Orientation dependence of the ionization of CO and NO in an intense femtosecond two-color laser field

Two-color (800- and 400-nm) short (45-fs) linearly polarized pulses are used to ionize and dissociate CO and NO. The emission of C${}^q$${}^{+}$, N${}^q$${}^{+}$, and O${}^{+}$ fragments indicates that the higher ionization rate occurs when the peak electric field points from C to O in CO and from N to O in NO. This preferred direction is in agreement with that predicted by Stark-corrected strong-field-approximation calculations.

Figure 1

Density plot of the asymmetry of emission of electrons from Xe at an intensity of (0.7± 0.1) × 10${}^{14}$ W/cm${}^2$ as a function of electron energy and two-color phase ϕ. A projection of the yield versus electron energy is shown on a logarithmic scale in the left panel, while the bottom panel shows plots of asymmetry versus phase for two chosen slices of electron energy.

Figure 2

(a) Density plot of down electrons as a function of electron energy and phase. (b) Theoretical TDSE calculation for this process [28].

Figure 3

Density plot of the asymmetry of emission of C${}^{+}$ ions from CO at an intensity of 2 × 10${}^{14}$ W/cm${}^2$ as a function of two-color phase ϕ and KER. A projection of the yield versus KER is shown in the left panel, while the bottom panel shows plots of asymmetry versus phase for two chosen slices of the KER.

Figure 4

Similar to Fig. 3, but for C${}^{2+}$ ions.

Figure 5

Similar to Fig. 3, but for O${}^{+}$ ions.

Figure 6

Similar to Fig. 3, but for N${}^{+}$ from NO at an intensity of 3 × 10${}^{14}$ W/cm${}^2$.

Figure 7

Similar to Fig. 3, but for O${}^{+}$ ions from NO.

Figure 8

Similar to Fig. 1, but for a CO target.

Figure 9

Similar to Fig. 2, but for a CO target.

Figure 10

Schematic of the HOMO of (a) CO and (b) NO.

Figure 11

Calculated ionization rates for CO as a function of the angle between the electric field and the molecular axis. The field pointing from C to O corresponds to an angle of 0˚. (a) The dashed black curve denotes the MO-ADK theory [5] and the solid red curve denotes the MO-ADK theory corrected for the Stark effect. (b) The dashed black curve denotes the SFA calculation and the solid red curve denotes the SFA calculation corrected for the Stark effect.

Figure 12

Similar to Fig. 11, but for NO.