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[en] This paper reports measurement of random uncertainties in resonant characteristics (resonance frequency and quality factor) of micro electromechanical system (MEMS) resonators. We employ different methods to extract resonant characteristics of 4 different MEMS resonators which are either clamped-free or clamped-clamped beams. Each beam type operates either in air or in a partial vacuum, and therefore, different vacuum levels can be examined. Three different methods, including frequency sweep, impulse response, and thermal noise, are applied to each resonator type excited with electrostatic or piezo-crystal actuation. We make a thorough analysis and comparison for three different methods. Depending on device type and operating condition, there exists a better and recommended way to extract resonant characteristics of MEMS resonators. For example, the impulse response is best-suited for the quality factor measurement of a clamped-clamped beam operating in a vacuum. Our results show that the quality factor of MEMS resonators may be noticeably different and exhibit appreciable systematic and random uncertainties, and suggests a better way to extract the quality factor for a given situation.
[en] We experimentally investigate a stable freestanding whispering gallery mode (WGM) microlaser based on polymer microdisk formed by a ∼500 µ m diameter microfiber knot. A quality factor of about 14 700 and a relatively low lasing threshold with about 38.0 µ J/pulse are demonstrated in this structure. When a polymer microdisk is pumped by a 532 nm wavelength pulse laser, WGM lasing with a free spectral range (FSR) of 0.15 nm is observed from the polymer microdisk laser. This work provides a convenient and efficient approach to achieving a WGM microlaser based on a polymer microdisk and collecting the output light. (letter)
[en] The intrinsic damping for the acoustic vibrations of single gold nanorods excited by ultrafast laser has been studied through the atomistic simulations. It is shown that the intrinsic damping for the breathing mode is strongly sensitive to the nanorod sizes, which is very likely due to the different energy redistributions between the vibrational modes of nanorods and could play a non-negligible role in the broad distribution of the experimentally measured breathing-mode quality factors. In comparison, the intrinsic damping for the extensional vibration of gold nanorods appears much less influenced by the variations of nanorod dimensions. Moreover, we also find that the intrinsic mechanism is a significant source for the vibrational damping of gold nanorods, particularly for the breathing mode.
[en] Latest progress of ILC high gradient SRF cavity R and D at Jefferson Lab will be presented. 9 out of 10 real 9-cell cavities reached an accelerating gradient of more than 38 MV/m at a unloaded quality factor of more than 8 · 109. New understandings of quench limitation in 9-cell cavities are obtained through instrumented studies of cavities at cryogenic temperatures. Our data have shown that present limit reached in 9-cell cavities is predominantly due to localized defects, suggesting that the fundamental material limit of niobium is not yet reached in 9-cell cavities and further gradient improvement is still possible. Some examples of quench-causing defects will be given. Possible solutions to pushing toward the fundamental limit will be described.
[en] Novel nonstandard beams improve target dose conformity as compared to conventional methods, but also increase the complexity of dosimetry procedures. As recent studies demonstrated the invalidity of absorbed dose-to-water-based protocols to nonstandard beams, a new workgroup of the IAEA, endorsed by AAPM, published a formalism in preparation of a new protocol applicable to nonstandard beams. Although applying correction factors (kQ) to nonstandard beam measurements is recommended in the upcoming protocol, conceptual problems in regards to nonstandard conditions are yet to be resolved. Furthermore, accurate measurements of kQ factors for nonstandard beams need to be performed. In such measurements, accurate uncertainty estimation is also essential, especially in the case where corrections factors are found below the percent level. Evaluations of uncertainties are also important in order to evaluate limiting factors in nonstandard beam dosimetry or to perform sensitivity studies in the design of suitable nonstandard reference fields in the lead up to the new protocol. One goal of the study is to isolate the factors responsible for non-unity corrections in modulated beams, and provide solutions to improve fundamental concepts to be used for nonstandard beams reference dosimetry protocols. Another goal is to provide methods to estimate uncertainties accurately in the measurements of nonstandard beam kQ factors, and complement experimental procedures as well as insights on the uncertainty levels achievable in nonstandard beam dosimetry
[en] A compact, near-diffraction-limited laser diode end-pumped 2 µ m Tm:YAG Innoslab laser was demonstrated for the first time. A maximum output power of 36.4 W was achieved under the incident pump power of 184 W, corresponding to a slope efficiency of 23.4% with respect to the incident pump power. The beam quality factors M 2 were measured to be 1.44 in the stable direction and 1.23 in the unstable direction. (letter)
[en] PIC simulations is taken to get the oscillating process of the X band coaxial magnetron. Though the oscillating process would be affected by the spurious mode, the magnetron could work properly if the loss tangent of the attenuator exceeds 0.010. Otherwise the magnetron would be unable to work. So attenuators with loss tangent exceeding 0.010 are needed for coaxial magnetrons. The quality factors of the prime mode and N/2-1 mode in coaxial magnetrons with different attenuators are obtained. The results indicate that it would be effective to absorb N/2-1 mode if the loss tangent of attenuators exceeds 0.010, confirming the PIC results. (authors)
[en] We investigate the feasibility of both one photon and two photon fluorescence excitation using whispering gallery mode microresonators. We report the linear and non linear fluorescence real-time detection of labeled IgG covalently bonded to the surface of a silica whispering gallery mode resonator (WGMR). The immunoreagents have been immobilized onto the surface of the WGMR sensor after being activated with an epoxy silane and an orienting layer. The developed immunosensor presents great potential as a robust sensing device for fast and early detection of immunoreactions. We also investigate the potential of microbubbles as nonlinear enhancement platform. The dyes used in these studies are dylight800, tetramethyl rhodamine isothiocyanate, rhodamine 6G and fluorescein. All measurements were performed in a modified confocal microscope. - Highlights: • One photon fluorescence overlaps with the semiconductor pump laser gain bandwidth. • We report on the feasibility to excite two photon fluorescence in microbubble resonators. • Our functionalization process maintains a good quality factor of the microresonator.
[en] In this paper, we investigate energy harvesting from underwater base excitation of a piezoelectric composite beam. Four different geometric configurations are experimentally studied in which the beam is either fully submerged or is partially immersed, with an eighth, a quarter, or a half of its length vibrating underwater. The frequency and the amplitude of base excitation are systematically varied along with the shunting resistance to investigate the principles of piezoelectric energy harvesting from underwater vibrations. Results demonstrate that increasing the wet length produces a consistent reduction of the resonance frequency and the quality factor of underwater vibrations. On the other hand, the harvested power is found to generally decrease as the submersion length is increased. Experimental results are interpreted through a distributed piezohydroelastic model that accounts for added mass and nonlinear hydrodynamic damping effects. A reduced order modal model is further established to parametrically explore the system response across a variety of geometrical and physical parameters. (paper)
[en] This paper presents a new CMOS LC-VCO with a 2.95-3.65 GHz tuning range. The large tuning range is achieved by tuning curve compensation using a novel varactor configuration, which is mainly composed of four accumulation-mode MOS varactors (A-MOS) and two bias voltages. The proposed varactor has the advantages of optimizing quality factor and tuning range simultaneously, linearizing the effective capacitance and thus greatly reducing the amplitude-to-phase modulation (AM-PM) conversion. The circuit is validated by simulations and fabricated in a standard 0.18 μm 1P6M CMOS process. Measured phase noise is lower than -91 dBc at 100 kHz offset from a 3.15 GHz carrier while measured tuning range is 21.5% as the control voltage varies from 0 to 1.8 V. The VCO including buffers consumes 2.8 mA current from a 1.8 V supply.