Multipass pump and amplification schemes with a disk Yb:YAG active element: allowance for overlapping of forward and backward pump and signal waves

A model describing multiple passes of pump and amplified radiation pulses through a disk active element taking into account the overlapping of different parts of each pulse within the active medium is proposed. Cases of a millisecond pump pulse, as well as a micro- and a nanosecond amplified pulse, are analyzed in the heat storage mode for a disk active element. It is shown that the use of a large number of passes for pumping a disk active element at low pump absorption efficiency is favorable for creating a high degree of excitation of the medium, since the pump intensity is reduced substantially. At a low excitation degree, it is sufficient to use a small number of passes through the active element, which significantly simplifies the optical scheme of the mirror system that redirects the pump radiation to the active element. It is also shown that the multipass amplification in the active disk element is more efficient for short, nanosecond pulses than for long, microsecond pulses in terms of both the amplification efficiency and the resulting shape distortions of the amplified pulse.