In the design of a diode-pumped slab solid-state laser, the knowledge
of the temperature distribution and the thermal lensing in the medium
is very important when attempting to achieve high output power in the
TEM00 mode. A general 3D analytical calculation is given of the temper
ature distribution in a slab of finite size, side-pumped by many laser
diodes; the spatial distribution of the pump power is taken into acco
unt. An approximate thermal focal length is calculated from the temper
ature distribution. Three different ways of cooling the slab are treat
ed and included in the model as boundary conditions. We derive general
solutions of the heat distribution for each case of cooling. The test
of the model includes numerical calculations applied to the case of o
ur slab prototype and a comparison with experimental measurements is m
ade.