A theoretical investigation of an optically-pumped mid-infrared intersubband semiconductor laser is presented. The influence of electrons and dopant ions on the conduction band structure is simulated with a self-consistent Poisson-Schrödinger solver. Electron-polar optical phonon interactions are calculated by using a macroscopic phonon model with electromagnetic boundary conditions. In order to assess the influence of the electronic temperature on the device optical performances, electron dynamics under optical pumping are investigated within a rate equation model where particle and energy flow equations are derived from Boltzmann's equation with Fermi statistics. Our calculations show that population inversion between the first and second excited states can occur at 77 K under intersubband optical excitation.