Laser-induced modification of an excited-state vibrational wave packet in neutral H2 observed in a pump-control scheme

We observe and modify a molecular vibrational wave packet in an electronically excited state of the neutral hydrogen molecule. In an extreme-ultraviolet (XUV) time-domain absorption spectroscopy experiment, we launch a vibrational wave packet in the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mi>D</a:mi><a:mmultiscripts><a:mi mathvariant="normal">Π</a:mi><a:mi>u</a:mi><a:none/><a:mprescripts/><a:none/><a:mn>1</a:mn></a:mmultiscripts><a:mspace width="0.16em"/><a:mn>3</a:mn><a:mi mathvariant="normal">p</a:mi><a:mi>π</a:mi></a:mrow></a:math> state of <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:msub><e:mi mathvariant="normal">H</e:mi><e:mn>2</e:mn></e:msub></e:math> and track its time evolution via the coherent dipole response. The reconstructed time-dependent dipole from experimentally measured XUV absorption spectra provides access to the revival of the vibrational wave packet, which we control via an intense near-infrared (NIR) pulse. Tuning the intensity of the NIR pulse, we observe the revival of the wave packet to be significantly modified, which is supported by the results of a multilevel simulation as well as an analytical model based on state-specific phase shifts. The NIR field is applied only 7 fs after the creation of the wave packet but influences its evolution up to at least its first revival at 270 fs. This experimental approach for nonlocal-in-time laser modification of quantum dynamics in a pump-control scheme enabled by molecular self-probing is generally applicable to a large range of molecules and materials as it only requires the observation of absorption spectra.