Anomalous ionization efficiency by few-cycle pulses in the multiphoton ionization regime

We theoretically study the effect of laser pulse durations on the ionization yield of hydrogen atoms and negative hydrogen ions. By numerically solving the time-dependent Schrödinger equation we find that the ionization efficiency by few-cycle pulses is unexpectedly larger than that by many-cycle pulses at low intensities when multiphoton ionization is the dominant ionization mechanism.

Figure 1

(Color online) Ionization yield of the one-dimensional H atom as a function of peak intensity for different numbers of cycles with the (a) sine-squared and (b) Gaussian pulses. The laser wavelength is $800\mathrm{nm}$.

Figure 2

(Color online) Ionization yield of the three-dimensional H atom as a function of peak intensity for different numbers of cycles. The pulse shape is Gaussian and the laser wavelength is $800\mathrm{nm}$.

Figure 3

(Color online) Detachment yield of the one-dimensional ${\mathrm{H}}^{-}$ ion as a function of peak intensity for different numbers of cycles with the (a) sine-squared and (b) Gaussian pulses. The laser wavelength is $4\mu \mathrm{m}$.

Figure 4

(Color online) Detachment yield of the three-dimensional ${\mathrm{H}}^{-}$ ion as a function of laser intensity for different numbers of cycles. The pulse shape is Gaussian and the laser wavelength is $4\mu \mathrm{m}$.