The impact of pulse duration on multiphoton ionization in the soft X-ray regime

Richter, M.; Сорокин, А. А.; Tiedtke, K.

doi:10.1117/12.2021298

Cited by 2 publications

(6 citation statements)

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“…This might point to collective 4d electron excitations for these higher charges because the strength of such a mechanism does not explicitly depend on the pulse duration. The scheme was already proposed for the particular multiphoton ionization of Xe [23,26] in the vicinity of the 4d giant resonance [44][45][46][47] to explain the very high charge states in comparison to other rare gases and was subject of a substantial and controversial discussion [22][23][24][25][26][27].…”

Section: Prl 112 213002 (2014) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 99%

“…In the simplest approximation of a damped harmonic plasma oscillation, the energy transfer from a high-intensity EUV field to a single Xe atom is proportional to the radiant exposure H without dependence on the pulse duration [26,27]. Naturally, this semiclassical approach applies only for higher intensities (and charges) on Xe in the vicinity of the 4d giant resonance and is not in conflict with models based on perturbation theory for lower intensities and charges and other rare gases without a collective giant resonance.…”

Section: Prl 112 213002 (2014) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 99%

“…The role of the 4d giant resonance and the impact of collective electron excitation on this particular behavior are still-open scientific questions of fundamental importance [22][23][24][25][26]. Since the different multiphoton schemes depend in different ways on the FEL pulse duration, as has recently been summarized [27], photoionization experiments at varying pulse duration may help to disentangle the underlying mechanisms. Experiments at the Linac Coherent Light Source (LCLS) have demonstrated that sequences of inner-shell excitation in the harder x-ray regime and successive refilling via Auger decay is the dominating mechanism for the complete stripping of the electrons on Ne atoms [16].…”

mentioning

confidence: 99%

“…For a distinct comparison, the plots were taken at selected pulse energies so that the radiant exposure H ¼ W=A had almost the same value of 1.45 J=cm 2 for both of them. Dividing the radiant exposure of a radiation pulse by the pulse duration yields the peak irradiance E ¼ H=τ ¼ W=ðAτÞ, which represents the key quantity of the radiation field to describe the rate of a simultaneous n-photon process according to the general power law of low-order perturbation theory [27,35],…”

mentioning

confidence: 99%

“…In contrast to simultaneous multiphoton ionization, the number of pure sequential multiphoton processes per pulse does not explicitly depend on the pulse duration in cases where relaxation processes do not play a significant role [27]. Hence, spectra taken at the same radiant exposure should be identical.…”

mentioning

confidence: 99%

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Time-Dependent Multiphoton Ionization of Xenon in the Soft-X-Ray Regime

et al. 2014

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The time-dependent multiphoton ionization of xenon atoms is studied with femtosecond pulses in the excitation range of the 4d giant resonance at the photon energy of 93 eV. Benefiting from a new operation mode of the free electron laser FLASH, the measurements are performed with varying pulse durations. A strong dependence of the ion charge distribution on the pulse duration allows the different multiphoton mechanisms behind the multiple photoionization of xenon to be disentangled up to a charge state of Xe 10þ . The results up to Xe 8þ are well explained by sequences of single photon, multiphoton, and Auger processes, but higher charge state generation suggests the need for collective electron multiphoton excitations. DOI: 10.1103/PhysRevLett.112.213002 PACS numbers: 32.80.Rm, 32.80.Fb, 41.60.Cr, 42.50.Hz The highly intense and ultrashort radiation pulses of the new free electron laser (FEL) facilities in Europe [1,2], the United States [3], and Japan [4,5] can significantly extend the study of interaction of x rays with matter to the nonlinear regime of multiphoton processes. A number of fascinating FEL experiments of multiphoton ionization have already been carried out on solids, clusters, molecules, and on free atoms [[6,7,8,9], and references therein]. Whereas in the regime of optical femtosecond lasers, simultaneous multiphoton, above-threshold, and strongfield ionization are the mechanisms of relevance [10,11], the nonlinear interaction of soft and hard x rays with atoms at photon energies above the first ionization threshold has been shown to be dominated by sequential processes in which an excited atom or ion created in a preceding step represents the target for a subsequent step [12][13][14][15][16][17][18][19][20]. For higher ionization charges and ionization thresholds which exceed the photon energy, the mechanisms may be rather complex because simultaneous multiphoton ionization processes come into play for the higher steps of an ionization sequence [12,21].A prime example is the multiphoton multiple ionization of Xe in the vicinity of the so-called 4d giant resonance in the extreme ultraviolet (EUV) between 90 eV and 110 eV photon energy where charge states up to Xe 21þ were observed at irradiance levels in the order of 10 16 W=cm 2[22]. A sequential scheme requires 19 steps and almost 60 EUV photons to generate Xe 21þ from atomic Xe, and more than a single photon is required for each step from Xe 7þ on. The role of the 4d giant resonance and the impact of collective electron excitation on this particular behavior are still-open scientific questions of fundamental importance [22][23][24][25][26]. Since the different multiphoton schemes depend in different ways on the FEL pulse duration, as has recently been summarized [27], photoionization experiments at varying pulse duration may help to disentangle the underlying mechanisms. Experiments at the Linac Coherent Light Source (LCLS) have demonstrated that sequences of inner-shell excitation in the harder x-ray regime and successive refilling via A...

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