Reconstruction of ionization probabilities from spatially averaged data inNdimensions

Abstract

We present an analytical inversion technique which can be used to recover ionization probabilities from spatially averaged data in an N-dimensional detection scheme. The solution is given as a power series in intensity. For this reason, we call this technique a multiphoton expansion (MPE). The MPE formalism was verified with an exactly solvable inversion problem in 2D, and probabilities in the postsaturation region, where the intensity-selective scanning approach breaks down, were recovered. In 3D, ionization probabilities of Xe were successfully recovered with MPE from simulated (using the ADK tunneling theory) ion yields. Finally, we tested our approach with intensity-resolved benzene ion yields showing a resonant multiphoton ionization process. By applying MPE to this data (which was artificially averaged) the resonant structure was recoveredsuggesting that the resonance in benzene may have been observable in spatially averaged data taken elsewhere.

Intensity-resolved ionization yields of aniline with femtosecond laser pulses

“…This decrease is a telltale sign of the elimination of volumetric weighting in intensity-resolved ionization experiments due to the increasing role of higher-order MPI processes and fragmentation of the parent ion [8,12,13]. Inspection of benzene fragmentation at intensities of 30, 50, 80, and 100 TW/cm 2 reveals a sharp onset of fragmentation at 80 TW/cm 2 and is responsible for the postsaturation decrease, but not the decrease following the kink and is consistent with that found in [3,9].…”

“…For A q+ (where q > 1) atomic ions, the lessening of slopes are the result of saturation of nonsequential processes while for the singly charged atomic ions A + , the decreases in slope have been attributed to population trapping ( [7] and references therein). As will be shown for the benzene and aniline parent molecular ions, the slopes prior to saturation take on near-integer values consistent with ionization through an intermediate state [9]. In the intensity range of 3 × 10 13 to 8 × 10 13 W/cm 2 our data deviate from those of Ref.…”

“…Analogously, in the current work, we find that aniline (amino-benzene) molecules having a phenyl ring exhibit similar ionization dynamics with the prototypical aromatic molecule benzene. By generalizing upon the ionization mechanism recently put forward for benzene [8,9], we conclude that the frontier orbitals, in addition to a low-lying 3s-Rydberg state, are responsible for the observed nonlinearities in the ion yield curves. * jstroha1@physics.tamu.edu In experiments, accurate measurements of ionization probabilities as a function of a well-defined intensity are hindered by the broad range of intensities within a laser beam.…”

“…Compared to nanosecond pulses, femtosecond pulses promote efficient parent ion formation of the molecules by exceeding the dissociation rates and allowing the resulting parent ions to be identified with a TOF spectrometer [15]. To the best of our knowledge, intensityresolved ion yields as a function of laser intensity and for ultrashort, 800-nm pulses have only been reported for benzene [8,9], but not for aniline. We will demonstrate why the setups used in previous experiments could not have shown the now revealed REMPI-like process of these molecules under the interaction with ultrashort pulses.…”

Ultrafast REMPI in benzene and the monohalobenzenes without the focal volume effect

“…We focus ultrashort (50 fs, 804 nm) pulses into the target vapor and record ion yields as a function of pulse energy from a micrometersized interaction volume only, inside which the intensity varies by less than 1/14th of a decade on a logarithmic intensity axis. This small variation, without the need for deconvolution, [12][13][14][15][16] eliminates focal averaging. Further details on the method used to suppress signal averaging can be found in the Appendix.…”