# Laser induced Ionization

We know that when a linearly polarised laser field interacts with a diatomic molecule ionization happens when the molecular axis is along the laser-field direction.

However, in case of a circularly polarised light, it is seen that ionization can happen when laser electric field is perpendicular to the molecular axis as well (ionization along the laser-field direction is still dominant).

How can we understand this mechanism?

• I doubt that the first paragraph is correct. – Pieter Apr 4 '18 at 14:23
• @Pieter Actually I was looking at these phenomena in a strong laser field (tunneling regime) ...intensity about 10^15 W/cm2 – Bikash Apr 4 '18 at 14:34
• Aha. I was thinking of ordinary photoemission with a UV laser or something similar. – Pieter Apr 4 '18 at 14:43

Maybe it is too late to answer this question but let me give you an answer for you and for those who see this question. Around the intensity of the laser field of $$10^{15}$$ $$W/cm^2$$, both a tunneling ionization and a over-the-barrier ionization can take place depending on the type of molecule or timing of a pulsed laser field. With low ionization energy and at the time when the pulsed laser field peaks, over-the-barrier ionization can take place. Otherwise, tunneling ionization takes place.