Experimental observation of the elusive double-peak structure in R-dependent strong-field ionization rate of H2+

نویسندگان

  • Han Xu
  • Feng He
  • D. Kielpinski
  • R.T. Sang
  • I.V. Litvinyuk
چکیده

When a diatomic molecule is ionized by an intense laser field, the ionization rate depends very strongly on the inter-nuclear separation. That dependence exhibits a pronounced maximum at the inter-nuclear separation known as the "critical distance". This phenomenon was first demonstrated theoretically in H2(+) and became known as "charge-resonance enhanced ionization" (CREI, in reference to a proposed physical mechanism) or simply "enhanced ionization"(EI). All theoretical models of this phenomenon predict a double-peak structure in the R-dependent ionization rate of H2(+). However, such double-peak structure has never been observed experimentally. It was even suggested that it is impossible to observe due to fast motion of the nuclear wavepackets. Here we report a few-cycle pump-probe experiment which clearly resolves that elusive double-peak structure. In the experiment, an expanding H2(+) ion produced by an intense pump pulse is probed by a much weaker probe pulse. The predicted double-peak structure is clearly seen in delay-dependent kinetic energy spectra of protons when pump and probe pulses are polarized parallel to each other. No structure is seen when the probe is polarized perpendicular to the pump.

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عنوان ژورنال:

دوره 5  شماره 

صفحات  -

تاریخ انتشار 2015