Search results for "HRES"
showing 10 items of 695 documents
The general expression for the transition amplitude of two-photon ionization of atomic hydrogen
2003
Two-photon ionization of atomic hydrogen with an excess photon is revisited. The non-relativistic dipole approximation and Coulomb Green function (CGF) formalism are applied. Using the CGF Sturmian expansion straightforwardly, one gets the radial transition amplitude in the form of an infinite sum over Gauss hypergeometric functions which are polynomials. It is convergent if all intermediate states are in the discrete spectrum. In the case of two-photon ionization with an excess photon, when photoionization is also possible, intermediate states are in the continuum. We performed the explicit summation over intermediate states and got a simple general expression for the radial transition amp…
Multi-longitudinal mode emission in a bidirectional laser model
2011
Multi-longitudinal mode emission is a fundamental issue in laser physics. Interestingly enough, the mechanisms responsible for the transition from single- to multi-longitudinal mode emission have not been completely clarified yet. For example, it is well known that in unidirectional ring lasers the Rabi splitting of the lasing transition can lead to multimode emission even in a homogeneously broadened medium, the so called Risken-Nummedal—Graham-Haken instability (RNGHI) [1]. In spite of being known since the late sixties, only in the recent years a couple of experiments have demonstrated “dressed” versions of the RNGHI [2], i.e., up to day there are not clear demonstrations of this basic m…
Evidence for degenerate mirrorless lasing in alkali metal vapor: forward beam magneto-optical experiment
2018
We report an experimental observation of degenerate mirrorless lasing in forward direction under excitation of a dilute atomic Rb vapor with a single linearly polarized cw laser light resonant with cycling Fe > Fg atomic D2 transitions. Light polarized orthogonally to the laser light is generated for the input light intensity exceeding a threshold value of about 3 mW/cm^2. Application of a transverse magnetic field directed along the input light polarization reveals a sharp about 20 mG wide magnetic resonance centered at B = 0. Increasing the incident light intensity from 3 to 300 mW/cm^2, the generated light undergoes rapid amplitude increase followed by a decline and resonance broadeni…
Measuring charge based quantum bits by a superconducting single-electron transistor
2002
Single-electron transistors have been proposed to be used as a read-out device for Cooper pair charge qubits. Here we show that a coupled superconducting transistor at a threshold voltage is much more effective in measuring the state of a qubit than a normal-metal transistor at the same voltage range. The effect of the superconducting gap is to completely block the current through the transistor when the qubit is in the logical state 1, compared to the mere diminishment of the current in the normal-metal case. The time evolution of the system is solved when the measuring device is driven out of equilibrium and the setting is analysed numerically for parameters accessible by lithographic alu…
Laser action in electrically driven quantum dot matrix
2007
A lasing system based on electrically driven quantum dot matrix is proposed, where population inversion of the dot matrix is obtained by rapid (nonadiabatic) switching on of in-plane electric field as a pumping force. Numerical analysis of electron-photon system kinetics is performed for various electric fields and temperatures. For parabolic type of confinement in QDs, a convenient amplification of contribution from several levels is indicated. The relevant analysis utilises an exact solution of Cauchy problem for an infinite chain of linear differential equations.
Lasing condition for trapped modes in subwavelength--wired PT--symmetric resonators
2021
The ability to control the laser modes within a subwavelength resonator is of key relevance in modern optoelectronics. This work deals with the theoretical research on optical properties of a PT-symmetric nano-scaled dimer formed by two dielectric wires, one is with loss and the other with gain, wrapped with graphene sheets. We show the existence of two non-radiating trapped modes which transform into radiating modes by increasing the gain–loss parameter. Moreover, these modes reach the lasing condition for suitable values of this parameter, a fact that makes these modes achieve an ultra high quality factor that is manifested on the response of the structure when it is excited by a plane wa…
Transverse effects in ring fiber laser multimode instabilities
2000
We study the influence of the transverse structure of pump and lasing fields and of the width of the doped region on the conditions for the appearance of the multimode instability in an ${\mathrm{Er}}^{3+}$-doped ring fiber laser. We show that the instability can be inhibited while maintaining a large output power when the radius of the doped region is a fraction of the core radius.
The τ+τ− production cross section near threshold revisited
2003
Next-to-next-to-leading contributions to the cross section sigma(e+e- -> tau+tau-) at energies close to threshold are analysed, taking into account the known non-relativistic effects and O(alpha^2) corrections. The numerical changes with respect to previous works are small, but the new corrections give a true estimate of the uncertainty in the theoretical calculation.
Ionization of atomic hydrogen with up to four excess photons by circularly and linearly polarized light
2012
The above threshold ionization (ATI) is investigated for H in ns states. The total generalized cross sections are calculated for up to 4 excess photons using perturbation theory and modified Coulomb Green's function Sturmian expansion.
Measurement and interpretation of the polarization of the x-ray line emission of heliumlike Fe XXV excited by an electron beam
1996
The linear polarization of the 1s2p${\mathrm{}}^{1}$${\mathit{P}}_{1}$\ensuremath{\rightarrow}1${\mathit{s}}^{2}$${\mathrm{}}^{1}$${\mathit{S}}_{0}$ resonance line, the 1s2p${\mathrm{}}^{3}$${\mathit{P}}_{1,2}$\ensuremath{\rightarrow}1${\mathit{s}}^{2}$${\mathrm{}}^{1}$${\mathit{S}}_{0}$ intercombination lines, and the 1s2s${\mathrm{}}^{3}$${\mathit{S}}_{1}$\ensuremath{\rightarrow}1${\mathit{s}}^{2}$${\mathrm{}}^{1}$${\mathit{S}}_{0}$ forbidden line was measured in heliumlike Fe XXV excited near threshold by a monoenergetic electron beam. The measurement was carried out with a high-resolution x-ray spectrometer employing a set of two analyzing crystals that acted as polarizers by selectivel…