arXiv subjects

J. L. Collier

Publications and source records attributed to J. L. Collier.

5 recordsLinked to original sources

arXiv2010

Observation of a Long-Wavelength Hosing Modulation of a High-Intensity Laser Pulse in Underdense Plasma

We report the first experimental observation of a long-wavelength hosing modulation of a high-intensity laser pulse. Side-view images of the scattered optical radiation at the fundamental wave-length of the laser reveal a transverse oscillation of the laser pulse during its propagation through underdense plasma. The wavelength of the oscillation λ_hosing depends on the background plasma density n_e and scales as λ_hosing~n_e^-3/2. Comparisons with an analytical model and 2-dimensional particle-in-cell simulations reveal that this laser hosing can be induced by a spatio-temporal asymmetry of the intensity distribution in the laser focus which can be caused by a misalignment of the parabolic focussing mirror or of the diffraction gratings in the pulse compressor.

physics.plasm-ph↗

arXiv2010

Atomic excitation during recollision-free ultrafast multi-electron tunnel ionization

Modern intense ultrafast pulsed lasers generate an electric field of sufficient strength to permit tunnel ionization of the valence electrons in atoms. This process is usually treated as a rapid succession of isolated events, in which the states of the remaining electrons are neglected. Such electronic interactions are predicted to be weak, the exception being recollision excitation and ionization caused by linearly-polarized radiation. In contrast, it has recently been suggested that intense field ionization may be accompanied by a two-stage `shake-up' reaction. Here we report a unique combination of experimental techniques that enables us to accurately measure the tunnel ionization probability for argon exposed to 50 femtosecond laser pulses. Most significantly for the current study, this measurement is independent of the optical focal geometry, equivalent to a homogenous electric field. Furthermore, circularly-polarized radiation negates recollision. The present measurements indicate that tunnel ionization results in simultaneous excitation of one or more remaining electrons through shake-up. From an atomic physics standpoint, it may be possible to induce ionization from specific states, and will influence the development of coherent attosecond XUV radiation sources. Such pulses have vital scientific and economic potential in areas such as high-resolution imaging of in-vivo cells and nanoscale XUV lithography.

physics.atom-ph↗

arXiv2007

Isolated vibrational wavepackets in D2+: Defining superposition conditions and wavepacket distinguishability

Tunnel ionization of room-temperature D$_2$ in an ultrashort (12 femtosecond) near infra-red (800 nm) pump laser pulse excites a vibrational wavepacket in the D2+ ions; a rotational wavepacket is also excited in residual D2 molecules. Both wavepacket types are collapsed a variable time later by an ultrashort probe pulse. We isolate the vibrational wavepacket and quantify its evolution dynamics through theoretical comparison. Requirements for quantum computation (initial coherence and quantum state retrieval) are studied using this well-defined (small number of initial states at room temperature, initial wavepacket spatially localized) single-electron molecular prototype by temporally stretching the pump and probe pulses.

physics.chem-ph↗

arXiv2007

Mapping the Evolution of Optically-Generated Rotational Wavepackets in a Room Temperature Ensemble of D$_2$

A coherent superposition of rotational states in D$_2$ has been excited by nonresonant ultrafast (12 femtosecond) intense (2 $\times$ 10$^{14}$ Wcm$^{-2}$) 800 nm laser pulses leading to impulsive dynamic alignment. Field-free evolution of this rotational wavepacket has been mapped to high temporal resolution by a time-delayed pulse, initiating rapid double ionization, which is highly sensitive to the angle of orientation of the molecular axis with respect to the polarization direction, $θ$. The detailed fractional revivals of the neutral D$_2$ wavepacket as a function of $θ$ and evolution time have been observed and modelled theoretically.

quant-ph↗

arXiv2005

Enabling pulse compression and proton acceleration in a modular ICF driver for nuclear and particle physics applications

The existence of efficient ion acceleration regimes in collective laser-plasma interactions opens up the possibility to develop high-energy physics facilities in conjunction with projects for inertial confinement nuclear fusion (ICF) and neutron spallation sources. In this paper, we show that the pulse compression requests to make operative these acceleration mechanisms do not fall in contradiction with current technologies for high repetition rate ICF drivers. In particular, we discuss explicitly a solution that exploits optical parametric chirped pulse amplification and the intrinsic modularity of the lasers aimed at ICF.

physics.acc-ph↗