Ultraviolet Lasing Research Articles

Multipeak ultraviolet lasing based on F-P mode from in-situ ZnO nanowire

Abstract High-quality ultraviolet singlemode and multimode lasing from zinc oxide nanowires are highly desirable. In this paper, we achieve high-Q lasing oscillation in vertically grown Zinc oxide (ZnO) microwires. The broad gain range reaches 13 lasing modes under high-energy excitation. We observe multiple peak emissions from the Fabry-Perot (F-P) lasing mode. In contrast, nanorod arrays with low aspect ratios exhibit amplified spontaneous emission (ASE) due to significant diffraction losses. Our work demonstrates that high-quality ZnO nanowires with an appropriate aspect ratio realize high-Q ultraviolet multipeak lasing based on F-P mode. These findings will benefit the design and fabrication of nanolasers based on nanowires.

Architecture for Surface-Emitting Lasers with On-Demand Lasing Wavelength by Nanowire Optical Cavities.

Despite the importance and exciting progress of surface-emitting (SE) semiconductor lasers, we have limited choices of lasing wavelength even today. From an application viewpoint, it is desirable to have an architecture that can allow SE lasing in a wide spectral range, based on the need of applications. Herein, we demonstrate a path for SE lasers with lasing wavelength on demand by exploiting III-nitride nanowire optical cavities formed by low-temperature selective area epitaxy (SAE), combined with fine-tuning of substrate patterns and photonic bands. Moreover, in this study, we focus on the device demonstration in the ultraviolet (UV) spectral range, considering the severe lag in developing SE lasers in the UV wavelength range compared to longer wavelengths, e.g., near-infrared (NIR), as well as the potential applications enabled by UV lasers such as solar blind optical wireless communications. Ultralow threshold wavelength-tunable SE UV lasing is achieved by optical pumping. Moreover, SE UV lasing under direct electric current injection is also achieved. This study not only represents an important step in the journey of SE UV laser development but, more importantly, it lays the ground for SE lasers with lasing wavelength on demand, broadly from NIR to UV.

Emission behaviors from ZnO microwire pumped CsPbBr3 perovskite microwire.

Perovskite semiconductor materials have attracted significant attention in the fields of photovoltaics and luminescence due to their excellent photoelectric properties, such as high carrier mobility, high absorption coefficient, and high fluorescence quantum yield. In particular, low-dimensional metal-halide perovskite microcrystalline materials have been reported to exhibit low-dimensional lasing phenomena and laser devices due to their high gain and widely tunable bandgap. In this Letter, one-dimensional (1-D) ZnO microwires with their ultraviolet lasing emissions are utilized as an excitation source to pump CsPbBr3 microwire on hybrid ZnO-CsPbBr3 microscale structures. At higher excitation, the amplified spontaneous emission (ASE) behaviors from CsPbBr3 microwire are realized with ultralow threshold by indirect pumping from the ZnO lasing emission for the first time, to the best of our knowledge. In comparison, the ASE behaviors from the CsPbBr3 microwire directly pumped by Nd:YAG Q-switched laser and continuous wave laser are also performed at room temperature. There are also no multimode lasing behaviors observed. The paper provides a new method to achieve a low threshold on-chip microlaser by a high-quality perovskite micro-nano structure.

On-Chip Monolithically Integrated UltravioletLow-Threshold Plasmonic Metal-Semiconductor Heterojunction Nanolasers.

The metal-semiconductor heterojunction is imperative for the realization of electrically driven nanolasers for chip-level platforms. Progress in developing such nanolasers has hitherto rarely been realized, however, because of their complexity in heterojunction fabrication and the need to use noble metals that are incompatible with microelectronic manufacturing. Most plasmonic nanolasers lase either above a high threshold (101 -103 MW cm-2 ) or at a cryogenic temperature, and lasing is possible only after they are removed from the substrate to avoid the large ohmic loss and the low modal reflectivity, making monolithic fabrication impossible. Here, for the first time, record-low-threshold, room-temperature ultraviolet (UV) lasing of plasmon-coupled core-shell nanowires that are directly grown on silicon is demonstrated. The naturally formed core-shell metal-semiconductor heterostructure of the nanowires leads to a 100-fold improvement in growth density over previous results. This unprecedentedly high nanowire density creates intense plasmonic resonance, which is outcoupled to the resonant Fabry-Pérot microcavity. By boosting the emission strength by a factor of 100, the hybrid photonic-plasmonic system successfully facilitates a record-low laser threshold of 12kW cm-2 with a spontaneous emission coupling factor as high as ≈0.32 in the 340-360nm range. Such architecture is simple and cost-competitive for future UV sources in silicon integration.

GaN Ultraviolet Laser based on Bound States in the Continuum (BIC)

AbstractOptical bound states in the continuum (BICs), realizing substantial suppression of out‐of‐plane radiative losses, have been utilized to realize strong light confinement and optical modes with high quality‐factor (Q). Lasing actions with narrow linewidths based on optical BIC modes have been demonstrated in the near‐infrared and the visible ranges, but BIC‐based lasers in the ultraviolet (UV) region have not been reported. As light sources possessing wavelengths at the UV scale are essential in various fields, the strategy to design compact UV lasers based on high‐Q modes and directional emissions is highly desirable. Here, the first BIC‐based laser in the UV region is demonstrated by designing a 1D periodic resist structure on top of a GaN film. Using the symmetric‐protected BIC mode, the fabricated laser is having a directional single‐mode lasing emission with a small full‐width at half‐maximum of 0.10 nm and beam divergence of 1.5°. The lasing action is observed with a periodic structure area corresponding to a structure side length as small as 8 µm. Moreover, the wavelength control of the UV lasing is achieved by varying the period and temperature. This work provides strategies to design UV lasers having a small footprint together with narrow‐linewidth and out‐of‐plane emissions.

Simultaneous ultraviolet, visible, and near-infrared continuous-wave lasing in a rare-earth-doped microcavity

Microlaser with multiple lasing bands is critical in various applications, such as full-color display, optical communications, and computing. Here, we propose a simple and efficient method for homogeneously doping rare earth elements into a silica whispering-gallery microcavity. By this method, an Er-Yb co-doped silica microsphere cavity with the highest quality (Q) factor (exceeding 108) among the rare-earth-doped microcavities is fabricated to demonstrate simultaneous and stable lasing covering ultraviolet, visible, and near-infrared bands under room temperature and a continuous-wave pump. The thresholds of all the lasing bands are estimated to be at the submilliwatt level, where both the ultraviolet and violet continuous wave upconversion lasing from rare earth elements has not been separately demonstrated under room temperature until this work. This ultrahigh-Q doped microcavity is an excellent platform for high-performance multiband microlasers, ultrahigh-precision sensors, optical memories, and cavity-enhanced light–matter interaction studies.

Ultraviolet C random lasing at 230–280 nm from Pr3+ doped bulk crystal resonators by two-photon absorption

Ultraviolet solid-state light sources, especially in the short-wave ultraviolet band, are attracting great attention for potential applications in high-density optical data storage, biomedical research, and water and air purification and sterilization. As one of the means to generate solid-state short-wavelength lasers, upconversion technology, which can transform a low-energy photon to a high-energy photon, has a simple structure and does not require strict phase-matching conditions. However, because of the high non-radiative decay rate during multiphoton absorption process, the short-wave upconversion ultraviolet lasing is still difficult to achieve. Here, under 450 nm blue laser excitation, we have successfully obtained ultraviolet C random lasing from a Pr3+ doped YPO4 single crystal via two-photon absorption. Presently, ultraviolet C random lasing with the wavelength range of 230–280 nm is the shortest wavelength for upconversion lasing emission.

Ultralarge anti-Stokes lasing through tandem upconversion

Coherent ultraviolet light is important for applications in environmental and life sciences. However, direct ultraviolet lasing is constrained by the fabrication challenge and operation cost. Herein, we present a strategy for the indirect generation of deep-ultraviolet lasing through a tandem upconversion process. A core–shell–shell nanoparticle is developed to achieve deep-ultraviolet emission at 290 nm by excitation in the telecommunication wavelength range at 1550 nm. The ultralarge anti-Stokes shift of 1260 nm (~3.5 eV) stems from a tandem combination of distinct upconversion processes that are integrated into separate layers of the core–shell–shell structure. By incorporating the core–shell–shell nanoparticles as gain media into a toroid microcavity, single-mode lasing at 289.2 nm is realized by pumping at 1550 nm. As various optical components are readily available in the mature telecommunication industry, our findings provide a viable solution for constructing miniaturized short-wavelength lasers that are suitable for device applications.

Effect of substrates on lasing properties of GaN transferable membranes

Transferable membranes were separated from the GaN epitaxial sheet with lift-off (LLO) technology. After the LLO process, the GaN membrane was removed onto various substrates, and then we can create different interfacial conditions, such as GaN attached with Si and GaN attached to Au. The substrate dependent photoluminescence (PL) properties of GaN membranes are studied by PL and time-resolution photoluminescence (TRPL) measurements in situ. Lasing oscillations are observed in the GaN membranes. The lasing features – which include the lasing spectra, Q factor, laser threshold, mode number, carrier dynamics and resonance mechanism – are systematically analyzed. We obtain, for GaN on a Si substrate, two series of ultraviolet lasing emissions with Fabry-Pérot (F–P) mode at the same excitation position. Furthermore, lasing of the GaN membranes can be altered by Au film at the back end of it via the phenomenon of lasing mode merger and red shift. Comparing with the Si substrate, Au film on the back can balance the lasing oscillations through decreasing the threshold value, unifying the resonant modes, and increasing the carrier combination rate. This research provides a feasible method for the realization of flexible membrane lasers.

Electrically driven optical resonance of spherical ZnO whispering gallery mode microcavity

Spherical microcavities with low optical loss and high quality factor are attractive candidates for functional applications, including whispering gallery mode lasers, intracellular lasers, ultrasensitive biosensors, etc. In particular, electrically driven devices are beneficial for several applications such as optoelectronic integration. However, it is difficult to realize the electrically driven optoelectronic functions. In this study, the high-quality ZnO microspheres are fabricated by using a laser ablation method, and an excellent ultraviolet lasing system is achieved by optical pumping. Moreover, ultraviolet electroluminescence analysis demonstrates that ZnO microspheres are bonded to the p-GaN substrate. Furthermore, distinct resonant modes are obtained after inserting an appropriate AlN buffer layer at the n-ZnO/p-GaN interface. The optoelectronic behavior, charge carrier transportation, and recombination mechanism of the structure are systematically analyzed, and related interface modification, energy band alignment, and optical gain/loss contrast are also discussed. Overall, the results provide useful insights on further exploration of electrically pumped ZnO microsphere lasers.

Floating GaN whispering gallery mode micro-ring lasing with Burstein–Moss effect

A floating GaN micro-ring is fabricated by standard semiconductor technology. Under pump power conditions, ultraviolet lasing with a quality factor of 3600 is obtained. Resonant mode analysis indicates that the lasing spectra contain two types of whispering gallery modes and one type of Fabry–Perót mode. With the increase in pumping power, the state filling induced Burstein–Moss effect is observed and understood through synchronous measurement of photoluminescence and time resolution photoluminescence spectra.

Side-mode suppression in ultraviolet quasi-semicircle microlaser cavity

We report a quasi-semicircle GaN ultraviolet microcavity laser. Poincaré map of the quasi-semicircle cavity shows periodic, quasi-periodic and chaotic optical trajectories. Finite-element-method optical near-field distribution patterns of the periodic optical modes agree with the optical loops in the quasi-semicircle cavity. Based on the numerical results, optically pumped lasing experiment shows that ultraviolet multimode lasing action from different optical resonance modes can be effectively stimulated at low pumping intensity in the quasi-semicircle GaN cavity, and the side-mode suppression phenomenon can be obtained at high pumping intensity. Because the possible period optical loops are quasi-periodic and unstable, the quasi-whispering-gallery mode lasing with higher quality factor prefer to dominate the lasing action under high pumping. The experimental and simulated lasing modes suggest that side-mode suppression phenomenon can be caused by the mode competition between quasi-whispering-gallery modes and other quasi-periodic modes.

Lasing up to 380 K in a sublimated GaN nanowire

We report on GaN nanowire lasers fabricated by selective-area sublimation, and we show that sublimated GaN nanowires can exhibit ultraviolet lasing action under optical pumping beyond room temperature, up to 380 K. We study by microphotoluminescence the temperature-dependent behavior of single nanowire lasers between 7 K and 380 K and extract a characteristic temperature of T = 126 K. We finally present a statistical study of the maximum lasing temperature in individual sublimated GaN nanowires and use it to assess the performance of the selective-area sublimation method for nanowire-based lasing applications.

High Circular Polarized Nanolaser with Chiral Gammadion Metal Cavity

We demonstrate a circularly polarized laser with the metal-gallium-nitride gammadion nanocavities. The ultraviolet lasing signal was observed with the high circular dichroism at room temperature under pulsed optical pump conditions. Without external magnetism which breaks the time-reversal symmetry to favor optical transitions of a chosen handedness, the coherent outputs of these chiral nanolasers show a dissymmetry factor as high as 1.1. The small footprint of these lasers are advantageous for applications related to circularly polarized photons in future integrated systems, in contrast to the bulky setup of linearly-polarized lasers and quarter-wave plates.

(Invited) Atomic Resolution, Coordinated Electron Microscopy Characterization of 2D Layers Synthesized By Confinement Heteroepitaxy (CHet) Technique

Since the discovery of graphene in 2004 [1] there has been a flurry of activity in investigating two dimensional (2D) materials, because of their superlative properties: spin-orbit coupling, massless Dirac fermions, mechanical strength, thermal and chemical stability [2]. Remarkably, the in-plane hexagonal symmetry of graphene is largely responsible for its behavior. However, the zero-band gap of graphene presents hurdles to its use as a semiconductor. This has spurred interest in synthesis other van der Waals 2D structures, such as h-BN [3] and more recently 2D Gallium Nitride (2D GaN) [4].The synthesis of 2D Nitrides was first reported in 2016 by applying Confinement Heteroepitaxy (CHet) process to form a 2D Gallium Nitride (GaN) layer with 1-2 atom thickness. In this technique, a silicon carbide (SiC) substrate is graphitized and deliberately damaged using oxygen plasma to provide a two-step intercalation path. First a metal (like Gallium, or other group V metal) through evaporation is intercalated between the graphene and SiC substrate. Then, to complete the half reaction, nitrogen is introduced by ammonia annealing at 700 °C to form a 1-layer thick III-nitride.In this study, the growth method is extended from 2D GaN to variety of other 2D metals (Indium), Nitrides (InN) and alloys (InGa alloys). We employ a coordinated approach to understand the surface in both plan and cross-section view – linking through a variety of electron microscopy techniques, including auger electron spectroscopy (AES), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Bright-field, Dark-field, aberration-corrected STEM-HAADF imaging, and atomic-scale electron energy loss spectroscopy (EELS) mapping using a Gatan K2 SI direct electron detector and other techniques mapping were all applied to characterize the SiC/2D-layer/graphene interface. These electron microscopy techniques allow a precise, local measurement of the atomic structure of these new materials, including such growth parameters as the effect of graphene on the 2D layer stability, the effect of the SiC step edges on the layers structure, and the effect of the plasma type and source used in damaging the graphene on the 2D layer chemistry. Plasmon mapping also describes the unique bonding in the materials and their electronic structure. Ultimately, the measurements presented here characterize a whole new class of nanomaterials and provide insight on the fundamentals of the intercalation growth process. 1. Novoselov, K.S., et al., Electric field effect in atomically thin carbon films. Science, 2004. 306(5696): p. 666-669.2. Soldano, C., A. Mahmood, and E. Dujardin, Production, properties and potential of graphene. Carbon, 2010. 48(8): p. 2127-2150.3. Watanabe, K., T. Taniguchi, and H. Kanda, Direct-bandgap properties and evidence for ultraviolet lasing of hexagonal boron nitride single crystal. Nature Materials, 2004. 3(6): p. 404-4094. Al Balushi, Z.Y., et al., Two-dimensional gallium nitride realized via graphene encapsulation. Nature Materials, 2016. 15(11): p. 1166-1171. Figure 1

Progress on ultraviolet organic electroluminescence and lasing

This review focusses on UV organic light-emitting diodes and organic solid-state lasers, and covers their recent development from organic chromophores and device configuration to practical applications.

A contrivance of 277 nm DUV LD with B0.313Ga0.687N/B0.40Ga0.60N QWs and AlxGa1–xN heterojunction grown on AlN substrate

In this paper, an ultraviolet C-band laser diode lasing at 277 nm composed of B0.313Ga0.687N/B0.40Ga0.60N QW/QB heterostructure on Mg and Si-doped AlxGa1–xN layers was designed, as well as a lowest reported substitutional accepter and donor concentration up to NA = 5.0 × 1017 cm–3 and ND = 9.0 × 1016 cm–3 for deep ultraviolet lasing was achieved. The structure was assumed to be grown over bulk AlN substrate and operate under a continuous wave at room temperature. Although there is an emphasizing of the suitability for using boron nitride wide band gap in the deep ultraviolet region, there is still a shortage of investigation about the ternary BGaN in aluminum-rich AlGaN alloys. Based on the simulation, an average local gain in quantum wells of 1946 cm–1, the maximum emitted power of 2.4 W, the threshold current of 500 mA, a slope efficiency of 1.91 W/A as well as an average DC resistance for the V–I curve of (0.336 Ω) had been observed. Along with an investigation regarding different EBL, designs were included with tapered and inverse tapered structure. Therefore, it had been found a good agreement with the published results for tapered EBL design, with an overweighting for a proposed inverse tapered EBL design.

Blue‐Pumped Deep Ultraviolet Lasing from Lanthanide‐Doped Lu6O5F8 Upconversion Nanocrystals

AbstractDeep ultraviolet (UV) lasers are essential for enormous use ranging from medical and life science to environmental and industrial applications. Herein, a class of blue‐pumped microcavity lasers operating in the deep UV region is demonstrated by using Lu6O5F8:Pr/Gd@Lu6O5F8 upconversion nanocrystals as the gain medium. A hot‐injection synthesis is developed for tuning dimensions of the Lu6O5F8 nanocrystals. By synthesizing large‐sized nanocrystals and using inert shell coating, deep ultraviolet emission at 315 nm by blue excitation at 447 nm is realized for the first time in colloidal solutions. Mechanistic investigations suggest that the upconversion stems from sequential absorption of two blue photons by Pr3+ ions followed by energy transfer to Gd3+ emitters. By virtue of their small particle size and high dispersibility, the upconversion nanocrystals are readily incorporated into silica resin microcavities with a bottle‐like geometry. Lasing emissions of tunable optical characteristics are achieved from the microcavities through the formation of whispering gallery modes. These findings pave the way for constructing compact lasers operating in the deep UV regime by pumping with sophisticated long‐wavelength lasers.

Random Lasing in ZnO Nanopowders Based on Multiphoton Absorption for Ultrafast Upconversion Application

This study reports ultraviolet picosecond random lasing (RL) based on multiphoton absorption in zinc oxide (ZnO) nanopowders with a mean size of ∼100 nm under femtosecond optical excitation. Upconversion random lasing is achieved with an excitation wavelength increasing from 600 to 1800 nm, corresponding to a five-photon excitation. The RL threshold has a slight positive relationship with excitation wavelength, except for a significant increase with four-photon excitation at 1200–1300 nm, demonstrating promising upconversion lasing properties of ZnO nanopowders. A remarkably lower RL threshold is observed at long excitation wavelengths ranging from 1500 to 1800 nm than that for four-photon pumping (1200–1300 nm) processes. Defect states in ZnO are suggested to be the reason that results in the excitation wavelength dependence of random lasing. Transient RL characteristics are investigated using time-resolved photoluminescence measurements, with the RL pulse delay time and pulse width observed to decrease ...

Temperature and excitation dependent ultraviolet lasing in vertically oriented ZnO nanowires

Vertically oriented ZnO nanowires grown by a catalyst free chemical vapor deposition technique on c-plane of sapphire substrate show band-edge related excitonic lasing features. High resolution X-ray, scanning electron microscopy and photoluminescence analyses are collectively employed to understand the lasing behaviour from the nanowires. The nanowires show high degree of crystallinity, strong c-axis preferred orientation as well as relative in-plane alignment and sixfold hexagonal symmetry of the wurtzite phase. The nanowires are optically pumped using a 325 nm laser source and the emission characteristics are studied in detail by varying temperature and excitation intensity. The nanowires show the onset of lasing characteristics below 150 K which become prominent at 3.4 K with sharp multimodal emission characteristics. The threshold pump power for the onset of lasing is found to be of 14.5 mW at 3.4 K. Even though with increasing optical pumping, the lasing features from the nanowires lost their prominence being suppressed by spontaneous excitonic and defect transitions above 150 K.