Page 248 - High Power Laser Handbook

216 So l i d - S t at e La s e r s Nd:YAG Ceramic ThinZag® High-Power Laser Development 217

Figure 9.13 The three ThinZag modules: TZ-1, TZ-2, and TZ-3 (from left to
right). Interestingly, there is not a significant size change in the modules as
the power increases from about 1 kW laser output (TZ-1) to more than 15 kW
laser output (TZ-3).

the height of the Nd:YAG slabs. The TZ-2 device uses 1-cm-high slabs,
while the TZ-3 uses 3-cm-high slabs. Because the pump intensity in
both devices is the same, the output from the TZ-3 module, compared
with the TZ-2 module, is expected to be greater by a factor of 3. Since
the TZ-2 module produced about 5.6 kW, the TZ-3 is expected to pro-
duce about 16.8 kW. Figure 9.13 shows the TZ-1, TZ-2, and TZ-3
lasers. Note the small change in the devices’ overall dimensions,
which produces more than an order of magnitude higher power
when scaling from the TZ-1 to the TZ-3. Initial short-pulse measure-
ments performed on the TZ-3 demonstrated outputs to 16.8 kW out-
put using a stable cavity, as shown in Fig. 9.14.
The TZ-3 laser module operates, as did all the previous ThinZag
laser modules, with laser medium distortions that are low order
(mainly cylinder) and slowly varying (time scales of seconds). Modi-
fications to the laser module continue to improve the device’s ther-
mal control, which in turn influences the medium quality when under
full-power extraction.
9.1.4 Coupling Three TZ-3 Modules
Three TZ-3 modules were coupled in series as a single-aperture
power oscillator. (Three is the minimum number of modules needed
to operate with an unstable cavity for good beam quality.) The laser
model calculations shown in Fig. 9.15 indicate that with three mod-
ules, optimum feedback for good extraction occurs at a little over
40 percent reflectivity. For graded reflectivity output couplers, the