Quantum control of high-energy harmonic generation by pulse shaping

High harmonic generation (HHG) is the most extreme high-order nonlinear optical process, which can be selectively enhanced at lower photon energies around ~40eV by using temporally shaped laser pulses [1]. Here we demonstrate the ability for enhancing the HHG flux and spectrum at higher photon energies around ~100eV, relevant for imaging and magnetic spectroscopies. By changing the spectral phase of the 800nm driving laser pulses using a genetic algorithm, we can enhance the total HHG flux, or selectively enhance individual HHG orders, or spectrally shift the HHG peaks. These control capabilities can be explained by intra-atomic phase matching on attosecond timescales [2]. Here the phase of the driving laser is optimized so that HHG bursts from each half cycle of the laser pulse interfere coherently, leading to enhancement or suppression in HHG spectrum. This demonstrates that we can extend these quantum control capabilities to higher photon energies, to design and tailor HHG sources for applications in ultrafast spectroscopy, resonant magnetic scattering, and hyperspectral imaging.
[1] Bartels et al., Nature 406, 164 (2000)
[2] Christov et al., Phys. Rev. Lett. 86, 5458 (2001)