Graphs for the design of laser mirrors at normal incidence

• Published in: Optics and laser technology 1973-04, Vol.5 (2), p.60-68
• Main Author: Mahlein, H.F.
• Format: Article
• Language: English
• ISSN: 0030-3992; 1879-2545
• DOI: 10.1016/0030-3992(73)90039-X

The results of computer calculations concerning the reflectivity in the stop-band at normal incidence are given for periodic multilayer systems made out of layers of ZnS and MgF 2 of equal optical thickness. General formulae are derived to distinguish between the maxima and minima of the reflectivity at the centre of the stop-bands and for the calculation of the width of the stop-band of higher order mirrors as a function of the wavelength. The bandwidth of higher order mirrors and the reflectivity at the centre of the stop-band are presented in a number of graphs for systems with up to 18 layers on substrates with varying refractive index. Quarter-wave layer anti-reflection coatings are treated as special cases. The process of designing laser mirrors can be simplified using the graphs. They may also be useful during the evaporation process when thickness monitoring is done by optical methods. An example of a partially reflecting mirror is given. This uses a flat minimum of reflectivity at the centre of the stop-band to obtain an almost constant reflectivity over the total width of the stop-band.