Effect of infrared coating nonuniformity on optical systems

For precision optical systems, the focus and tilt errors caused by coating thickness nonuniformity can be a serious concern. These errors are wavelength dependent and hence cannot be compensated in an IR optical system by aligning and focusing with an auxiliary visible alignment laser. It is shown here that the coating design can be modified so as to make the aberrations caused by coating thickness nonuniformity approximately equal at the IR design wavelength and the wavelength of the auxiliary laser. In that case, focusing and alignment with an auxiliary laser can substantially correct the effect of coating nonuniformity.