Field-Free Orientation of CO Molecules by Femtosecond Two-Color Laser Fields

De, Sankar; Znakovskaya, I.; Ray, D.; Anis, Fatima; Johnson, Nora G.; Bocharova, I.; Magrakvelidze, Maia; Esry, B. D.; Cocke, C. L.; Litvinyuk, Igor; Kling, Matthias F.

doi:10.1103/physrevlett.103.153002

Cited by 262 publications

(183 citation statements)

References 25 publications

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“…The use of nonresonant two-color laser fields [35,37,38] showed a further promising route to molecular orientation, as it can be implemented in an all-optical setup without the need for additional electric fields or lossy state-selection stages. Nevertheless, the presence of an electric field in the form of a nanosecond laser pulse was a limitation, until the two-color scheme could be successfully applied in an impulsive orientation experiment without the need of any additional fields [39]. The major limitation in the latter approach was the low degree of orientation.…”

Section: Introductionmentioning

confidence: 99%

Two-pulse orientation dynamics and high-harmonic spectroscopy of strongly-oriented molecules

Kraus

Baykusheva

Wörner

2014

J. Phys. B: At. Mol. Opt. Phys.

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Abstract. We present the detailed analysis of a new two-pulse orientation scheme that achieves macroscopic field-free orientation at the high particle densities required for attosecond and high-harmonic spectroscopies [P. M. Kraus et al., arxiv:1311.3923]. Carbon monoxide (CO) molecules are oriented by combining a one-color and a delayed two-color non-resonant femtosecond laser pulses. High-harmonic generation is used to probe the oriented wave-packet dynamics and reveals that a very high degree of orientation (N up /N total = 0.82) is achieved. We further extend this approach to orienting carbonyl sulfide (OCS) molecules. We show that the present two-pulse scheme selectively enhances orientation created by the hyperpolarizability interaction whereas the ionization-depletion mechanism plays no role. We further control and optimize orientation through the delay between the one-and two-color pump pulses. Finally, we demonstrate a complementary encoding of electronic structure features, such as shape resonances, in the even-and odd-harmonic spectrum. The achieved progress makes two-pulse field-free orientation an attractive tool for a broad class of time-resolved measurements.

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Section: Introductionmentioning

confidence: 99%

Two-pulse orientation dynamics and high-harmonic spectroscopy of strongly-oriented molecules

Kraus

Baykusheva

Wörner

2014

J. Phys. B: At. Mol. Opt. Phys.

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“…Furthermore, appropriately time-delayed trains of alignment pulses have been employed to enhance the alignment quality [212]. Orientation of the molecule has been achieved by employing two-colour alignment pulses [213] and the possibility of inducing field-free 3-dimensional alignment via two orthogonally polarised pulses has been proposed [214] and demonstrated [215].…”

Section: Impulsive 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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“…In these filaments, however, the alignment pulse undergoes strong nonlinearities and spatial self-confinement upon propagation and the molecules to be aligned are exposed to a laser peak power of typically 5×10 13 W/cm 2 . Such high intensities can provoke unwanted excitation and damage (particularly for biological samples) prior to the alignment and interrogation [33]. Depending on the gas species under examination the process of filamentation may even require higher intensities, e.g.…”

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confidence: 99%

“…The elimination of a randomly oriented molecule distribution is beneficial for numerous applications including high harmonic generation [12][13][14], THz emission [15,16], the control of chemical, surface [17] and photoreactions whose rates depend on the molecular orientation, and others [18][19][20]. The two mostly applied alignment techniques are based on intense nIR femtosecond laser pulses where alignment is achieved by means of molecular two-color excitation [21] or through the formation of elongated plasma channels (filaments) [22]. Both of these alignment procedures require typically high laser pulse intensities (10 13 W/cm 2 ) which may cause unwanted ionization and excitation of electronic-vibronic states during the interaction.…”

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confidence: 99%

Air nonlinear dynamics initiated by ultra-intense lambda-cubic terahertz pulses

Shalaby

Hauri

2015

Applied Physics Letters

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Abstract:We report on the measurement of the instantaneous Kerr nonlinearity and the retarded alignment of air molecules CO 2 , N 2 and O 2 triggered by an intense, lambda-cubic terahertz pulse. The strong-field, impulsive low-frequency excitation (4 THz) leads to field-free alignment dynamics of these molecules thanks to the THz-induced transient dipole moments in the otherwise non-polar molecules. The strong coupling to the terahertz electric transient results in the excitation of coherent long-living rotational states at ambient pressure. Beyond fundamental investigations of nonlinear properties in gases, our results suggest a novel route towards field-free molecular alignment at laser intensity well below the ionization threshold.Air turns into a nonlinear medium for electromagnetic waves under exceptionally strong fields that manifest itself in phenomena like the instantaneous Kerr nonlinearities and retarded molecular alignment [1]. Up to present, the minuscule nonlinear response of air has limited the exploration of its nonlinear properties to the optical frequency regime owing to the availability of intense near-infrared (nIR) lasers (e.g Ti:sapphire with a carrier frequency 380 THz). From a fundamental science point of view nonlinear excitation of air (and other gases) by pulses with a lower carrier frequency, in the so-called terahertz gap Up to now both the observation of Kerr nonlinearities and molecular alignment in air at THz frequencies was hampered by the technological void of intense sources [3][4][5][6][7][8][9]. Field-free alignment/orientation of molecules is conventionally done by nIR laser technology which allows for preparing the molecules in a

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Field-Free Orientation of CO Molecules by Femtosecond Two-Color Laser Fields

Cited by 262 publications

References 25 publications

Two-pulse orientation dynamics and high-harmonic spectroscopy of strongly-oriented molecules

Two-pulse orientation dynamics and high-harmonic spectroscopy of strongly-oriented molecules

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

Air nonlinear dynamics initiated by ultra-intense lambda-cubic terahertz pulses

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