  The accurate assessment of the local tritium concentration in the tokamak
first wall by means of the laser-induced desorption (LID) diagnostic is sought
as one the key solutions to monitoring the local radioactive tritium content in
the first wall of the fusion reactor ITER. Numerical models of gas desorption
from solids used for LID simulation are usually closed with the one-dimensional
heat transport models. In this study, the temperature dynamics of a target
irradiated by a short laser pulse during LID are analyzed by means of the
two-dimensional heat transport model to assess the validity of using
one-dimensional approximation for recovering the diagnostic signal. The
quantitative estimates for the parameters governing the heat transfer are
presented. The analytical expressions for the sample temperature distribution
resolved both in time and space are derived. The sensitivity analysis of the
obtained relations to uncertainties in the experimental parameters is
performed. It is shown that, depending of the ratio between the laser spot
radius and heat diffusion length, the one-dimensional approach can noticeably
overestimate the sample temperature in the limit of small laser spot radius,
resulting in more than 100 % larger amounts of tritium desorbed from the
irradiated target, compared to the two-dimensional approximation. In the limit
of large laser spot radius, both approaches yield comparable amounts of
desorbed tritium.
