Multiple Detachment of the SF₆^– Molecular Anion with Shaped Intense Laser Pulses

Abstract

Interaction of molecular SF6(-) anions with intense near-IR laser pulses is found to produce cationic fragments by nonsequential multiple detachment. Dissociative ionization channels that lie more than 20 eV above the threshold energy for double detachment are observed. Mass-resolved product yields are presented and analyzed as a function of the femtosecond laser pulse energy, pulse shape, and polarization ellipticity. The observed strong suppression of multiple detachment by pre-pulses, induced with negative third-order dispersion of the transform-limited fs laser pulse, is interpreted as suppression of a nonsequential process by early single detachment. However, in contrast to the relatively simple picture of a rescattering mechanism characterized by acute sensitivity to polarization ellipticity that dominates double ionization of neutral species and was reported for the atomic F(-) anion, multiple detachment of the molecular anion is found to exhibit only mild ellipticity dependence.

Z-scan method for nonlinear saturation intensity determination, using focused intense laser beams

“…However, the difference between the saturation intensities derived for molecular and atomic cations are much smaller despite the significant difference in the corresponding appearance energies. We interpret the apparent discrepancy of the I sat and appearance energy trends to be due to the particular highly efficient intense field mechanism for multiple detachment from a molecular anion system [17]. It is possible that efficient excitation to high-lying potential curves prior to dissociation result in directly competing channels for atomic and molecular cation production, which are hence similar in saturation properties.…”

“…Similarly, product depletion by sequential processes [30,36,38] with similar saturation may shift I sat of the initial product to lower values due to the rise of a secondary process. In this paper we demonstrate the Z-scan method measuring saturation intensities spanning two orders of magnitude for SF 6 − nonlinear single and nonsequential [17] multiple photodetachment processes. Nevertheless, the method is not limited to ion-laser interaction measurements and is well suited for practically any intense field experiment, examining the interaction with a finite depth target.…”

“…3 shows selected Z-scan simulations, performed assuming n = 2,4, and 10; Figure 4 shows a schematic representation of our experimental setup for the study of intense laser interactions with molecular and cluster ions, previously described in Ref. [17]. Briefly, cold molecular and cluster anions of interest are generated in a pulsed supersonic expansion Even-Lavie ion source [41].…”

“…The temporal compression of amplified laser pulses down to the femtosecond pulse durations leads, even at moderate focusing conditions, to peak field intensities exceeding the binding forces experienced by electrons inside atoms and molecules. Light matter interactions in this intense field regime were studied in atomic [4][5][6][7] and molecular systems [2,[8][9][10] as well as in non-neutral cationic [11][12][13] and anionic [14][15][16][17] systems. Intense laser fields bring forth a variety of nonlinear phenomena, such as the ac stark-shift [18], bond softening [19,20], multiphoton ionization [2,21], above-threshold ionization [22], Coulomb explosion [23,24], and more [25][26][27].…”

Simultaneous 3D coincidence imaging of cationic, anionic, and neutral photo-fragments

“…[25][26][27] Using a fast anion beam target and a similar concept of an electrostatic spectrometer, we are able to investigate different competing dissociation and electron detachment channels in intense field interaction with atomic, molecular, and cluster anions. [28][29][30][31][32][33] The photofragment spectrometer design allows coincidence detection of all the possible dissociation products on the same detector, including the anionic, cationic, and neutral fragments. In the present study, we describe the design, calibration, and optimization of the photofragment spectrometer as well as an analytic model for extracting channel specific KER spectra from 3D coincidence imaging data.…”