The usual method to determine the ablation threshold of solid samples by ultrashort laser pulses is done by focusing the
laser beam on the samples surface by a known lens, requires the knowledge of all the geometrical parameters (lens focus,
beam propagation parameters, beam quality, sample position), and a series of measurements for different pulse energies.
We present here a simpler method for determining ultrashort laser pulses ablation threshold for solid samples. The
method uses a focusing lens, and requires only the knowledge of the pulse power, employing a diagonal translation of
the sample through the laser beam waist, resulting in a pattern etched on the sample surface. The ablation threshold value
is obtained measuring only one dimension of this pattern and a straightforward mathematical relation, There is no need
to know any other geometrical parameter of the laser beam or of the lens used. The technique was employed to
determine the ablation threshold of pure and Cr doped LiSAF samples for 20 picoseconds pulses, and a dependence with
the Cr concentration was observed.