Operating range of dielectric mirrors for lasers

It is shown that an allowance for the absorption in the reflecting layers is needed in calculations of the frequency characteristics of laser mirrors. We shall report numerical calculations for typical mirrors operating in the visible range and consisting of constant-thickness layers with the ratio of the refractive indices amounting to 1.7. This makes it possible to find the dependence of the absorption coefficient A on the frequency ω for any ratio of the bulk extinction coefficients of dielectrics. The operating energy of lasers is ω_max/ω_min≈1.3 between the values of the absorption coefficient A differing by a factor of two. Outside this range the losses rise steeply (partially when the number of layers is large) and they may exceed the nominal value by tens of times.