Self-action effects in ionization and fragmentation of toluene by femtosecond laser pulses

Tang, Xinlan; Becker, Andreas; Liu, Weiwei; Sharifi, Soheil; Kosareva, O.G.; Kandidov, V.P.; Agostini, P.; Chin, See Leang

doi:10.1007/s00340-005-1760-2

Cited by 7 publications

(8 citation statements)

References 17 publications

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“…The sample molecules are ionized by the laser beam and focused by a lens at the entrance of the time-of-flight chamber. The focusing lens is also used as the window of the chamber to minimize self-focusing effects that could appear if an external lens were used, as distortions of the light field by phase modulation have been found to affect MS measurements. , The polarization of the laser is horizontal as it enters the mass spectrometer and perpendicular to the ion collection optics. We attenuate the beam to 170 μJ/pulse unless otherwise noted, and no phase distortions due to the self-focusing are observed.…”

Section: Experimental Methodsmentioning

confidence: 99%

Control of Molecular Fragmentation Using Shaped Femtosecond Pulses

et al. 2008

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The possibility that chemical reactions may be controlled by tailored femtosecond laser pulses has inspired recent studies that take advantage of their short pulse duration, comparable to intramolecular dynamics, and high peak intensity to fragment and ionize molecules. In this article, we present an experimental quest to control the chemical reactions that take place when isolated molecules interact with shaped near-infrared laser pulses with peak intensities ranging from 1013 to 1016 W/cm2. Through the exhaustive evaluation of hundreds of thousands of experiments, we methodically evaluated the molecular response of 16 compounds, including isomers, to the tailored light fields, as monitored by time-of-flight mass spectrometry. Analysis of the experimental data, taking into account its statistical significance, leads us to uncover important trends regarding the interaction of isolated molecules with an intense laser field. Despite the energetics involved in fragmentation and ionization, the integrated second-harmonic generation of a given laser pulse (ISHG), which was recorded as an independent diagnostic parameter, was found to be linearly proportional to the total ion yield (IMS) generated by that pulse in all of our pulse shaping measurements. Order of magnitude laser control over the relative yields of different fragment ions was observed for most of the molecules studied; the fragmentation yields were found to vary monotonically with IMS and/or ISHG. When the extensive changes in fragmentation yields as a function of IMS were compared for different phase functions, we found essentially identical results. This observation implies that fragmentation depends on a parameter that is responsible for IMS and independent from the particular time-frequency structure of the shaped laser pulse. With additional experiments, we found that individual ion yields depend only on the average pulse duration, implying that coherence does not play a role in the observed changes in yield as a function of pulse shaping. These findings were consistently observed for all molecules studied (p-, m-, o-nitrotoluene, 2,4-dinitrotoluene, benzene, toluene, naphthalene, azulene, acetone, acetyl chloride, acetophenone, p-chrolobenzonitrile, N,N-dimethylformamide, dimethyl phosphate, 2-chloroethyl ethyl sulfide, and tricarbonyl-[eta5-1-methyl-2,4-cyclopentadien-1-yl]-manganese). The exception to our conclusion is that the yield of small singly-charged fragments resulting from a multiple ionization process in a subset of molecules, were found to be highly sensitive to the phase structure of the intense pulses. This coherent process plays a minimal role in photofragmentation; therefore, we consider it an exception rather than a rule. Changes in the fragmentation process are dependent on molecular structure, as evidenced in a number of isomers, therefore femtosecond laser fragmentation could provide a practical dimension to analytical chemistry techniques.

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Section: Experimental Methodsmentioning

confidence: 99%

Control of Molecular Fragmentation Using Shaped Femtosecond Pulses

et al. 2008

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“…Recently, the application of an intense ultrashort laser to ionize and dissociate molecules has attracted considerable attention. − The conventional knowledge of the high-power laser ionization−dissociation of molecules is that the molecule is first ionized in the intense laser field, followed by fragmentation of the molecular ions. − …”

Section: Introductionmentioning

confidence: 99%

“…4 Recently, the application of an intense ultrashort laser to ionize and dissociate molecules has attracted considerable attention. [7][8][9][10][11][12][13][14] The conventional knowledge of the high-power laser ionization-dissociation of molecules is that the molecule is first ionized in the intense laser field, followed by fragmentation of the molecular ions. [7][8][9][10][11][12][13][14][15][16][17][18] In this paper, we shall report the experimental results of the high-power laser ionization-dissociation of CH 4 performed using the 800-nm laser with a pulse duration of 48 fs and with a laser intensity that varies from 1.5 × 10 14 W/cm 2 to 1.9 × 10 15 W/cm 2 .…”

Section: Introductionmentioning

confidence: 99%

Experimental and Theoretical Investigation of High-Power Laser Ionization and Dissociation of Methane

et al. 2007

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The main purpose of this paper is to report the high-power laser ionization-dissociation of CH(4) at various femtosecond (fs) laser intensities (from 1 x 10(14) W/cm(2) to 2 x 10(15) W/cm(2)) with a laser pulse duration of 48 fs. The generalized molecular Keldysh theory has been applied to calculate the ionization yields for CH(4)+ and CH(4)++. Outside the influence of the fs intense laser, we propose to calculate the mass spectra due to the decomposition of CH(4)+ and CH(4)++, using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The agreement between the experimental mass spectra and calculated mass spectra seems to be reasonable.

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“…The kinetic energy carried by the positively charged fragments is expected to depend on the excitation state of the molecule prior to fragmentation. Intense laser field fragmentation necessarily operates in a non-linear regime, and the fragmentation patterns depend strongly on the characteristics of the pulse [19,20], while for the case of x-ray fragmentation performed in the linear regime the ion-fragmentation patterns should not depend on x-ray intensity.…”

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confidence: 99%