Fig. 1. High-energy pulsed single-frequency amplifier based on very-large-mode-area Er-doped fiber^[15]. (a) Cross section of polarization-maintaining Er-doped fiber with mode field area of 1100 μm²; (b) measured beam quality and beam profile of 541 μJ microsecond single-frequency laser based on fiber shown in Fig. 1(a)

Fig. 2. Different large-mode-area active fiber designs. (a) Cross section of 115 μm×115 μm Er-doped silica fiber based on PAS glass substrate^[16]; (b) cross section of Er/Yb co-doped multifilament-core fiber with core number of 39 and core region size of 24 μm×32 μm^[19]; (c) cross section of polarization-maintaining Yb-doped tapered fiber^[22]; (d) cladding diameter of tapered fiber versus fiber length^[22]

Fig. 3. Distribution of strain employed to gain fiber in pulsed single-frequency laser power amplifier stage ^[31]

Fig. 4. 3 ns pulsed single-frequency fiber laser amplifier with average power of 913 W and repetition rate of 10 MHz^[33].

Fig. 5. Pulsed single-frequency fiber amplifier with peak power of 128 kW based on 12 cm long Er/Yb co-doped phosphate fiber^[34].

Fig. 6. 600 μJ pulsed single-frequency fiber amplifier based on cascaded 35 μm/250 μm and 50 μm/400 μm Yb-doped fibers^[43]. (a) Experimental setup; (b) measured laser average power and energy versus pump power with beam quality of 600 μJ pulsed laser shown in inset

Fig. 7. 2.2 mJ single-frequency fiber amplifier at 1572 nm based on polarization-maintaining Er-doped silicate fiber with 50 μm core diameter^[55]. (a) Experimental setup; (b) pulse energy versus 1480 nm pump power with laser beam profile under pulse energy of 1.8 mJ shown in inset

Fig. 8. Experimental setup of high-efficient pulsed single-frequency fiber amplifier at 1.5 μm based on cascaded Er-doped and Er/Yb co-doped fibers^[56]