We demonstrate the capability of ab-initio time-dependent R-matrix theory to obtain accurate harmonic generation spectra of noble-gas atoms at Near-IR wavelengths between 1200 and 1800 nm and peak intensities up to 1.8 × 10 14 W/cm 2 . To accommodate the excursion length of the ejected electron, we use an angular-momentum expansion up to Lmax = 279. The harmonic spectra show evidence of atomic structure through the presence of a Cooper minimum in harmonic generation for Kr, and of multielectron interaction through the giant resonance for Xe. The theoretical spectra agree well with those obtained experimentally.

PACS numbers: 32.80.Gc 31.15.VSeveral omissions in our recent discussion on strong-field photodetachment [1] have been brought to our attention since the work was published. Calculations solving the time-dependent Schrödinger equation (TDSE) for electron rescattering from F − have been carried out previously using the single active electron approximation [2,3]. The ejected-electron distributions presented in [2,3] show clear evidence for the importance of electron rescattering in strong-field photodetachment, and agree well with calculations based on the strong-field approximation.Our ejected-electron spectra, presented in [1], show the same general features as in [2,3]. However, our calculations are based on the solution of the TDSE for a full, 10-electron system, demonstrating the high quality of the final wavefunction obtained using a fully ab initio approach. The capability to describe all electrons also allows us to assess the importance of electron correlations in the multiphoton ionization process, thus going beyond the results previously reported in the literature.As a consequence of our oversight of [2, 3], we misrepresented the results presented in [4] where the rescattering process was found but not shown explicitly [5].Finally, we point out that early studies of the use of the strong field approximation for electron rescattering were previously presented in [6,7]. More recently, angle resolved spectra have been measured experimentally for above threshold detachment of Br − , with a strong-field approximation model providing almost indistinguishable theoretical results [8].

We apply the time-dependent R-matrix method to investigate harmonic generation from Ne + at a wavelength of 390 nm and intensities up to 10 15 Wcm −2 . The 1s 2 2s 2 2p 4 ( 3 P e , 1 D e , and 1 S e ) states of Ne 2+ are included as residual-ion states to assess the influence of interference between photoionization channels associated with these thresholds. The harmonic spectrum is well approximated by calculations in which only the 3 P e and 1 D e thresholds are taken into account, but no satisfactory spectrum is obtained when a single threshold is taken into account. Within the harmonic plateau, extending to about 100 eV, individual harmonics can be suppressed at particular intensities when all Ne 2+ thresholds are taken into account. The suppression is not observed when only a single threshold is accounted for. Since the suppression is dependent on intensity, it may be difficult to observe experimentally.

We present ab initio studies of photoelectron spectra for above threshold detachment (ATD) of F − anions in short, 1300 nm and 1800 nm laser pulses. We identify and assess the importance of electron rescattering in strong-field photodetachment of a negative ion through comparison with an analytic, Keldysh-type approach, demonstrating the capability of ab-initio computation in the challenging near-IR regime. We further assess the influence of the strong electron correlation on the photodetachment.PACS numbers: 32.80.Gc 31.15.VElectron rescattering is one of the fundamental processes occuring in the interaction between matter and intense light fields [1]. The mechanism is a critical part of the well known three-step or recollision model for high harmonic generation (HHG) or strong field double ionisation. According to the model an electron is first ionised, then driven by a strong laser field, before recolliding with the parent ion, either recombining, leading to HHG [2,3], or rescattering, leading to high-energy electron emission [4,5], or non-sequential double ionisation [6].Electron rescattering also encodes structural information about the residual ion into the wavepacket of the ejected electron and can thus be exploited as an experimental probe of the structure of the parent ion [1]. The technique is especially sensitive as the current density of a recolliding electron wavepacket exceeds that of conventional electron sources by several orders of magnitude [7]. Furthermore, the inherently subcycle and phase-locked nature of the recollision process gives access to electron dynamics on the attosecond scale, via information embedded in the photoelectron spectrum [8,9].One of the open questions in strong-field science concerns the importance of electron rescattering for negative ions. Significant progress has been made in understanding and controlling the equivalent process in neutral atoms and positive ions [10], but above-threshold detachment (ATD) presents a different challenge. The small binding energy allows detachment at low intensities. Hence to reach significant recollision energies, nearinfrared (NIR) laser fields are required. In addition, the absence of the Coulomb potential makes it easier for the electron wavepacket to spread out, reducing the effect of rescattering [4,5]. While evidence for rescattering from negative ions has been found experimentally [11], no verification has yet been provided from ab initio theory. A theoretical approach, based on first order correction to the strong field approximation, was able to reproduce experimental results from Br − and F − , [12] but a more recent study, using a numerical solution of the time-dependent Schrödinger equation (TDSE), found "no qualitative evidence of rescattering" for H − [13]. In this report we demonstrate that ab-initio theory can be used to investigate rescattering in the NIR regime.An additional complication in the description of negative ions is the much larger influence of dielectronicrepulsion. Several approximate methods have been empl...

We present ab initio studies of photoelectron spectra for above threshold detachment (ATD) of F − anions in short, 1300 nm and 1800 nm laser pulses. We identify and assess the importance of electron rescattering in strong-field photodetachment of a negative ion through comparison with an analytic, Keldysh-type approach, demonstrating the capability of ab-initio computation in the challenging near-IR regime. We further assess the influence of the strong electron correlation on the photodetachment.PACS numbers: 32.80.Gc 31.15.V-Electron rescattering is one of the fundamental processes occuring in the interaction between matter and intense light fields [1]. The mechanism is a critical part of the well known three-step or recollision model for high harmonic generation (HHG) or strong field double ionisation. According to the model an electron is first ionised, then driven by a strong laser field, before recolliding with the parent ion, either recombining, leading to HHG [2, 3], or rescattering, leading to high-energy electron emission [4,5], or non-sequential double ionisation [6].Electron rescattering also encodes structural information about the residual ion into the wavepacket of the ejected electron and can thus be exploited as an experimental probe of the structure of the parent ion [1]. The technique is especially sensitive as the current density of a recolliding electron wavepacket exceeds that of conventional electron sources by several orders of magnitude [7]. Furthermore, the inherently subcycle and phase-locked nature of the recollision process gives access to electron dynamics on the attosecond scale, via information embedded in the photoelectron spectrum [8,9].One of the open questions in strong-field science concerns the importance of electron rescattering for negative ions. Significant progress has been made in understanding and controlling the equivalent process in neutral atoms and positive ions [10], but above-threshold detachment (ATD) presents a different challenge. The small binding energy allows detachment at low intensities. Hence to reach significant recollision energies, nearinfrared (NIR) laser fields are required. In addition, the absence of the Coulomb potential makes it easier for the electron wavepacket to spread out, reducing the effect of rescattering [4,5]. While evidence for rescattering from negative ions has been found experimentally [11], no verification has yet been provided from ab initio theory. A theoretical approach, based on first order correction to the strong field approximation, was able to reproduce experimental results from Br − and F − , [12] but a more recent study, using a numerical solution of the time-dependent Schrödinger equation (TDSE), found "no qualitative evidence of rescattering" for H − [13]. In this report we demonstrate that ab-initio theory can be used to investigate rescattering in the NIR regime.An additional complication in the description of negative ions is the much larger influence of dielectronicrepulsion. Several approximate methods have been emp...

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Municipal sludge handling is a major problem facing wastewater treatment plants due to the high costs of treatment and disposal. This issue is of special importance in Jordan because of the critical economic situation as well as the lack of ®nancial support for such nonpro®t projects. This study investigates the possibility of solving this problem by testing a method of sludge stabilization that requires minimum initial and operating costs. The method tested here is sludge stabilization by composting which is an attempt to transform sludge into a safe, nuisance free, humus like product that can be applied safely to land and can become a source of income that would recover the costs of processing.Two types of composting systems were tested in this study, aerated static pile and windrow. Results obtained indicate that composting of dried sludge was not possible due to the extremely low moisture content; which was overcome by sludge seeding and mixing with amendment and bulking agents. This resulted in ef®cient stabilization and reduction of the amount of organic matter in the ®nal compost. The experimental results obtained also indicate that both systems (aerated static pile and windrow) are ef®cient. The organic content of the sludge was reduced in the windrow system by 46% and in the aerated static pile by 66%. In addition, the total volatile solids had decreased in the windrow and the aerated pile by 26 and 73%, respectively. The heavy metals content of the ®nal compost was examined and found to comply with the international standards.

We present an analysis of the appearance of the Cooper Minimum in singly ionized argon in both the photoionization cross-section (PICS) and high-harmonic generation (HHG) spectrum. We employ two computational approaches based on the same R-matrix technique to provide a coherent description of the atomic structure of the Ar + system, finding that the PICS and HHG spectrum are affected differently by the inclusion of additional residual ion states and the improved description of correlation effects. Both the PICS and HHG spectrum possess a clear minimum for all atomic structure models used, with the centre of the minimum at 55 eV in the PICS and 60 eV in the HHG spectrum for the most complete description employed. The HHG minimum is systematically shifted to higher energies with respect to the PICS minimum. We also find that the initial magnetic alignment (magnetic quantum number) of the Ar + system does not affect substantially the position and shape of the HHG minimum (given a sufficiently detailed atomic structure description), but the harmonic yield is enhanced by two-orders of magnitude for ML = 1 over ML = 0. We also perform similar calculations for neutral argon, finding that this system is more sensitive to enhancements in the atomic structure description.PACS numbers: 32.80. Rm, 42.65.Ky