Cavity #1...#4
DAVID HAVRILLA
High-reflector mirror
Lasers
Folding mirrors
Output-coupler mirror
Many product and process ramifi- ner core, with a maximum temperature at the centerline
cations are embedded in the word of the rod. This temperature differential causes thermal
“disk” when referring to diode- gradients and distortion of the rod, and limits the beam
pumped disk lasers. Their unique quality of rod-style YAG lasers. By comparison, the disk
geometry and abil- (roughly 14 mm in di-
ity to solve the fundamental beam-quality What makes disk geometry ameter and 0.2 mm
and transmission issues usually associ- thick) is mounted to
ated with Nd:YAG rod-style lasers make so ideal and how does disk- a water-cooled block
disk lasers an innovative choice. Besides (heat sink), which also
performance improvements in electrical laser technology solve the doubles as a resonator
efficiency, beam quality, focal length, limitations of beam quality mirror. Because the standoff, and focused spot size, several laser disk’s face is mounted
materials-processing advantages are also and fiber length inherent in to the block and the
apparent with diode-pumped disk lasers. disk is very thin—a high
rod-style lasers? The answers surface-area-to-lasing-
Attributes of the disk medium volume ratio—
The higher beam quality attainable with to these questions catapult the cooling is extremely
the diode-pumped disk laser (as com- efficient and results in a
pared to the lamp- and diode-pumped the disk laser into a new era nearly negligible thermal
rod laser) is primarily a function of the gradient. And, as is the
ability to dissipate heat from the lasing of YAG laser technology. case with rod-laser cavi-
medium. The YAG rod (roughly 6 mm in ties, disk cavities can be
diameter and 150 mm in length) is cooled by water that coupled in series to increase output power (see Fig. 1).
circulates past the outer diameter of the rod, resulting In addition to its much better beam quality, the disk
in a relatively cool outer skin and a relatively hot in- laser yields another important benefit compared to diode-
pumped rod lasers: disk lasers allow longer fiber lengths
for beam delivery. Though the full explanation and under-
FIGURE 1. As with rod lasers, disk-laser cavities can be coupled in series to increase output power up to kilowatt levels.
DAVID HAVRILLA is product manager for YAG lasers at Trumpf, 47711 Clipper St., Plymouth, MI 48170; e-mail: david. havrilla@us.trumpf.com; lying physics are complicated, a few simple statements can www.trumpf.com. be made. First, back reflection (either from the workpiece
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