Pair Production in Vacuum by an Alternating Field

We discuss the creation of pairs of charged particles in an alternating electric field. The dependence on the frequency is computed and found negligible. We obtain a formula for the field intensities required in order to observe the effect $E\gtrsim \frac{m{\omega }_{0}c}{esinh\left(\frac{\hslash {\omega }_0}{4m{c}^2}\right)}$.