Temporal separation of ${\mathrm{H}}_2$ double-ionization channels using intense ultrashort $10\text{−}\mathrm{fs}$ laser pulses

Double ionization channels of ${\mathrm{H}}_2$ are separated in the time domain using ultrashort $10\text{−}\mathrm{fs}$ laser pulses in the ${10}^{13}–{10}^{15}\mathrm{W}{\mathrm{cm}}^{-2}$ intensity range. Charge resonance enhanced ionization does not contribute anymore to double ionization because the ${\mathrm{H}}_2^{+}$ ion does not have enough time to stretch up to the critical internuclear distance. Using a pump-probe excitation scheme, this process is shown to be very sensitive for the detection of pre- and post-pulses situated at a few tens of femtoseconds from the maximum pulse envelope.

Figure 1

Interferometric autocorrelation (IAC) of $10\text{−}\mathrm{fs}$ laser pulses. The experimental and calculated signals are given, respectively, by the full and dotted curves. The IAC curve is calculated using the Fourier transform of the frequency domain electric field and assuming a constant spectral phase.

Figure 2

Proton spectra recorded from ${\mathrm{H}}_2$ using $10\text{−}\mathrm{fs}$ laser pulses at $3.2\times {10}^{15}\mathrm{W}{\mathrm{cm}}^{-2}$ peak intensity. Full curve: no group delay dispersion compensation. Dotted curve: insertion of a $2\text{−}\mathrm{mm}$-thick fused silica plate in the laser optical path for group delay dispersion compensation.

Figure 3

Proton spectra recorded from ${\mathrm{H}}_2$ using $10\text{−}\mathrm{fs}$ pump, probe, and pump-probe laser excitation schemes. Dashed curve: pump pulse at $1.4\times {10}^{15}\mathrm{W}{\mathrm{cm}}^{-2}$. Dotted curve: probe pulse at $3.4\times {10}^{13}\mathrm{W}{\mathrm{cm}}^{-2}$. Full curve: the same above the pump and probe pulses, where the probe pulse delay is $24\mathrm{fs}$.

Figure 4

Integrated proton signals from ${\mathrm{H}}_2$ recorded with two identical $10\text{−}\mathrm{fs}$ laser pulses as a function of the pulses delay. For each pulse, the peak laser intensity is $8.3\times {10}^{13}\mathrm{W}{\mathrm{cm}}^{-2}$. Lower curve: integrated proton signal from charge resonance enhanced ionization in the $2–4\mathrm{eV}$ energy range. Upper curve: integrated proton signal from short range double ionization in the $4–15\mathrm{eV}$ energy range.