Page 219 - High Power Laser Handbook

188 So l i d - S t at e La s e r s Zigzag Slab Lasers 189

Pump laser
diodes

Coolant extracts heat
from slab sides
Zigzag beam averages OPD
through hot slab center
Figure 8.1 Schematic of a traditional side-pumped zigzag slab. OPD: optical
path difference.

propagation is to average over the temperature gradients in the thin
dimension of the slab.
Figure 8.2 shows two different injection schemes into a YAG
(yttrium aluminum garnet) slab with refractive index n = 1.82. The
first scheme uses a near-Brewster cut that favors linearly p-polarized
light on the input face and that is often used in oscillators. At a slab
cut of 30.9° (Brewster is 28.8°), the losses for p-polarized light are min-
imal, and the refraction angle is such that the beam reflects from the
TIR surface parallel to the input face, optimally filling the slab. The
second approach uses near-normal incidence and is polarization
indifferent. The latter approach is best suited for two-pass amplifier
designs, in which the first pass may be p-polarized and the second
pass s-polarized. This approach creates small unextracted regions,
called dead zones, that reduce extraction efficiency by a small amount
(discussed later in this chapter) but that can also help provide areas
for mounting and sealing the slab.

Near-normal
incidence beam
Pumped region
30.9°

AR coating
Near-Brewster Near-Normal
Angle Slab Incidence Slab
(a) (b)
Figure 8.2 Propagation through a zigzag slab. (a) Near-Brewster cut for p-polarized
light and (b) near-normal incidence for polarization-independent propagation. AR:
antireflective