Coherent control of ultrafast extreme ultraviolet transient absorption

Ultrafast extreme ultraviolet (XUV) transient absorption is the process by which atoms and molecules absorb light on a time-scale faster than the lifetime of the states involved. Coherent control uses quantum coherences to manipulate quantum pathways in light-matter interactions. Here we combine the two. We show that we can control the absorption spectral lineshape, changing it from Lorentzian to Fano to inverted Lorentzian and back again. The control is achieved by creating quantum coherence in the ground electronic state of hydrogen molecules, long before the arrival of the ultrafast XUV pulse. We show that the absorption can become negative at 12 eV, which is the optical gain. These observations provide new insights into the control of spectral lineshapes and open the way for achieving lasing without inversion in the XUV spectral range.

Automated summary

By generating quantum coherence in the ground electronic state of hydrogen molecules, we are able to control the absorption spectrum, making it negative at 12 eV, which is the optical gain. These findings offer new insights into controlling spectral lineshapes and pave the way for achieving lasing without inversion in the XUV spectral range.