If you want to know the theory behind using lasers, and light energy to aid the process, read this.
Quantum ionization
In quantum mechanics ionization can still happen classically where the electron has enough energy to make it over the potential barrier, but there is the additional possibility of tunnel ionization.
Tunnel ionization
Tunnel ionization is ionization due to quantum tunneling. In classical ionization an electron must have enough energy to make it over the potential barrier, but quantum tunneling allows the electron simply to go through the potential barrier instead of going all the way over it because of the wave nature of the electron. The probability of an electron tunneling through the barrier drops off exponentially with the width of the potential barrier. Therefore, an electron with a higher energy can make it further up the potential barrier, leaving a much thinner barrier to tunnel through and thus a greater chance to do so.
Non-sequential ionization
When the fact that the electric field of light is an alternating electric field is combined with tunnel ionization, the phenomenon of non-sequential ionization emerges. An electron that tunnels out from an atom or molecule may be sent right back in by the alternating field, at which point it can either recombine with the atom or molecule and release any excess energy, or it also has the chance to further ionize the atom or molecule through high energy collisions. This additional ionization is referred to as non-sequential ionization for two reasons: one, there is no order to how the second electron is removed, and two, an atom or molecule with a +2 charge can be created straight from an atom or molecule with a neutral charge, so the integer charges are not sequential. Non-sequential ionization is often studied at lower laser-field intensities, since most ionization events are sequential when the ionization rate is high.
http://en.wikipedia.org/wiki/Ionizeand more
Tunnel ionization
Tunnel ionization is a process in which electrons in an atom (or a molecule) pass through the potential barrier and escape from the atom (or molecule). In an intense electric field, the potential barrier of an atom (molecule) is distorted drastically. Therefore, the length of the barrier that electrons have to pass decreases and electrons can escape from the atom (molecule) easily.
As an electric field of light is an alternating electric field, the direction of the electric field reverses after the half period of the field. Because electrons have a charge, electrons escaping by tunnel ionization come and go to the atom (molecule) in every half period. In this process, some electrons recombine with the nucleus (nuclei). Because the electrons have gained a large quantity of kinetic energy by acceleration from the electric field, surplus energy is released as light. The energy of this light is so high that this method is an effective way of generating ultraviolet light.
When the recombination does not occur, further ionization proceeds by collision between high-energy electrons and a parent atom (molecule). Consequently, a multivalent ion is created and this ion is collapsed by Coulomb repulsion. This is called Coulomb explosion.
http://en.wikipedia.org/wiki/Tunnel_ionization