Dynamics of laser-induced molecular alignment in the impulsive and adiabatic regimes: A direct comparison

Torres, Ricardo; Nalda, R. de; Marangos, J. P.

doi:10.1103/physreva.72.023420

Cited by 110 publications

(114 citation statements)

References 38 publications

Supporting

Mentioning

111

Contrasting

Order By: Relevance

“…2(d) and Fig. 2(e) show histograms of the FT of the calculation and the experimental data respectively, the peak positions corresponding to the dominant beat frequencies between [19] for an initially randomly aligned ensemble of room temperature D2 molecules. For a particular ∆t and θ, the false colour-scale indicates the wavepacket probability with a thermal average.…”

mentioning

confidence: 99%

“…In the present work, the spatio-temporal evolution of the D 2 rotational wavepacket has been simulated following the procedure described in [19]. Briefly, a thermal ensemble of rigid rotors is considered, each of which gives rise to a superposition of rotational states, |Ψ Ji Mi = J≥|Mi| F JiJ (t)|JM i in which F JiJ (t ) are the timedependent complex coefficients (note that M i is conserved in a linearly polarized field).…”

mentioning

confidence: 99%

See 1 more Smart Citation

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

et al. 2007

Self Cite

View full text Add to dashboard Cite

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...

show abstract

mentioning

confidence: 99%

mentioning

confidence: 99%

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

et al. 2007

Self Cite

View full text Add to dashboard Cite

show abstract

“…In a simple model, we may assume that it occurs when the internuclear separation of the expanding nuclear wavepacket passes through a value that matches the returning electron wavelength at that time. We therefore define a simple condition for suppression of harmonic emission in this dynamic system as 2R(t)cos(θ m ) = λ(t), where θ m is the modal value of the alignment distribution σ(θ) at the peak of the pulse, calculated by the method detailed in [20]. Here sech^2 pulses of FWHM 30 fs and peak intensities 3.0 x 10 14 Wcm -2 and 2.2 x 10 14 Wcm -2 are used to calculate the evolution of σ(θ) under the pulse envelope.…”

mentioning

confidence: 99%

Dynamic Two-Center Interference in High-Order Harmonic Generation from Molecules with Attosecond Nuclear Motion

et al. 2008

Self Cite

View full text Add to dashboard Cite

Abstract:We report a new dynamic two-centre interference effect in High-HarmonicGeneration from H 2 , in which the attosecond nuclear motion of H 2 + initiated at ionisation causes interference to be observed at lower harmonic orders than would be the case for static nuclei. To enable this measurement we utilise a recently developed technique for probing the attosecond nuclear dynamics of small molecules. The experimental results are reproduced by a theoretical analysis based upon the strong field approximation which incorporates the temporally dependent two-centre interference term.High-harmonic generation (HHG) has proven to be a rich area of study over the last decade, finding application in a number of fields of laser science, such as coherent X-ray production [1,2] , attosecond pulse generation [3][4][5], and time resolved probing of nuclear dynamics [6,7]. HHG has also led to important advances towards the goal of structural imaging of small molecules [8][9][10][11][12][13][14][15], the harmonic emission depending strongly on the nature of the molecular orbital involved. This is seen most clearly within the Strong Field Approximation (SFA), in which the amplitude for HHG is determined by the Fourier transform of the bound state wavefunction.The wavefunctions relevant to HHG are those describing the propagated continuum electron ( c ψ ), and the bound electronic state from which the electron was ionised ( g ψ ). Recollision of the electron wavepacket with its parent ion results in a high local electron density (described by

show abstract

“…This typically happens through collisions with other molecules and can be avoided by maintaining a low molecular density in the laser-molecule interaction region. Like in the case of adiabatic alignment, increasing degrees of impulsive alignment are achieved with increasing molecular polarisability and decreasing rotational temperature of the molecular ensemble [207]. However, in the impulsive regime the degree of rotational excitation solely depends on the total energy deposited in the molecular system.…”

Section: Impulsive Alignmentmentioning

confidence: 99%

“…In the impulsive regime, the laser pulse duration is much shorter than the characteristic rotational period of the molecule [207]. Here, the laser pulse coherently couples the rotational states of the molecule and thus creates a rotational wavepacket that is initially aligned along the laser pulse polarisation.…”

Section: Impulsive Alignmentmentioning

confidence: 99%

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

Oppermann

2014

Springer Theses

View full text Add to dashboard Cite

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.

show abstract

Dynamics of laser-induced molecular alignment in the impulsive and adiabatic regimes: A direct comparison

Cited by 110 publications

References 38 publications

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

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

Dynamic Two-Center Interference in High-Order Harmonic Generation from Molecules with Attosecond Nuclear Motion

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

Contact Info

Product

Resources

About