Quasi-whispering Gallery Modes Research Articles

Ultrafast intermode parametric scattering dynamics in room-temperature polariton condensates

Parametric scattering dynamics are general and of crucial importance for cavity exciton polaritons. Here, parametric scattering process driven by exciton polariton condensates has been revealed in a 1D ZnO microcavity between the whispering-gallery mode and quasiwhispering-gallery mode. When the occupation of the produced polariton condensate is dense enough, polariton condensates formed on quasiwhispering-gallery mode can be scattered towards the ground state of the adjacent whispering-gallery modes at higher and lower energies. By using the femtosecond angle-resolved spectroscopic imaging technique, the ultrafast dynamics of this intermode polariton parametric scattering have been explicitly observed. The scattering towards a higher mode occurs faster than that to a lower-energy mode by less than a picosecond. The revealed dynamics can not only expand the present investigations on polariton parametric scattering, but also promote the potential applications in, e.g., quantum information processing.

Optical modes in the perovskite CsPbX3 semicircular and circular microcavity

In this paper, we used the finite element method to numerically study the possible optical resonance modes in the all-inorganic metal halide perovskite (CsPbX3, [Formula: see text], Br, I) semicircular and circular microcavities. For the semicircular microcavity, the quasi-three-period mode has the highest quality factor among quasi-whispering gallery mode (WGM), two-period mode and four-period mode. The quality factors of the four resonance modes all increase linearly for the larger cavity size. In addition, the circular perovskite microcavities present the WGM patterns with extremely high-quality factors, which indicates that the circular perovskite microcavity has the potential application in the optical microcavity or laser device.

Two-round quasi-whispering gallery mode exciton polaritons with large Rabi splitting in a GaN microrod.

We investigate the exciton polaritons and their corresponding optical modes in a hexagonal GaN microrod at room temperature. The dispersion curves are measured by the angle-resolved micro-photoluminescence spectrometer, and two types of exciton polaritons are identified with the help of the finite-difference time-domain simulation. By changing the pump position, the photon part of the exciton polaritons is found to switch between the quasi-whispering gallery modes and the two-round quasi-whispering gallery modes. The exciton polaritons formed by the latter are observed and distinguished for the first time, with a giant Rabi splitting as large as 2Ω = 230.3 meV.

Application of ZnO Nanorods Based Whispering Gallery Mode Resonator in Optical Immunosensors

In this research a whispering gallery mode (WGM) resonator based on vertically oriented ZnO nanorods, which were formed on silicon surface (silicon/ZnO-NRs), has been applied in the design of optical immunosensor that was dedicated for the determination of grapevine virus A-type (GVA) proteins. Vertically oriented ZnO-NRs were grown on silicon substrates by atmospheric pressure metal organic chemical vapor deposition (APMOCVD) and the silicon/ZnO-NRs structures formed were characterized by structural and optical methods. Optical characterization demonstrates that silicon/ZnO-NRs-based structures can act as ‘whispering gallery mode’ (WGM) resonator where quasi-whispering gallery modes (quasi-WGMs) are generated. These quasi-WGMs were experimentally observed in the visible and infrared ranges of the photoluminescence spectra. In order to design an immuno-sensing system the anti-GVA antibodies were immobilized on the surface of silicon/ZnO-NRs and in this way silicon/ZnO-NRs/anti-GVA structure was formed. The immobilization of anti-GVA antibodies and then the interaction of silicon/ZnO-NRs/anti-GVA structure with GVA proteins (GVA-antigens) resulted in an opposite shifts of the WGMs peaks in the visible range of the photoluminescence spectra observed as a defect-related photoluminescence emission of ZnO-NRs. Here designed silicon/ZnO-NRs/anti-GVA immuno-sensing structure demonstrates the sensitivity towards GVA-antigens in the concentration range of 1-200 ng/ml. Bioanalytical applicability of the silicon/ZnO-NRs-based structures in the WGMs registration mode is discussed.

Periodic Radiation Patterns and Circulating Direction of Lasing Light by Quasi Whispering Gallery Mode in Hexagonal GaN Microdisk

We have experimentally elucidated the periodic radiation patterns and circulating direction of the lasing light generated by the quasi-whispering-gallery mode (QWGM) in a hexagonal GaN microdisk. The radiated lasing light from the microdisk is highly directional, with the high intensities of the obtained radiated lasing light having a periodic spacing of 120° in the planar direction. The results show that the QWGM-generated lasing light circulates in a single direction in the microdisk, namely, either clockwise or counter-clockwise.

Modal domains and selectivity in large square lasers

Modes in square resonators have C4v symmetry. A special set of modes in these resonators have odd parities and behave like whispering gallery modes. These quasi-whispering gallery modes have high quality factors and exhibit interesting features. In particular, higher order quasi-whispering gallery modes present nodes that seem to be grouped into smaller domains. We show that the removal of one of these domains does not significantly affect a particular mode but can lead to significant increment in the radiation losses of other modes. This mode selectivity process can eventually be used to develop quasi single-mode lasers.

Polariton lasing of quasi-whispering gallery modes in a ZnO microwire

We report the experimental observation of the quasi-whispering-gallery mode (quasi-WGM) polariton lasing in a one dimensional ZnO microrod cavity at room temperature. Under nonresonant optical pulsed excitation, we measure the pumping power dependence of the emission intensity and the blueshift of the polariton modes, and a fairly low lasing threshold for the quasi-WG mode is determined. We also measure the lasing threshold versus the photon-exciton detuning by dispersion simulations. These experiment results show that both of the WGMs with higher Q factors and the quasi-WGMs with lower Q factors can lase when the detuning between the optical modes and the exciton energies is optimum.

Quasi-Whispering Gallery Mode Lasing Action in an Asymmetric Hexagonal GaN Microdisk

The optical properties of an asymmetric hexagonal GaN microdisk, fabricated via crystal growth by radio-frequency plasma-assisted molecular beam epitaxy (rf-MBE), were investigated by experimental and theoretical methods to clarify the contribution of the light confinement modes of quasi-whispering gallery modes (QWGMs). Under the optically pumped condition, a lasing action was observed from the asymmetric GaN microdisk, indicating that there is a resonant scheme of QWGMs in such a microcavity of a GaN microdisk. In addition, the analysis of the light response of hexagonal GaN microdisk models by a three-dimensional finite difference time-domain method (3D-FDTD) indicates that the QWGMs preferentially contribute to a lasing action even in a microcavity with a regular hexagonal configuration with side lengths of 1 to 2 µm. The results of the experiment and the numerical analysis strongly indicate that it is important to take not only the WGM but also the QWGMs into account to clarify the optical responses of resonant modes in a hexagonal microdisk configuration.

Optically Pumped Lasing Action with Unusual Wavelength of Approximately 390 nm in Hexagonal GaN Microdisks Fabricated by Radio-Frequency Plasma-Assisted Molecular Beam Epitaxy

Hexagonal GaN microdisks exhibiting lasing action with unusual wavelengths of approximately 390 nm under an optically pumped condition have been investigated. The lasing action was caused by the resonant modes of the whispering gallery mode and/or quasi-whispering gallery mode in the hexagonal microdisks. A cross-sectional transmission electron microscopy observation indicated that multiple crystalline boundaries, which are formed by stacking faults, were included in the specific GaN microdisks exhibiting such an unusual lasing action. The origin of the optical gain was discussed, based on the modification of the crystal structure associated with the stacking faults.

Quasi-whispering gallery modes in ZnO microtowers

We show that the laser spectra of ZnO films composed of particles that look like microtowers represent two bands with practically constant spectral distances between their peaks. By numerical analysis, we show that these two bands are due to whispering gallery modes (WGM), and one of these bands corresponds to the quasi-whispering gallery mode. Thus, we obtain here the first clear demonstration of the existence of quasi-WGMs, and show, in addition, that the width of the bands is caused by random spread of sizes of the ZnO particles in the lasing part.

Lasing Action on Whispering Gallery Mode of Self-Organized GaN Hexagonal Microdisk Crystal Fabricated by RF-Plasma-Assisted Molecular Beam Epitaxy

GaN hexagonal microdisks were fabricated on Ti-mask (4 nm in thickness) nanohole-patterned m-plane (10-10) GaN substrates by radio frequency-plasma-assisted molecular beam epitaxy. The GaN hexagonal microdisks, which were supported by ~300 nm-diameter GaN nanocolumns, consisted of thin hexagonal c-plane plates with a hexagon side length of 1-2 m and a typical thickness of 200 nm. The GaN hexagonal microdisks were optically pumped under a high optical excitation density with a 355-nm-wavelength Nd:YAG laser, and ultraviolet lasing actions on the quasi-whispering gallery mode (WGM) were observed at room temperature. The lasing wavelength was 372 nm and the threshold excitation density was approximately 250 kW/cm2. The quasi-WGM resonance was numerically analyzed using a simple plane wave model and a 2-D-flnite difference time domain method, the behaviors of the WGM and quasi WGM were analyzed, revealing that the quasi-WGM has a higher Q-factor, thus, it was clarified that the laser actions of the GaN hexagonal microdisks occurred on the quasi-WGM resonance.

Quasi-whispering gallery modes of exciton-polaritons in a ZnO microrod

We report the photoluminescence (PL) investigations of quasi-whispering gallery mode (quasi-WGM) polaritons in a ZnO microrod at room temperature. By using the confocal micro-PL spectroscopic technique, we observe the clear optical quasi-WGMs. These quasi-WGMs appeared in the ultraviolet (UV) emission region where the cavity modes strongly couple with excitons and form polaritons. The quasi-WGMs polaritons can be well described by the plane wave interference and the coupling oscillator model.