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Coherent control beyond population control and spectral interferences is demonstrated on the interferences and intensity of the two Autler-Townes ͑AT͒ components in the photoelectron spectrum of K atoms, using a sequence of two intense time-delayed femtosecond laser pulses. Photoelectron spectra were taken at various delay times between the two laser pulses and at different laser intensities at a fixed delay time. With respect to the interferences in the AT doublet the role of time delay and laser intensity is interchangeable for (n ϩ0.5) excitation. Strong laser fields or the optical phase of the delayed laser pulse allow the quantum mechanical phase of an atomic state to be manipulated in a symmetrical fashion. The observations are discussed in terms of a two-level model coupled to the continuum. For suitable combinations of the laser intensity of the first pulse and the time delay, the second laser pulse leaves the excited state population unchanged.

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Articles you may be interested inLaboratory transferability of optimally shaped laser pulses for quantum control J. Chem. Phys. 140, 074302 (2014); 10.1063/1.4863137 Effect of temporal pulse shape on optical damage Appl. Phys. Lett. 90, 041110 (2007); 10.1063/1.2431705 Femtosecond pulse shaping using a liquid-crystal display: Applications to depth profiling analysis Rev. Sci. Instrum. 76, 086104 (2005);

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Femtosecond laser pulse induced ultrafast plasma dynamics studies of water breakdown in the range up to 250ps are reported. We combine transient imaging techniques together with spectrally resolved reflection spectroscopy to monitor the early breakdown dynamics at the water surface with a laser intensity being 1.5 above threshold. We observe a 20ps delay before the plasma expands with an initial velocity of 5900m∕s. The transient electron density after formation of the plasma is 1.2×1021∕cm3. A recombination on a picosecond time scale with a rate of (1.6×10−9±0.3×10−9)cm3∕s is found.