<title>Ionization of biomolecules in high-intensity laser fields</title>

Abstract

The majority of previous femtosecond laser ionization studies have been carried out on atomic, diatomic or small polyatomic molecules. The understanding of interaction of intense laser pulses with polyatomic molecules is at a preliminary stage. It was difficult to examine the behavior of more complex molecules in the presence of intensive laser field due to their involatility and thermal lability. In the ionization experiments performed in the current research the polyatomic molecules irradiated with ≈ 30 fs laser pulses, at wavelength 800nm do not exhibit an extensive fragmentation, and produce multiply charged ions in the intensity range of 10¹⁴W/cm². Studies of ionization mechanisms in the case of femtosecond ionization have revealed that the dissociation paths can be avoided. To establish an intact ionization of molecules two regimes of photodissociation can be distinguished: absorption-dissociationionization (ADI) and absorption-ionization-dissociation (AID) regime. It was discovered that the crucial parameter for the post-ionization experiments is the energy necessary for ionization of the neutral species. The ionization efficiency depends strongly from the precise timing of the laser pulses and from the geometrical overlap of the focus of the postionizing laser beam with the emitted particle cloud.