Nonintrusive monitoring and quantitative analysis of strong laser-field-induced impulsive alignment

Renard, Vincent; Renard, M.; Rouzée, Arnaud; Guérin, S.; Jauslin, H. R.; Lavorel, B.; Faucher, O.

doi:10.1103/physreva.70.033420

Cited by 84 publications

(83 citation statements)

References 29 publications

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“…Impulsive alignment is achieved by creating a superposition of rotational quantum states which produces a time-dependent observable, revealed as a revival structure. Measurements like ionization [22,23], nonlinear optical methods [24,25], or HHG [11,26,27] are sensitive to this rotational wave packet and have been extensively used in the past [28,29]. Furthermore, recent studies have shown that changes in the revival dynamics can also occur when orbitals of different symmetry are involved [30][31][32].…”

Section: Introductionmentioning

confidence: 99%

N2 HOMO-1 orbital cross section revealed through high-order-harmonic generation

et al. 2017

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We measure multi-orbital contributions to high harmonic generation from aligned nitrogen. We show that the change in revival structure in the cutoff harmonics has a counterpart in the angular distribution when a lower-lying orbital contributes to the harmonic yield. This angular distribution is directly observed in the laboratory without any further deconvolution. Because of the high degree of alignment we are able to distinguish angular contributions of the highest occupied molecular orbital 1 (HOMO-1) orbital from angle-dependent spectroscopic features of the HOMO. In particular, we are able to make a direct comparison with the cross section of the HOMO-1 orbital in the extreme ultraviolet region.

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Section: Introductionmentioning

confidence: 99%

N2 HOMO-1 orbital cross section revealed through high-order-harmonic generation

et al. 2017

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“…However, rotational wavepackets have been previously observed in heavy many-electron systems (N 2 [6], O 2 [13,14], CO 2 [15,16], CS 2 [16], I 2 [17] etc. ), where rotations occur with periods on the picosecond time scale.…”

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confidence: 99%

Mapping the evolution of optically generated rotational wave packets in a room-temperature ensemble ofD2

et al. 2007

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A coherent superposition of rotational states in D2 has been excited by nonresonant ultrafast (12 femtosecond) intense (2 × 10 14 Wcm −2 ) 800 nm laser pulses leading to impulsive dynamic alignment. Field-free evolution of this rotational wavepacket has been mapped to high temporal resolution by a time-delayed pulse, initiating rapid double ionization, which is highly sensitive to the angle of orientation of the molecular axis with respect to the polarization direction, θ. The detailed fractional revivals of the neutral D2 wavepacket as a function of θ and evolution time have been observed and modelled theoretically.PACS numbers: 42.50. Hz, 33.80.Gj, 33.80.Wz The importance of being able to enforce spatial order on an initially random ensemble of molecules has been recognized since the discovery of steric effects in chemical reactions [1]. Traditional 'brute force' techniques employing strong DC fields [2,3] have recently yielded to new, more subtle and yet more powerful and versatile techniques using intense laser systems [4,5]. In particular intense femtosecond pulses have been successfully used to align molecules along an axis for application in areas such as the study of fragmentation dynamics [6,7], high harmonic generation [8,9] and the creation of single cycle laser pulses [10]. In this case the alignment of a molecule (or spatial ordering of an ensemble of molecules) evolves temporally following the creation of a rotational wavepacket by a linearly polarized laser pulse of far shorter duration than the natural period of rotation.In this Letter, we report on a detailed ultrafast study of the temporal evolution of such a rotational wavepacket in the neutral deuterium molecule D 2 . The wavepacket is created impulsively by a 12 femtosecond laser pulse, with temporal and angular ordering probed at some later time with a similar pulse that initiates sequential double. Such high resolution measurements represent the state-of-theart in ultrafast molecular physics in the high rotational frequency limit as dictated by this most fundamental and theoretically tractable of molecules.It is known that an intense linearly polarized laser pulse interacting with an ensemble of molecules generates a degree of spatial alignment from a random ensemble [4,5]. The only condition for this phenomenon is that the molecular polarizability is anisotropic. Thus, the induced dipole moment created in the interaction with the electric field of the laser generates a torque that causes the axis of maximum polarizability to librate around the polarization vector of the laser field. Quantum mechanically, the process is described as a sequence of Rabi-type cycles accompanied by the exchange of two quanta of angular momentum between the molecule and the laser field. If the aligning pulse duration is much greater than the rotational period, the system evolves adiabatically to the the so-called pendular states, which dissipate as soon as the laser pulse passes [12]. However, when the pulse duration is much shorter than the rotational perio...

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“…Nevertheless, molecular alignment can be identified qualitatively in any process that is sensitive to the orientation of the molecular structure in the laboratory frame. This has been demonstrated for strong field ionisation in form of high harmonic generation [217,218] and Kerr effect birefringence induced processes [219], where the recorded signal depends on the alignment of the molecule with respect to the linear laser polarisation. Revival structures have further been obtained from Coulomb explosion detected via a TOF spectrometer [220], where the detected fragmentation yields depend on the orientation of the molecule with respect to the spectrometer axis.…”

Section: Detecting and Characterising Molecular Alignmentmentioning

confidence: 99%

Resolving Strong Field Dynamics in Cation States of CO_2 via Optimised Molecular Alignment

Oppermann

2014

Springer Theses

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In this thesis, the role of the molecular structure in strong field induced processes in CO 2 is resolved by the use of optimised impulsive molecular alignment. Two processes were investigated: recollision induced ionisation and the dissociation of the molecular ion CO + 2 . Both processes are driven by the initial tunneling ionisation of CO 2 . Through the use of molecular alignment, the orbital symmetries of the involved molecular ionic states were resolved, revealing the internal molecular dynamics in the form of ionisation and excitation pathways.A novel data analysis procedure was developed to extract the alignment distribution and rotational temperature of the impulsively aligned molecular ensemble. This facilitated the optimisation of molecular alignment in mixed gas samples and was demonstrated for N 2 , O 2 and CO 2 seeded in Ar.The recollision induced or nonsequential double ionisation (NSDI) of CO 2 was then studied in the molecular frame. The process was fully characterised by measuring the shape of the recolliding electron wavepacket and the angularly resolved inelastic electronion recollision cross section. The results reveal the contribution from both the ionic ground and first excited state of CO + 2 to the NSDI mechanism. This study was extended to the strong field induced dissociation of impulsively aligned CO + 2 . It was found that dissociation is driven by a parallel dipole transition from the second excited ionic state B to the predissociating state C, whilst recollision excitation was shown to not play a role. The strong field induced coupling of the ionic states B and C could thus be controlled by the laser polarisation.The results obtained in this thesis further the understanding of population dynamics of cation states in strong field processes. This is of special interest for extending molecular strong field physics to the study of electronic degrees of freedom and their coupling to the nuclear motion. had hoped for in a research degree and I cannot thank Jon enough for making it such an enriching experience, both professionally and personally.

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Nonintrusive monitoring and quantitative analysis of strong laser-field-induced impulsive alignment

Cited by 84 publications

References 29 publications

N2 HOMO-1 orbital cross section revealed through high-order-harmonic generation

N2 HOMO-1 orbital cross section revealed through high-order-harmonic generation

Mapping the evolution of optically generated rotational wave packets in a room-temperature ensemble ofD2

Resolving Strong Field Dynamics in Cation States of CO_2 via Optimised Molecular Alignment

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