Spontaneous emission from a microwave-driven four-level atom in an anisotropic photonic crystal

The spontaneous emission from a microwave-driven four-level atom embedded in an anisotropic photonic crystal is studied. Due to the modified density of state(DOS) in the anisotropic photonic band gap(PBG) and the coherent control induced by the coupling fields, spontaneous emission can be significantly enhanced when the position of the spontaneous emission peak gets close to the band gap edge. As a result of the closed-loop interaction between the fields and the atom,the spontaneous emission depends on the dynamically induced Autler–Townes splitting and its position relative to the PBG.Interesting phenomena, such as spectral-line suppression, enhancement and narrowing, and fluorescence quenching, appear in the spontaneous emission spectra, which are modulated by amplitudes and phases of the coherently driven fields and the effect of PBG. This theoretical study can provide us with more efficient methods to manipulate the atomic spontaneous emission.     

Emission and absorption quantum noise measurement with an on-chip resonant circuit

Using a quantum detector, a superconductor-insulator-superconductor junction, we probe separately the emission and absorption noise in the quantum regime of a superconducting resonant circuit at equilibrium. At low temperature the resonant circuit exhibits only absorption noise related to zero point fluctuations, whereas at higher temperature emission noise is also present. By coupling a Josephson junction, biased above the superconducting gap, to the same resonant circuit, we directly measure the noise power of quasiparticles tunneling through the junction at two resonance frequencies. It exhibits a strong frequency dependence, consistent with theoretical predictions.     

Position Dependent Spontaneous Emission Spectra of a Λ-Type Atomic System Embedded in a Defective Photonic Crystal

We investigate the position dependent spontaneous emission spectra of a Λ-type three-level atom with one transition coupled to the free vacuum reservoir and the other one coupled to a double-band photonic band gap reservoir with a defect mode in the band gap.It is shown that,for the atom at the defect location,we have a two-peak spectrum with a wide dark line due to the strong coupling between the atom and the defect mode.While,when the atom is far from the defect location(or in the absence of the defect mode),the spectrum has three peaks with two dark lines due to the coupling between the atom and the photonic band gap reservoir with the largest density of states near the band edges.On the other hand,we have a four-peak spectrum for the atom at the space in between.Moreover,the average spontaneous emission spectra of the atoms uniformly embedded in high dielectric or low dielectric regions are described.It is shown that the atoms embedded in high(low) dielectric regions far from the defect location,effectively couple to the modes of the lower(upper) photonic band.However,the atoms embedded in high dielectric or low dielectric regions at the defect location,are coupled mainly to the defect modes.While,the atoms uniformly embedded in high(low) dielectric regions with a normal distance from the defect location,are coupled to both of defect and lower(upper) photonic band modes.     

Tunable single-mode fiber-VCSEL using an intracavity polymer microlens

We report a tunable, single-mode vertical cavity surface-emitting laser (VCSEL) format suitable for array operation, power scaling, fiber coupling, and operation in isolated environments such as those required by atom optics. The devices are fiber VCSELs, consisting of a semiconductor gain and mirror structure separated from a mirror-coated optical fiber by an air (or vacuum) gap. The gain structure has polymer microlenses fabricated on its surface, of characteristics suitable to focus the oscillating mode on both cavity mirrors, ensuring stable fundamental mode emission and high fiber coupling efficiency. We demonstrate such devices in continuous-wave operation at 1.03 microm at room temperature, with a single-mode tuning range of 13 nm, laser threshold as low as 2.5 mW, and a maximum fiber-coupled output power of 10 mW.     

Spin reorientation and magnon-phonon hybridization in a ferromagnet

A model is presented for the magnetic excitations and magnon-phonon coupling in a localised moment ferromagnet in which spins can reorientate by application of a magnetic field. The model is suitable for those materials which possess a spin wave gap at zero wave vector and therefore the magnon and acoustic phonon branches can intersect. A magnon-phonon coupling linear in both spin and phonon operators is employed which has proved successful for the ferrous salts. The main effect of the applied field is to modify the spin wave gap, and to introduce a critical value for the coupling constant which enables the system to remain stable as the gap goes to zero. Furthermore the wave vector of the anticrossing point decreases as the spin wave gap increases and therefore the value of the sound velocity determined by high resolution inelastic neutron experiments is dependent on the gap.     

Energy-exchange processes by tunneling electrons

Resistive heating, emission heating or cooling (e.g., the Nottingham effect), and thermal fluctuation radiation are examples of energy exchange processes which are fundamental in electron field emission and in tunneling junctions of scanning tunneling microscopy. These exchange processes are analyzed for both electronic tunneling processes. We first discuss the energy delivered by a monoatomic tip in the field emission process. Strong phonon excitation is expected for field emission currents exceeding 1 nA. Secondly we present a theoretical calculation of the thermal deposition associated with the Nottingham effect in a tunneling junction. The calculation is based on the free electron model for the electrode materials and the tunneling process across a planar vacuum gap. Our results show that the thermal power is deposited not only at the electron receiving electrode but also at the emitting electrode. This originates from a finite probability for electrons below the Fermi level to tunnel through the tunneling barrier replaced by electrons starting from the Fermi level. The comparison between the calculations and the recent STM measurements is given. Finally we discuss the other energy exchange processes in the tunneling junction, and conclude that the thermal coupling between the tip and the sample of STM is extremely small under UHV conditions. This is important for high temperature STM.     

Efficient single-photon sources based on low-density quantum dots in photonic-crystal nanocavities

An efficient single-photon source based on low-density InGaAs quantum dots in a photonic-crystal nanocavity is demonstrated. The single-photon source features the effects of a photonic band gap, yielding a single-mode spontaneous emission coupling efficiency as high as beta = 92% and a linear polarization degree up to p = 95%. This appealing performance makes it well suited for practical implementation of polarization-encoded schemes in quantum cryptography.     

Electromagnetically induced exciton mobility in a photonic band gap

It is suggested that an exciton in the engineered vacuum of a photonic-band-gap-quantum-well heterostructure exhibits electromagnetically induced anomalous quantum dynamics. The exciton is dressed by coherent emission and reabsorption of virtual photons near the photonic band edge and captured in momentum space, lowering its energy by 1-10 meV and lowering its effective mass by 4-5 orders of magnitude. The photonic band gap simultaneously enables strong coupling to confined optical modes and long exciton lifetime.     

纳米ZnO薄膜的激子光致发光特性

报道了纳米ZnO薄膜激子光致发光(PL)与温度的关系。首先利用低压金属有机化学气相沉积(LPMOCVD)技术生长ZnS薄膜,然后将ZnS薄膜在氧气中于800℃下热氧化2h获得纳米ZnO薄膜。X射线衍射(XRD)结果表明,纳米ZnO薄膜具有六角纤锌矿多晶结构且具有择优(002)取向。室温下观察到一束强的紫外(326eV)光致发光(PL)和很弱的深能级(DL)发射。根据激子峰的半高宽(FWHM)与温度的关系,确定了激子纵向光学声子(LO)的耦合强度(ГLO)。     

Enhancement in UV emission and band gap by Fe doping in ZnO thin films

Enhancement of the optical band gap of ZnO from 3.14 to 3.29 eV has been obtained using Fe dopant. Undoped and doped ZnO films are deposited by sol-gel spin coating. XRD patterns indicate polycrystalline nature and hexagonal wurtzite structure of Zn_1?xFe_xO films. EDX analysis confirms the presence of iron dopant. The photoluminescence spectra show an ultraviolet emission peak at 398 nm (NBE emission) and defect emission peak at 485 nm. Intensity of the NBE emission is much higher for the doped samples with its ratio to defect emission intensity highest for 2 at. %doping. The NBE emission shifts to higher energy with increasing dopant concentration in a manner similar to that exhibited by the band gap. Surface morphology has been studied using FESEM.     

Silicon nitride PhC nanocavities as versatile platform for visible spectral range devices

We propose silicon nitride two-dimensional photonic crystal resonators as flexible platform to realize photonic devices based on spontaneous emission engineering of nanoemitters in the visible spectral range. The versatility of our approach is demonstrated by coupling the two dipole-like modes of a closed band gap H1 nanocavity with: (i) DNA strands marked with Cyanine 3 organic dyes, (ii) antibodies bounded to fluorescent proteins and (iii) colloidal semiconductor nanocrystals localized in the maximum of the resonant electric field. The experimental results are in good agreement with the numerical simulations, highlighting the good coupling of the nanocavities with both organic and inorganic light emitters.     

3D periodic structures grown on silicon by radiation of a pulsed Nd:YAG laser and their field emission properties

Periodic three-dimensional structures were successfully grown on single crystal Si wafers either bare or Au-covered under their exposure to a pulsed radiation of a Nd:YAG laser in vacuum. The structures protrude above the initial wafer surface for 10 μm while their spatial period is about 70 μm. The coupling of the laser radiation to Si surface is related to the thermal non-linear absorption of the near band gap radiation. The structures exhibit an efficient field emission with an average emission current of 5 mA/cm² and is sensitive to the post-treatment of samples. The drawbacks of the emission current densities are discussed.     

金纳米颗粒等离激元对不同形貌氧化锌薄膜发光性能的调控

采用化学气相沉积法制备了纳米棒状的氧化锌纳米结构薄膜和没有纳米棒的氧化锌薄膜,通过直流溅射在所制备的有纳米棒和没有纳米棒的氧化锌薄膜上淀积约3 nm厚的金纳米颗粒薄膜,研究了金纳米颗粒对不同表面形貌氧化锌薄膜的发光特性的影响。实验发现金纳米颗粒的存在使具有纳米棒的氧化锌薄膜的紫外发射增强,但使来自缺陷的可见光发射受到很大的抑制。通过比较有纳米棒和没有纳米棒的氧化锌薄膜在镀金纳米颗粒前后的发光特性,发现金表面等离激元对氧化锌发光的调控取决于氧化锌的表面形貌,纳米棒的存在更有利于金纳米颗粒等离激元调控氧化锌的发光特性。     

Blueshifts of emission energy from InAs quantum dots in GaAs matrix due to narrowed interdot spacing: a token of the integrity of a nanostructure

The shifts of emission energy from InAs quantum dots (QDs) in the GaAs matrix due to change in the QD stacking period have been numerically analyzed by investigating the strain modified shifts of band edges. Narrower stacking results in a blueshift of emission energy from direct band gap transition provided the QD spacing is wide enough to avoid electronic coupling. Through a comparison with existing experimental results in the literature, processing methods and variables that have benefits in achieving a blueshift have been inferred. A blueshift through decreased QD spacing has been proposed as a token of the integrity of a processed QD nanostructure . PACS 68.65.+g; 78.66.Fd     

金属-介质-金属渔网超表面结构调控的荧光辐射：空间选择性激发和双增强

增强荧光辐射在生物成像、高灵敏探测、集成光源等方面都具有重要的应用价值.金属纳米颗粒的周围或者金属纳米结构的间隙都可以产生强的电磁场,相应的,这些结构附近的局域态密度也被极大地增强.虽然增强荧光辐射已经在多种金属纳米颗粒和颗粒对中被证明,但是利用金属纳米结构对荧光分子的吸收和辐射过程同时进行调制仍然是一个有挑战的问题.本文研究了金属-介质-金属超表面对荧光辐射的调控,其中局域表面等离激元(LSP)和磁等离激元(MPP)分別与于分子的吸收和辐射过程发中耦合相互作用.对于吸收过程,LSP的耦合作用使得可以通过旋转泵浦激光的偏振态来实现荧光分子的空间选择激发.此外,MPP模式的偏振依赖特性使得矩形渔网结构中的荧光分子的辐射波长和偏振态也受到调控.实验观测结果经过了时域有限差分模拟的验证.本文报道的纳米结构在光辐射器件和纳米尺度集成光源等方面都具有潜在的应用价值.     

Electroluminescence in vapor grown CuGaS2

Electroluminescence emission has been obtained in the compound CuGaS₂ with In and Au contacts. Such emission is mainly ascribed to the injection of minority carriers from the In contact. The electroluminescent spectrum presents some peaks at energies lower than gap energy showing that electroluminescence is mainly due to a recombination into levels localized in the gap. A weak emission at an energy near the gap has also been observed.     

速调管双间隙双耦合口输出结构

基于等效电路理论,提出了一种双间隙双耦合口输出结构的设计方法及计算双耦合口输出腔外观品质因数的方法。利用三维电磁场软件,设计了满足阻抗频率特性要求的双间隙单耦合口输出结构及前置腔和输出腔分别具有相同参数的双间隙双耦合口结构。然后,将两者的阻抗频率特性进行比较,通过微调整该输出腔与耦合槽的尺寸,可以得到与单耦合口输出结构一致的阻抗频率特性曲线。     

Variation of spontaneous emission in the opal stop-band with an enhanced refractive-index contrast

Photoluminescence spectra of an opal with an anatase layer grown on its inner surface were studied. Measurements were carried out with a high angular resolution at various pump power levels and detection angles. The intensity and probability of emission were found to acquire an anisotropy corresponding to the frequency and angular dispersion of the first opal photonic band gap. As the pump power increases, the suppression of spontaneous emission in the photonic band gap is shown to be replaced by its amplification. The amplification of spontaneous emission is tentatively assigned to the existence of localized defect optical modes in the photonic band gap.     

Reconstruction of emission coefficients for a non-axisymmetric coupling arc by algebraic reconstruction technique

A preliminary investigation of tomographic reconstruction of an asymmetric arc plasma has been carried out. The objective of this work aims at reconstructing emission coefficients of a non-axisymmetric coupling arc from measured intensities by means of an algebraic reconstruction technique (ART). In order to define the optimal experimental scheme for good quality with limited views, the dependence of the reconstruction quality on three configurations (four, eight, ten projection angles) are presented and discussed via a displaced Gaussian model. Then, the emission coefficients of a free burning arc are reconstructed by the ART with the ten-view configuration and an Abel inversion, respectively, and good agreement is obtained. Finally, the emission coefficient profiles of the coupling arc are successfully achieved with the ten-view configuration. The results show that the distribution of emission coefficient for the coupling arc is different from centrosymmetric shape. The ART is perfectly suitable for reconstructing emission coefficients of the coupling arc with the ten-view configuration, proving the feasibility and utility of the ART to characterize an asymmetric arc.     

Time-resolved imaging of the electrical breakdown of planar microelectrode gap in atmospheric air

The aim of this study was to obtain time-resolved images of the electrical breakdown of a planar microelectrode gap along the surface of a glass substrate in atmospheric air. The obtained images revealed details of the events leading to the breakdown. First, a point light emission appeared at the cathode, indicating breakdown initiated by the field emission of electrons from the cathode under extremely high electric fields. Then, a flare-like broad light emission was generated at the anode. Finally, breakdown occurred over the entire gap by the expansion and merger of the two emissions.