  In this study we explore the possibility of using the process of
electron-positron pair creation in strong laser fields as a tool for measuring
the intensity of the corresponding laser radiation. In the initial state we
consider either free electron gas or gas of neutral xenon, the electrons of
which get ionized. Once these seed electrons gain sufficient energy in the
external laser field, they can emit high-energy photons which subsequently
decay producing electron-positron pairs via the Breit-Wheeler mechanism. By
detecting the resulting positrons, one can recover the value of the laser
intensity by means of the one-to-one correspondences deduced in the present
investigation. We analyze two different configurations of the external field:
the setup involving an individual focused laser pulse and the combination of
two counterpropagating laser pulses. Performing numerical calculations and
analyzing their accuracy, we demonstrate that based on our estimates, the laser
intensity can be determined within the range
$10^{23}$-$10^{26}~\text{W}/\text{cm}^2$ with a relative uncertainty of
$10$-$50 \%$.
