Peculiarities of intense focused femtosecond laser pulses propagation in air under low pressure.
Results of theoretical and experimental researches of air pressure influence on the dimensional and power parameters of the preliminary focused GW femtosecond laser radiation are presented. The area of nonlinear focus of a laser beam is thoroughly examined. We show that in the rarefied air the achievement of higher values of laser radiation intensity in focal waist is possible due to the decrease of plasma blocking action.