Thermal shock and post-quench strength of lapped borosilicate optical glass

We have measured and modeled the thermal shock fracture and strength degradation of the commercially available BK-7 borosilicate crown optical glass as a function of surface finish prior to thermal shock testing. For surfaces lapped with alumina abrasives in the range 5–40 μm, the critical temperature drop for catastrophic fracture in thin disk samples increases with diminishing abrasive size, and changes from 123.7 ± 1.1 °C (for surfaces lapped with 40 μm abrasives) to 140.2 ± 2.8 °C (for surfaces lapped with 5 μm abrasives). There is little strength degradation for temperature drops smaller than critical, and post-quenching strength depends on surface finish. We correlate the measured thermal shock (critical) temperature drop with the glass thermal and mechanical properties and lapping-induced surface finish. We distinguish between ‘severe’ and ‘mild’ thermal shock conditions in terms of the applicable heat transfer coefficient and Biot number. We estimate that the depth of the strength-controlling cracks on the edge of the disk samples was about 33–42 μm.     

Ab initio investigation of the phase lag in coherent control of H(2).

An ab initio investigation of the excitation of an H(2) resonance, coupled to ionization and dissociation continua, was performed. The excitation occurs via a one- and a three-photon path where both fields have a variable but well-defined phase relation. While both continuum yields show an oscillatory behavior as the phase is varied, a pronounced phase lag between the two oscillations is observed, if the excitation energy is detuned from the resonant transition. The results are discussed in connection to a recent series of experiments performed on HI and the subsequent discussion on the possible origin of the observed phase lag.     

Multiphoton ionization of magnesium in a Ti-sapphire laser field

In this paper we report the theoretical results obtained for partial ionization yields and the above-threshold ionization (ATI) spectra of magnesium in a Ti: sapphire laser field (804 nm) in the range of short pulse duration (20-120 fs). Ionization yield, with linearly polarized light for a 120 fs laser pulse, is obtained as a function of the peak intensity motivated by recent experimental data [9]. For this, we have solved the time-dependent Schrödinger equation nonperturbatively on a basis of discretized states obtained with two different methods; one with the two-electron wavefunction relaxed at the boundaries, giving a quadratic discretized basis and the other with the two-electron wavefunction expanded in terms of Mg ⁺ -orbitals plus one free electron allowing the handling of multiple continua (open channels). Results, obtained with the two methods, are compared and advantages and disadvantages of the open-channel method are discussed.Received: 17 June 2003, Published online: 26 August 2003PACS: 32.80.Rm Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)G. Buic-Zloh: Permanent address: Institute for Space Sciences, P.O. Box MG-23, 76900 Bucharest-Mgurele, Romania.     

Laser-induced transitions between triply excited hollow states

We present an ab initio calculation of the Li+ photoion yield in the presence of laser coupling between the triply excited 2s(2)2p(2)P(o) and 2s2p(2) (2)D(e) resonances in lithium, the first of which is assumed excited by synchrotron radiation from the ground state. The laser coupling between the triply excited states is shown to lead to a significant and readily measurable modification of the line profile which provides a unique probe of the dipole strength between highly correlated triply excited states.     

Direct versus sequential double ionization of Mg with extreme-ultraviolet radiation

We present an ab initio calculation of multiphoton double ionization in atomic magnesium, the first of its type in an atom with a complex core, showing that direct correlated double electron ejection can be studied through analysis of the photoelectron energy spectrum, using currently or upcoming extreme-ultraviolet radiation sources.     

Basis-dependent dynamics of trapped Bose-Einstein condensates and analogies with semi-classical laser theory

We present a consistent second order perturbation theory for the lowest-lying condensed modes of very small, weakly-interacting Bose-Einstein condensates in terms of bare particle eigenstates in a harmonic trap. After presenting our general approach, we focus on explicit expressions for a simple three-level system, mainly in order to discuss the analogy of a single condensate occupying two modes of a trap with the semi-classical theory for two-mode photon lasers. A subsequent renormalization of the single-particle energies to include the dressing imposed by mean fields demonstrates clearly the consistency of our treatment with other kinetic approaches. Received 14 December 2001