Page 305 - Tunable Lasers Handbook

6 Transition Metal Solid-state Lssers 265

have not been observed up to concentrations as high as 0.05. It has been sug-
gested that this is possible because the adjacent substitutional sites do not share
F atoms and consequently are somewhat isolated. Such isolation tends to mini-
mize pair effects associated with concentration quenching.
The Lhermal and mechanical properties of these laser materials are not as
favorable as they are for oxide materials but this tends to be compensated by
their good thermo-optic properties. Thermal conductivity for LiCaAIF, is about
one-fourth of the thermal conductivity of BeA1,0, [38]. Still, the thermal con-
ductivity is sufficiently large to keep thermal-gradients at reasonable levels.
More debilitating is that the coefficients of thermal expansion for the two axes of
LiCa.41F6 are. unfortunately, significantly different, as noted in Table 3. How-
ever, the variation of the refractive index with temperature is negative, similar to
LiYF, or YLF. A negative variation of the refractive index with temperature miti-
gates the effects of thermally induced lensing. Thus, the thermal and mechanical
properties limit the amount of average power available from these laser materials
but do not produce the thermal lensing and depolarization found with some other
laser materials.

TABLE 3 Physical Properties of LiCaAIF,

Parameter Value Units

Lattice constants
LI axis 399.6
c axis 963.6
Densit> 2989
Heat capacity 938
Thermal conductivity
a axis 1.6
c axis 5.1
Thermal expansion
a axis --
31
c axis 3.6
Refractive index
a axis 1.3902
c axis 1.3889
Refractive index variation 10-6/K
a axis -4.2
c axis -4.6
Optical transparency Pm
Melting point .825 'C