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194 So l i d - S t at e La s e r s Zigzag Slab Lasers 195

8.3.2 Performance
An example of the traditional side-pumped slab lasers was the Defense
Advanced Research Projects Agency (DARPA)–sponsored DP25 preci-
sion laser machining (PLM) laser. The DP25 laser was able to scale the
average power to greater than 5 kW with good beam quality of 2.4 times
5
the diffraction limit (DL). The laser used a power oscillator, power-
amplifier approach with five identical gain modules (Fig. 8.7). Two of the
gain modules were used inside an unstable resonator to produce approx-
imately 2 kW of power, and three gain modules were used as single-pass
amplifiers, each delivering power on the order of 1 kW.
Figure 8.8 shows one of the slab gain modules with 15 diode
arrays pumping from each side of a 5 × 33 × 170 mm slab. Each diode

(a) (c)

(b)
HR
GRM

Figure 8.7 (a) DP25 laser in a 45 × 105 × 265 cm box, (b) schematic of the
optical layout in the box, and (c) laser with the top removed. GRM: graded reflectivity
mirror; HR: high reflector.

(a) (b)

Figure 8.8 One of five DP25 gain modules. (a) View of diode arrays and
(b) assembled.