Cavity Quality Factor Research Articles

Neon lasing (λ = 540.1 nm) in a dense optical cavity pumped by a pulsed inductive cylindrical discharge

The experimental results of the lasing characteristics dependence of the inductive neon laser (λ = 540.1 nm) on the optical cavity quality factor are presented. In the described experiments, the laser was operated in the amplified spontaneous emission mode. A frontal-substrate resonator (made according to the type of an open Fabry–Perot interferometer) was used, as well as a dense resonator with a reflection coefficient of the front mirror of 82%. Replacing the front substrate with an output mirror resulted in an increase in the lasing energy and optical pulse duration from 8.5 μJ to 41 μJ and from 10.0 ± 0.1 ns to 14.8 ± 0.1 ns, respectively. It is shown that the use of a dense resonator allows us to change the shape of the laser beam in the far field from annular to circular and to obtain intensity distribution close to uniform.

Flexible colloidal quantum dot lasers enabled by self-assembly

Colloidal quantum dot (CQD) lasers show promising applications in flexible optoelectronic devices, due to their tunable emission wavelength, narrow spectrum bandwidth and high power intensity. However, fabricating a flexible CQD laser is challenging because of the difficulties in fabricating optical cavities on flexible substrates using traditional microfabrication technologies. Herein, we propose a one-step self-assembly approach to fabricate flexible CQD supraparticle lasers. The whole assembly approach is processed in a liquid environment without surfactants, and the formed spherical CQD supraparticles are featured with smooth surfaces, serving as high-quality-factor whispering-gallery mode cavities to support laser oscillation. A low lasing threshold of 54 µJ/cm2 is observed while exciting a CQD supraparticle with pulsed femtosecond lasers. The calculated cavity quality factor of 963 for CQD supraparticle lasers is twofold larger than that of CQD lasers assembled with surfactants. Moreover, the CQD supraparticles can serve as free-standing lasers, which allows them to be deposited on flexible substrates such as paper and cloth. Furthermore, our CQD lasers show high stability, after being continuously photoexcited above the threshold for 400 min, their lasing intensity remains at 85.7% of the initial value. As bright, free-standing and long-term stable light sources, the assembled CQD lasers proposed in this work show potential applications in wearable devices and medical diagnosis.

Cooling of mechanical resonator in a hybrid intracavity squeezing optomechanical system.

A hybrid intracavity squeezing optomechanical cooling system, in which an auxiliary cavity couples to an optomechanical cavity with a nonlinear medium inside it, is proposed to realize the ground state cooling of the mechanical resonator in the highly unresolved sideband regime. We demonstrate that the quantum backaction heating can be suppressed perfectly by the intracavity squeezing, and the cooling process can be further promoted by adjusting the tunnel coupling between the coupled cavities. The scheme has good performance in resisting the environmental thermal noise and better tolerance for the auxiliary cavity quality factor and provides the possibility for the quantum manipulation of the mechanical resonator with large mass and low frequency.

Design and Testing of an Ultralow Q CBPM

High repetition rates are considered essential to meet the anticipated new demands of the free-electron laser (FEL) facility. To offer precise beam handling for high-repetition-rate FEL facilities operating in a multi-bunch mode, an ultralow quality factor ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> ) cavity beam position monitor (CBPM) is studied to distinguish nanosecond spaced electron bunches, enabling the independent position measurement of each bunch and reducing the contamination between bunch signals. The low- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\!Q$ </tex-math></inline-formula> CBPM consists of two cavities: a reference cavity and a position cavity. The reference cavity is mainly used for bunch charge normalization, and the position cavity can measure the beam position vertically and horizontally. This article studies the method to attain a low loaded quality factor for the CBPM and presents the design and preliminary test results. The test results show that both the loaded quality factors of the reference cavity and the position cavity can reach 13, which enables bunch position monitoring for those high repetition rate FEL facilities.

Electrically driven single microwire-based single-mode microlaser

Engineering the lasing-mode oscillations effectively within a laser cavity is a relatively updated attentive study and perplexing issue in the field of laser physics and applications. Herein, we report a realization of electrically driven single-mode microlaser, which is composed of gallium incorporated zinc oxide microwire (ZnO:Ga MW) with platinum nanoparticles (PtNPs, d ~ 130 nm) covering, a magnesium oxide (MgO) nanofilm, a Pt nanofilm, and a p-type GaN substrate. The laser cavity modes could resonate following the whispering-gallery mode (WGM) among the six side surfaces by total internal reflection, and the single-mode lasing wavelength is centered at 390.5 nm with a linewidth of about 0.18 nm. The cavity quality factor Q is evaluated to about 2169. In the laser structure, the usage of Pt and MgO buffer layers can be utilized to engineer the band alignment of ZnO:Ga/GaN heterojunction, optimize the p-n junction quality and increase the current injection. Thus, the well-designed device structure can seamlessly unite the electron-hole recombination region, the gain medium, and optical microresonator into the PtNPs@ZnO:Ga wire perfectly. Such a single MW microlaser is essentially single-mode regardless of the gain spectral bandwidth. To study the single-mode operation, PtNPs working as superabsorber can engineering the multimode lasing actions of ZnO:Ga MWs even if their dimensions are typically much larger than that of lasing wavelength. Our findings can provide a straightforward and effective scheme to develop single-mode microlaser devices based on one-dimensional wire semiconductors.

Optomagnonically tunable whispering gallery cavity laser wavelength conversion

We achieve laser wavelength conversion in an optomagnonical whispering gallery cavity by adjusting the strength of the applied static magnetic field. Numerical simulations are carried out on a yttrium iron garnet (YIG) sphere under different cavity quality factors or coupling strength. It is found that a high cavity quality factor will not always mean a high cavity excitation field for Gaussian lasers with finite linewidth. On state of the art, the high cavity quality factor will always mean the higher lightwave conversion rate. In addition, we also find that increasing the mode coupling strength is beneficial to the conversion of the laser. Our study provides new insights into generation of highly precise tunable coherent light.

Spontaneous emission enhancement based on thin-film chalcogenide/fluoride one dimensional photonic crystal

We report the fabrication of a one-dimensional photonic crystal microcavity via co-evaporation with electron beam/thermal evaporation process, which, to the best of our knowledge, is the first rare-earth doped one-dimensional photonic crystal based on chalcogenide/fluoride thin films. The microcavity was made of a half-wave dysprosium doped Ga2Se3 layer sandwiched between two embedded Ga2Se3/YF3 distributed Bragg reflectors. Near infrared transmittance spectra indicated that the stopband region from 1090 nm to 1515 nm was formed and a cavity resonance centered at 1342 nm. A cavity quality factor of 153 was achieved resulting in a 53-fold enhancement in spontaneous emission intensity. This photonic crystal microcavity configuration offers a new route to mid-wavelength and long-wavelength infrared fluorescence enhancement, which has attracted considerable interest for potential applications, such as fluorescence-based imaging and biomedical sensing.

Ac losses in field-cooled type I superconducting cavities

As superconductors are cooled below their critical temperature, stray magnetic flux can become trapped in regions that remain normal. The presence of trapped flux facilitates dissipation of ac current in a superconductor, leading to losses in superconducting elements of microwave devices. In type II superconductors, dissipation is well-understood in terms of the dynamics of vortices hosting a single flux quantum. In contrast, the ac response of type I superconductors with trapped flux has not received much attention. Building on Andreev’s early work (Andreev 1967 Sov. Phys. JETP 24 1019), here we show theoretically that the dominant dissipation mechanism is the absorption of the ac field at the exposed surfaces of the normal regions, while the deformation of the superconducting/normal interfaces is unimportant. We use the developed theory to estimate the degradation of the quality factors in field-cooled cavities, and we satisfactorily compare these theoretical estimates to the measured field dependence of the quality factors of two aluminum cavities. We also identify a regime in which the dissipated power depends weakly on the Ginzburg-Landau parameter; this makes it possible to apply our findings to cavities made of other materials, such as niobium.

Heat loads measurements at the XFEL cold linac

The European X-Ray Free Electron Laser (EuXFEL) at DESY is in operation since the beginning of 2017. The free electron laser is based on a superconducting linear accelerator that delivers electrons to the undulator section with beam energy up to 17.5 GeV. The linear accelerator consists of 96 cryomodules; each 12 m long module is an assembly of 8 superconducting cavities and one superconducting magnet. This paper focusses on the measurement of the static and dynamic heat loads of the cryomodules assembled in the linac. Heat loads are an important parameter to evaluate the efficiency of the refrigerator system, the quality of the cryomodule assembly and installation and the accelerating cavity performances, being the dynamic heat loads proportional to the cavity quality factor (Q0, the ratio of the stored energy to the dissipated energy). The paper describes at first the procedure to measure the static heat load without beam energy and the dynamic heat loads at different beam energy levels. The measurement results are then summarized and compared with the XFEL design values.

Analytical considerations for optimal axion haloscope design

Abstract The cavity haloscope provides a highly sensitive method to search for dark matter axions in the microwave regime. Experimental attempts to enhance the sensitivity have focused on improving major aspects, such as producing strong magnetic fields, increasing cavity quality factors, and achieving lowest possible noise temperatures. Minor details, however, also need to be carefully considered in realistic experimental designs. They are associated with non-uniform magnetic fields over the detection volume, noise propagation under attenuation and temperature gradients, and thermal disequilibrium in the cavity system. We take analytical approaches to these topics and offer optimal treatments for improved performance.

Ultrasensitive nanoscale optomechanical electrometer using photonic crystal cavities

Abstract High-precision detection of electric charge is critical for physical, chemical, and biological measurements. Nanophotonic optomechanical system confines the optical field at the nanoscale and enables a strong interaction between optical cavity and mechanical resonator. Its high optical quality factor cavity and strong optomechanical coupling are promising for precision sensing applications. Here an integrated optomechanical electrometer is proposed for the electric charge sensing using a zipper cavity with a suspended photonic crystal nanobeam (PCN) acting as a movable mechanical resonator. As the electrostatic force arising from the electric voltage to be measured interacts with the mechanical motion of the movable PCN and modulates its resonance through electrostatic stiffening effect, optomechanical coupling transduces the mechanical motion to the optical field with enhanced sensitivity. The resonance shift of the mechanical resonator can be monitored to detect the electric voltage with a sensitivity of 0.007 Hz / m V 2 $\mathrm{Hz}/\mathrm{m}{\mathrm{V}}^{2}$ . Moreover, the sensing performance can be further enhanced with the operation of the optomechanical electrometer in the self-sustained oscillation above threshold power. Owing to the narrow-linewidth of detector radio frequency (RF) spectrum with a large peak-to-noise floor ratio (up to 73.5 dB), the enhanced electrical sensitivity of 0.014 Hz / m V 2 $\mathrm{Hz}/\mathrm{m}{\mathrm{V}}^{2}$ is achieved with a high resolution of 1.37 m V 2 H z − 1 / 2 $1.37\,\mathrm{m}{\mathrm{V}}^{2}\mathrm{H}{\mathrm{z}}^{-1/2}$ . A theoretical minimal detectable electrostatic charge is calculated as 1.33 × 10 − 2 eH z − 1 / 2 $1.33{\times}{10}^{-2}\,\mathrm{eH}{\mathrm{z}}^{-1/2}$ by converting the measured electric voltage versus RF shift to an approximatively linear relationship. This on-chip optomechanical electrometry scheme provides a powerful solution to the ultrasensitive determination of charged nanoparticles in biological and chemical applications.

EXACT CALCULATIONS FOR ONE PHOTON MICROMASER WITH COHERENT INPUTS I

We report a numerical simulation of the action of the one 85 Rb atom micromaser which shows that the micromaser field evolves towards a steady state equilibrium when the condition that Tp t int satisfies. In this steady state regime the cavity field reaches a steady state after a sufficient number of atoms have passed through the cavity. The cavity temperature T and the cavity quality factor Q can produce a quantitive change when one of them or the two are changed but they are not responsible for the qualitative changes in the micromaser field. Evidently the only responsible parameter for these qualitative changes is the repetition time T p namely if T p t int then the micromaser field evolution is towards a steady state equilibrium. In contrast when T p reduced to the order of t int then the micromaser field evolution is controlled by the trapping state dynamics – no steady state is apparent in this case. The first going-up trapping state at n=3 plays a significant role in the early dynamics of the micromaser field. Moreover the state of the field ultimately evolves towards a mixed state rather than a pure state.

Solution-processed whispering-gallery-mode microsphere lasers based on colloidal CsPbBr3 perovskite nanocrystals

Perovskite nanocrystals (NCs) have emerged as attractive gain materials for solution-processed microlasers. Despite the recent surge of reports in this field, it is still challenging to develop low-cost perovskite NC-based microlasers with high performance. Herein, we demonstrate low-threshold, spectrally tunable lasing from ensembles of CsPbBr3 NCs deposited on silica microspheres. Multiple whispering-gallery-mode lasing is achieved from individual NC/microspheres with a low threshold of ∼3.1 μJ cm−2 and cavity quality factor of ∼1193. Through time-resolved photoluminescence measurements, electron–hole plasma recombination is elucidated as the lasing mechanism. By tuning the microsphere diameter, the desirable single-mode lasing is successfully achieved. Remarkably, the CsPbBr3 NCs display durable room-temperature lasing under ∼107 shots of pulsed laser excitation, substantially exceeding the stability of conventional colloidal NCs. These CsPbBr3 NC-based microlasers can be potentially useful in photonic applications.

Extended bound states in the continuum in a one-dimensional grating implemented on a distributed Bragg reflector

Abstract Bound states in the continuum (BICs) are observed in optical cavities composed of a high refractive index periodic structure embedded in significantly lower refractive index surroundings, enabling vertical confinement of the grating modes. Here, we propose a vertically nonsymmetric configuration, implemented on a high refractive index bulk substrate with a one-dimensional grating positioned on a distributed Bragg reflector (DBR). In this configuration, the grating modes are leaky, which could prohibit the creation of a BIC if the grating was implemented on uniform substrate. However, the judiciously designed DBR on which the grating is implemented reflects nonzero diffraction orders induced by the grating. We found that the laterally antisymmetric optical modes located at the center of the Brillouin zone of this structure create BICs that are robust against changes in the grating parameters, as long as the DBR reflects the diffraction orders. The configuration enables a high degree of design freedom, facilitating the realization of very high quality factor cavities in conventional all-semiconductor technology.

Integrated Whispering-Gallery-Mode Resonator for Solid-State Coherent Quantum Photonics.

Tailored photonics cavities enhance light-matter interactions, ultimately enabling a fully coherent quantum interface. Here, we report an integrated microdisk cavity containing self-assembled quantum dots to coherently route photons between different access waveguides. We measure a Purcell factor of Fexp = 6.9 ± 0.9 for a cavity quality factor of about 10,000, allowing us to observe clear signatures of coherent scattering of photons by the quantum dots. We show how this integrated system can coherently reroute photons between the drop and bus ports and how this routing is controlled by detuning the quantum dot and resonator or through the strength of the excitation beam, where a critical photon number less than one photon per lifetime is required. We discuss the strengths and limitations of this approach, focusing on how the coherent scattering and single-photon nonlinearity can be used to increase the efficiency of quantum devices such as routers or Bell-state analyzers.

Light-Harvesting in Biophotonic Optofluidic Microcavities via Whispering-Gallery Modes.

Phycobiliproteins are a class of light-harvesting fluorescent proteins existing in cyanobacteria and microalgae, which harvest light and convert it into electricity. Owing to recent demands on environmental-friendly and renewable apparatuses, phycobiliproteins have attracted substantial interest in bioenergy and sustainable devices. However, converting energy from biological materials remains challenging to date. Herein, we report a novel scheme to enhance biological light-harvesting through light-matter interactions at the biointerface of whispering-gallery modes (WGMs), where phycobiliproteins were employed as the active gain material. By exploiting microdroplets as a carrier for light-harvesting biomaterials, strong local electric field enhancement and photon confinement at the cavity interface resulted in significantly enhanced bio-photoelectricity. A threshold-like behavior was discovered in photocurrent enhancement and the WGM modulated fluorescence. Systematic studies of biologically produced photoelectricity and optical mode resonance were carried out to illustrate the impact of the cavity quality factor, structural geometry, and refractive indices. Finally, a biomimetic system was investigated by exploiting cascade energy transfer in phycobiliprotein assembly composed of three light-harvesting proteins. The key findings not only highlight the critical role of optical cavity in light-harvesting but also offer deep insights into light energy coupling in biomaterials.

Ultrashort Pulse Generation in Nanolasers by Means of Lorenz–Haken Instabilities

AbstractNearly half a century ago, the German physicist Hermann Haken proved that the laser dynamics could be described, under certain conditions, by the Lorenz equations, the paradigm of deterministic chaos. Unfortunately, its experimental realization has remained elusive for conventional laser materials and cavities mostly due to the extreme pumping conditions and the low cavity quality factors (“bad‐cavity condition”) required to achieve Lorenz–Haken (L‐H) self‐pulsing dynamics upon continuous wave excitation. In this paper, it is theoretically proved that dielectric and plasmonic nanolasers, that can naturally fulfill the bad‐cavity condition, may overcome the limitations of macroscopic cavities and make the observation of L‐H instabilities in visible‐IR solid‐state materials become a reality. Remarkably, the adequate choice of active material and cavity design enables the generation of trains of ultrashort pulses in the sub‐ps regime and with MHz–GHz repetition rates without the need of resorting to neither mode‐locking nor Q‐switching techniques. Thus, the results reported in this manuscript unveil a new paradigm in the generation of ultrashort pulses at the nanoscale.

Broadband Coupling of Fast Electrons to High-Q Whispering-Gallery Mode Resonators

Transmission electron microscopy is an excellent experimental tool to study the interaction of free electrons with nanoscale light fields. However, up to now, applying electron microscopy to quantum optical investigations was hampered by the lack of experimental platforms which allow a strong coupling between fast electrons and high-quality resonators. Here, as a first step, we demonstrate the broad-band excitation of optical whispering-gallery modes in silica microresonators by fast electrons. In the emitted coherent cathodoluminescence spectrum, a comb of equidistant peaks is observed, resulting in cavity quality factors larger than 700. These results enable the study of quantum optical phenomena in electron microscopy with potential applications in quantum electron-light metrology.

Resonance modes in moiré photonic patterns for twistoptics

Twistronics has been studied for manipulating electronic properties through a twist angle in the formed moiré superlattices of two dimensional layer materials. In this paper, we study twistoptics for manipulating optical properties in twisted moiré photonic patterns without physical rotations. We describe a theoretic approach for the formation of single-layer twisted photonic pattern in square and triangular lattices through an interference of two sets of laser beams arranged in two cone geometries. The moiré period and the size of unit super-cell of moiré patterns are related to the twist angle that is calculated from the wavevector ratio of laser beams. The bright and dark regions in moiré photonic pattern in triangular lattices are reversible. We simulate E-field intensities and their cavity quality factors for resonance modes in moiré photonic pattern in square lattices. Due to the bandgap dislocation between the bright and dark regions, the resonance modes with very high quality-factors appears near bandgap edges for the moiré photonic pattern with a twist angle of 9.5 degrees. At the low frequency range, the resonance modes can be explained as Mie resonances. The cavity quality factor decreases for resonance modes when the twist angle is increased to 22.6 degrees.

Micro-mechanical assembly and characterization of high-quality Fabry–Pérot microcavities for the integration of two-dimensional materials

Integrating monolayers of two-dimensional semiconductors into optical microcavities is challenging because of the very few available approaches to coat the monolayers with dielectric materials without damaging them. Some strategies have been developed, but they either rely on complicated experimental settings and expensive technologies or limit the achievable cavity quality factors. Thus, high quality Fabry–Pérot microcavities are not widely available to the community focusing on light-matter coupling in atomically thin materials. Here, we detail a recently developed technique to micro-mechanically assemble Fabry–Pérot microcavities. Our approach promotes strong coupling conditions with excitons in atomically thin materials, it does not rely on difficult or expensive technologies, it is reproducible, and it yields microcavities with quality factors approaching 4000. It is ideally suitable for engineering coupled monolayer-cavity systems of advanced complexity in small-scale laboratories.