1s-2p Transition Research Articles

Exciting positronium with a solid-state UV laser: the Doppler-broadened Lyman-α transition

A tunable, pulsed laser was used to excite the Lyman-α transition (1S–2P) of positronium (Ps). The laser system has a large bandwidth of GHz at nm, providing significant coverage of the Doppler-broadened, single-photon transition. The infra-red fundamental of a Nd:YAG laser was converted to ultraviolet by a series of solid-state, nonlinear processes, centred about an unseeded optical parametric oscillator, from which the bulk of the ultimate bandwidth derives. The Ps atoms were created by bombarding mesoporous silica with positrons, and the Doppler-width of the 1S–2P transition of the resulting ensemble was measured to be GHz (equivalent to K). It is envisaged that the UV laser will be incorporated into a two-step process to efficiently form Rydberg states of Ps, with potential applications in synthesis of cold antihydrogen, gravity measurements with antimatter, or for injection of electrons and positrons into a stellarator.

Nonadiabatic spectral redshift of high-order harmonics with the help of a VUV pulse

We theoretically investigate the nonadiabatic spectral redshift of high-order harmonics with the help of a VUV pulse. It is found that the nonadiabatic spectral redshift of high-order harmonics can be observed when a weak VUV pulse is properly added in the falling part of the fundamental laser due to the nonadiabatic response of the dipole to rapid change of laser intensity. Further time-frequency analysis shows that the high-order harmonics are mainly generated in the falling part of the fundamental pulse. This is because the VUV pulse enhances the ionization in the falling part of the fundamental pulse by the 1s-2p transition of $\text{H}{e}^{+}$. In addition, this scheme is also used to observe the nonadiabatic spectral blueshift of high-order harmonics by changing the time delay between the fundamental laser and the VUV pulse.

Spontaneous light emission by atomic hydrogen: Fermi's golden rule without cheating

Focusing on the 2p–1s transition in atomic hydrogen, we investigate through first order perturbation theory the time evolution of the survival probability of an electron initially taken to be in the excited (2p) state. We examine both the results yielded by the standard dipole approximation for the coupling between the atom and the electromagnetic field – for which we propose a cutoff-independent regularisation – and those yielded by the exact coupling function. In both cases, Fermi's golden rule is shown to be an excellent approximation for the system at hand: we found its maximal deviation from the exact behaviour of the system to be of order 10−8/10−7. Our treatment also yields a rigorous prescription for the choice of the optimal cutoff frequency in the dipole approximation. With our cutoff, the predictions of the dipole approximation are almost indistinguishable at all times from the exact dynamics of the system.

Design and Synthesis of CdWO4:Sb3+ Phosphor Based on sp Energy Level Regularities of Sb3+ Ion

Sb3+‐activated CdWO4 phosphors were designed according to sp energy levels regularities of Sb3+ ion in some inorganic compounds. The sp energy levels regularities of Sb3+ in dozens of compounds were established with the aid of the dielectric theory of the chemical bond for complex crystals: EA = 6.2187−1.7584he, EB = 7.019−1.957he, EC = 7.259−1.964he. Environmental factor he of Cd site was calculated to be 1.6583 with the refined crystal structure and refractive index of CdWO4:Sb3+. Sb3+‐doped CdWO4 was synthesized through a precipitation method and its structure was refined with the General Structure Analysis System. The transition energy of A band of Sb3+ in CdWO4 can be predicted to be 3.312 eV (374 nm), according to the relationship equation between EA and environmental factor he. By monitoring the 521 nm emission band, the excitation spectrum gives a weak excitation band peaking at 355 nm, which was assigned to the 1S0–3P1 transition of Sb3+ according to our prediction. Thus, Sb3+‐doped CdWO4 phosphor was designed and synthesized successfully based on sp energy levels regularities of Sb3+ ion. This work is a great help to understand the spectroscopy of Sb3+ ion and will be useful for the design and development of Sb3+‐doped phosphors for applications.

A streak camera study of superfluorescence at multiple wavelengths from helium atoms excited using free electron laser pulses

We report the observation of superfluourescence at wavelengths (in air) of 501.6 nm, 667.8 nm, and 728.1 nm following the excitation of helium atoms with free-electron laser pulses at wavelengths of 53.7 nm (n = 3 excitation) and 52.2 nm (n = 4 excitation). The observed wavelengths of the superfluorescence pulses correspond to 1s3p–1s2s, 1s3d–1s2p, and 1s3s–1s2p transitions. Observation of superfluorescence on these transitions implies either competing cascade decays, or direct excitation of non-dipole allowed transitions. We have studied the time structure of the emitted pulses using a streak camera, and the results cannot be explained by straightforward considerations using the usual model for two-level superfluorescence.

Crystal structure and luminescence properties of Bi3+ activated Ca2Y3Sb3O14 phosphors in near UV region

A novel Ca2Y3Sb3O14: Bi3+ phosphor was synthesized and its crystal structure, photoluminescence (PL) properties was investigated. Ca2Y3Sb3O14 crystallized as a monoclinic structure with a space group of I2m/11 and lattice constants of a=7.4129(7)Å, b=10.4428(1)Å, c=7.3898(8)Å and α=90.049°. Ca2Y3Sb3O14: Bi3+ could be efficiently excited in the wavelength range of 270–400nm. With the increase of Bi3+ concentration, the most efficient excitation wavelength of the phosphors moved from 320 to 350nm. When excited under 310–350nm, the phosphors emit a broad band with a maximum intensity appearing at about 420–460nm due to the 3P1–1S0 transition of Bi3+. The relationship between the PL properties and the crystal structure was discussed. Due to the efficient excitation in the near UV region and the strong blue to cyan emission, Ca2Y3Sb3O14: Bi3+ would be a potential blue phosphor for near UV white light-emitting diodes, or a potential donor system for designing single-composition white-light phosphors based on energy transfer.

Polarization spectroscopy of the 1S0-3P1 transition of mercury isotopes at 253.7 nm

We experimentally observe polarization spectroscopy (PS) of the 1S0-3P1 transition of mercury atom gases at 253.7 nm. The PS signal can be observed in all six richly abundant isotopes and the PS signal of six transitions for laser cooling are all clear and of a dispersive line shape.The optimized pumppower and probe power are found for thePSof 202Hg.We find the linearly polarized component in the pumpbeamwill distort the original PSsignal due to the use of linear PS. Consequently, the purity of the pump beam is crucial to laser frequency stabilization by PS.

Observation of 1S0-3P0 transition of bosonic strontium in the Lamb-Dicke regime

We report experiments on the observation of the 1S0-3P0 transition spectrum of 88Sr in the Lamb-Dicke regime. After going through a two-stage magneto-optical trap (MOT), 88Sr cold atoms with number of about 1 \times 105 and a longitudinal temperature of 8.4 μK are loaded into a one-dimensional (1D) optical lattice, which is realized with a semiconductor laser at 813.4 nm. Using the magnetic field-inducing 3P1 state mixing into 3P0 state, the spectroscopy of the 1S0-3P0 transition with a linewidth of 180 Hz is detected.

Fabrication of ZnWO4:Sm3+, Bi3+, Li+ with tunable white light-emitting properties for W-LEDs

The color-tunable phosphor ZnWO4:Sm3+, Bi3+, Li+ has been prepared via a solid–state reaction method. The white light was attributed to the color mixture of blue–green and orange–red emission, which originated from the charge transfer transition of W–O and the transition emission of Sm3+, respectively. The obtained phosphors exhibited a strong traditional band at 305nm and a new band at about 351nm which comes from the 1S0–3P1 transition of Bi3+. White light with tunable color emission for ZnWO4:Sm3+, Bi3+, Li+ phosphors were demonstrated by simply controlling the ratio of Sm3+/Li+. The calculated chromaticity coordinates were varying from blue to white region. When excited at about 351nm, these phosphors have a strong orange–red light. These results indicate that the phosphor of ZnWO4:Sm3+, Bi3+, Li+ which can generate tunable blue–white–red light may be a promising element for cost-effective diodes with near ultraviolet white light emitting properties.

Mechanisms of level population in gas lasers pumped by ionizing radiation

AbstractThe mechanisms of level population in high pressure gas lasers pumped by ionizing radiation at the 3p-3s transitions of neon, the d-p transitions of argon, krypton, xenon, and triplet lines of mercury are analyzed. It is shown that dissociative recombination of molecular ions with electrons is not the basic process responsible for populating the p levels of inert gas atoms. It is assumed that the most likely channel for d-level population is direct excitation of atoms by secondary electrons and excitation transfer from buffer gas atoms, with p levels being populated by transitions from upper levels. Dissociative recombination of mercury molecular ions with electrons is the basic process responsible for populating the 73S1 level of mercury atoms.

Recently published line strengths for the transition array 3s–3p in C I, N II and O III: a critical review

Recently calculated atomic structure data for C I, N II and O III are reviewed and analyzed by performing J-file sum rule tests. The line strengths of the 3s–3p transition array are analyzed. In the case of neutral carbon and ionized nitrogen data, the LS-forbidden transitions are included in the analysis.

High-Sensitivity In situ Fluorescence Imaging of Ytterbium Atoms in a Two-Dimensional Optical Lattice with Dual Optical Molasses

We developed a dual molasses technique which enabled us to perform high-sensitivity in situ fluorescence imaging of ytterbium (Yb) atoms in a two-dimensional optical lattice prepared in a thin glass cell. This technique successfully combines two different kinds of optical molasses for Yb atoms, that is, the one using the 1S0–1P1 transition which provides high-resolution in the in situ fluorescence imaging and the other using the 1S0–3P1 transition for cooling the atoms in the optical lattice. We performed in situ imaging of 174Yb atoms and could observe a Moiré pattern with a period of about 6 µm produced by the molasses beam with 556 nm and the optical lattice with 532 nm, which implies that the temperature was kept below the lattice depth during the fluorescence imaging. The number of photons per atom is estimated to be enough for single atom detection with our imaging system. This result is quite promising for the realization of an Yb quantum gas microscope.

Binding energy and nonlinear optical properties of an on-center hydrogenic impurity in a spherical quantum dot placed at the center of a cylindrical nano-wire: Comparison of hydrogenic donor and acceptor impurities

The binding energies and corresponding wave functions of ground and first excited states (1s, 2p) of on-center hydrogenic donor and acceptor impurities are calculated using finite difference approximation in the effective mass framework. The on-center impurities are assumed to be in an InAs spherical quantum dot which is located at the center of a GaAs cylindrical nano-wire. To test the validity of applied method the eigenvalues of ground and first excited states are compared with reported results which have been calculated by finite element methods and it is shown that the finite difference approximation is more accurate in this particular case. In addition, the oscillator strength, linear, third-order nonlinear and total optical absorption coefficients and refractive index changes have been calculated for 1s–2p transition by means of the compact density matrix approach. The results show that presence of impurity causes a blue shift in optical spectrum which is larger for acceptor impurity. Also, the amplitude of absorption coefficient, refractive index changes and oscillator strength depend on the absence, presence and type of impurity. Moreover, it is found that the saturation condition can be tuned by type of impurity and critical incident optical intensity is enhanced in presence of acceptor impurity.

Soft x-ray emission from solar wind charge exchange in the laboratory

We have observed the emission spectra in collisions of bare oxygen ions with a helium gas target in the soft x-ray region with a window-less silicon drift detector at the collision energy range of 48–80 keV. The dominant soft x-ray emission corresponds to the 1s–2p transition of hydrogen-like oxygen O7+ produced by the single-electron charge exchange reaction. Other emission lines are the 1s–3p, 1s–4p and 1s–5p transitions of O7+, and also the 1s2–1s2p transition of O6+ produced by the true double-electron capture. The cascades from the upper states result in a large population of the 2p state, even though the direct capture into the 2p state is extremely scarcer than those into the 3p, 4p and 5p states.

Investigation of the influence of inner-shell photoionization and photoexcitation on the Heα spectrum in photoionized plasmas

The present paper investigates the influence of inner shell photoionization and photoexcitation on the Heα, i.e., the 1s2 to 1s2p transition in He-like ions, and the associated satellite spectra in photoionized plasmas. A comparison of the importance of these processes is made relative to other atomic processes as a function of the electron temperature and irradiation conditions. For the formation of the Heα and the satellite spectra, the K-shell photoionization is found to have significant contribution under low radiation temperature and/or intensity, when lithium- and beryllium-like ions have high abundance, but highly ionized H-like ions are rare.

Applications oriented design of Bi3+ doped phosphors

Based on the relationships between Bi3+ energy levels and environmental factor he in phosphors established before, positions of A band of Bi3+ in ZnWO4 and CdWO4 are predicted to lie in near ultraviolet region. ZnWO4:Bi3+ and CdWO4:Bi3+ were prepared via a precipitation method. By examining their photoluminescence, it was confirmed that Bi3+ 1S0-3P1 transition are located around 340 and 350 nm, matching well with predicted results, 357 nm and 377 nm, respectively. The emission spectra indicate that they can be effectively excited by 340 and 350 nm ultraviolet light, exhibiting a satisfactory green performance (560 and 537 nm), according with ultraviolet chip.

Optimization of Doppler-free magnetically induced dichroic locking spectroscopy on the 1S0–3P1 transition of a neutral mercury atom

Doppler-free dichroic locking (DFDL) spectroscopy on the 1S0–3P1 transition of neutral mercury (Hg) atoms is observed in a 5 mm long vapour cell. The performance of the DFDL signal, such as its slope and amplitude, is investigated in detail. The optimal axial magnetic field and cell temperature (optical depth) for the observed seven transitions are also highlighted. We also demonstrate an important application of DFDL spectroscopy in the frequency stabilization of an ultraviolet laser on the transition of 200Hg.

Diagnosing the plasma nonuniformity in an iron opacity experiment by spatially resolved Al 1s-2p absorption spectroscopy

Generating a well-characterized hot-dense sample is of great importance to high quality opacity measurements. In this paper, we report on an experimental investigation of the plasma nonuniformity in a radiatively heated iron opacity sample by spatially resolved Al 1s-2p absorption spectroscopy. The iron sample was tamped by plastic at both sides and was heated by thermal x-ray radiation generated in a gold Hohlraum, and an Al layer attached to it was used as a tracer for temperature diagnosis. Spatially resolved 1s-2p transition absorption spectra of the Al tracer were measured by the technique of point-projection-spectroscopy, and temperatures in the sample were obtained by comparing the measured spectra with detailed-term-accounting model calculations, with the density of the sample deduced using a combination of side-on radiography and radiative hydrodynamic simulation. The results showed the existence of axial temperature nonuniformity in the sample, and these temperature variations have been used to explain the shift of iron 2p-3d transition absorption feature along the axial direction of the Hohlraum used to heat the sample successfully.

Interaction of atomic hydrogen with a UV pulse: model based calculations of the energy transfers from the laser field into both the electron kinetic energy and the harmonics

We study both the above-threshold ionization spectrum and harmonics generation resulting from the interaction of atomic hydrogen with a UV pulse. Our calculations are based on the solution of the time-dependent Schrödinger equation in momentum space where the kernel of the non-local Coulomb potential is replaced by a sum of separable potentials, each of them supporting one bound state of atomic hydrogen. It is shown that the interaction of hydrogen with a field, the frequency of which corresponds to the 1s-2p transition, leads, quite unexpectedly, to the emission of very energetic electrons.

Strongly driven resonant Auger effect treated by an open-quantum-system approach

We present theoretical studies of a two-step resonant Auger process at high x-ray intensity. Tuning a short x-ray pulse to the initially closed resonant channel of the 1s-2p transition in singly ionized neon, the initially neutral neon target is valence ionized. Subsequently, the strong resonant x-ray field transfers an inner-shell electron to the created outer valence vacancy, thereby creating a core-excited state. The strong resonant coupling, giving rise to Rabi oscillations involving a core transition, results in a modification of the resonant Auger-electron spectral line profile. If the valence photoelectron remains unobserved, the system of the residual ion undergoing the resonant Auger decay can be treated by an open quantum system approach. The resonant Auger-electron spectral line shape is shown to be determined by an analog of the reduced density matrix that depends on two time arguments. The equations of motion of this reduced density matrix are derived and numerical results are presented, in support of the recent experimental verification [E. Kanter et al., Phys. Rev. Lett. 107, 233001 (2011)] of this nonlinear x-ray optical effect.