EUROnu-WP6 2010 Report
This is a summary of the work done by the Working Package 6 (Physics) of the EU project "EUROnu" during the second year of activity of the project.
hep-ph↗
arXiv subjects
T. Li
Publications and source records attributed to T. Li.
Femtosecond Population Inversion and Stimulated Emission of Dense Dirac Fermions in Graphene
We show that strongly photoexcited graphene monolayers with 35fs pulses quasi-instantaneously build up a broadband, inverted Dirac fermion population. Optical gain emerges and directly manifests itself via a negative optical conductivity for the first 200fs, where stimulated emission completely compensates absorption loss in the graphene layer. Our experiment-theory comparison with two distinct electron and hole chemical potentials reproduce absorption saturation and gain at 40fs, revealing, particularly, the evolution of the transient state from a hot classical gas to a dense quantum fluid with increasing the photoexcitation.
cond-mat.mes-hall↗
Interim Design Report
The International Design Study for the Neutrino Factory (the IDS-NF) was established by the community at the ninth "International Workshop on Neutrino Factories, super-beams, and beta- beams" which was held in Okayama in August 2007. The IDS-NF mandate is to deliver the Reference Design Report (RDR) for the facility on the timescale of 2012/13. In addition, the mandate for the study [3] requires an Interim Design Report to be delivered midway through the project as a step on the way to the RDR. This document, the IDR, has two functions: it marks the point in the IDS-NF at which the emphasis turns to the engineering studies required to deliver the RDR and it documents baseline concepts for the accelerator complex, the neutrino detectors, and the instrumentation systems. The IDS-NF is, in essence, a site-independent study. Example sites, CERN, FNAL, and RAL, have been identified to allow site-specific issues to be addressed in the cost analysis that will be presented in the RDR. The choice of example sites should not be interpreted as implying a preferred choice of site for the facility.
hep-ex↗
Hertz-level Measurement of the 40Ca+ 4s 2S1/2-3d 2D5/2 Clock Transition Frequency With Respect to the SI Second through GPS
We report a frequency measurement of the clock transition of a single ^40Ca^+ ion trapped and laser cooled in a miniature ring Paul trap with 10^-15 level uncertainty. In the measurement, we used an optical frequency comb referenced to a Hydrogen maser, which was calibrated to the SI second through the Global Positioning System (GPS). Two rounds of measurements were taken in May and June 2011, respectively. The frequency was measured to be 411 042 129 776 393.0(1.6) Hz with a fractional uncertainty of 3.9{\times}10^-15 in a total averaging time of > 2{\times}10^6 s within 32 days.
physics.atom-ph↗
An Optical Fibre Pulse Rate Multiplier for Ultra-low Phase-noise Signal Generation
In this letter we report on an all optical-fibre approach to the synthesis of ultra-low noise microwave signals by photodetection of femtosecond laser pulses. We use a cascade of Mach-Zehnder fibre interferometers to realize stable and efficient repetition rate multiplication. This technique increases the signal level of the photodetected microwave signal by close to 18 dB, that in turn, allows us to demonstrate a phase noise level of 118 dBc/Hz at 1 Hz and -160 dBc/Hz at 10 MHz from 12 GHz signal. The noise floor of the fiber multiplier and photodetection system alone is around -164 dBc/Hz at the same offset frequency, which is very close to the fundamental shot noise floor
physics.optics↗
Plasmonic Airy Beam on Metal Surface
Optical Airy beam, as a novel non-diffracting and self-accelerating wave packet, has generated great enthusiasm since its first realization in 2007, owing to its unique physics and exciting applications. Here, we report a new form of this intriguing wave packet - plasmonic Airy beam, which is experimentally realized on a silver surface for the first time. By particular diffraction processes in a carefully designed nano-array structure, a novel planar Airy beam of surface plasmon polariton (SPP) is directly generated and a structural dependent phase tuning method is proposed to modulate the beam properties. This SPP Airy beam is regarded as a two-dimensional (2D) subwavelength counterpart of the 3D optical Airy beam in free space, allowing for on-chip photonic manipulations. Moreover, it possibly suggests a breakthrough in recognition of this unique wave packet in a polariton regime after its previous evolution from free particle to pure optical wave.
physics.optics↗
Amplitude to phase conversion of InGaAs pin photo-diodes for femtosecond lasers microwave signal generation
When a photo-diode is illuminated by a pulse train from a femtosecond laser, it generates microwaves components at the harmonics of the repetition rate within its bandwidth. The phase of these components (relative to the optical pulse train) is known to be dependent on the optical energy per pulse. We present an experimental study of this dependence in InGaAs pin photo-diodes illuminated with ultra-short pulses generated by an Erbium-doped fiber based femtosecond laser. The energy to phase dependence is measured over a large range of impinging pulse energies near and above saturation for two typical detectors, commonly used in optical frequency metrology with femtosecond laser based optical frequency combs. When scanning the optical pulse energy, the coefficient which relates phase variations to energy variations is found to alternate between positive and negative values, with many (for high harmonics of the repetition rate) vanishing points. By operating the system near one of these vanishing points, the typical amplitude noise level of commercial-core fiber-based femtosecond lasers is sufficiently low to generate state-of-the-art ultra-low phase noise microwave signals, virtually immune to amplitude to phase conversion related noise.
physics.optics↗
High-sensing properties of magnetic plasmon resonances in double- and triple-rod structures
We numerically investigated the magnetic plasmon resonances in double-rod and triple-rod structures (DRSs and TRSs, respectively) for sensing applications. According to the equivalent circuit model, one magnetic plasmon mode was induced in the DRS. Due to the hybridization effect, two magnetic plasmon modes were obtained in the TRS. Compared with the electric plasmon resonance in a single-rod structure (SRS), the electromagnetic fields near the DRS and TRS were much more localized in the dielectric surrounding the structures at the resonance wavelengths. This caused the magnetic plasmon resonance wavelengths to become very sensitive to refractive index changes in the environment medium. As a result, a large figure of merit that is much larger than the electric plasmon modes of SRS could be obtained in the magnetic plasmon modes of DRS and TRS. These magnetic plasmon mode properties enable the use of DRSs and TRSs as sensing elements with remarkable performance.
cond-mat.mtrl-sci↗
Electric and Magnetic Excitation of Coherent Magnetic Plasmon Waves in a One-dimensional Meta-chain
A one-dimensional diatomic meta-chain with equal-size holes and different-length slits is designed. Broadband coherent magnetic plasmon waves (MPW) are formed in such a system, excited by both the electric resonance in the slits and the magnetic resonance in the holes in a wide range of incidence angles (00-400) and broad frequency bands (200-230 THz). The dispersion properties of the MPW measured in our experiments agree with the theoretical calculation based on the Lagrange model. The coherent MPWs reported in this paper may have applications in subwavelength integrated nanocircuits.
cond-mat.mtrl-sci↗
Spaser in Coupled Metamaterials: The gain effect in a magnetic plasmon waveguide
Loss is a crucial problem in plasmonic integrated optical circuits and metamaterials. The Er, Yb codoped gain material is introduced into a magnetic plasmon waveguide composed of a chain of nanosandwiches in order to solve the loss problem in such subwavelength waveguide. The magnetic plasmon mode and a higher order mode are chosen as the signal and pump light to enhance the radiation and pump efficiencies. The signal light propagating in the waveguide is investigated with different Er3+ doping concentration and signal decay time. It is shown that the gain effect can not only compensate the loss but also is able to amplify the signal, when exceeding certain threshold values of doping concentration and signal decay time.
physics.optics↗
Isoscalar giant resonances in the Sn nuclei and implications for the asymmetry term in the nuclear-matter incompressibility
We have investigated the isoscalar giant resonances in the Sn isotopes using inelastic scattering of 386-MeV alpha-particles at extremely forward angles, including 0deg. We have obtained completely "background-free inelastic-scattering spectra for the Sn isotopes over the angular range 0deg--9deg and up to an excitation energy of 31.5 MeV. The strength distributions for various multipoles were extracted by a multipole decomposition analysis based on the expected angular distributions of the respective multipoles. We find that the centroid energies of the isoscalar giant monopole resonance (ISGMR) in the Sn isotopes are significantly lower than the theoretical predictions. In addition, based on the ISGMR results, a value of K_{tau} = -550 \pm 100 MeV is obtained for the asymmetry term in the nuclear incompressibility. Constraints on interactions employed in nuclear structure calculations are discussed on the basis of the experimentally-obtained values for K_(infty) and K_(tau).
nucl-ex↗
Modeling the directed transmission and reflection enhancements of the lasing spaser in active metamaterials
Simultaneously enhanced reflectance and transmittance greater than 35 dB are demonstrated for the lasing spaser (or spasing) behavior in an active fishnet metamaterial. In mimicking a lasing cavity, an equivalent active slab with Lorentz dispersion for the index of refraction is established to model the spasing metamaterial through the Fabry-Perot effect. Numerical and theoretical results show good agreement in the equal enhancement of reflectance and transmittance, as well as the non-monotonic dependence of the spasing intensity on the gain coefficient. In addition, directed emission of the spasing beam is verified numerically.
physics.optics↗
Optical Observations of the Rapidly Expanding Type Ia Supernova 2007gi
We present optical photometry and spectra for the Type Ia supernova (SN Ia) 2007gi in the nearby galaxy NGC 4036. SN 2007gi is characterized by extremely high-velocity (HV) features of the intermediate-mass elements (Si, Ca, and S), with expansion velocities ($v_{\rm exp}$) approaching $\sim$15,500 km s$^{-1}$ near maximum brightness (compared to $\sim$10,600 km s$^{-1}$ for SNe Ia with normal $v_{\rm exp}$). SN 2007gi reached a $B$-band peak magnitude of 13.25$\pm$0.04 mag with a decline rate of $Δm_{15}(B)$(true) = 1.33$\pm$0.09 mag. The $B$-band light curve of SN 2007gi demonstrated an interesting two-stage evolution during the nebular phase, with a decay rate of 1.16$\pm$0.05 mag (100 days)$^{-1}$ during $t = 60$--90 days and 1.61$\pm0.04$ mag (100 days)$^{-1}$ thereafter. Such a behavior was also observed in the HV SN Ia 2006X, and might be caused by the interaction between supernova ejecta and circumstellar material (CSM) around HV SNe Ia. Based on a sample of a dozen well-observed $R$-band (or unfiltered) light curves of SNe Ia, we confirm that the HV events may have a faster rise time to maximum than the ones with normal $v_{\rm exp}$.
astro-ph.SR↗
Proton decay from the isoscalar giant dipole resonance in $^{58}$Ni
Proton decay from the 3$\hbarω$ isoscalar giant dipole resonance (ISGDR) in $^{58}$Ni has been measured using the ($α,α'p$) reaction at a bombarding energy of 386 MeV to investigate its decay properties. We have extracted the ISGDR strength under the coincidence condition between inelastically scattered $α$ particles at forward angles and decay protons emitted at backward angles. Branching ratios for proton decay to low-lying states of $^{57}$Co have been determined, and the results compared to predictions of recent continuum-RPA calculations. The final-state spectra of protons decaying to the low-lying states in $^{57}$Co were analyzed for a more detailed understanding of the structure of the ISGDR. It is found that there are differences in the structure of the ISGDR as a function of excitation energy.
nucl-ex↗
Suppression of radiation loss by hybridization effect in two coupled split-ring resonators
This paper investigates the radiation properties of two coupled split-ring resonators (SRRs). Due to electromagnetic coupling, two hybrid magnetic plasmon modes were induced in the structure. Our calculations show that the radiation loss of the structure was greatly suppressed by the hybridization effect. This led to a remarkable increase in the Q-factor of the coupled system compared to the single SRR. By adjusting the distance between the two SRRs, the Q-factor changed correspondingly due to different electromagnetic coupling strengths. This resulted in a coupled structure that functioned as a new type of nanocavity with an adjustable Q-factor.
physics.optics↗
Coupled magnetic plasmons in metamaterials
Magnetic metamaterials consist of magnetic resonators smaller in size than their excitation wavelengths. Their unique electromagnetic properties were characterized by the effective media theory at the early stage. However, the effective media model does not take into account the interactions between magnetic elements; thus, the effective properties of bulk metamaterials are the result of the "averaged effect" of many uncoupled resonators. In recent years, it has been shown that the interaction between magnetic resonators could lead to some novel phenomena and interesting applications that do not exist in conventional uncoupled metamaterials. In this paper, we will give a review of recent developments in magnetic plasmonics arising from the coupling effect in metamaterials. For the system composed of several identical magnetic resonators, the coupling between these units produces multiple discrete resonance modes due to hybridization. In the case of a system comprising an infinite number of magnetic elements, these multiple discrete resonances can be extended to form a continuous frequency band by strong coupling. This kind of broadband and tunable magnetic metamaterial may have interesting applications. Many novel metamaterials and nanophotonic devices could be developed from coupled resonator systems in the future.
physics.optics↗
Structural-configurated magnetic plasmon bands in connected ring chains
Magnetic resonance coupling between connected split ring resonators (SRRs) and magnetic plasmon (MP) excitations in the connected SRR chains were theoretically studied. By changing the connection configuration, two different coupling behaviors were observed, and therefore two kinds of MP bands were formed in the connected ring chains, accordingly. These MPs were revealed with positive and negative dispersion for the homo- and anti-connected chain, respectively. Notably, these two MP modes both have wide bandwidth due to the conductive coupling. Moreover, the anti-connected chain is found supporting a novel negative propagating wave with a wide band starting from zero frequency, which is a fancy phenomenon in one-dimensional system.
physics.optics↗
Optically pumped nanolaser based on two magnetic plasmon resonance modes
We propose and analyze theoretically a double magnetic plasmon resonance nanolaser, in which Ytterbium-erbium co-doped material is used as the gain medium. Through design of the double magnetic resonance modes, pumping light (980nm) can be resonantly absorbed and laser light (1550nm) can be resonantly generated simultaneously. We introduce a set of rate equations combined to describe the operation of the laser and predict the lasing condition. According to our calculations, the disadvantage that pumping light is difficult to be absorbed by a thin slab of gain materials can be overcome.
physics.optics↗