Fig. 1. Schematic of zigzag light path in slab

Fig. 2. Schematic of amplifier gain unit

Fig. 3. Theoretical result of small signal gain coefficient distribution

Fig. 4. Power distribution of different positions within two slabs for "series and then 2-pass". (a) Slab 1; (b) slab 2

Fig. 5. Power distribution of different positions within two slabs for "2-pass and then series". (a) Slab 1; (b) slab 2

Fig. 6. Opticalpath schematic of laser system

Fig. 7. (a) Fluorescence distribution of slab light cross section; (b) transmission wavefront

Fig. 8. Output power as a function of pump power

Fig. 9. (a) Wavefront at output power 5.4 kW; (b) far field spot at output power 5.4 kW

Fig. 10. Far-field spot of the beam. (a) Without spacial filter; (b) with spacial filter