Spaser Research Articles

Two‐Photon Pumped Wavelength‐Tunable Single‐Mode Plasmonic Nanolaser with Ultralow Threshold

AbstractNonlinear optics play an important role in laser technology, optical communication, integrated optics, and other fields. However, conventional two‐photon lasing faces challenges such as high thresholds and large size, which hinder the miniaturization of lasers. In this study, the structure of single‐crystal Au/Al2O3/CsPbBr3 (ScAu/Al2O3/CPB) is constructed to achieve two‐photon pumped frequency upconversion single‐mode plasmonic lasing. The strong spatial confinement and near‐field enhancement of surface plasmons in metals enable the plasmonic lasing mode output in a hybrid nanocavity, significantly reducing the lasing threshold. Additionally, by applying external mechanical strain, the resonant wavelength of the lasing mode is dynamically regulated, further reducing the threshold to 0.48 mJ cm−2 based on piezo‐electronic effect. These results provide an effective strategy for all‐optical integration and the development of smaller, faster, and more efficient nanophotonics devices.

Plasmonic Hinge Modes in Metal-Coated Nanolasers.

Plasmonic lasers have traditionally been built on flat metal substrates. Here, we introduce substrate-free plasmonic lasers created by coating semiconductor particles with an optically thin layer of noble metal. This architecture supports plasmonic "hinge" modes highly localized along the particle's edges and corners, exhibiting Purcell factors exceeding 100 and Q-factors of 15-20 near the plasmon resonance frequency. We demonstrate hinge-mode lasing in submicron CsPbBr3 perovskite cubes encapsulated with conformal 15-nm-thick gold shells. The lasing is achieved with 480-nm nanosecond pumping at 10 pJ/μm2 through the translucent gold layer, producing a line width of 0.6 at 538 nm. Their rapidly decaying evanescent fields outside the gold coating show distinct sensitivities to long- and short-range external perturbations. Our results suggest the potential of these novel laser modes for sensing and imaging applications.

Room‐Temperature Lasing of Dual‐Metal Nanoparticle Surface Lattice Resonance with Monolithic InGaAs Multiple Quantum Wells on GaAs Substrates

This study demonstrates the surface lattice resonance (SLR) laser utilizing asymmetric dual‐metallic nanoparticle arrays, incorporating a high‐refractive‐index material, which exhibits a confinement factor of 16%, enhancing the coupling between metal and dielectric materials. Multiple quantum wells (MQWs) are integrated with plasmonic SLR in the proposed structure. Through theoretical design and experimental validation, the MQW plasmonic SLR laser exhibits excellent high Q‐factor and stable operation at room temperature. This demonstration enhances laser performance and achieves low‐threshold operation with a laser threshold as low as ≈2.39 MW cm−2. This study's design of plasmonic SLR lasers further advances the realization of optoelectronic device applications.

Ultra-thin size-controllable surface plasmon polariton laser by PDMS-assisted imprinting

Plasmonic laser has great potential to overcome the optical diffraction limit, playing a crucial role in advancing nanophotonics and nanoelectronics for on-chip integration. However, current plasmonic lasers face several challenges, such as the difficulty in controlling nanowire (NW) size, disordered arrangement, and complicated fabrication process. Herein, ultra-thin gain media for plasmonic lasers below the cutoff size of the photonic mode are prepared using the polydimethylsiloxane-assisted imprinting. This method enables precise control over the size of the perovskite NW, with the minimum size achievable being 60 nm. As a result, the plasmonic lasing is achieved from the CsPbBr3 NW-based device with a threshold as low as ∼49.13 μJ cm−2 and a Quality Factor (Q) of 1803 at room temperature, demonstrating its capability for achieving high-quality lasing. Meanwhile, a dual-pumping time-resolved fluorescence study suggests that the radiative recombination lifetime of CsPbBr3 NWs is shortened by a factor of 10 due to the Purcell effect, confirming the plasmonic effect exhibited by the device. Furthermore, a plasmonic laser array is developed using this method, demonstrating the applicability of the imprinting method in complex graphic fabrication. This breakthrough provides a solution for the application of plasmonic laser arrays in optoelectronic integration.

Plasmonic triple compound cavity random lasing: fabrication and characterization

Plasmonic triple compound cavity random lasing: fabrication and characterization

Design of an ultrafast plasmonic nanolaser for high-intensity broadband emission operating at room temperature.

We propose a plasmonic nanolaser based on a metal-insulator-semiconductor-insulator-metal (MISIM) structure, which effectively confines light on a subwavelength scale (∼λ/14). As the pump power increases, the proposed plasmonic nanolaser exhibits broadband output characteristics of 20 nm, and the maximum output power can reach 20 µW. Furthermore, the carrier lifetime at the upper energy level in our proposed structure is measured to be about 400 fs using a double pump-probe excitation. The ultrafast characteristic is attributed to the inherent Purcell effect of plasmonic systems. Our work paves the way toward deep-subwavelength mode confinement and ultrafast femtosecond plasmonic lasers in spaser-based interconnected, eigenmode engineering of plasmonic nanolasers, nano-LEDs, and spontaneous emission control.

Wavelength selective beam-steering in a dual-mode multi-layer plasmonic laser

Due to its improved localization and confinement of light in single or multiple wavelength modes, nanolasers based on plasmonic crystals have grown in popularity in recent years. However, the lasing modes are not spatially separated, making applying different modes to different applications difficult. This work demonstrates an effective technique for spatially separating the two modes of a merged lattice metal nanohole array-based dual-mode plasmonic laser. A flat dielectric metasurface-based beam-splitter that exploits phase gradient profiles on the interfaces has been added to the laser to separate the modes into distinct spatial beams. The proposed structure successfully separates two modes by ∼23°, and the separation can be raised to ∼63° by tuning structural parameters such as the radius of the nanocylinders and the number of supercell rows. In addition, multiple beams can be generated, allowing for manual beam steering. This approach has a high emission output with a narrow linewidth, clarity, and a substantial degree of future tunability potential. The proposed integrated structure will provide a novel means of device miniaturization and may also serve advanced optical applications such as optical communication, quantum optics, interferometry, spectroscopy, and light detection and ranging (LiDAR).

Broad-band-enhanced plasmonic random laser in silver nanostar arrays

As a novel optical device, the plasmonic random laser has unique working principle and emission characteristics. However, the simultaneous enhancement of absorption and emission by plasmons is still a problem. In this paper, we propose a broad-band-enhanced plasmonic random laser. Two-dimensional silver (Ag) nanostar arrays were prepared using a bottom-up method with the assistance of self-assembled nanosphere templates. The plasmon resonance of Ag nanostars contributes to the pump light absorption and photoluminescence (PL) of RhB. Coherent random lasing was achieved in RhB@PVA film based on localized surface plasmon resonance (SPR) dual enhancement and scattering feedback of Ag nanostars. Ag nanostars prepared with different nanosphere diameters affect the laser emission wavelength. In addition, the random laser device achieves wavelength tunability on a flexible substrate under mechanical external force.

Ultrafast wavelength sweeping of surface plasmon lasing in planar metal grating with semiconductor gain

Surface plasmon (SP) lasing, characterized by strong light–matter interaction at a metal interface, can derive from SP cavities coupled with a semiconductor gain material. With this setup, we demonstrate ultrafast wavelength sweeping of SP lasing in a metal grating. When the device was optically pumped by ultrashort pulses with sufficient power, a wavelength sweep over 10 nm within 50 ps was obtained in the telecom band of 1550 nm. Based on the pump-power-dependent lasing wavelength change in combination with finite-difference time-domain simulation, we attribute the wavelength sweep to a modulation of the SP cavity that induces changes in the refractive index from changes in the carrier density. Such a refractive index change is a critical factor in determining SP cavity resonance.

Anti-psoriasis effect of 18β-glycyrrhetinic acid by breaking CCL20/CCR6 axis through its vital active group targeting GUSB/ATF2 signaling

BackgroundPsoriasis is an immune-mediated chronic inflammatory skin disease. Current research suggests that the long-term persistence and recurrence of psoriasis are closely related to the feedback loop formed between keratinocytes and immune cells, especially in Th 17 or DC cells expressing CCR6. CCL20 is the ligand of CCR6. Therefore, drugs that block the expression of CCL20 or CCR6 may have a certain therapeutic effect on psoriasis. Glycyrrhetinic acid (GA) is the main active ingredient of the plant drug licorice and is often used to treat autoimmune diseases, including psoriasis. However, its mechanism of action is still unclear. MethodsPsoriasis like skin lesion model was established by continuously applying imiquimod on the back skin of normal mice and CCR6-/- mice for 7 days. The therapeutic and preventive effects of glycyrrhetinic acid (GA) on the model were observed and compared. The severity of skin injury is estimated through clinical PASI scores and histopathological examination. qRT-PCR and multiple cytoline assay were explored to detect the expression levels of cytokines in animal dorsal skin lesions and keratinocyte line HaCaT cells, respectively. The dermis and epidermis of the mouse back were separated for the detection of CCL20 expression. Transcription factor assay was applied to screen, and luciferase activity assay to validate transcription factors regulated by GA. Technology of surface plasmon laser resonance with LC-MS (SPR-MS), molecular docking, and enzyme activity assay were used to identified the target proteins for GA. Finally, we synthesized different derivatives of 18beta-GA and compared their effects, as well as glycyrrhetinic acid (GL), on the skin lesion of imiquimod-induced mice to evaluate the active groups of 18beta-GA. Results18β-glycyrrhetinic acid (GA) improved IMQ-induced psoriatic lesions, and could specifically reduce the chemokine CCL20 level of the epidermis in lesion area, especially in therapeutic administration manner. The process was mainly regulated by transcription factor ATF2 in the keratinocytes. In addition, GUSB was identified as the primary target of 18βGA. Our findings indicated that the subject on molecular target research of glycyrrhizin should be glycyrrhetinic acid (GA) instead of glycyrrhizic acid (GL), because GL showed little activity in vitro or in vivo. Apart from that, α, β, -unsaturated carbonyl in C11/12 positions was crucial or unchangeable to its activity of 18βGA, while proper modification of C3 or C30 position of 18βGA may vastly increase its activity. ConclusionOur research indicates that 18βGA exerted its anti-psoriasis effect mainly by suppressing ATF2 and downstream molecule CCL20 predominately through α, β, -unsaturated carbonyl at C11/12 position binding to GUSB in the keratinocytes, and then broke the feedback loop between keratinocytes and CCR6-expressing immune cells. GA has more advantages than GL in the external treatment of psoriasis. A highlight of this study is to investigate the influence of special active groups on the pharmacological action of a natural product, inspired by the molecular docking result.

QbD-assisted synthesis and exploration of plasmonic laser activatable nanoGold seeds for photothermal and photodynamic therapy of cancer cells

QbD-assisted synthesis and exploration of plasmonic laser activatable nanoGold seeds for photothermal and photodynamic therapy of cancer cells

Advancements in nanoscale coherent emitters: The development of substrate-free surface plasmon nanolasers

The surface plasmon effect can be used to confine electromagnetic fields to a small footprint measuring tens of nanometers. The resultant resonant cavities function as optimal coherent light sources with subwavelength scale configurations. The plasmonic laser sources based on nanoshell structures, in particular, have demonstrated the potential for use in the detection of subcellular mesoscopic molecular structures. However, this structure has a high plasmon dephasing rate, which can increase the threshold of the device, making it difficult to achieve electrically excited structures, thereby rendering them unsuitable as an active component for integration into optoelectronic circuits. A different approach to confining electromagnetic fields involves using a propagating surface plasmon laser structured on a planar layered semiconductor–insulator–metal. This design enables the surface plasmon to propagate along the direction of the nanowire and offers the potential to achieve electrically driven structures by injecting current into the semiconductor nanowire. Consequently, this structure is more effective in guiding energy into integrated optoelectronic circuits compared to the isotropic radiation of nanoshell structures. However, this design also necessitates a supporting substrate, resulting in the actual device volume exceeding the nanoscale and, in some cases, even larger than the size of a cell. This limitation hinders the application of integrated optoelectronic circuits at the micro/nanoscale for bio-applications. To address these challenges, we developed a substrate-free surface plasmon polariton laser. We demonstrated that allowing direct contact between the film and the air significantly reduced the laser threshold. Furthermore, the device maintained its operational capability across different surfaces.

Plasmonic lasing in highly lossy nanocylinder arrays under optical pumping

Plasmonic lasing in highly lossy nanocylinder arrays under optical pumping

Coupling Between Lattice and Waveguide Modes in Semiconductor Plasmonic Crystal Lasers

Semiconductor-based plasmonic crystal lasers (PCLs) have narrow linewidth, small divergence angle, excellent thermal stability, and great potential for ultra-high-speed communications. The underlying mechanism and lasing modes for their operation is unfolded in this work. We find that the waveguide mode coupling with the surface plasmonic mode plays an essential role in the semiconductor-based PCLs. The simulation and experimental data reveal that the cooperation of the dielectric layers and the metallic nano-pillar array gives the needed resonant mode of high-quality factor. The mode coupling strength has to be properly designed to make these intriguing devices working.

Sustained Feedback-Induced Oscillations in a Hybrid Single Mode Semiconductor Plasmonic Laser

Sustained Feedback-Induced Oscillations in a Hybrid Single Mode Semiconductor Plasmonic Laser

Energy transfer assisted plasmonic random laser emission from polymer optical fiber

Here, we analyzed the effect of a donor molecule (Rh6G) on the random laser emission of an acceptor molecule (Rh640 perchlorate) coated on the surface of a polymer optical fiber. Due to the energy transfer mechanism, the random lasing threshold of Rh640 perchlorate was found to be reduced in the presence of Rh6G. Also, the emission spectrum of Rh640 perchlorate was blue-shifted with the addition of Rh6G. Meanwhile, there is an enhancement in the lasing threshold of Rh6G in the presence of Rh640 perchlorate. The present study demonstrates that by properly adjusting the concentrations of both donor and acceptor molecules, we can obtain a dual-color random laser emission from polymer optical fiber.

Chemical Sensing and Analysis with Optical Nanostructures

Nanostructures and nanomaterials, especially plasmonic nanostructures, often show optical properties that conventional materials lack and can manipulate light, as well as various light–matter interactions, in both their near-field and far-field regions with a high efficiency. Thanks to these unique properties, not only can they be used to enhance the sensitivity of chemical sensing and analysis techniques, but they also provide a solution for designing new sensing devices and simplifying the design of analytical instruments. The earliest applications of optical nanostructures are surface-enhanced spectroscopies. With the help of the resonance field enhancement of plasmonic nanostructures, molecular signals, such as Raman, infrared absorption, and fluorescence can be significantly enhanced, and even single-molecule analysis can be realized. Moreover, the resonant field enhancements of plasmonic nanostructures are often associated with other effects, such as optical forces, resonance shifts, and photothermal effects. Using these properties, label-free plasmonic sensors, nano-optical tweezers, and plasmonic matrix-assisted laser desorption/ionization have also been demonstrated in the past two decades. In the last few years, the research on optical nanostructures has gradually expanded to non-periodic 2D array structures, namely metasurfaces. With the help of metasurfaces, light can be arbitrarily manipulated, leading to many new possibilities for developing miniaturized integrated intelligent sensing and analysis systems. In this review, we discuss the applications of optical nanostructures in chemical sensing and analysis from both theoretical and practical aspects, aiming at a concise and unified framework for this field.

Design and Fabrication of Room Temperature Electrically Pumped ZnO Nanowire Hybrid Plasmonic Lasers

Plasmonic lasers have attracted much attention because they can break through the diffraction limit, but due to the large metal loss limitations, electrically driven plasmonic lasers mainly work at low temperatures to achieve sufficient gain. Therefore, we proposed electrically pumped nanowire plasmonic lasers at room temperature. Here, the metal/insulator/semiconductor (MIS) structure was applied to reduce the metal loss by separating the active area and the metal layer through the insulator. We illustrate the superiority of plasmonic laser performance by comparing plasmonic and photon lasers at room temperature. Our research provides some experimental basis for the realization of future optoelectronic integration.

Replica symmetry breaking in a colloidal plasmonic random laser with gold-coated triangular silver nanostructures.

Plasmonic random lasers have drawn significant attention recently due to their versatility, low threshold, and the possibility of achieving tunable and coherent/incoherent outputs. However, in this Letter, the phenomenon of replica symmetry breaking is reported in intensity fluctuations of a rarely used colloidal plasmonic random laser (RL) illumination. Triangular nanosilver scatter particles produced incoherent RL action when used in a dimethylformamide (DMF) environment in a Rhodamine-6G gain medium. The use of gold-coated triangular nanosilver as the scatterer in place of triangular nanosilver offered a dual contribution of scattering and lower photo-reabsorption, which caused a reduction in the lasing threshold energy of 39% compared to that obtained with the latter. Further, due to its long-term photostability and chemical properties, a phase transition from the photonic paramagnetic to the glassy phase is observed experimentally in the RL system used. Interestingly, the transition occurs at approximately the lasing threshold value, which is a consequence of stronger correlation of modal behaviors at high input pump energies.

Plasmonic multi-wavelength random laser by gold nanoparticles doped into glass substrate

Plasmonic multi-wavelength random laser by gold nanoparticles doped into glass substrate