Discover the most talked about and latest scientific content & concepts.

Concept: Q factor


The newly proposed in-plane resonant nano-electro-mechanical (IP R-NEM) sensor, that includes a doubly clamped suspended beam and two side electrodes, achieved a mass sensitivity of less than zepto g/Hz based on analytical and numerical analyses. The high frequency characterization and numerical/analytical studies of the fabricated sensor show that the high vacuum measurement environment will ease the resonance detection using the capacitance detection technique if only the thermoelsatic damping plays a dominant role for the total quality factor of the sensor. The usage of the intrinsic junction-less field-effect-transistor (JL FET) for the resonance detection of the sensor provides a more practical detection method for this sensor. As the second proposed sensor, the introduction of the monolithically integrated in-plane MOSFET with the suspended beam provides another solution for the ease of resonance frequency detection with similar operation to the junction-less transistor in the IP R-NEM sensor. The challenging fabrication technology for the in-plane resonant suspended gate field-effect-transistor (IP RSG-FET) sensor results in some post processing and simulation steps to fully explore and improve the direct current (DC) characteristics of the sensor for the consequent high frequency measurement. The results of modeling and characterization in this research provide a realistic guideline for these potential ultra-sensitive NEM sensors.

Concepts: Transistor, Resonance, Harmonic oscillator, Optical cavity, Electronics terms, Damping, RLC circuit, Q factor


High-Q guided resonance modes in two-dimensional photonic crystals, enable high field intensity in small volumes that can be exploited to realize high performance sensors. We show through simulations and experiments how the Q-factor of guided resonance modes varies with the size of the photonic crystal, and that this variation is due to loss caused by scattering of in-plane propagating modes at the lattice boundary and coupling of incident light to fully guided modes that exist in the homogeneous slab outside the lattice boundary. A photonic crystal with reflecting boundaries, realized by Bragg mirrors with a band gap for in-plane propagating modes, has been designed to suppress these edge effects. The new design represents a way around the fundamental limitation on Q-factors for guided resonances in finite photonic crystals. Results are presented for both simulated and fabricated structures.

Concepts: Crystal, Optics, Resonance, Colloidal crystal, Band gap, Photonic crystal, Optical cavity, Q factor


The piezoelectric lateral-electric-field-excited resonator based on an X-cut lithium niobate plate has been investigated. Two rectangular electrodes were applied on one side of the plate so that the lateral electric field components were parallel to the crystallographic Y-axis and excited the longitudinal wave in the gap between the electrodes. The region around the electrodes was covered with a special absorbing varnish to suppress the spurious oscillations. The effect of the absorbing coating width on the resonant frequency and Q-factor of the lateral field-excited resonator was studied in detail with the series and parallel resonances for different width of the gap between the electrodes. As a result, we found experimentally the parameter regions of pure resonances and the boundaries of value variation for resonance frequency, Q-factor, and effective electromechanical coupling coefficient.

Concepts: Resonator, Wave, Resonance, Harmonic oscillator, Acoustic resonance, Standing wave, Optical cavity, Q factor


Quartz-enhanced photoacoustic spectroscopy (QEPAS) is a sensitive gas detection technique which requires frequent calibration and has a long response time. Here we report beat frequency (BF) QEPAS that can be used for ultra-sensitive calibration-free trace-gas detection and fast spectral scan applications. The resonance frequency and Q-factor of the quartz tuning fork (QTF) as well as the trace-gas concentration can be obtained simultaneously by detecting the beat frequency signal generated when the transient response signal of the QTF is demodulated at its non-resonance frequency. Hence, BF-QEPAS avoids a calibration process and permits continuous monitoring of a targeted trace gas. Three semiconductor lasers were selected as the excitation source to verify the performance of the BF-QEPAS technique. The BF-QEPAS method is capable of measuring lower trace-gas concentration levels with shorter averaging times as compared to conventional PAS and QEPAS techniques and determines the electrical QTF parameters precisely.

Concepts: Resonator, Sound, Pitch, Resonance, Beat, Infrared, Musical tuning, Q factor


Ultrahigh-quality (Q) factor microresonators have a lot of applications in the photonics domain ranging from low-threshold nonlinear optics to integrated optical sensors. Glass-based whispering gallery mode (WGM) microresonators are easy to produce by melting techniques, however they suffer from surface contamination which limits their long-term quality factor to a few 10(8). Here we show that an optical gain provided by erbium ions can compensate for residual losses. Moreover it is possible to control the coupling regime of an ultrahigh Q-factor three port microresonator from undercoupling to spectral selective amplification by changing the pumping rate. The optical characterization method is based on frequency-swept cavity-ring-down-spectroscopy. This method allows the transmission and dispersive properties of perfectly transparent microresonators and intrinsic finesses up to 4.0 × 10(7) to be measured. Finally we characterize a critically coupled fluoride glass WGM microresonator with a diameter of 220 μm and a loaded Q-factor of 5.3 × 10(9) is demonstrated.

Concepts: Optics, Optical fiber, Laser, Spectrum, Sensor, Nonlinear optics, Photonics, Q factor


A 10-mm cavity length magnetooptically Q-switched Nd:GdVO4 laser was demonstrated using a single-crystalline ferrimagnetic rare-earth iron garnet film. To design the Q-switching system, the magnetic, optical, and magnetooptical properties of the garnet film were measured. The diode pumped solid-state laser cavity was constructed using a 190-μm-thick garnet film with 58% transmittance. The garnet film had maze-shaped magnetic domains, and the domain walls disappeared when a field of over 200 Oe was applied. Therefore, the polarization state of the transmitted light was modified by modulating the magnetization, and a Q-switched pulse output with a pulse width of 5 ns and peak power of 255 W was achieved in the 10-mm-long cavity. The physical limitation of the pulse width was discussed with the calculated results.

Concepts: Magnetic field, Laser, Laser science, Q factor, Q-switching, Gain-switching


Nanostructured metals have received significant amount of attention in recent years due to their exciting plasmonic and photonic properties enabling strong-field localization, light concentration, and strong absorption and scattering at their resonance frequencies. Resonant plasmonic and metamaterial absorbers are of particular interest for applications in wide variety of technologies including photothermal therapy, thermophotovoltaics, heat assisted magnetic recording, hot-electron collection, and biosensing. However, it is rather challenging to realize ultra-narrow absorption bands using plasmonic materials due to large optical losses in metals that decrease the quality factor of optical resonators. Here, we theoretically and experimentally demonstrate an ultra-narrow band absorber (NBA) based on the surface lattice resonances (SLR) in periodic nanowire and nanoring arrays on optically thick, reflecting metallic films. In experiments, we observed ultra-narrow band resonant absorption peaks with a bandwidth of 12 nm and absorption amplitude exceeding 90% at visible frequencies. We demonstrate that the resonance absorption wavelength, amplitude of the absorption peak and the bandwidth can be controlled by tuning the periodicity and the thickness nanoring and nanowire arrays. Unlike conventional plasmonic absorbers utilizing common metal-insulator-metal (MIM) stacks, our narrowband absorber consists solely of metals therefore facilitating stronger optical interaction between the SLR of periodic nanostructures and the highly reflective film. Moreover, by introducing asymmetry to the nanoring/nanowire hybrid system, we observe the spectral evolution of resonance splitting enabled by strong coupling between two individual SLRs arising from nanoring and nanowire arrays. Designing such all-metallic nanostructure arrays is a promising route for achieving ultra-narrow band absorbers which can be used as absorption filters, narrow-band thermal emitters in thermophotovoltaics, and plasmonic biosensors.

Concepts: Optics, Resonator, Sound, Resonance, Standing wave, Optical cavity, RLC circuit, Q factor


For the study and application of graphene membranes, it is essential to have means to control their tension, resonance frequency and temperature. Here, we present an on-chip heater platform for local tuning of in-plane tension in graphene mechanical resonators. By Joule heating of a metallic suspension ring we show thermomechanical resonance frequency tuning in a graphene nanodrum, which is accompanied by an increase in its quality factor, which we attribute to an increase of the in-plane tension. The in-situ control of temperature, in-plane tension, resonance frequency and quality factor of suspended two-dimensional (2D) nanodrums makes this device a unique platform for investigating the origin of dissipation in these ultra-thin structures and can be of fundamental importance for studying the thermal properties of 2D materials. Moreover, by simultaneously controlling the heater and the backgate voltage, we can independently control the resonance frequency and quality factor, which is of great importance for applications in sensors and resonant mechanical filters.

Concepts: Resonator, Resonance, Electric heating, Acoustic resonance, Q factor


We design and numerically analyze a high-quality (Q)-factor, high modulation depth, multiple Fano resonance device based on periodical asymmetric paired bars in the near-infrared regime. There are four sharp Fano peaks arising from the interference between subradiant modes and the magnetic dipole resonance mode that can be easily tailored by adjusting different geometric parameters. The maximal Q-factor can exceed 105 in magnitude, and the modulation depths ΔT can reach nearly 100%. Combining the narrow resonance line-widths with strong near-field confinement, we demonstrate an optical refractive index sensor with a sensitivity of 370 nm/RIU and a figure of merit of 2846. This study may provide a further step in sensing, lasing, and nonlinear optics.

Concepts: Optics, Fundamental physics concepts, Refraction, Refractive index, Magnetic moment, Wave, Resonance, Q factor


The main parameters of magnetoelastic resonators in the detection of chemical (i.e., salts, gases, etc.) or biological (i.e., bacteria, phages, etc.) agents are the sensitivity S (or external agent change magnitude per Hz change in the resonance frequency) and the quality factor Q of the resonance. We present an extensive study on the experimental determination of the Q factor in such magnetoelastic resonant platforms, using three different strategies: (a) analyzing the real and imaginary components of the susceptibility at resonance; (b) numerical fitting of the modulus of the susceptibility; © using an exact mathematical expression for the real part of the susceptibility. Q values obtained by the three methods are analyzed and discussed, aiming to establish the most adequate one to accurately determine the quality factor of the magnetoelastic resonance.

Concepts: Resonance, Q factor