Intense-field dissociation dynamics of D2+ molecular ions using ultrafast laser pulses

The dynamics of dissociation of pre-ionized D2+ molecules using intense (10^12–10^15 W cm-2), ultrashort (50 fs), infrared (? = 790 nm) laser pulses are examined. Use of an intensity selective scan technique has allowed the deuterium energy spectrum to be measured over a broad range of intensity. It is found that the dominant emission shifts to lower energies as intensity is increased, in good agreement with corresponding wavepacket simulations. The results are consistent with an interpretation in terms of bond softening, which at high intensity (approximately >3 × 10^14 W cm-2) becomes dominated by dissociative ionization. Angular distribution measurements reveal the presence of slow molecular dissociation, an indication that vibrational trapping mechanisms occur in this molecule.

Rescattering-enhanced dissociation of a molecular ion

Dissociation of the CO2+ ion has been investigated in an intense ultrafast (55 fs) laser field by employing an intensity-selective scan technique and comparing the signals from linearly and circularly polarized pulses. Nonsequential contributions have been observed, highlighting the role of rescattering in the dissociative process.

On the recollision-free excitation of krypton during ultrafast multi-electron tunnel ionization

The probability of multiple ionization of krypton by 50 femtosecond circularly polarized laser pulses, independent of the optical focal geometry, has been obtained for the first time. The excellent agreement over the intensity range 100 TW cm-2 to 100 PW cm-2 with the recent predictions of Kornev et al (2003 Phys. Rev. A 68 043414) provides the first experimental confirmation that non-recollisional electronic excitation can occur in strong-field ionization. This is particularly true for higher stages of ionization, when the laser intensity exceeds 10 PW cm-2 as the energetic departure of the ionized electron(s) diabatically distorts the wavefunctions of the bound electrons. By scaling the probability of ionization by the focal volume, we discuss why this mechanism was not apparent in previous studies.

Metastable dissociation of anions formed by electron attachment

A comprehensive analysis of metastable dissociation of 2, 4-dinitrotoluene (DNT) parent anions formed by attachment of electrons of controlled energy is presented. We characterize the energy dependence and kinetic energy release of the reaction which competes with autodetachment. A surprising finding is a highly exothermic metastable reaction triggered by the attachment of thermal electrons which we relate to the well-known electrostatic ignition hazards of DNT and other explosives. Quantum chemical calculations are performed for dinitrobenzene in order to elucidate the process of NO abstraction.

Laser annealing of sputtered silicon for wafer-bonding applications

Sputtered silicon is investigated as a bonding layer for transfer of pre-processed silicon layers to various insulating substrates. Although the material appears suitable for low temperature processing, previous work has shown that gas trapped in the pores of the sputtered material is released at temperatures above 350 degrees C and further increases of temperature lead to destruction of any bonded interface. Pre-annealing at 1000 degrees C before bonding drives out gas and/or seals the surface, but for device applications where processing temperatures must be kept below about 300 degrees C, this technique cannot be used. In the current work, we have investigated the effect of excimer laser-annealing to heat the sputtered silicon surface to high temperature whilst minimising heating of the underlying substrate. Temperature profile simulations are presented and the results of RBS, TEM and AFM used to characterise the annealed layers. The results verify that gases are present in the sub-surface layers and suggest that while sealing of the surface is important for suppression of the out-diffusion of gases, immediate surface gas removal may also play a role. The laser-annealing technique appears to be an effective method of treating sputtered silicon, yielding a low roughness surface suitable for wafer bonding, thermal splitting and layer transfer.

Two-electron QED contributions to the ground-state binding energy in He-like Kr34+ ions

The two-electron QED contributions to the ground-state binding energy of Kr34+ ions have been determined in two independent experiments performed with electron beam ion traps (EBIT) in Heidelberg (HD) and Tokyo (BT, Belfast-Tokyo collaboration). X rays arising from radiative recombination (RR) of free electrons to the ground state of initially bare Kr36+ and hydrogenlike Kr35+ ions were observed as a function of the interacting electron energy. The K edge absorption by thin Eu and W foils provided fixed photon energy references used to measure the difference in binding energy Delta E-2e between the H- and He-like Kr ions (Kr35+ and Kr34+, respectively). The two values agree well, yielding a final result of Delta E-2e=641.8 +/- 1.7 eV, confirming recent results of rigorous QED calculations. This accuracy is just of the order required to access screened radiative QED contributions.

Ancients inspire modern memory

A stencilling technique for depositing arrays of nanoscale ferroelectric capacitors on a surface could be useful in data storage devices.

Nested entangled states for distributed quantum channels

We find a coupling-strength configuration for a linear chain of N spins which gives rise to simultaneous multiple Bell states. We suggest a way such an interesting entanglement pattern can be used in order to distribute maximally entangled channels to remote locations and generate multipartite entanglement with a minimum-control approach. Our proposal thus provides a way to achieve the core resources in distributed information processing. The schemes we describe can be efficiently tested in chains of coupled cavities interacting with three-level atoms.