Aurore: A platform for ultrafast sciences.

We present the Aurore platform for ultrafast sciences. This platform is based on a unique 20 W, 1 kHz, 26 fs Ti:sapphire laser system designed for reliable operation and high intensity temporal contrast. The specific design ensures the high stability in terms of pulse duration, energy, and beam pointing necessary for extended experimental campaigns. The laser supplies 5 different beamlines, all dedicated to a specific field: attosecond science (Aurore 1), ultrafast phase transitions in solids (Aurore 2 and 3), ultrafast luminescence in solids (Aurore 4), and femtochemistry (Aurore 5). The technical specifications of these five beamlines are described in detail, and examples of the recent results are given.

Real-time determination of enantiomeric and isomeric content using photoelectron elliptical dichroism.

The fast and accurate analysis of chiral chemical mixtures is crucial for many applications but remains challenging. Here we use elliptically-polarized femtosecond laser pulses at high repetition rates to photoionize chiral molecules. The 3D photoelectron angular distribution produced provides molecular fingerprints, showing a strong forward-backward asymmetry which depends sensitively on the molecular structure and degree of ellipticity. Continuously scanning the laser ellipticity and analyzing the evolution of the rich, multi-dimensional molecular signatures allows us to observe real-time changes in the chemical and chiral content present with unprecedented speed and accuracy. We measure the enantiomeric excess of a compound with an accuracy of 0.4% in 10 min acquisition time, and follow the evolution of a mixture with an accuracy of 5% with a temporal resolution of 3 s. This method is even able to distinguish isomers, which cannot be easily distinguished by mass-spectrometry.

Multiphoton photoelectron circular dichroism of limonene with independent polarization state control of the bound-bound and bound-continuum transitions.

Photoionization of randomly oriented chiral molecules with circularly polarized light leads to a strong forward/backward asymmetry in the photoelectron angular distribution. This chiroptical effect, referred to as Photoelectron Circular Dichroism (PECD), was shown to take place in all ionization regimes, from single photon to tunnel ionization. In the Resonance Enhanced Multiphoton Ionisation (REMPI) regime, where most of the table-top PECD experiments have been performed, understanding the role of the intermediate resonances is currently the subject of experimental and theoretical investigations. In an attempt to decouple the role of bound-bound and bound-continuum transitions in REMPI-PECD, we photoionized the (+)-limonene enantiomer using two-color laser fields in [1 + 1'] and [2 + 2'] ionization schemes, where the polarization state of each color can be controlled independently. We demonstrate that the main effect of the bound-bound transition is to break the sample isotropy by orientation-dependent photoexcitation, in agreement with recent theoretical predictions. We show that the angular distribution of PECD strongly depends on the anisotropy of photoexcitation to the intermediate state, which is different for circularly and linearly polarized laser pulses. On the contrary, the helicity of the pulse that drives the bound-bound transition is shown to have a negligible effect on the PECD.

Attosecond-resolved photoionization of chiral molecules.

Chiral light-matter interactions have been investigated for two centuries, leading to the discovery of many chiroptical processes used for discrimination of enantiomers. Whereas most chiroptical effects result from a response of bound electrons, photoionization can produce much stronger chiral signals that manifest as asymmetries in the angular distribution of the photoelectrons along the light-propagation axis. We implemented self-referenced attosecond photoelectron interferometry to measure the temporal profile of the forward and backward electron wave packets emitted upon photoionization of camphor by circularly polarized laser pulses. We measured a delay between electrons ejected forward and backward, which depends on the ejection angle and reaches 24 attoseconds. The asymmetric temporal shape of electron wave packets emitted through an autoionizing state further reveals the chiral character of strongly correlated electronic dynamics.

Femtosecond time-resolved electronic relaxation dynamics in tetrathiafulvalene.

In the present paper, the ultrafast electronic relaxation of tetrathiafulvalene (TTF) initiated around 4 eV is studied by femtosecond time-resolved velocity-map imaging. The goal is to investigate the broad double structure observed in the absorption spectrum at this energy. By monitoring the transients of the parent cation and its fragments and by varying the pump and the probe wavelengths, two internal conversions and intramolecular vibrational relaxation are detected both on the order of a few hundred of femtoseconds. Photoelectron images permit the assignment of a dark electronic state involved in the relaxation. In addition, the formation of the dimer of TTF has been observed.

Multi-channel electronic and vibrational dynamics in polyatomic resonant high-order harmonic generation.

High-order harmonic generation in polyatomic molecules generally involves multiple channels of ionization. Their relative contribution can be strongly influenced by the presence of resonances, whose assignment remains a major challenge for high-harmonic spectroscopy. Here we present a multi-modal approach for the investigation of unaligned polyatomic molecules, using SF6 as an example. We combine methods from extreme-ultraviolet spectroscopy, above-threshold ionization and attosecond metrology. Fragment-resolved above-threshold ionization measurements reveal that strong-field ionization opens at least three channels. A shape resonance in one of them is found to dominate the signal in the 20-26 eV range. This resonance induces a phase jump in the harmonic emission, a switch in the polarization state and different dynamical responses to molecular vibrations. This study demonstrates a method for extending high-harmonic spectroscopy to polyatomic molecules, where complex attosecond dynamics are expected.

268 nm photodissociation of ClN3: a femtosecond velocity-map imaging study.

We report the first time-resolved study of the photochemistry of chlorine azide (ClN3) by femtosecond velocity-map imaging (fs-VMI). The dissociation dynamics are initiated at 4.6 eV and the photofragments are detected by multiphoton ionization using an intense laser field centered at 803 nm. A dissociation time of 262 ± 38 fs was measured from the rising time of the co-fragments N3 and Cl. The time dependency of the angular distribution of N3, which converges from ß2 ~ 2 to ß2 = 1.61 ± 0.07 in 170 ± 45 fs, reveals the parallel nature of the transition dipole moment.

Inhomogeneous high harmonic generation in krypton clusters.

High order harmonic generation from clusters is a controversial topic: conflicting theories exist, with different explanations for similar experimental observations. From an experimental point of view, separating the contributions from monomers and clusters is challenging. By performing a spectrally and spatially resolved study in a controlled mixture of clusters and monomers, we are able to isolate a region of the spectrum where the emission purely originates from clusters. Surprisingly, the emission from clusters is depolarized, which is the signature of statistical inhomogeneous emission from a low-density source. The harmonic response to laser ellipticity shows that this generation is produced by a new recollisional mechanism, which opens the way to future theoretical studies.

High-harmonic transient grating spectroscopy of NO2 electronic relaxation.

We study theoretically and experimentally the electronic relaxation of NO(2) molecules excited by absorption of one ∼400 nm pump photon. Semiclassical simulations based on trajectory surface hopping calculations are performed. They predict fast oscillations of the electronic character around the intersection of the ground and first excited diabatic states. An experiment based on high-order harmonic transient grating spectroscopy reveals dynamics occurring on the same time scale. A systematic study of the detected transient is conducted to investigate the possible influence of the pump intensity, pump wavelength, and rotational temperature of the molecules. The quantitative agreement between measured and predicted dynamics shows that, in NO(2), high harmonic transient grating spectroscopy encodes vibrational dynamics underlying the electronic relaxation.

Conical intersection dynamics in NO2 probed by homodyne high-harmonic spectroscopy.

Conical intersections play a crucial role in the chemistry of most polyatomic molecules, ranging from the simplest bimolecular reactions to the photostability of DNA. The real-time study of the associated electronic dynamics poses a major challenge to the latest techniques of ultrafast measurement. We show that high-harmonic spectroscopy reveals oscillations in the electronic character that occur in nitrogen dioxide when a photoexcited wave packet crosses a conical intersection. At longer delays, we observe the onset of statistical dissociation dynamics. The present results demonstrate that high-harmonic spectroscopy could become a powerful tool to highlight electronic dynamics occurring along nonadiabatic chemical reaction pathways.

Time-resolved predissociation of the vibrationless level of the B state of CH3I.

The predissociation dynamics of the vibrationless level of the first Rydberg 6s (B (1)E) state of CH(3)I has been studied by femtosecond-resolved velocity map imaging of both the CH(3) and I photofragments. The kinetic energy distributions of the two fragments have been recorded as a function of the pump-probe delay, and as a function of excitation within the umbrella and stretching vibrational modes of the CH(3) fragment. These observations are made by using (2 + 1) Resonant Enhanced MultiPhoton Ionization (REMPI) via the state of CH(3) to detect specific vibrational levels of CH(3). The vibrational branching fractions of the CH(3) are recovered by using the individual vibrationally state-selected CH(3) distributions to fit the kinetic energy distribution obtained by using nonresonant multiphoton ionization of either the I or the CH(3) fragment. The angular distributions and rise times of the two fragments differ significantly. These observations can be rationalized through a consideration of the alignment of the CH(3) fragment and the effect of this alignment on its detection efficiency. Two additional dissociation channels are detected: one associated with Rydberg states near 9.2 eV that were observed previously in photoelectron studies, and one associated with photodissociation of the parent cation around 15 eV.

Quantum interference in NO2.

This paper investigates the origin of a quantum interference observed when NO(2) is dissociatively ionized by short pulses of ultraviolet light. We describe time-resolved measurements of NO(+), O(+), and NO(2)(+) ions produced following the interaction of NO(2) with a approximately 70 fs duration pulse centered close to 400 nm and a subsequent time-delayed probe pulse close to 269, 205, or 400 nm. A quantum beat oscillation with a period of 524 fs and a characteristic damping time of 8 ps is observed on all transient ion signals. We investigate the effect of tuning the central wavelength of the excitation pulse over a 12 nm range, and we discuss the potential importance of three possible multiphoton pathways involving one, two, and three pump photons. We conclude that the ionization pathway responsible for the beat signal is most likely due to a process involving the absorption of two pump photons and two probe photons. This presents an interesting problem with respect to the interpretation of the mechanism responsible for the quantum interference signature since the electronic states of NO(2) reached at the two-photon level are all thought to be extremely short-lived and to dissociate on a time scale that is far shorter than the characteristic damping time of the oscillatory signals. We suggest that a possible explanation for the observed dynamics is associated with a minor dissociation channel of the (2)(2)B(2) state of NO(2) through its interaction with the longer lived (2)(2)A(1) state.

[Oocyte donation: parents's secrets and lies]. / Don d'ovocytes: secrets et mensonges.

BACKGROUND: Since 1994, oocyte donation in France must be organized anonymously, in compliance with the bioethics law. The donation is free and any publicity to enrol donors is forbidden. In this system, the recipients are encouraged to incite a donor to visit the recipient's fertility unit. These donors are called "symbolic" donors, since they allow the recipient to be entitred to receive oocytes from another anonymous donor. According to the law, this procedure can be performed both anonymously and non-anonymously. OBJECTIVES: We wanted to study the implication of the anonymous system, focusing on the secret of the child's conception and on the relationship between the recipient family and the "symbolic" donor. MATERIAL AND METHODS: We contacted all the patients (n=83) who had children with oocyte donation in our center between 1988 and 1998. These patients participated in an interview conducted with a standardized questionnaire. RESULTS: Fourteen (17.8%) of the couples were lost to follow-up and three declined to participate. Five recipient couples preferred a non-anonymous donation. In all, 70% of the couples had not yet told their child about the donation. They had mentioned the IVF but not the donation despite of the fact that 50% of symbolic donors came from the family of the recipients, 34% from their friends, or 6% from their professional environment; 10% were not related to the recipients. Long after the child's birth, 25% of the recipients had no contact with the symbolic donor but 41% had selected her as the child's godmother and 15% of symbolic donors were the first to be informed of the birth of the child. After the donation, a gift was offered to the "symbolic" donor by 57% of couples, 33% did not know how to thank them (retribution is forbidden by law) and 10% of couples mentioned that their donor refused any gift. Concerning the donor whose oocytes were used, 63% of recipients did not want to know anything about her. 20% would have liked to have medical information and 13% would like to have all kind of information about her. Only 2% of recipients would have liked to know her identity and 2% would have liked to meet her. CONCLUSION: In agreement with earlier reports in the literature, the majority (70%) of the parents did not inform their child about the oocyte donation even though the symbolic donor was in contact with the child (being his aunt or his godmother for example). The French system has created a double debt: one related to the real donor and another related to the symbolic donor. In the long run, the parents have found a way to humanize this technique: they have given a symbolic place of godmother to the volunteer donor.

Single dose application of cetrorelix in combination with clomiphene for friendly IVF: results of a feasibility study.

A prospective randomized feasibility study was carried out on 10 patients undergoing IVF treatment using a single-dose LHRH antagonist protocol (cetrorelix, Cetrotide) with clomiphene citrate in combination with either human menopausal gonadotrophin (HMG) (n = 5) or recombinant human FSH (rFSH) (n = 5). Both treatment-groups, HMG and rFSH, were comparable with regard to age (33.2 +/- 2.6 versus 34.4 +/- 4.0 years) BMI (23.2 +/- 2.6 versus 22.7 +/- 1.6) and cause of infertility. They yielded comparable results concerning gonadotrophin dose (19.8 +/- 8.7 versus 17.0 +/- 8.9), stimulation days (6.5 +/- 2.0 versus 5.8 +/- 1.9) and live births (one versus two). No premature LH surge (LH >10 IU/ml and progesterone >1 ng/ml) occurred. The overall baby take-home rate was 30%. In a small number of patients, cetrorelix could be shown to effectively prevent premature LH surges in stimulation protocols combining clomiphene with gonadotrophins with an excellent baby take-home rate per started cycle of 30%.

Observation of coherent transients in ultrashort chirped excitation of an undamped two-level system.

The effects of coherent excitation of a two-level system with a linearly chirped pulse are studied theoretically and experimentally [in Rb (5s-5p)] in the low field regime. The coherent transients are measured directly on the excited state population on an ultrashort time scale. A sharp step corresponds to the passage through resonance. It is followed by oscillations resulting from interferences between off-resonant and resonant contributions. We finally show the equivalence between this experiment and Fresnel diffraction by a sharp edge.

[Impact of systematically freezing embryos on ovum donation]. / Retentissement de la congélation embryonnaire systématique dans l'exercice du don d'ovocytes.

In France, all embryos obtained after ovum donation have to be frozen. We present a brief background on this policy and expose our results, then discuss the rationale of such a policy in order to upgrade knowledge on the mechanism of vertical HIV transmission.

Nonadiabatic Multielectron Dynamics in Strong Field Molecular Ionization.

We report the observation of a general strong field ionization mechanism due to highly nonadiabatic multielectron excitation dynamics in polyatomic molecules. We observe that such excitation mechanisms greatly affect molecular ionization, fragmentation, and energetics. We characterized this phenomenon as a function of optical frequency, intensity, and molecular properties.

Towards disentangling coupled electronic-vibrational dynamics in ultrafast non-adiabatic processes

Femtosecond time-resolved photoelectron spectroscopy is emerging as a new technique for investigating polyatomic excited state dynamics. Due to the sensitivity of photoelectron spectroscopy to both electronic configurations and vibrational dynamics, it is well suited to the study of non-adiabatic processes such as internal conversion, which often occur on sub-picosecond time scales. We discuss the technical requirements for such experiments, including lasers systems, energy- and angle-resolved photoelectron spectrometers and new detectors for coincidence experiments. We present a few examples of these methods applied to problems in diatomic wavepacket dynamics and ultrafast non-adiabatic processes in polyatomic molecules.

[Palliative care in non-cancerous diseases]. / Soins palliatifs au cours des affections non cancéreuses.

Palliative treatment is instituted at a particular point in the course of a potentially fatal disease. This palliative phase is often less well-defined than in cancer. Treatment mainly aims at slowing the course of the disease and maintaining the best quality of life possible for the patient. Palliative management of acquired immuno-deficiency syndrome (AIDS) is complicated by the context of the disease, the specific symptoms during the palliative and terminal stages and by the discovery of new antiviral-treatments. The irreversible degeneration in successive steps observed in amyotrophic lateral sclerosis (ALS) requires coordination from the onset among the various actors participating in patient management. In extreme situations, when symptoms are uncontrollable, inducing sleep can be considered.