Orientation-dependent forward-backward photoelectron holography from asymmetric molecules

Orientation-dependent photoelectron holography from the one-electron polar molecular ion HeH2+ in linearly polarized few-cycle laser fields is studied numerically. We identify four dominant holography patterns simultaneously with one shot of lasers and show that these are sensitive to the molecular structure and the orientation angle between the molecular axis and laser polarization direction. Due to the preferential enhanced ionization from one direction of the molecular axis, two kinds of forward photoelectron holography and two backward holography interference patterns predicted by a semiclassical model showup simultaneously for parallel orientation. Coulomb focusing effects are shown to be crucial for the backward scattering holography and a weak forward scattering holography channel with relatively small overlap. In contrast, after increasing the orientation angle, the backward scattering patterns disappears gradually because of the smaller scattering cross sections. Only one forward scattering holography can be clearly identified in the perpendicular orientation. Ultrashort and intense laser pulses are shown to be preferred for photoelectron holography. Intercycle interference rings in the above-threshold ionization are suppressed and consequently the intracycle rescattering signals are enhanced.