W}{{\rm cm}^2}$ is the [*critical intensity*]{}. Moreover, $\lambda_c$ and $\tau_c$ are the Compton wavelength and time introduced above.

Results and Discussion {#seq:Ex+Res}
======================

Here, we aim at providing some rough estimates of the number of photons resulting from the stimulated photon emission process. To this end we assume the original multicycle laser pulse characterized by its wavelength $\lambda$, pulse energy $W$ and pulse duration $\tau$ to be split into two counter-propagating pulses of energy $W/2$ to be focused down to the diffraction limit with $f^\#=1$, and give the numbers of emitted photons per shot. The experimental scenario is sketched in Fig. \[fig:cartoon\].

The counter-propagating laser pulses are superimposed to form a standing electromagnetic wave within their overlapping foci; cf. [Eq. ]{} above. Assuming Gaussian beams, the effective focus area is conventionally defined to contain $86\%$ of the beam energy ($1/e^2$ criterion for the intensity). Correspondingly, the mean intensity for each beam is estimated as $$I\approx \frac{0.86\,(W/2)}{\tau\,\sigma}\,,
\label{eq:Ipump}$$ with focus area $\sigma\approx\pi\lambda^2$. For completeness, also note that the divergence $\theta$ of a Gaussian beam in the considered limit is given by $\theta=\frac{1}{\pi}$ [@Siegman] (cf. Fig. \[fig:cartoon\]). Therewith, all physical parameters in Eqs.  and are specified and the number of emitted photons 