Peculiarities of molecule photodissociation under influence of ultrashort electromagnetic pulses: Nonlinear dependence of probability on pulse duration

[Display omitted] •Photodissociation of molecules induced by ultrashort electromagnetic pulses in the femto- and sub-femtosecond range. •Formulation in terms of the total dissociation probability over the entire pulse duration. •Results show that even for linear radiation intensity, photodissociation probability dependence on pulse duration can be nonlinear. •Determination of the conditions for the occurence of the observed nonlinearity. •The findings may be used to develop a new method of photodissociation control by changing electromagnetic radiation pulse duration. The paper considers novel behavior of molecule photodissociation probability under the influence of electromagnetic pulses in the femtosecond range. The study considers as examples the photodissociation of methane, ethylene and water molecules. The probability of photodissociation under radiation is calculated as a function of pulse duration for different values of the carrier frequency. In the limit of long pulses, the process probability, as expected, increases linearly with pulse duration. However, the dependence of photodissociation probability on pulse duration for the pulses in the femto- and sub-femtosecond ranges exhibits strong nonlinearity. The nonmonotonic effects occur at carrier pulse frequencies corresponding to the minimum values of the photodissociation cross-section. It is remarkable that the observed nonlinearity is described in the frame of the first order of perturbation theory for relatively small field amplitude and unrelated to the strong field effects. The proposed method of describing photodissociation is quite general and suitable for studying such processes under the influence of electromagnetic pulses of any duration.