layer PtSe2. The distinct six-fold polarization dependence pattern observed in the SHG intensity reflects the inherent threefold rotational symmetry inherent to the PtSe2 crystal structure. Remarkably, the SHG intensity of 4-layer PtSe2 surpasses that of mechanically exfoliated monolayer molybdenum disulfide (MoS2) by approximately two orders of magnitude (60-fold), underscoring its exceptional second-order nonlinear optical response. Combined with its ultrahigh air-stability, these distinctive nonlinear optical characteristics position two-dimensional PtSe2 as a promising candidate for ultrathin nonlinear nanophotonic devices. [ABSTRACT FROM AUTHOR]

Functional two-dimensional (2D) materials have been extensively explored for a wide range of applications such as energy generation, low-power computing, and biosensing. In this work, we present an approach involving the integration of six-layer platinum diselenide (PtSe2) as an interlayer between the thin gold film and SiO2 substrate to induce spontaneous formation of plasmonic nanostructures (nanoribbons) on the upper gold film (∼8 nm) under 1030 nm femtosecond laser irradiation. The formation of periodic nanostructures is attributed to the periodic energy deposition that occurs in the PtSe2 layers under intense femtosecond laser pulses. Notably, the self-assembled gold nanostructures exhibit a distinctive polarization-dependent plasmonic response in the near-infrared spectral region and could be directly fabricated in a centimeter scale within several minutes. This straightforward method for self-assembling plasmonic nanostructures using layered materials may expand the utility of functional 2D materials and advance the cost-effective and large-area fabrication of plasmonic thin-film nanostructures in a simplified manner. [ABSTRACT FROM AUTHOR]

The size‐ and shape‐dependent localized surface plasmon properties of metallic nanoparticles (NPs) enable nanoscale‐enhanced near‐field applications in a wide range of fields, including spectroscopy, nonlinear optics, and sensing. Orderly assembled NPs can construct plasmonic metamaterials for light manipulation at a subwavelength scale, exhibiting new collective properties in resonant modes regulated by plasmon coupling between their fundamental components. Despite the recognition of its significant advantages in photonics integration, plasmonic‐based tailored optical responses for practical applications have remained elusive due to limitations in scaling up processes, as neither etching nor assembly can design and fabricate embedded plasmonic devices into functional devices/structures. Here, the assembly of plasmonic NPs is demonstrated by ultrafast laser‐induced writing‐on‐demand inside solids, tailoring their distribution and sizes. By controlling the laser scanning speed, the in situ redistribution of NPs is observed. Plasmon mediated local energy deposition is considered as the main mechanism driving nano‐patterning at a subwavelength range. A direct nano‐printing is realized by utilizing the resonant optical response of laser‐modified NP structures/patterns. This work paves the way for directly induced NP composite structures inside transparent materials at a well‐defined and controlled depth for plasmonic applications. [ABSTRACT FROM AUTHOR]

Vanadium dioxide (VO2) has been one of the most significant functional materials for its prominent property change during phase transition. Here the modulation in crystallinity and morphology of VO2 thin film is achieved by femtosecond laser direct writing. Both the local crystallization from an amorphous phase and self-organized periodical structures are generated due to the well-controlled femtosecond laser energy deposition and controlled accumulation. The dynamic evolution of either the volumetric or surface nano-/micro-structure depends strongly on the femtosecond laser conditions, revealed by changes of the Raman bands and reflectance spectra at visible wavelengths. Based on the distinguishable color display performance of differently processed regions, a four-color-level image has been drawn on a VO2 thin film. This work proposes an elaborate "annealing by light" and optical property modulation method for the VO2, paving the way to producing complex integrated multi-functional devices for color display and data storage. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides (TMDs) have attracted broad interest in photonics owing to their unique electric band structures, which triggers various applications for functional devices. However, the optical absorbance of TMDs is relatively low because of the atomic-scale thickness, limiting further development of TMDs-based nonlinear optical devices. Here, we propose an effective method to enhance the nonlinear optical properties of TMDs using plasmons, which are from embedded silver (Ag) nanoparticles (NPs) inside the fused silica substrate. In such a configuration, the third-order nonlinear absorption coefficient of MoS2 with non-contact Ag NPs is one order of magnitude higher than that of pure monolayer MoS2 under excitation of 515 nm light, and at 1030 nm, the reverse saturable absorption switches to the saturable absorption due to the plasmonic implication. In addition, the mechanism of plasmon-enhanced nonlinear optical properties is confirmed by results of both transient absorption spectroscopy and near-field electromagnetic field simulation. This study on plasmon-enhanced third-order nonlinearity of MoS2 expands the boundaries of TMDs-based optical nonlinearity engineering. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides (TMDs) have attracted broad interest in photonics owing to their unique electric band structures, which triggers various applications for functional devices. However, the optical absorbance of TMDs is relatively low because of the atomic-scale thickness, limiting further development of TMDs-based nonlinear optical devices. Here, we propose an effective method to enhance the nonlinear optical properties of TMDs using plasmons, which are from embedded silver (Ag) nanoparticles (NPs) inside the fused silica substrate. In such a configuration, the third-order nonlinear absorption coefficient of MoS2 with non-contact Ag NPs is one order of magnitude higher than that of pure monolayer MoS2 under excitation of 515 nm light, and at 1030 nm, the reverse saturable absorption switches to the saturable absorption due to the plasmonic implication. In addition, the mechanism of plasmon-enhanced nonlinear optical properties is confirmed by results of both transient absorption spectroscopy and near-field electromagnetic field simulation. This study on plasmon-enhanced third-order nonlinearity of MoS2 expands the boundaries of TMDs-based optical nonlinearity engineering. [ABSTRACT FROM AUTHOR]

The Faraday rotation originates from the mechanism by which the time‐reversal symmetry in the material is broken by the external magnetic field. It is the basis for the development of some magneto‐optical devices, such as optical isolators. In integrated optics and telecommunications, nonreciprocal photonic devices with high transmittance and strong Faraday rotation are desired for low‐cost, compact optical systems. Localized surface plasmon resonance (LSPR) from the metallic nanoparticles in dielectrics allows the light localization in subwavelength scales, boosting the interaction between nanoparticles and materials, which results in a number of plasmon‐enhanced effects. Herein, the strong Faraday rotation in BK7 glass by embedded metallic nanoparticles through LSPR is reported. It is elucidated that the mechanism of Faraday rotation is the near‐field enhancement of spin–photon coupling effect in the presence of an external magnetic field. The Verdet constant of the thin‐layer BK7 glass with embedded Au nanoparticles is determined as high as 5059.7 rad T−1 m−1 at 532 nm, exhibiting excellent magneto‐optical features. This work opens a new avenue to develop the subwavelength magneto‐optical devices with embedded metallic nanoparticles. [ABSTRACT FROM AUTHOR]

Efficient nonlinear frequency conversion, such as second-harmonic generation in ultracompact structures, is essential for the development of modern nanophotonic devices. Here, we demonstrate intense second-harmonic emission in scalable embedded Ag nanoparticle arrays fabricated by ion implantation into BK7 glass. The interparticle coupling effect significantly enhances the local field at the nanogap (gap size ∼ 1 nm) of two neighboring Ag nanoparticles and finally amplifies second-harmonic emission generated at the surface of plasmonic nanoparticles. Notably, the intensity of second-harmonic emission in embedded Ag nanoparticle arrays is comparable to that of two-dimensional transition metal dichalcogenides under the excitation of a fundamental wave at 1064 nm and independent of the incident polarization angles. Our work offers a promising strategy on the rapid fabrication of low-cost nonlinear optical nanostructures with great environmental stability. [ABSTRACT FROM AUTHOR]

Developing efficient methods for boosting light–matter interactions is critical to improve the functionalities of two-dimensional (2D) transition metal dichalcogenides toward next-generation optoelectronic devices. Here, we demonstrate that the light–matter interactions in tungsten disulfide (WS2) monolayer can be significantly enhanced by introducing an air-stable functional substrate (fused silica with embedded plasmonic Ag nanoparticles). Distinctive from conventional strategies, the Ag nanoparticles are embedded under the surface of fused silica via ion implantation, forming a functional substrate for WS2 monolayer with remarkably environmental stability. A tenfold photoluminescence enhancement in WS2 monolayer has been achieved due to the plasmonic effect of Ag nanoparticles. This work offers a strategy to fabricate the plasmon-2D hybrid system at low cost and large scale and paves the way for their applications in optoelectronics and photonics. [ABSTRACT FROM AUTHOR]

A topological bound state in the continuum (TBIC) is a novel topological phase that has attracted significant attention. Different from conventional topological insulators (TIs), where boundary states reside within gaps, TBICs can support unconventional boundary states that remain isolated from the surrounding bulk states. In this work, we experimentally demonstrate multiple TBICs in photonic bilayer trimer lattices using femtosecond laser writing technology. By modulating the interlayer coupling between two trimer chains, we observe the emergence of two distinct types of TBICs. Moreover, we experimentally achieve the coexistence of in-gap topological states and TBICs and demonstrate the transformation between them. Our work unveils new insights into the flexible construction of TBICs, and this method can be easily applied to other one-dimensional topological structures, offering promising avenues for further research.

Two-dimensional (2D) van der Waals heterostructures (vdW HSs) composed of transition metal dichalcogenides (TMDCs) have emerged as frontrunners in the optoelectronics field, owing to their exceptional optical and electrical properties. Recent research on the intrinsic interlayer charge transfer mechanism has been primarily focused on the Type II HSs, while metal-semiconductor (MS) vertical HSs, promising for advancing photodetector technology, have received comparatively less attention. Here, we reveal the first experimental observation of photothermionic effect-assisted ultrafast interlayer charge transfer in the NbS 2 /MoS 2 heterostructure using femtosecond transient absorption technology and first-principles calculations, effectively ignoring the Schottky barrier height. We demonstrate that within 500 fs, charge transfer occurs from NbS 2 to MoS 2 in the heterostructure, resulting in supplementary carrier generation in the visible spectrum when excited with infrared light below the MoS 2 bandgap, at wavelengths of 1030 and 1500 nm. Such promising characteristics of 2D NbS 2 -semiconductor heterostructures offer a potential platform for synergistically combining low contact resistance with broadband photocarrier generation, marking a significant advancement in optoelectronics and light harvesting.

The thickness-dependent third-order nonlinear optical properties of two-dimensional β-InSe and its potential applications as a saturable absorber in pulsed laser generation are investigated. InSe sheets with different layers are prepared by the chemical vapor deposition. Using open-aperture femtosecond Z-scan technique at 1030 nm, the modulation depth and nonlinear absorption coefficient are obtained to be 36% and -1.6 × 10 4 cm·GW -1 , respectively. The intrinsic mechanism of the layer-dependent energy band structure evolution is analyzed based on density functional theory, and the theoretical analysis is consistent with the experimental results. Based on a waveguide cavity, a Q-switched mode-locked laser at 1 µm with a repetition frequency of 8.51 GHz and a pulse duration of 28 ps is achieved by utilizing the layered InSe as a saturable absorber. This work provides an in-depth understanding of layer-dependent properties of InSe and extends its applications in laser technology for compact light devices.