Observation of Quantum beats in two photon ionization of argon.

An accompanying experimental study uses two asynchronous lasers to create and ionize a wave packetof low lying states of argon. It was observed that by varying the wavelength, starkly different photoionization signals were obtained. This technique has been used before when studying autoionizing statesin argon [1]. Here we theoretically study one and two photon ionization from one such wavepacket bymeans of multichannel quantum defect theory treating the delayed laser as a time dependent perturbation.We find that two the processes posses a remarkably different photo electron spectrogram and that, asobserved in the experiment, both signals show quantum beats in the delay between the lasers. Wealso explore here the importance of the intermediate states that give rise to this difference and someproperties, in both phase and amplitude, of the asymmetry coefficients in the angular distribution aswell as the photo electron signal.

References

[1] A Plunkett, MA Alarcon, JK Wood, CH Greene, and A Sandhu. Raman interferometry between au-toionizing states to probe ultrafast wavepacket dynamics with high spectral resolution. arXiv preprintarXiv:2111.03975, 2021.