Laser-dressed absorption in atomic helium is studied, both theoretically and experimentally, by transient absorption spectroscopy using isolated 400-as pulses centered at 22 eV and 12-fs near-infrared (NIR) pulses with 780-nm central wavelength. Multiple features in the helium singly excited bound-state spectrum are observed only when the NIR and attosecond pulses are overlapped in time. Theoretical analysis indicates that these light-induced structures (LISs) are the intermediate states in resonant, second-order processes that transfer population to multiple dipole forbidden states. The use of broadband, coherent extreme ultraviolet (XUV) radiation allows observation of these LISs without specifically tuning to a two-photon resonance, as would be required with narrowband XUV light. The strength and position of the LISs depend strongly on the NIR intensity and the pump-probe delay. © 2012 American Physical Society.
Publication Source (Journal or Book title)
Physical Review A - Atomic, Molecular, and Optical Physics
Chen, S., Bell, M., Beck, A., Mashiko, H., Wu, M., Pfeiffer, A., Gaarde, M., Neumark, D., Leone, S., & Schafer, K. (2012). Light-induced states in attosecond transient absorption spectra of laser-dressed helium. Physical Review A - Atomic, Molecular, and Optical Physics, 86 (6) https://doi.org/10.1103/PhysRevA.86.063408