Search

Your search keyword '"Liontos, I."' showing total 36 results
Start Over Author "Liontos, I."
36 results on '"Liontos, I."'

1. Generation of energetic highly elliptical extreme ultraviolet radiation

Author

Vassakis, E., Orfanos, I., Liontos, I., Charalambidis, D., Tzallas, P., and Skantzakis, E.

Subjects
Physics - Atomic Physics, Physics - Optics
Abstract

In this study the generation of energetic coherent extreme ultraviolet (XUV) radiation with controlled polarization, is reported. The XUV radiation results from the process of high harmonic generation (HHG), in a gas phase atomic medium, driven by an intense two-color circularly polarized counter-rotating laser field, under loose focusing geometry conditions. The energy of the XUV radiation emitted per laser pulse is found to be of the order of ~100 nJ with the spectrum spanning from 17 to 26 eV. The demonstrated energy values along with tight focusing geometries is sufficient to induce nonlinear processes and challenges the perspectives for ultrafast investigations of chiral phenomena in the XUV spectral region., Comment: 17 pages, 5 Figures

Published
2021

2. Quantum path interferences in high-order harmonic generation from aligned diatomic molecules

Author

Chatziathanasiou, S., Liontos, I., Skantzakis, E., Kahaly, S., Kahaly, M. Upadhyay, Tsatrafyllis, N., Faucher, O., Witzel, B., Papadakis, N., Charalambidis, D., and Tzallas, P.

Subjects
Physics - Atomic Physics, Physics - Optics
Abstract

Electron quantum path interferences in strongly laser-driven aligned molecules and their dependence on the molecular alignment is an essential open problem in strong-field molecular physics. Here, we demonstrate an approach which provides direct access to the observation of these interference processes. The approach is based on the combination of the time-gated-ion-microscopy technique with a pump-probe arrangement used to align the molecules and generate high-order harmonics. By spatially resolving the interference pattern produced by the spatiotemporal overlap of the harmonics emitted by the short and long electron quantum paths, we have succeeded in measuring in situ their phase difference and disclose their dependence on molecular alignment. The findings constitute a vital step towards an understanding of strong-field molecular physics and the development of attosecond spectroscopy approaches without the use of auxiliary atomic references., Comment: 7 pages, 3 figures

Published
2020
Full Text
View/download PDF

3. Phase-matching mechanism for high-harmonic generation in the overdriven regime driven by few-cycle laser pulses

Author

Schötz, J., Förg, B., Schweinberger, W., Liontos, I., Masood, H. A., Kamal, A. M., Jakubeit, C., Kling, N. G., Paasch-Colberg, T., Högner, M., Pupeza, I., Alharbi, M., Kling, M. F., and Azzeer, A. M.

Subjects
Physics - Optics, Physics - Atomic Physics
Abstract

Isolated attosecond pulses (IAPs) produced through laser-driven high-harmonic generation (HHG) hold promise for unprecedented insight into biological processes via attosecond x-ray diffraction with tabletop sources. However, efficient scaling of HHG towards x-ray energies has been hampered by ionization-induced plasma generation impeding the coherent buildup of high-harmonic radiation. Recently, it has been shown that these limitations can be overcome in the so-called 'overdriven regime' where ionization loss and plasma dispersion strongly modify the driving laser pulse over small distances, albeit without demonstrating IAPs. Here, we report on experiments comparing the generation of IAPs in argon and neon at 80 eV via attosecond streaking measurements. Contrasting our experimental results with numerical simulations, we conclude that IAPs in argon are generated through ionization-induced transient phase-matching gating effective over distances on the order of 100 $\mu$m. We show that the decay of the intensity and blue-shift due to plasma defocussing are crucial for allowing phase-matching close to the XUV cutoff at high plasma densities. We perform simulations for different gases and wavelengths and show that the mechanism is important for the phase-matching of long-wavelength, tightly-focused laser beams in high-pressure gas targets, which are currently being employed for scaling isolated attosecond pulse generation to x-ray photon energies., Comment: 22 pages, 13 figures

Published
2019
Full Text
View/download PDF

7. Phase-Matching for Generation of Isolated Attosecond XUV and Soft-X-Ray Pulses with Few-Cycle Drivers

Author

Schötz, J., primary, Förg, B., additional, Schweinberger, W., additional, Liontos, I., additional, Masood, H. A., additional, Kamal, A. M., additional, Jakubeit, C., additional, Kling, N. G., additional, Paasch-Colberg, T., additional, Biswas, S., additional, Högner, M., additional, Pupeza, I., additional, Alharbi, M., additional, Azzeer, A. M., additional, and Kling, M. F., additional

Published
2020
Full Text
View/download PDF

8. Non-linear processes in the extreme ultraviolet

Author

Orfanos, I, primary, Makos, I, additional, Liontos, I, additional, Skantzakis, E, additional, Major, B, additional, Nayak, A, additional, Dumergue, M, additional, Kühn, S, additional, Kahaly, S, additional, Varju, K, additional, Sansone, G, additional, Witzel, B, additional, Kalpouzos, C, additional, Nikolopoulos, L A A, additional, Tzallas, P, additional, and Charalambidis, D, additional

Published
2020
Full Text
View/download PDF

12. Attosecond pulse metrology

Author

Orfanos, I., primary, Makos, I., additional, Liontos, I., additional, Skantzakis, E., additional, Förg, B., additional, Charalambidis, D., additional, and Tzallas, P., additional

Published
2019
Full Text
View/download PDF

13. Probing Molecular Influence on Photoemission Delays

Author

Biswas, Shubhadeep, primary, Liontos, I., additional, Kamal, A. M., additional, Kling, N. G., additional, Alharbi, A. F., additional, Alharbi, M., additional, Azzeer, A. M., additional, Worner, H. J., additional, Landsman, A. S., additional, Kling, M. F., additional, Forg, B., additional, Schotz, J., additional, Schweinberger, W., additional, Ortmann, L., additional, Zimmermann, T., additional, Pi, L.-W., additional, Baykusheva, D., additional, and Masood, H. A., additional

Published
2019
Full Text
View/download PDF

14. The ejection of triatomic molecular hydrogen ions H3+ produced by the interaction of benzene molecules with ultrafast laser pulses.

Author

Kaziannis, S., Liontos, I., Karras, G., Corsi, C., Bellini, M., and Kosmidis, C.

Subjects
*HYDROGEN ions, *BENZENE, *ULTRASHORT laser pulses, *STOPPING power (Nuclear physics), *DISSOCIATION (Chemistry), *MOLECULAR structure
Abstract

The ejection process of triatomic molecular hydrogen ions produced by the interaction of benzene with ultrafast laser pulses of moderate strong intensity (∼1014 W/cm2) is studied by means of TOF mass spectrometry. The H3+ formation can only take place through the rupture of two C–H bonds and the migration of hydrogen atoms within the molecular structure. The H3+ fragments are released with high kinetic energy (typically 2–8 eV) and at laser intensities ≥1014 W/cm2, well above that required for the double ionization of benzene, suggesting that its formation is taking place within multiply charged parent ions. The relative ejection efficiency of H3+ molecular hydrogen ions with respect to the atomic ones is found to be strongly decreasing as a function of the laser intensity and pulse duration (67–25 fs). It is concluded that the H3+ formation is only feasible within parent molecular precursors of relatively low charged states and before significant elongation of their structure takes place, while the higher multiply charged molecular ions preferentially dissociate into H+ ions. The ejection of H2+ ions is also discussed in comparison to the production of H3+ and H+ ions. Finally, by recording the mass spectra of two deuterium label isotopes of benzene (1,2-C6H4D2, 1,4-C6H4D2) it is verified that the ejection efficiency of some molecular fragments, such as D2H+, DH+, is dependent on the specific position of hydrogen atoms in the molecular skeleton prior dissociation. [ABSTRACT FROM AUTHOR]

Published
2009
Full Text
View/download PDF

17. Ramsey spectroscopy of bound atomic states with extreme ultraviolet laser harmonics

Author

Liontos I., Cavalieri S., Corsi C., Eramo R., Kaziannis S., Pirri A., Sali E., and Bellini M.

Subjects
VACUUM-ULTRAVIOLET, TIME-DELAY SPECTROSCOPY, HIGH-ORDER HARMONICS
Abstract

We report the experimental measurement of Ramsey interference fringes in the single-photon excitation to a high-lying bound state of atomic argon by pairs of phase-locked, time-delayed, extreme UV high-order harmonic pulses at 87 nm. High-visibility Ramsey fringes are observed for delays larger than 100 ps, thus demonstrating a potential resolving power >10^5 at this wavelength.

Published
2010

19. Single and double ionization of strontium in the vicinity of four-photon excitation of the 5p(2) (1)S(0) doubly excited state

Author

Liontos, I., Cohen, S., and Bolovinos, A.

Subjects
picosecond pulses, ba atoms, above-threshold ionization, theoretical-analysis, charged ions, laser optogalvanic spectroscopy, even-parity, multiphoton double ionization, autoionizing states, multi-photon ionization
Abstract

We report on the single and double multiphoton ionization of ground state Sr atoms observed in an atomic beam experiment with laser pulses of similar to 5 ns duration, maximum intensity similar to 4 x 10(11) W cm(-2) and within the 710-740 nm wavelength range. The Sr(+) spectrum consists of two strong lines originating from three-photon resonant four-photon ionization of bound states, a number of weak autoionizing resonances and a broad line due to four-photon excitation of the doubly excited 5p(2) (1)S(0) state. The latter, along with a strong, broad and structured spectral feature, is also evident in the wavelength dependence of the doubly charged Sr(2+) ion. A weakly evident but reproducible inflection point ('knee' structure) appears in the intensity dependence of the Sr(2+) yield at the location of the 5p2 1S0 resonance. A complementary fluorescence experiment revealed the accumulation of population in the 5p(1/2,3/2), 6s(1/2) and 5d(3/2,5/2) excited Sr(+) states during the laser pulse. All fluorescence signals depend on laser wavelength in a manner similar to the recorded Sr(+) spectrum. The population accumulation in the 5p(1/2,3/2) ionic states unambiguously proves the absorption of two photons above the first 5s(1/2) atomic threshold while that of the 5d(3/2),(5/2) and 6s(1/2) ones suggest the absorption of at least two more. Since under our laser pulse duration and intensity the absorption of such a number of photons in an unstructured continuum is highly improbable, it may be concluded that the process is mediated by dense manifolds of near-resonant doubly excited states, their role in the dynamics of laser - atom interaction under our conditions being far more crucial than in studies conducted using intense ultrashort pulses. Journal of Physics B-Atomic Molecular and Optical Physics

Published
2008

20. Two-photon ionization spectra of calcium above the 4s(1/2) threshold

Author

Cohen, S., Liontos, I., Bolovinos, A., Lyras, A., Benech, S., and Bachau, H.

Subjects
quantum-defect theory, eigenchannel r-matrix, 3-photon ionization, theoretical-analysis, laser optogalvanic spectroscopy, neutral ca, excitation, autoionizing states, single-photon, energy-levels
Abstract

Two-photon ionization of ground state calcium is investigated both experimentally and theoretically in the 374 - 323 nm spectral range. The spectra are dominated by the presence of the 4p(2) S-1(0) perturber and by members of even parity 3dnd J = 0, 2 (4

Published
2006

21. Human leukocyte antigens as genetic markers in Greek patients with sporadic pancreatic cancer

Author

Kouerinis, IA Zografos, G Tarassi, KE Athanasiades, TH and Liontos, I Gorgoilis, VG Korkolis, I Konstandoulakis, WM and Fotiadis, CI Androulakis, G Papasteriades, CA

Abstract

Purpose: In this study we investigated the relationship between specific HLA antigens and sporadic pancreatic cancer in Greek population. Methods: The allele frequencies of serologically and molecular defined class I and II HLA antigens were studied in 60 unrelated patients with pancreatic cancer histologically confirmed. The results obtained for HLA frequencies were compared with those of 105 healthy control subjects (control group). Results: Increased frequencies of HLA-A30 (16.7 vs. 3.8%; P < 0.01; OR = 5.05), A31 (9.5 vs. 1.9%; P < 0.05; OR = 5.72), B18 (31.7 vs. 14.3%,- P < 0.05; OR = 2.78) and Cw7 (53.3 vs. 21.9%; P < 0.01; OR = 4.07) were observed in patients with pancreatic cancer in comparison to the control subjects. Conclusions: This study demonstrates the association between specific HLA antigens and pancreatic cancer development in whites and suggests a genetic susceptibility factor for the disease.

Published
2004

22. Single and double ionization of magnesium via four-photon excitation of the 3p(2) S-1(0) autoionizing state: Experimental and theoretical analysis

Author

Liontos, I., Bolovinos, A., Cohen, S., and Lyras, A.

Subjects
ba atoms, resonances, alkali-metal atoms, mg, multiphoton ionization, laser-radiation, threshold, mechanism, dynamics, absorption
Abstract

Single and double ionization of ground state Mg atoms is observed in an atomic beam experiment in the 584-596 nm spectral range with a maximum intensity of 9x10(11) W/cm(2) and pulses of ns duration. The Mg+ spectrum consists of a single broad resonance whose position is very sensitive to laser intensity and it is attributed to the four-photon excitation of the doubly excited 3p(2) S-1(0) state. For intensities higher than 2x10(11) W/cm(2) a considerable double ionization yield is obtained. The Mg2+ spectra are composed of two lobes, each one dominating at different intensities. These observations can be interpreted by a sequential mechanism in which doubly charged ions are created by multiphoton resonant ionization of the excited 3p(1/2,3/2) Mg+ states (with negligible contribution from the 3s(1/2) ionic ground state) after the single ion production has saturated. The population of these excited ionic states suggests the absorption of two photons above the first ionization threshold of Mg. This interpretation is unambiguously confirmed by a complementary fluorescence experiment. Moreover, both ionization and fluorescence spectra as well as ionization yields are very well reproduced by a theoretical model based on a combination of density matrix and rate equations, taking into account the near-resonant coupling between the 3p(2) S-1(0) and 3p3d P-1(1) autoionizing states and employing calculated parameters for both Mg and Mg+. It is thus pointed out that for visible ns pulses of moderate intensity the autoionizing resonances play a crucial role in the multiphoton sequential double ionization of alkaline-earth-metal atoms. Physical Review A

Published
2004

33. Strong laser-induced coupling between autoionizing states: the case of the four-photon-excited 3p² ¹S0 state of magnesium.

Author

Dimitriou, A., Cohen, S., Lyras, A., and Liontos, I.

Subjects
AUGER effect, PHOTONS, LASER beams, MAGNESIUM ions, ABSORPTION, PHOTOELECTRON spectroscopy, GROUND state (Quantum mechanics)
Abstract

We investigate the interaction of ground-state Mg atoms with tuneable laser radiation of ~5 ns duration and moderate intensity (≤1012 W cm-2), capable of exciting the 3p² ¹S0 autoionizing state by four photons. For the corresponding photon energy range, this level is strongly one-photon coupled both with bound (third photon) and, primarily, a multitude of other autoionizing states (fifth photon). The coupling is strong enough to induce the absorption of up to six photons before the atom is ionized, creating thus population into the first excited 3pj Mg+ levels which subsequently decay radiatively to the 3s1/2 ionic ground state. The earlier studies devoted to this excitation scheme were thorough but partial. Particularly, the issues concerning the five-photon excited levels were not addressed. In this work, the examined wavelength range is greatly extended to include these states. Moreover, the interaction is characterized in more detail by employing an array of experimental techniques, namely Mg+ ion and photoelectron spectroscopy (including photoelectron angular distributions (PADs) from four- and five-photon ionization) as well as fluorescence spectroscopy where the 3pj→3s1/2 decay is monitored. The experimental data show that most of these five-photon excited levels undergo blue ac Stark shifts which are occasionally nonlinear with respect to the laser intensity and comparable to or even larger in magnitude than the large redshift of the 3p² ¹S0 state itself. Finally, for the latter state, the wavelength dependence of four-photon PAD measurements is suggestive of a situation reminiscent of an ac Stark splitting picture. [ABSTRACT FROM AUTHOR]

Published
2012
Full Text
View/download PDF

34. Two-photon ionization spectra of calcium above the 4s1/2threshold

Author

Cohen, S, Liontos, I, Bolovinos, A, Lyras, A, Benec'h, S, and Bachau, H

Abstract

Two-photon ionization of ground state calcium is investigated both experimentally and theoretically in the 374-323 nm spectral range. The spectra are dominated by the presence of the 4p2 1S0perturber and by members of even parity 3dnd J= 0, 2 (4 ? n? 10) and 3dns J= 2 (6 ? n? 12) autoionizing Rydberg series, the latter appearing as window resonances. No single-photon resonances are observed. The majority of recorded lines are identified using older stepwise spectroscopic data while there is a number of newly discovered low-lying members. The two previously unobserved 3dns, n? 12, series members are treated using a semi-empirical multichannel quantum defect theory (MQDT) model. Moreover, the low-lying part of the observed predominantly singlet spectrum is fairly well reproduced by theoretical calculations, combining a configuration interaction approach with B-splines basis functions and neglecting relativistic effects. The agreement between theory and experiment becomes less satisfactory as we move towards higher lying resonances dominated by singlet-triplet mixing effects, which are evident in the experimental data while neglected in the calculations.

Published
2006
Full Text
View/download PDF

36. The ejection of triatomic molecular hydrogen ions H(3) (+) produced by the interaction of benzene molecules with ultrafast laser pulses.

Author

Kaziannis S, Liontos I, Karras G, Corsi C, Bellini M, and Kosmidis C

Abstract

The ejection process of triatomic molecular hydrogen ions produced by the interaction of benzene with ultrafast laser pulses of moderate strong intensity ( approximately 10(14) W/cm(2)) is studied by means of TOF mass spectrometry. The H(3) (+) formation can only take place through the rupture of two C-H bonds and the migration of hydrogen atoms within the molecular structure. The H(3) (+) fragments are released with high kinetic energy (typically 2-8 eV) and at laser intensities >or=10(14) W/cm(2), well above that required for the double ionization of benzene, suggesting that its formation is taking place within multiply charged parent ions. The relative ejection efficiency of H(3) (+) molecular hydrogen ions with respect to the atomic ones is found to be strongly decreasing as a function of the laser intensity and pulse duration (67-25 fs). It is concluded that the H(3) (+) formation is only feasible within parent molecular precursors of relatively low charged states and before significant elongation of their structure takes place, while the higher multiply charged molecular ions preferentially dissociate into H(+) ions. The ejection of H(2) (+) ions is also discussed in comparison to the production of H(3) (+) and H(+) ions. Finally, by recording the mass spectra of two deuterium label isotopes of benzene (1,2-C(6)H(4)D(2), 1,4-C(6)H(4)D(2)) it is verified that the ejection efficiency of some molecular fragments, such as D(2)H(+), DH(+), is dependent on the specific position of hydrogen atoms in the molecular skeleton prior dissociation.

Published
2009
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results