STSM by Jorge Alejandro Budagosky Marcilla, Institute for Biocomputation and Physics of Complex Systems (Zaragoza), with Esa Räsänen, Tampere University of Technology (Tampere)
On February 16th, 2014 (7 days)


Optimal control of high harmonic generation

At sufficiently high intensities, matter reacts non-linearly to light, and may re-emit at integer multiples (harmonics) of the frequency of the incoming source. The spectrum of atoms and molecules exposed to very intense laser pulses was found to present unexpectedly high harmonics, and its shape was observed to have a plateau extending over many orders of magnitude – a process known as high harmonic generation (HHG). The light emitted in this manner is coherent and may reach the extreme ultraviolet and soft X-ray frequency regime. These properties can be of paramount importance for many technological and scientific purposes.

We examine computationally the possibility of optimizing the HHG spectrum of Hydrogen atoms by shaping a laser pulse in the THz range. The spectra are computed with a fully quantum mechanical description, by explicitly computing the time-dependent dipole moment of the systems, which are modeled in one dimension. Specifically, by the optimal control theory (OCT), we studied the possibility of arbitrarily adjusting the plateau extension in harmonic spectra.

Preliminary results obtained so far show that it is possible to optimize the HHG spectrum in order to arbitrarily extend the plateau length. The length of the plateau can be controlled not only by using a frequency window (target) or by increasing the pulse intensity, but increasing the length of this. In general, we have observed the presence of characteristic structures in the pulses that can be directly associated with particular processes (ionization, recombination, etc.). The latter is still under discussion.

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