We suggest the theory describing generation of a harmonic resonant with the transition from ground to autoionizing state of the generating particle. Calculating both harmonic amplitudes and phases, we study the attopulse generation using these harmonics.
$^1$ Department of atomic physics, plasma physics and microelectronics, Faculty of Physics, Lomonosov Moscow State University. Moscow 119991, Russia.
$^2$ Theoretical department, A.M. Prokhorov General Physics Institute of Russian Academy of Sciences, Moscow 119191, Russia.
$^3$ Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region, 141700, Russia.