Showing papers on "Stark effect published in 2013"

Dynamical polarizability of atoms in arbitrary light fields: general theory and application to cesium

Abstract: We present a systematic derivation of the dynamical polarizability and the ac Stark shift of the ground and excited states of atoms interacting with a far-off-resonance light field of arbitrary polarization. We calculate the scalar, vector, and tensor polarizabilities of atomic cesium using resonance wavelengths and reduced matrix elements for a large number of transitions. We analyze the properties of the fictitious magnetic field produced by the vector polarizability in conjunction with the ellipticity of the polarization of the light field.

The chemical bond in external electric fields: Energies, geometries, and vibrational Stark shifts of diatomic molecules

Abstract: It is shown that the response of molecular properties of diatomics such as the total energy, the bond length, and the vibrational Stark shift to an external homogenous electric field (EF) can be predicted from field-free observable properties such as the equilibrium bond length, the bond dissociation energy, the polarizability and dipole moment functions, and the vibrational frequency. Delley [J. Mol. Struct.: THEOCHEM 434, 229 (1998)] suggested to approximate the potential energy surface under an EF by a Morse function augmented with a EF term proportional to the internuclear separation. In this work, this term is replaced by the expression of the field-induced energy change which yields a field-perturbed Morse potential that tends to a constant asymptotic limit when the EF term itself become proportional to the sum of the polarizabilities of the separated atoms. The model is validated by comparison with direct calculations on nine diatomics, five homo-nuclear (H2 ,N 2 ,O 2 ,F 2, and Cl2) and four hetero-nuclear (HF, HCl, CO, and NO), covering a range and combinations of dipole moments and polarizabilities. Calculations were conducted at the quadratic configuration interaction with single and double excitations (QCISD) and density functional theory (DFT)-B3LYP levels of theory using the 6-311++G(3df,2pd) basis set. All results agree closely at the two levels of theory except for the Stark effect of NO which is not correctly predicted by QCISD calculations as further calculations, including at the coupled cluster with single and double excitation (CCSD) level of theory, demonstrate. © 2013 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4820487]

Experimental investigation of the transition between Autler-Townes splitting and electromagnetically-induced transparency models

Abstract: Summary form only given. If in general the transparency of an initially absorbing medium for a probe field is increased by the presence of a control field on an adjacent transition, two very different processes can be invoked to explain it. One of them is a quantum Fano interference between two paths in the three-level system, which occurs even at low control intensity and gives rise to electromagnetically-induced transparency (EIT), the other one is the appearance of two dressed states in the excited level at higher control intensity, corresponding to the Autler-Townes splitting (ATS). This distinction is particularly critical for instance for the implementation of slow light or optical quantum memories. In a recent paper, P. M. Anisimov, J. P. Dowling and B. C. Sanders proposed a quantitative test to objectively discerning ATS from EIT. We experimentally investigated this test with cold atoms and demonstrated that it is very sensitive to the specific properties of the medium. In this study, we use an ensemble of cold Cesium atoms trapped in a MOT, interacting with light via a Λ-type scheme on the D2 line. Absorption profiles are obtained for various values of the control Rabi frequency Ω between 0.1Γ and 4Γ, where Γ is the natural linewidth.

Second-harmonic generation spectroscopy of excitons in ZnO

Abstract: Nonlinear optics of semiconductors is an important field of fundamental and applied research, but surprisingly the role of excitons in the coherent processes leading to harmonics generation has remained essentially unexplored. Here we report results of a comprehensive experimental and theoretical study of the three-photon process of optical second-harmonic generation (SHG) involving the exciton resonances of the noncentrosymmetric hexagonal wide-band-gap semiconductor ZnO in the photon energy range of $3.2$--$3.5$ eV. Resonant crystallographic SHG is observed for the $1s(A,B)$, $2s(A,B)$, $2p(A,B)$, and $1s(C)$ excitons. We show that SHG signals at these exciton resonances are induced by the application of a magnetic field when the incident and the SHG light wave vectors are along the crystal $z$ axis where the crystallographic SHG response vanishes. A microscopic theory of SHG through excitons is developed, which shows that the nonlinear interaction of coherent light with excitons has to be considered beyond the electric-dipole approximation. Depending on the particular symmetry of the exciton states SHG can originate from the electric- and magnetic-field-induced perturbations of the excitons due to the Stark effect, the spin as well as orbital Zeeman effects, or the magneto-Stark effect. The importance of each mechanism is analyzed and discussed by confronting experimental data and theoretical results for the dependences of the SHG signals on photon energy, magnetic field, electric field, crystal temperature, and light polarization. Good agreement is obtained between experiment and theory proving the validity of our approach to the complex problem of nonlinear interaction of light with ZnO excitons. This general approach can be applied also to other semiconductors.

A Hot Electron–Hole Pair Breaks the Symmetry of a Semiconductor Quantum Dot

Abstract: The best-understood property of semiconductor quantum dots (QDs) is the size-dependent optical transition energies due to the quantization of charge carriers near the band edges. In contrast, much less is known about the nature of hot electron–hole pairs resulting from optical excitation significantly above the bandgap. Here, we show a transient Stark effect imposed by a hot electron–hole pair on optical transitions in PbSe QDs. The hot electron–hole pair does not behave as an exciton, but more bulk-like as independent carriers, resulting in a transient and varying dipole moment which breaks the symmetry of the QD. As a result, we observe redistribution of optical transition strength to dipole forbidden transitions and the broadening of dipole-allowed transitions during the picosecond lifetime of the hot carriers. The magnitude of symmetry breaking scales with the amount of excess energy of the hot carriers, diminishes as the hot carriers cool down and disappears as the hot electron–hole pair becomes an e...

Distance Dependent Electron Transfer at TiO2 Interfaces Sensitized with Phenylene Ethynylene Bridged RuII–Isothiocyanate Compounds

Abstract: Excess electrons present in semiconductor nanocrystallites generate a significant electric field, yet the role this field plays in molecular charge transfer processes remains poorly understood. Three ruthenium bipyridyl cis-Ru(bpy)(LL)(NCS)2 compounds, where LL is a 4-substituted bpy, with zero, one, or two phenylene ethynylene bridge units, were anchored to mesoporous nanocrystalline TiO2 thin films to specifically quantify interfacial charge transfer with chromophores designed to be set at variable distances from the surface. Injection of electrons into TiO2 resulted in a blue shift of the metal-to-ligand charge transfer absorption consistent with an underlying Stark effect. The electroabsorption data were used to quantify the electric field experienced by the compounds that decreased from 0.85 to 0.22 MV/cm as the number of OPE spacers increased from 0 to 2. Charge recombination on the 10–8–10–5 s time scale correlated with the magnitude of the electric field with an apparent attenuation factor β = 0.1...

Imaging Electric Fields in SERS and TERS Using the Vibrational Stark Effect.

Abstract: Electric fields associated with Raman enhancements are typically inferred from changes in the observed scattering intensity. Here, we use the vibrational Stark effect from a nitrile reporter to determine the electric-field-dependent frequency shift of cyanide (CN) on a gold (Au) surface. Electroplated Au surfaces with surface-enhanced Raman (SERS) activity exhibit larger Stark shifts near the edge and in areas with large roughness. The Stark shift is observed to correlate with the intensity of a coadsorbed thiophenol molecule. Gap-mode tip-enhanced Raman scattering (TERS), using a Au nanoparticle tip, shows dramatic shifts in the CN stretch that correlate to enhancement factors of 1013 in the gap region. The observed peak widths indicate that the largest fields are highly localized. Changes in the nitrile stretch frequency provide a direct measurement of the electric fields in SERS and TERS experiments.

Photoinduced ultrafast dynamics of the triphenylamine-based organic sensitizer D35 on TiO2, ZrO2 and in acetonitrile

Abstract: The relaxation dynamics of the dye D35 has been characterized by transient absorption spectroscopy in acetonitrile and on TiO2 and ZrO2 thin films. In acetonitrile, upon photoexcitation of the dye via the S0 → S1 transition, we observed ultrafast solvation dynamics with subpicosecond time constants. Subsequent decay of the S1 excited state absorption (ESA) band with a 7.1 ps time constant is tentatively assigned to structural relaxation in the excited state, and a spectral decay with 203 ps time constant results from internal conversion (IC) back to S0. On TiO2, we observed fast (<90 fs) electron injection from the S1 state of D35 into the TiO2 conduction band, followed by a biphasic dynamics arising from changes in a transient Stark field at the interface, with time constants of 0.8 and 12 ps, resulting in a characteristic blue-shift of the S0 → S1 absorption band. Several processes can contribute to this spectral shift: (i) photoexcitation induces immediate formation of D35˙+ radical cations, which initially form electron–cation complexes; (ii) dissociation of these complexes generates mobile electrons, and when they start diffusing in the mesoporous TiO2, the local electrostatic field may change; (iii) this may trigger the reorientation of D35 molecules in the changing electric field. A slower spectral decay on a nanosecond timescale is interpreted as a reduction of the local Stark field, as mobile electrons move deeper into TiO2 and are progressively screened. Multiexponential electron–cation recombination occurs on much longer timescales, with time constants of 30 μs, 170 μs and 1.4 ms. For D35 adsorbed on ZrO2, there is no clear evidence for a transient Stark shift, which suggests that initially formed cation–electron (trap state) complexes do not dissociate to form mobile conduction band electrons. Multiexponential decay with time constants of 4, 35, and 550 ps is assigned to recombination between cations and trapped electrons, and also to a fraction of D35 molecules in S1 which decay by IC to S0. Differential steady-state absorption spectra of D35˙+ in acetonitrile and dichloromethane provide access to the complete D0 → D1 band. The absorption spectra of D35 and D35˙+ are well described by TDDFT calculations employing the MPW1K functional.

Ultrafast Charge Photogeneration in Semiconducting Carbon Nanotubes

Abstract: We show that excitons are not the unique outcome of photoexcitation in single-walled carbon nanotubes (SWNTs). Our experiments of transient photoinduced absorption suggest that charge carriers are formed with quantum yield of a few percent and that such species strongly affect the long-lived transient spectrum. Photogenerated charge carriers induce strong local electric fields that shift by the Stark effect the second subband exciton absorption in SWNTs, resulting in a characteristic derivative shape of the transient absorption spectra.

Laser-imposed phase in resonant absorption of an isolated attosecond pulse

Abstract: We calculate resonant absorption line shapes in helium atoms subject to the combination of an attosecond pulse of XUV radiation and a delayed, few-cycle infrared (IR) laser pulse. We are in particular interested in how the resonant features evolve with the delay between the fields and with increasing IR intensity. We first compare the single-atom absorption calculated by a nonperturbative solution of the time-dependent Schr\"odinger equation (TDSE) to a simple model in which the resonant absorption is modified only by a laser-imposed phase (LIP) that originates in the instantaneous ac Stark shift of the resonant state. We find that the LIP model can explain many features of the resonant absorption, including the direction of the resonance energy shift and the onset of dispersive line shapes with increasing IR intensity. We also find, however, that the LIP model predicts the energy shifts and the line shapes only qualitatively when the resonant states are strongly IR coupled to nearby states. We then use a coupled solution of the Maxwell wave equation and the TDSE to examine how the line shapes are modified by propagation effects at helium densities such that the resonant absorption is strong. We find that when the resonant absorption saturates, their line shapes are strongly modified due to reshaping of the attosecond pulse time profile during propagation. This in turn alters the ultrafast absorption and emission dynamics.

Generation of strong electric fields in an ice film capacitor

Abstract: We present a capacitor-type device that can generate strong electrostatic field in condensed phase. The device comprises an ice film grown on a cold metal substrate in vacuum, and the film is charged by trapping Cs+ ions on the ice surface with thermodynamic surface energy. Electric field within the charged film was monitored through measuring the film voltage using a Kelvin work function probe and the vibrational Stark effect of acetonitrile using IR spectroscopy. These measurements show that the electric field can be increased to ∼4 × 108 V m−1, higher than that achievable by conventional metal plate capacitors. In addition, the present device may provide several advantages in studying the effects of electric field on molecules in condensed phase, such as the ability to control the sample composition and structure at molecular scale and the spectroscopic monitoring of the sample under electric field.

Dynamic polarizabilities for the low-lying states of Ca+

Abstract: The dynamic polarizabilities of the 4s, 3d, and 4p states of Ca+, are calculated using a relativistic structure model. The wavelengths at which the Stark shifts between different pairs of transitions are zero are computed. Experimental determination of the magic wavelengths can be used to estimate the ratio of the f(3dJ -> 4pJ') and f(4s1/2 -> 4pJ') oscillator strengths. This could prove valuable in developing better atomic structure models and, in particular, lead to improved values of the polarizabilities needed in the evaluation of the blackbody radiation shift of the Ca+ ion.

Nd3+-doped Ca3Ga2Ge3O12 garnet: A new optical pressure sensor

Abstract: A pressure-induced shift of the emission spectrum corresponding to the near infrared 4F3/2 → 4I9/2 transition of Nd3+ ions in a calcium gadolinium germanium garnet was obtained in the interval from ambient conditions up to 23 GPa in order to test its suitability as an optical pressure sensor. Although several Nd3+ non-equivalent centers are present in this garnet, which complicates the assignation of the optical transitions, the R1,R2 → Z5 transitions are unequivocally characterised and fit the requirements of an ideal optical pressure sensor. Results obtained for these emission peaks indicate large pressure coefficients of −8.8 and −10.8 cm−1 GPa−1; meanwhile, the rest of the R1,R2 → Z1−4 emissions remain almost unchanged under pressure. This behaviour is ascribed to the influence of the crystal-field at high pressure on the Z5 Stark level of the ground state and can be easily reproduced exclusively by varying the cubic term of fourth rank of the crystal-field Hamiltonian, which accounts for the Nd3+ ion...

Dynamics of local Stark effect observed for a complete D149 dye-sensitized solar cell.

Abstract: A complete, functioning dye-sensitized solar cell made of popular indoline D149 sensitizer is studied by means of transient absorption in visible light in the time scale of nanoseconds to seconds. Photocurrent and photovoltage decays are also measured under the same experimental conditions. A local electric field causing a Stark shift of the D149 absorption band is found to strongly influence the transient spectra and kinetics. The presence of electrons in titania has a major contribution to the Stark shift and the effect disappears over many time scales with an average rate of 5 × 103 s−1. This is much slower than the decay of the oxidized dye (2 × 106 s−1) but, on the other hand, significantly faster than the decay of electrons in titania nanoparticles (3 × 102 s−1 at standard AM1.5 irradiation and open circuit conditions). Possible explanations of this phenomenon are discussed. Electron recombination from the titania conduction band to the oxidized dyes proceeds at an average rate of 2–16 × 104 s−1, depending on the excitation energy density, and does not influence the efficiency of dye regeneration.

Theoretical investigation of stark effect on shallow donor binding energy in InGaN spherical QD-QW

Abstract: In this paper, a simultaneous study of electric field and impurity's position effects on the ground-state shallow-donor binding energy in GaN│InGaN│GaN spherical quantum dot-quantum well (SQD-QW) as a function of the ratio of the inner and the outer radius is reported. The calculations are investigated using variational approach within the framework of the effective-mass approximation. The numerical results show that: (i) the binding energy is strongly affected by the external electric field and the SQD-QW dimension, (ii) a critical value of spherical system's radius is obtained constituting the limit of three dimension confinement and spherical thin layer confinement and (iii) the Stark shift increases with increasing electric field and it is more pronounced around the position of the impurity corresponding to the binding energy maxima than in the spherical layer extremities.

ac Stark effect in the electronic continuum and its impact on the photoionization of atoms by coherent intense short high-frequency laser pulses

Abstract: We investigate the photoionization of an atom by a high-frequency strong coherent laser pulse, where the energy of a single photon is sufficient to ionize the system. Ab initio theory exemplified by numerical calculations of the photoionization of the hydrogen atom illustrates that the laser pulse induces a time-dependent ac (or dynamic) Stark shift of the binding energy of the system due to interaction with the electronic continuum. The energy shift follows the pulse envelope. Because of this shift, the energy of the emitted photoelectron also follows the intensity envelope of a short laser pulse. This results in a strong dynamic interference of the photoelectrons of the same kinetic energy emitted at different times, when the pulse arrives and expires, respectively. The dynamic interference leads to interesting modifications of the photoionization process and results in a multiple peak structure in the photoelectron spectrum. The present work provides a detailed theoretical and numerical study of the results reported in Demekhin and Cederbaum [Phys. Rev. Lett. 108, 253001 (2012)]. The working equations are derived explicitly and an extended analysis of the theory is provided. Additional results are presented. In particular, we demonstrate that the dynamic interference can be controlled by the intensity, duration, and shape of the pulse envelope.

The ethyl radical in superfluid helium nanodroplets: Rovibrational spectroscopy and ab initio computations

Abstract: The ethyl radical has been isolated and spectroscopically characterized in 4He nanodroplets. The band origins of the five CH stretch fundamentals are shifted by < 2 cm−1 from those reported for the gas phase species [S. Davis, D. Uy, and D. J. Nesbitt, J. Chem. Phys. 112, 1823 (2000)10.1063/1.480746; T. Haber, A. C. Blair, D. J. Nesbitt, and M. D. Schuder, J. Chem. Phys. 124, 054316 (2006)10.1063/1.2140740]. The symmetric CH2 stretching band (v1) is rotationally resolved, revealing nuclear spin statistical weights predicted by G12 permutation-inversion group theory. A permanent electric dipole moment of 0.28 (2) D is obtained via the Stark spectrum of the v1 band. The four other CH stretch fundamental bands are significantly broadened in He droplets and lack rotational fine structure. This broadening is attributed to symmetry dependent vibration-to-vibration relaxation facilitated by the He droplet environment. In addition to the five fundamentals, three a1′ overtone/combination bands are observed, and ea...

Magneto-Stark effect of excitons as the origin of second harmonic generation in ZnO.

Abstract: The magneto-Stark effect of excitons is demonstrated to be an efficient source of optical nonlinearity in hexagonal ZnO. Strong resonant second harmonic generation signals induced by an external magnetic field are observed in the spectral range of 2s and 2p excitons. The microscopic theoretical analysis shows that for excitons with a finite wave vector, exciton states of opposite parity are mixed by an effective odd parity electric field induced by the magnetic field despite its even parity. The field, spectral, and polarization dependencies of the second harmonic generation intensity validate the proposed mechanism. The observed phenomenon is not limited to a certain symmetry class and therefore must be effective in other semiconductors.

Towards a direct transition energy measurement of the lowest nuclear excitation in229Th

Abstract: The isomeric first excited state of the isotope 229Th exhibits the lowest nuclear excitation energy in the whole landscape of known atomic nuclei. For a long time this energy was reported in the literature as 3.5(5) eV, however, a new experiment corrected this energy to 7.6(5) eV, corresponding to a UV transition wavelength of 163(11) nm. The expected isomeric lifetime is τ = 3-5 hours, leading to an extremely sharp relative linewidth of ΔE/E ≈ 10−20, 5-6 orders of magnitude smaller than typical atomic relative linewidths. For an adequately chosen electronic state, the frequency of the nuclear ground-state transition will be independent from influences of external fields in the framework of the linear Zeeman and quadratic Stark effect, rendering 229mTh a candidate for a reference of an optical clock with very high accuracy [1]. Moreover, in the literature speculations about a potentially enhanced sensitivity of the ground-state transition of 229mTh for eventual time-dependent variations of fundamental constants (e.g. fine structure constant α) can be found [3,4]. We report on our experimental activities that aim at a direct identification of the UV fluorescence of the ground-state transition energy of 229mTh. A further goal is to improve the accuracy of the ground-state transition energy as a prerequisite for a laser-based optical control of this nuclear excited state, allowing to build a bridge between atomic and nuclear physics and open new perspectives for metrological as well as fundamental studies.

Unraveling the internal dynamics of the benzene dimer: a combined theoretical and microwave spectroscopy study

Abstract: We report a combined theoretical and microwave spectroscopy study of the internal dynamics of the benzene dimer, a benchmark system for dispersion forces. Although the extensive ab initio calculations and experimental work on the equilibrium geometry of this dimer have converged to a tilted T-shaped structure, the rich internal dynamics due to low barriers for internal rotation have remained largely unexplored. We present new microwave spectroscopy data for both the normal (C6H6)2 and partially deuterated (C6D6)(C6H6) dimers. The splitting patterns obtained for both species are unraveled and understood using a reduced-dimensionality theoretical approach. The hindered sixfold rotation of the stem can explain the observed characteristic 1 : 2 : 1 tunneling splitting pattern, but only the concerted stem rotation and tilt tunneling motion, accompanied by overall rotation of the dimer, yield the correct magnitude of the splittings and their strong dependence on the dimer angular momentum J that is essential to explain the experimental data. Also the surprising observation that the splittings are reduced by 30% for the mixed (C6D6)C(C6H6)S dimer in which only the cap (C) in the T-shaped structure is deuterated, while the rotating stem (S) monomer is the same as in the homodimer, is understood using this approach. Stark shift measurements allowed us to determine the dipole moment of the benzene dimer, μ = 0.58 ± 0.051 D. The assumption that this dipole moment is the vector sum of the dipole moments induced in the monomers by the electric field of the quadrupole on the other monomer yields a calculated value of μ = 0.63 D. Furthermore, the observed Stark behavior is typical for a symmetric top, another confirmation of our analysis.

Predicting Mutation-Induced Stark Shifts in the Active Site of a Protein with a Polarized Force Field

Abstract: The electric field inside a protein has a significant effect on the protein structure, function, and dynamics. Recent experimental developments have offered a direct approach to measure the electric field by utilizing a nitrile-containing inhibitor as a probe that can deliver a unique vibration to the specific site of interest in the protein. The observed frequency shift of the nitrile stretching vibration exhibits a linear dependence on the electric field at the nitrile site, thus providing a direct measurement of the relative electric field. In the present work, molecular dynamics simulations were carried out to compute the electric field shift in human aldose reductase (hALR2) using a polarized protein-specific charge (PPC) model derived from fragment-based quantum-chemistry calculations in implicit solvent. Calculated changes of electric field in the active site of hALR2 between the wild type and mutants were directly compared with measured vibrational frequency shifts (Stark shifts). Our study demons...

Diffusive suppression of AC-Stark shifts in atomic magnetometers.

Abstract: In atomic magnetometers, the vector AC-Stark shift associated with circularly polarized light generates spatially varying effective magnetic fields, which limit the magnetometer response and serve as sources of noise. We describe a scheme whereby optically pumping a small subvolume of the magnetometer cell and relying on diffusion to transport polarized atoms allows a magnetometer to be operated with minimal sensitivity to the AC-Stark field.

Ar I and Ne I spectral line shapes for an abnormal glow discharge diagnostics

Abstract: We report the results of an Ar I and Ne I line shape study in an abnormal glow discharge operating in argon and neon. The spectral lines were observed along the axis of a cylindrical glow discharge parallel (side-on) and perpendicular (end-on) to the cathode surface. The side-on spectra show spectral line shifting and sometimes simultaneous shifting and splitting in the cathode fall region of the glow discharge. The results of the measured line shift with available data for the dc Stark effect are used for measurement of electric field strength in the cathode fall region of the glow discharge. Electron temperatures of 2860 K and 4770 K in the negative glow region of argon and neon discharges, respectively, were determined from the relative intensities of Ar I or Ne I lines using the Boltzmann plot technique. An electron number density of ≈1020 m−3 (±25%) in the negative glow region of the argon discharge was determined from the widths of two plasma-broadened Ar I lines using theoretical Stark broadening data. The end-on recorded line profiles show 10–40% larger half-widths than the side-on recorded line profiles from the negative glow. This effect is a result of the superposition of line emission in the cathode fall region under the influence of the dc Stark effect on the line profile from the negative glow.

State-dependent potentials in a nanofiber-based two-color trap for cold atoms

Abstract: We analyze the ac Stark shift of a cesium atom interacting with far-off-resonance guided light fields in the nanofiber-based two-color optical dipole trap realized by Vetsch et al. [Phys. Rev. Lett. 104, 203603 (2010)]. Particular emphasis is given to the fictitious magnetic field produced by the vector polarizability of the atom in conjunction with the ellipticity of the polarization of the trapping fields. Taking into account the ac Stark shift, the atomic hyperfine interaction, and a magnetic interaction, we solve the stationary Schr\"odinger equation at a fixed point in space and find Zeeman-state-dependent trapping potentials. In analogy to the dynamics in magnetic traps, a local degeneracy of these state-dependent trapping potentials can cause spin flips and should thus be avoided. We show that this is possible using an external magnetic field. Depending on the direction of this external magnetic field, the resulting trapping configuration can still exhibit state-dependent displacement of the potential minima. In this case, we find nonzero Franck-Condon factors between motional states of the potentials for different hyperfine-structure levels and propose the possibility of microwave cooling in a nanofiber-based two-color trap.

Quantum Confined Stark Effect in Au8 and Au25 Nanoclusters

Abstract: The quantum confined Stark effect is investigated for the first time in bovine serum albumin (BSA) protected Au8 and Au25 nanoclusters. We observed a red-shift of 63 meV in Au8 nanoclusters upon an increase in pH from 2.14 to 12.0. Such behavior could be well explained in terms of the presence of a linear polar component and a quadratic polarizable component. In contrast, Au25 nanoclusters exhibit more complicated Stark shifts due to their specific core/semiring structure. A plateau of the Stark shift was observed in both absorption and fluorescence, showing an offset of 30 meV. The lifetime measurements confirm that the plateau is due to the screening effect of the semirings in Au25@BSA. Moreover, the dual fluorescent bands of Au25 nanoclusters exhibit two different Stark shifts of 79 and 52 meV, respectively. The experimental data indicate that the Stark shift in both Au8@BSA and Au25@BSA has a significant linear polar component due to their asymmetric structure. This study suggests that gold nanocluste...

Demonstration of a dynamic bandpass frequency filter in a rare-earth ion-doped crystal

Abstract: In this paper we propose and demonstrate a dynamic, narrow-bandpass frequency filter. This is generated in a rare-earth ion-doped crystal using a combination of spectral hole burning and Stark shifting. This filter can toggle within one microsecond between absorption and transmission, with ∼60 dB difference in attenuation, in two separate 1 MHz wide spectral regions. The filter demonstrated here is specifically designed as a component in a rare-earth ion-based quantum repeater protocol. However, this is a general technique that could also be applied for amplitude or phase modulation, or switching between more complicated spectral profiles.