Reply To "comment On 'photoionization Of Helium Atoms Irradiated With Intense Vacuum Ultraviolet Free-electron Laser Light. Part I. Experimental Study Of Multiphoton And Single-photon Processes'"

We do not agree with the conclusion of the Comment by Charalambidis questioning our observation of two-photon ionization of helium by intense radiation with 13 eV photons from a vuv free-electron laser. Two-photon ionization is clearly established by the detection of low-energy photoelectrons at ∼1.7 eV, which agrees very well with the expected energy for a two-photon ionization process. © 2006 The American Physical Society.743Laarmann, T., De Castro, A.R.B., Schulz, J., Wabnitz, H., Möller, T., (2005) Phys. Rev. A, 72, p. 023409. , PLRAAN. 1050-2947. 10.1103/PhysRevA.72.023409Ayvazyan, V., Baboi, N., Bohnet, I., Brinkmann, R., Castellano, M., Castro, P., Catani, L., Zapfe, K., (2002) Phys. Rev. Lett., 88, p. 104802. , PRLTAO. 0031-9007. 10.1103/PhysRevLett.88.104802Ayvazyan, V., Baboi, N., Bähr, J., Balandin, V., Beutner, B., Brandt, A., Bohnet, I., Schreiber H, -J., (2006) Eur. Phys. J. D, 37, p. 297. , EPJDF6. 1434-6060. 10.1140/epjd/e2005-00308-1Wabnitz, H., Bittner, L., De Castro, A.R.B., Döhrmann, R., Gürtler, P., Laarmann, T., Laasch, W., Yurkov, M., (2002) Nature (London), 420, p. 482. , NATUAS. 0028-0836. 10.1038/nature01197Laarmann, T., De Castro, A.R.B., Gürtler, P., Laasch, W., Schulz, J., Wabnitz, H., Möller, T., (2004) Phys. Rev. Lett., 92, p. 143401. , PRLTAO. 0031-9007. 10.1103/PhysRevLett.92.143401Laarmann, T., Rusek, M., Wabnitz, H., Schulz, J., De Castro, A.R.B., Gürtler, P., Laasch, W., Möller, T., (2005) Phys. Rev. Lett., 95, p. 063402. , PRLTAO. 0031-9007. 10.1103/PhysRevLett.95.063402Wabnitz, H., De Castro, A.R.B., Gürtler, P., Laarmann, T., Laasch, W., Schulz, J., Möller, T., (2005) Phys. Rev. Lett., 94, p. 023001. , PRLTAO. 0031-9007. 10.1103/PhysRevLett.94.023001Santra, R., Greene, C.H., (2004) Phys. Rev. A, 70, p. 053401. , PLRAAN 1050-2947 10.1103/PhysRevA.70.053401Tzallas, P., Charalambidis, D., Papadogiannis, N.A., Witte, K., Tsakiris, G.D., (2003) Nature (London), 426, p. 267. , NATUAS 0028-0836 10.1038/nature02091Papadogiannis, N.A., Nikolopoulos, L.A.A., Charalambidis, D., Tsakiris, G.D., Tzallas, P., Witte, K., (2003) Appl. Phys. B, 76, p. 721. , APDOEM 0946-2171Papadogiannis, N.A., Nikolopoulos, L.A.A., Charalambidis, D., Tsakiris, G.D., Tzallas, P., Witte, K., (2003) Phys. Rev. Lett., 90, p. 133902. , PRLTAO 0031-9007 10.1103/PhysRevLett.90.133902De Castro, A.R.B., Laarmann, T., Schulz, J., Wabnitz, H., Möller, T., (2005) Phys. Rev. A, 72, p. 023410. , PLRAAN. 1050-2947. 10.1103/PhysRevA.72.02341

Interaction of argon clusters with intense VUV-laser radiation: the role of electronic structure in the energy-deposition process

Sem informaçãoThe response of Ar clusters to intense vacuum-ultraviolet pulses is investigated with photoion spectroscopy By varying the laser wavelength, the initial excitation was either tuned to absorption bands of surface or bulk atoms of clusters. Multiple ionization is observed, which leads to Coulomb explosion. The efficiency of resonant 2-photon ionization for initial bulk and surface excitation is compared with that of the norresonant process at different laser intensities. The specific electronic structure of clusters plays almost no role in the explosion dynamics at a peak intensity larger than 1.8 X 10(12) W/cm(2). The inner ionization of atoms for resonant and nonresonant excitation is then saturated and the energy deposition is mainly controlled by the plasma heating rate. Molecular dynamics simulations indicate that standard collisional heating cannot fully account for the strong energy absorption.The response of Ar clusters to intense vacuum-ultraviolet pulses is investigated with photoion spectroscopy By varying the laser wavelength, the initial excitation was either tuned to absorption bands of surface or bulk atoms of clusters. Multiple ionization is observed, which leads to Coulomb explosion. The efficiency of resonant 2-photon ionization for initial bulk and surface excitation is compared with that of the norresonant process at different laser intensities. The specific electronic structure of clusters plays almost no role in the explosion dynamics at a peak intensity larger than 1.8 X 10(12) W/cm(2). The inner ionization of atoms for resonant and nonresonant excitation is then saturated and the energy deposition is mainly controlled by the plasma heating rate. Molecular dynamics simulations indicate that standard collisional heating cannot fully account for the strong energy absorption.921414Sem informaçãoSem informaçãoSem informaçãoWe thank A. Swiderski for technical support and the TTF team at DESY for providing the FEL beam and the photon diagnostics. This work was supported by DFG

Multiple ionization of rare gas atoms irradiated with intense VUV radiation

Sem informaçãoThe interaction of intense vacuum-ultraviolet radiation from a free-electron laser with rare gas atoms is investigated. The ionization products of xenon and argon atomic beams are analyzed with time-of-flight mass spectroscopy. At 98 nm wavelength and similar to10(13) W/cm(2) multiple charged ions up to Xe6+ (Ar4+) are detected. From the intensity dependence of multiple charged ion yields the mechanisms of multiphoton processes were derived. In the range of similar to10(12)-10(13) W/cm(2) the ionization is attributed to sequential multiphoton processes. The production of multiple charged ions saturates at 5-30 times lower power densities than at 193 and 564 nm wavelength, respectively.The interaction of intense vacuum-ultraviolet radiation from a free-electron laser with rare gas atoms is investigated. The ionization products of xenon and argon atomic beams are analyzed with time-of-flight mass spectroscopy. At 98 nm wavelength and similar to10(13) W/cm(2) multiple charged ions up to Xe6+ (Ar4+) are detected. From the intensity dependence of multiple charged ion yields the mechanisms of multiphoton processes were derived. In the range of similar to10(12)-10(13) W/cm(2) the ionization is attributed to sequential multiphoton processes. The production of multiple charged ions saturates at 5-30 times lower power densities than at 193 and 564 nm wavelength, respectively.94214Sem informaçãoSem informaçãoSem informaçãoWe thank A. Swiderski for technical support in the design and construction of the cluster experiment and the TTF team at DESY for providing the FEL beam and the photon diagnostics. One of the authors (H.W.) is grateful to Peter Lambropoulos for helpful comments. In addition, we thank R. Santra for making calculations available prior to publication

Photoionization of helium atoms irradiated with intense vacuum ultraviolet free-electron laser light. Part I. Experimental study of multiphoton and single-photon processes

Sem informaçãoThe interaction of He atoms with intense vacuum-ultraviolet light of a free-electron laser is investigated using time-of-flight mass spectroscopy and photoelectron spectroscopy. The atoms were irradiated with 100 fs pulses at 95 nm wavelength, which corresponds to similar to 13 eV photon energy. The ionization of He atoms is observed at a peak intensity of 10(10)-10(13) W/cm(2), which is due both to nonlinear multiphoton ionization with the fundamental wavelength and single-photon ionization with third harmonic radiation of the free-electron laser. The observation of two sharp photoelectron peaks in the kinetic energy spectra, that are separated by the photon energy, is in agreement with the numerical solution of the time-dependent Schrodinger equation. The calculation was done using the fully quantized field and a limited but representative set of basis states. The ionization rate dependence on the laser peak intensity indicates that: (a) The low-energy peak in the photoelectron spectra is mainly due to two-photon absorption of the fundamental, but (b) the high-energy peak at 15.4 eV is probably due to third harmonic FEL radiation. The theoretically predicted contribution from three-photon absorption of the fundamental is of about the same order of magnitude and could not be separated from the third harmonic background signal. Particularly, the photoelectron spectra and He+ time-of-flight data give evidence that the intensity of third harmonic light is high enough to perform single-shot spectroscopy on gas phase samples.The interaction of He atoms with intense vacuum-ultraviolet light of a free-electron laser is investigated using time-of-flight mass spectroscopy and photoelectron spectroscopy. The atoms were irradiated with 100 fs pulses at 95 nm wavelength, which corresponds to similar to 13 eV photon energy. The ionization of He atoms is observed at a peak intensity of 10(10)-10(13) W/cm(2), which is due both to nonlinear multiphoton ionization with the fundamental wavelength and single-photon ionization with third harmonic radiation of the free-electron laser. The observation of two sharp photoelectron peaks in the kinetic energy spectra, that are separated by the photon energy, is in agreement with the numerical solution of the time-dependent Schrodinger equation. The calculation was done using the fully quantized field and a limited but representative set of basis states. The ionization rate dependence on the laser peak intensity indicates that: (a) The low-energy peak in the photoelectron spectra is mainly due to two-photon absorption of the fundamental, but (b) the high-energy peak at 15.4 eV is probably due to third harmonic FEL radiation. The theoretically predicted contribution from three-photon absorption of the fundamental is of about the same order of magnitude and could not be separated from the third harmonic background signal. Particularly, the photoelectron spectra and He+ time-of-flight data give evidence that the intensity of third harmonic light is high enough to perform single-shot spectroscopy on gas phase samples.72218Sem informaçãoSem informaçãoSem informaçãoWe thank A. Swiderski for technical support in the design and construction of the experiment and the TTF team at DESY for running the accelerator, working on the FEL and the photon diagnostics. This work was supported by the DFG

Gastrointestinal Stents: Materials and Designs

Over the last 25 years stents have developed into an established way of restoring luminal patency throughout the gastrointestinal tract. Materials used as well as the construction of these devices have become more and more sophisticated in order to comply better with the complex environment they are inserted. The requirements vary greatly from organ to organ and stent behavior differs significantly between stent constructions. However this is not necessarily understood by many operators, as the choice of devices is now vast and in many cases decisions are made on availability and cost. An increasing challenge in malignant conditions is the improving survival of incurable patients, which now exceeds the traditional life expectancy of a stent by a factor of 2 to 3. Consequently more patients experience failure of their stent and require repeat interventions. This has a poor impact on patients’ quality of life and potentially on their survival. Re-intervention is often more difficult, carries the risk of additional complications and presents an additional economic burden to the health systems. This article illustrates current stent designs, their different behavior and their limitations

Towards an appreciation of ethics in social enterprise business models

How can a critical analysis of entrepreneurial intention inform an appreciation of ethics in social enterprise business models? In answering this question, we consider the ethical commitments that inform entrepreneurial action (inputs) and the hybrid organisations that emerge out of these commitments and actions (outputs). Ethical theory can be a useful way to re-orient the field of social enterprise so that it is more critical of bureaucratic (charitable) and market-driven (business) enterprises connected to neo-liberal doctrine. Social enterprise hybrid business models are therefore reframed as outcomes of both ethical and entrepreneurial intentions. We challenge the dominant conceptualisation of social enterprise as a hybrid blend of mission and market (purpose-versus-resource) by reframing hybridity in terms of the moral choice of economic system (redistribution, reciprocity and market) and social value orientation (personal, mutual or public benefit). We deconstruct the political foundations of charitable trading activities (CTAs), co-operative and mutual enterprises (CMEs) and socially responsible businesses (SRBs) by examining the rationalities (formal, social and substantive) and ethical commitments (utilitarian, communitarian, pragmatic) that underpin them. Whilst conceptual modelling of social enterprise is not new, this paper contributes to knowledge by developing a theory of social enterprise ethics based on the moral/political choices that are made by entrepreneurs (knowingly and unknowingly) when choosing between systems of economic exchange and social value orientation, then expressing it through a legal form

Enteral stent construction: Current principles

The insertion of self-expanding stents into malignant strictures of the small and large bowel has become a routine procedure around the world. However, stent development has happened very much on a “trial & error” approach, based mostly on bright ideas of enthusiastic individuals or marketing decisions by the manufacturer. A large variety of stents are commercially available, covered to a variable degree by a membrane to reduce tissue ingrowth. However, in vitro characteristics and in vivo behavior vary significantly between stents and few operators are aware of the differences. While the ideal stent still remains to be defined, it is important that interventionists understand the variations, in order to make the best possible choice for the individual patient. This article illustrates current principles of stent construction