39 research outputs found
Spectroscopie de phase multi-dimensionnelle de l'émission attoseconde moléculaire
When a low-frequency laser pulse is focused to a high intensity into a gas, the electric field of the laser light may become of comparable strength to that felt by the electrons bound in an atom or molecule. A valence electron can then be 'freed' by tunnel ionization, accelerated by the strong oscillating laser field and can eventually recollide and recombine with the ion. The gained kinetic energy is then released as a burst of coherent XUV light which is spectrally organized as harmonics of the fundamental driving field frequency.In high-harmonic molecular spectroscopy, the recombining electron wave-packet probes the structure of the molecule and the dynamics occurring in the ion left after tunnel ionization. The XUV burst is imprinted with this information which can be retrieved through an accurate characterization of the amplitude, phase and polarization of the harmonics. In the case of small molecules as nitrogen and carbon dioxide, impulsive alignment allows to change the direction of recombination of the electron wave-packet with respect to the molecular axis. The XUV burst from the molecular sample should then be characterized both along the spectral dimension and the alignment angle one, and this for the two polarization components. In this report, we present a new experimental scheme to perform two-source interferometry to measure the phase of the emission in aligned molecules along the alignment angle dimension. We how a refined spatio-spectral analysis of the fringe patterns obtained with this very stable interferometer allows one to extend high-harmonic spectroscopy from short to long trajectories. We then show how the combination of this setup together with RABBIT gives access to a bidimensionnal (spectrum and alignment angle) phase map with no arbitrary constant. Finally comparing two-source interferometry with transient grating spectroscopy leads to inconsistent results that can be interpreted taking into consideration polarization effects.Une molĂ©cule soumise Ă un champ laser infra-rouge intense (dans la gamme des 10 14 W.cmâ2) peut ĂȘtre ionisĂ©e par effet tunnel. Le paquet dâondes Ă©lectroniques (POE) ainsi libĂ©rĂ© est alors accĂ©lĂ©rĂ© par le champ laser et, lorsquâil repasse Ă proximitĂ© de lâion parent, il a une certaine probabilitĂ© de se recombiner dans son Ă©tat fondamental. Lors de cette recombinaison, le POE libĂšre son Ă©nergie sous la forme dâun flash attoseconde (1as=10 â18s) de rayons XUV. Cette Ă©mission cohĂ©rente est produite Ă chaque demi-cycle laser rĂ©sultant en un train dâimpulsions attosecondes. Dans le domaine spectral, ce train correspond Ă un spectre discret dâharmoniques de la frĂ©quence lasers. LâĂ©tape de recombinaison de lâĂ©lectron avec lâion parent peut ĂȘtre considĂ©rĂ©e comme une sonde de la structure des orbitales de valence molĂ©culaires participant Ă la gĂ©nĂ©ration dâharmoniques et de la dynamique ayant lieu dans lâion pendant lâexcursion de lâĂ©lectron dans le continuum. En caractĂ©risant en amplitude, phase et polarisation, lâĂ©mission harmonique associĂ©e Ă cette recombinaison, il est possible de remonter Ă ces informations structurales et dynamiques avec une prĂ©cision de lâordre de lâĂ
ngström et une rĂ©solution attoseconde. En particulier, la phase de lâĂ©mission harmonique qui est difficile Ă caractĂ©riser, encode des informations indispensables Ă la bonne comprĂ©hension des processus ayant lieu dans le milieu de gĂ©nĂ©ration. Nous prĂ©sentons les principes et testons de nouvelles techniques permet tant de caractĂ©riser la phase de lâĂ©mission attoseconde suivant plusieurs dimensions Ă la fois et dans un laps de temps optimisĂ©. Dans une premiĂšre partie, nous prĂ©sentons une mĂ©thode permettant de caractĂ©riser rapidement la phase spectrale de lâĂ©mission harmonique, fondĂ©e sur un modĂšle en champ fort de la photoionisation Ă deux couleurs (RABBIT). Nous introduisons ensuite une nouveau dispositif interfĂ©romĂ©trique Ă deux sources, permettant de mesurer les variations de phase de lâĂ©mission attoseconde induites par lâexcitation dâun paquet dâondes rotationnelles ou vibrationnelles. Ce dispositif trĂšs stable, compact et sobre Ă©nergĂ©tiquement repose sur lâutilisation dâun Ă©lĂ©ment optique de diffraction (DOE) binaire. AprĂšs avoir qualifiĂ© notre dispositif par des simulations numĂ©riques et des expĂ©riences prĂ©liminaires, nous montrons quâil est si sensible quâil permet de mesurer les variations de phase en fonction du paramĂštre dâexcitation pour diffĂ©rentes trajectoires Ă©lectroniques dans le continuum. Pour lâazote et le dioxyde de carbone, les mesures expĂ©rimentales montrent des variations de phase trĂšs diffĂ©rentes pour les deux premiĂšres trajectoires Ă©lectroniques. Ce DOE est ensuite utilisĂ© pour mesurer la phase de lâĂ©mission harmonique dans les molĂ©cules alignĂ©es dans les mĂȘmes conditions expĂ©rimentales que le RABBIT. Les deux expĂ©riences menĂ©es successivement donnent des rĂ©sultats compatibles que nous combinons par deux mĂ©thodes diffĂ©rentes : le CHASSEUR et le MAMMOTH. Enfin, nous proposons de combiner le DOE avec un rĂ©seau transitoire pour caractĂ©riser simultanĂ©ment la phase de l'Ă©mission attoseconde molĂ©culaire suivant deux axes de polarisation diffĂ©rents. Ces diffĂ©rentes techniques de mesure de phase nous ont permis dâĂ©tudier prĂ©cisĂ©ment lâĂ©mission harmonique suivant diffĂ©rentes dimensions (angle dâalignement, intensitĂ© de gĂ©nĂ©ration, trajectoire Ă©lectronique) et dâen tirer de nouvelles informations sur le mĂ©canisme de gĂ©nĂ©ration dans les molĂ©cules
Coherent laser cooling with trains of ultrashort laser pulses
We propose to extend coherent laser cooling from narrow-band to broad-band
transitions by using trains of ultrashort broadband pulses. We study
analytically two possible methods to reduce the momentum spread of a
distribution by several units of photon momentum in a single spontaneous
emission lifetime. We report on numerical simulations of one-dimensional laser
cooling of a two-level system with realistic parameters. The technique
introduced here is of high interest for efficient laser cooling of fast species
with short lifetime such as positronium
Disentangling Spectral Phases of Interfering Autoionizing States from Attosecond Interferometric Measurements
We have determined spectral phases of Ne autoionizing states from extreme ultraviolet and midinfrared attosecond interferometric measurements and ab initio full-electron time-dependent theoretical calculations in an energy interval where several of these states are coherently populated. The retrieved phases exhibit a complex behavior as a function of photon energy, which is the consequence of the interference between paths involving various resonances. In spite of this complexity, we show that phases for individual resonances can still be obtained from experiment by using an extension of the Fano model of atomic resonances. As simultaneous excitation of several resonances is a common scenario in many-electron systems, the present work paves the way to reconstruct electron wave packets coherently generated by attosecond pulses in systems larger than heliumWork supported by the ERC proof-of-concept Grant No. 780284-Imaging-XChem within the seventh framework program of the European Union, the MINECO Project No. FIS2013-42002-R, the EU-H2020- LASERLABEUROPE-654148, the ANR Projects No. ANR-15-CE30-0001-CIMBAAD, No. ANR-11- EQPX0005-ATTOLAB, and No. ANR-10-LABX-0039- PALM, the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award no. DEGF02-04ER15614, and the NSF Grant No. PHY-1607588. Calculations were performed at CCC-UAM and Marenostrum Supercomputer Center. F. M. acknowledges support from the âSevero Ochoaâ Programme for Centres of Excellence in R&D (MINECO, Grant No. SEV-2016- 0686) and the âMarĂa de Maeztuâ Programme for Units of Excellence in R&D (Grant No. MDM-2014-0377
High complexity femtosecond pulse duplicator
This paper presents a theoretical and numerical study of a 0-Ï fan-out phase grating
placed in the Fourier plane of a spatio-spectral pulse shaper followed by a spherical focusing lens.
It is shown that this device acts as a high complexity femtosecond pulse duplicator designed
for two source interferometry. At the focus of the lens, the electric field displays two spatially
separated intense spots in which relative delay can be continuously tuned over 4 orders of
magnitude, typically from a few attoseconds to a few tens of femtoseconds. Because the two
pulses do not spatially overlap, their intensity remains unchanged when the relative delay is
smaller than the pulse duration. Detailed simulations of the shaped electric field are presented
Multidimensionnal Phase Spectroscopy of the Attosecond Molecular Emission
Une molĂ©cule soumise Ă un champ laser infra-rouge intense (dans la gamme des 10 14 W.cmâ2) peut ĂȘtre ionisĂ©e par effet tunnel. Le paquet dâondes Ă©lectroniques (POE) ainsi libĂ©rĂ© est alors accĂ©lĂ©rĂ© par le champ laser et, lorsquâil repasse Ă proximitĂ© de lâion parent, il a une certaine probabilitĂ© de se recombiner dans son Ă©tat fondamental. Lors de cette recombinaison, le POE libĂšre son Ă©nergie sous la forme dâun flash attoseconde (1as=10 â18s) de rayons XUV. Cette Ă©mission cohĂ©rente est produite Ă chaque demi-cycle laser rĂ©sultant en un train dâimpulsions attosecondes. Dans le domaine spectral, ce train correspond Ă un spectre discret dâharmoniques de la frĂ©quence lasers. LâĂ©tape de recombinaison de lâĂ©lectron avec lâion parent peut ĂȘtre considĂ©rĂ©e comme une sonde de la structure des orbitales de valence molĂ©culaires participant Ă la gĂ©nĂ©ration dâharmoniques et de la dynamique ayant lieu dans lâion pendant lâexcursion de lâĂ©lectron dans le continuum. En caractĂ©risant en amplitude, phase et polarisation, lâĂ©mission harmonique associĂ©e Ă cette recombinaison, il est possible de remonter Ă ces informations structurales et dynamiques avec une prĂ©cision de lâordre de lâĂ
ngström et une rĂ©solution attoseconde. En particulier, la phase de lâĂ©mission harmonique qui est difficile Ă caractĂ©riser, encode des informations indispensables Ă la bonne comprĂ©hension des processus ayant lieu dans le milieu de gĂ©nĂ©ration. Nous prĂ©sentons les principes et testons de nouvelles techniques permet tant de caractĂ©riser la phase de lâĂ©mission attoseconde suivant plusieurs dimensions Ă la fois et dans un laps de temps optimisĂ©. Dans une premiĂšre partie, nous prĂ©sentons une mĂ©thode permettant de caractĂ©riser rapidement la phase spectrale de lâĂ©mission harmonique, fondĂ©e sur un modĂšle en champ fort de la photoionisation Ă deux couleurs (RABBIT). Nous introduisons ensuite une nouveau dispositif interfĂ©romĂ©trique Ă deux sources, permettant de mesurer les variations de phase de lâĂ©mission attoseconde induites par lâexcitation dâun paquet dâondes rotationnelles ou vibrationnelles. Ce dispositif trĂšs stable, compact et sobre Ă©nergĂ©tiquement repose sur lâutilisation dâun Ă©lĂ©ment optique de diffraction (DOE) binaire. AprĂšs avoir qualifiĂ© notre dispositif par des simulations numĂ©riques et des expĂ©riences prĂ©liminaires, nous montrons quâil est si sensible quâil permet de mesurer les variations de phase en fonction du paramĂštre dâexcitation pour diffĂ©rentes trajectoires Ă©lectroniques dans le continuum. Pour lâazote et le dioxyde de carbone, les mesures expĂ©rimentales montrent des variations de phase trĂšs diffĂ©rentes pour les deux premiĂšres trajectoires Ă©lectroniques. Ce DOE est ensuite utilisĂ© pour mesurer la phase de lâĂ©mission harmonique dans les molĂ©cules alignĂ©es dans les mĂȘmes conditions expĂ©rimentales que le RABBIT. Les deux expĂ©riences menĂ©es successivement donnent des rĂ©sultats compatibles que nous combinons par deux mĂ©thodes diffĂ©rentes : le CHASSEUR et le MAMMOTH. Enfin, nous proposons de combiner le DOE avec un rĂ©seau transitoire pour caractĂ©riser simultanĂ©ment la phase de l'Ă©mission attoseconde molĂ©culaire suivant deux axes de polarisation diffĂ©rents. Ces diffĂ©rentes techniques de mesure de phase nous ont permis dâĂ©tudier prĂ©cisĂ©ment lâĂ©mission harmonique suivant diffĂ©rentes dimensions (angle dâalignement, intensitĂ© de gĂ©nĂ©ration, trajectoire Ă©lectronique) et dâen tirer de nouvelles informations sur le mĂ©canisme de gĂ©nĂ©ration dans les molĂ©cules.When a low-frequency laser pulse is focused to a high intensity into a gas, the electric field of the laser light may become of comparable strength to that felt by the electrons bound in an atom or molecule. A valence electron can then be 'freed' by tunnel ionization, accelerated by the strong oscillating laser field and can eventually recollide and recombine with the ion. The gained kinetic energy is then released as a burst of coherent XUV light which is spectrally organized as harmonics of the fundamental driving field frequency.In high-harmonic molecular spectroscopy, the recombining electron wave-packet probes the structure of the molecule and the dynamics occurring in the ion left after tunnel ionization. The XUV burst is imprinted with this information which can be retrieved through an accurate characterization of the amplitude, phase and polarization of the harmonics. In the case of small molecules as nitrogen and carbon dioxide, impulsive alignment allows to change the direction of recombination of the electron wave-packet with respect to the molecular axis. The XUV burst from the molecular sample should then be characterized both along the spectral dimension and the alignment angle one, and this for the two polarization components. In this report, we present a new experimental scheme to perform two-source interferometry to measure the phase of the emission in aligned molecules along the alignment angle dimension. We how a refined spatio-spectral analysis of the fringe patterns obtained with this very stable interferometer allows one to extend high-harmonic spectroscopy from short to long trajectories. We then show how the combination of this setup together with RABBIT gives access to a bidimensionnal (spectrum and alignment angle) phase map with no arbitrary constant. Finally comparing two-source interferometry with transient grating spectroscopy leads to inconsistent results that can be interpreted taking into consideration polarization effects
Spectroscopie de phase multi-dimensionnelle de l'émission attoseconde moléculaire
Une molĂ©cule soumise Ă un champ laser infra-rouge intense (dans la gamme des 10 14 W.cm 2) peut ĂȘtre ionisĂ©e par effet tunnel. Le paquet d ondes Ă©lectroniques (POE) ainsi libĂ©rĂ© est alors accĂ©lĂ©rĂ© par le champ laser et, lorsqu il repasse Ă proximitĂ© de l ion parent, il a une certaine probabilitĂ© de se recombiner dans son Ă©tat fondamental. Lors de cette recombinaison, le POE libĂšre son Ă©nergie sous la forme d un flash attoseconde (1as=10 18s) de rayons XUV. Cette Ă©mission cohĂ©rente est produite Ă chaque demi-cycle laser rĂ©sultant en un train d impulsions attosecondes. Dans le domaine spectral, ce train correspond Ă un spectre discret d harmoniques de la frĂ©quence lasers. L Ă©tape de recombinaison de l Ă©lectron avec l ion parent peut ĂȘtre considĂ©rĂ©e comme une sonde de la structure des orbitales de valence molĂ©culaires participant Ă la gĂ©nĂ©ration d harmoniques et de la dynamique ayant lieu dans l ion pendant l excursion de l Ă©lectron dans le continuum. En caractĂ©risant en amplitude, phase et polarisation, l Ă©mission harmonique associĂ©e Ă cette recombinaison, il est possible de remonter Ă ces informations structurales et dynamiques avec une prĂ©cision de l ordre de l Ă
ngström et une rĂ©solution attoseconde. En particulier, la phase de l Ă©mission harmonique qui est difficile Ă caractĂ©riser, encode des informations indispensables Ă la bonne comprĂ©hension des processus ayant lieu dans le milieu de gĂ©nĂ©ration. Nous prĂ©sentons les principes et testons de nouvelles techniques permet tant de caractĂ©riser la phase de l Ă©mission attoseconde suivant plusieurs dimensions Ă la fois et dans un laps de temps optimisĂ©. Dans une premiĂšre partie, nous prĂ©sentons une mĂ©thode permettant de caractĂ©riser rapidement la phase spectrale de l Ă©mission harmonique, fondĂ©e sur un modĂšle en champ fort de la photoionisation Ă deux couleurs (RABBIT). Nous introduisons ensuite une nouveau dispositif interfĂ©romĂ©trique Ă deux sources, permettant de mesurer les variations de phase de l Ă©mission attoseconde induites par l excitation d un paquet d ondes rotationnelles ou vibrationnelles. Ce dispositif trĂšs stable, compact et sobre Ă©nergĂ©tiquement repose sur l utilisation d un Ă©lĂ©ment optique de diffraction (DOE) binaire. AprĂšs avoir qualifiĂ© notre dispositif par des simulations numĂ©riques et des expĂ©riences prĂ©liminaires, nous montrons qu il est si sensible qu il permet de mesurer les variations de phase en fonction du paramĂštre d excitation pour diffĂ©rentes trajectoires Ă©lectroniques dans le continuum. Pour l azote et le dioxyde de carbone, les mesures expĂ©rimentales montrent des variations de phase trĂšs diffĂ©rentes pour les deux premiĂšres trajectoires Ă©lectroniques. Ce DOE est ensuite utilisĂ© pour mesurer la phase de l Ă©mission harmonique dans les molĂ©cules alignĂ©es dans les mĂȘmes conditions expĂ©rimentales que le RABBIT. Les deux expĂ©riences menĂ©es successivement donnent des rĂ©sultats compatibles que nous combinons par deux mĂ©thodes diffĂ©rentes : le CHASSEUR et le MAMMOTH. Enfin, nous proposons de combiner le DOE avec un rĂ©seau transitoire pour caractĂ©riser simultanĂ©ment la phase de l'Ă©mission attoseconde molĂ©culaire suivant deux axes de polarisation diffĂ©rents. Ces diffĂ©rentes techniques de mesure de phase nous ont permis d Ă©tudier prĂ©cisĂ©ment l Ă©mission harmonique suivant diffĂ©rentes dimensions (angle d alignement, intensitĂ© de gĂ©nĂ©ration, trajectoire Ă©lectronique) et d en tirer de nouvelles informations sur le mĂ©canisme de gĂ©nĂ©ration dans les molĂ©cules.When a low-frequency laser pulse is focused to a high intensity into a gas, the electric field of the laser light may become of comparable strength to that felt by the electrons bound in an atom or molecule. A valence electron can then be 'freed' by tunnel ionization, accelerated by the strong oscillating laser field and can eventually recollide and recombine with the ion. The gained kinetic energy is then released as a burst of coherent XUV light which is spectrally organized as harmonics of the fundamental driving field frequency.In high-harmonic molecular spectroscopy, the recombining electron wave-packet probes the structure of the molecule and the dynamics occurring in the ion left after tunnel ionization. The XUV burst is imprinted with this information which can be retrieved through an accurate characterization of the amplitude, phase and polarization of the harmonics. In the case of small molecules as nitrogen and carbon dioxide, impulsive alignment allows to change the direction of recombination of the electron wave-packet with respect to the molecular axis. The XUV burst from the molecular sample should then be characterized both along the spectral dimension and the alignment angle one, and this for the two polarization components. In this report, we present a new experimental scheme to perform two-source interferometry to measure the phase of the emission in aligned molecules along the alignment angle dimension. We how a refined spatio-spectral analysis of the fringe patterns obtained with this very stable interferometer allows one to extend high-harmonic spectroscopy from short to long trajectories. We then show how the combination of this setup together with RABBIT gives access to a bidimensionnal (spectrum and alignment angle) phase map with no arbitrary constant. Finally comparing two-source interferometry with transient grating spectroscopy leads to inconsistent results that can be interpreted taking into consideration polarization effects.PARIS11-SCD-Bib. Ă©lectronique (914719901) / SudocSudocFranceF
Positronium laser cooling in a magnetic field
We study realistic 3D laser cooling of positronium (Ps) in the presence of a magnetic field. Triplet and singlet states mixing due to the magnetic field, and dynamical Stark effect, generally produce higher annihilation rates than in the zero-field case. 3D cooling is efficient only at very low field BâČ50mT and at high field values BâȘ0.7T. Near 100ns long laser pulses, spectrally broad enough to cover most of the Ps Doppler profile and with energy in the mJ range, are required to cool Ps. Simulations based on full diagonalization of the Stark and Zeeman Hamiltonian and a kinetic Monte Carlo algorithm exactly solving the rate equations indicate that an efficient cooling (typically from 300K down to below 50K) is possible even in a magnetic field. We also propose 3D moving molasses cooling that can produce a well-defined monochromatic Ps beam useful for applications
Pulsed production of antihydrogen
Antihydrogen atoms with K or sub-K temperature are a powerful tool to precisely probe the validity of fundamental physics laws and the design of highly sensitive experiments needs antihydrogen with controllable and well defined conditions. We present here experimental results on the production of antihydrogen in a pulsed mode in which the time when 90% of the atoms are produced is known with an uncertainty of ~250 ns. The pulsed source is generated by the charge-exchange reaction between Rydberg positronium atomsâproduced via the injection of a pulsed positron beam into a nanochanneled Si target, and excited by laser pulsesâand antiprotons, trapped, cooled and manipulated in electromagnetic traps. The pulsed production enables the control of the antihydrogen temperature, the tunability of the Rydberg states, their de-excitation by pulsed lasers and the manipulation through electric field gradients. The production of pulsed antihydrogen is a major landmark in the AEgÂŻIS experiment to perform direct measurements of the validity of the Weak Equivalence Principle
for antimatter