Page 239 - High Power Laser Handbook

208 So l i d - S t at e La s e r s Nd:YAG Ceramic ThinZag® High-Power Laser Development 209

Coolant flow can be
Thin solid-state material suspended longitudinal or vertical
between fused silica plates
Thin slab

Fused silica
window
outer surface
Zigzag beam path off outer
walls averages outpump Coolant
nonuniformities channels

Optical axis
Lasing material excitation can be from a
range of options:
Liquid coolant Flash lamps Aspect
removes waste heat Other lasers ratio
Diode laser arrays
Index matching reduces
polishing requirements
Figure 9.1 A schematic drawing of ThinZag configuration, including the key
features of the laser and laser beam optical path within the cell.

(< 0.15%/cm). These materials can also be produced in sizes that YAG
2
crystals cannot achieve (e.g., 400 × 400 mm slabs). 1–3
The unique properties of Nd:YAG ceramic combined with the
ThinZag laser configuration, developed by scientists and engineers at
Textron Defense Systems, have allowed scaling of these lasers to more
than 16 kW average power from a single laser module. Higher power
configurations involve a single-aperture power oscillator configura-
tion consisting of a number of identical modules operating in series.
Figure 9.1 shows a schematic diagram of the ThinZag configura-
tion. With this configuration, improved methods of thermal manage-
ment for high-power diode-pumped, solid-state slab lasers have been
demonstrated. This unique optical arrangement uses thin slabs of
solid-state gain material immersed in a flowing cooling fluid and
sandwiched between a pair of fused silica windows. The laser flux
zigzags through the gain medium in a nontraditional manner—that
is, it reflects off the outer surfaces of the fused silica windows rather
than off the outer surfaces of the lasing material. The ThinZag con-
figuration allows the use of thin slabs for good thermal control of the
laser medium using a near-field beam that has a near-unity aspect
ratio that is independent of the laser slab’s thickness.
Many features of this design can be varied almost indepen-
dently to allow optimization of key input parameters to improve
performance. This design’s orthogonal nature allows for indepen-
dent variation of parameters such as slab thickness, diode pump
intensity, diode pump distribution, thermal cooling rate, number
of slabs, and so on.
In addition to the recent development of ceramic Nd:YAG-based
devices, tests on a variety of laser gain media have been conducted