Photoemission and Ionization of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mrow><mml:mi mathvariant="normal">H</mml:mi><mml:mi mathvariant="normal">e</mml:mi></mml:mrow><mml:mo>+</mml:mo></mml:msup></mml:math>under Simultaneous Irradiation of Fundamental Laser and High-Order Harmonic Pulses

We theoretically study the response of ${\mathrm{H}\mathrm{e}}^{+}$ exposed simultaneously to an intense Ti:sapphire laser and its 27th or 13th harmonic pulses. High-order harmonic emission from ${\mathrm{H}\mathrm{e}}^{+}$ is enhanced by many orders of magnitude compared with the case of the fundamental pulse alone. Moreover, while an individual 10 fs laser (wavelength ${\ensuremath{\lambda}}_{F}=800\text{ }\text{ }\mathrm{n}\mathrm{m}$) or its 27th harmonic pulse with a peak intensity of $3\ifmmode\times\else\texttimes\fi{}{10}^{14}$ and ${10}^{13}\text{ }{\mathrm{W}\mathrm{/}\mathrm{c}\mathrm{m}}^{2}$, respectively, ionizes no more than $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ of ${\mathrm{H}\mathrm{e}}^{+}$, their combined pulse leads to a surprisingly high ${\mathrm{H}\mathrm{e}}^{2+}$ yield of $17%$.

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