Design approaches for optical thin films that recognize the key role of a design's total optical thickness are presented. These approaches are based primarily on the needle optimization technique but also utilize other optimization procedures. Using the described design approaches, an optical coating engineer can obtain a set of theoretical designs with different combinations of principal design metrics (merit function value, number of layers, and total design optical thickness); this extends opportunities for choosing the most practical and manufacturable design. We also show that some design problems have multiple solutions with nearly the same combinations of principal design metrics.

We have compared two kinds of dispersive mirrors (DMs) produced by magnetron sputtering and ion beam sputtering. One of them is a broadband DM which is known as double-angle DM, providing a group delay dispersion (GDD) of −40fs 2 in the range of 550-1050 nm. The other one is a robust highly dispersive mirror, which provides a GDD of about −275fs 2 at 800 nm and covers the wavelength range from 690 to 890 nm. For the first time, a comparison between magnetron-sputteringproduced and ion-beam-sputtering-produced dispersive mirrors is performed.Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Antireflection coatings have been the subject of two books and of numerous scientific and technical papers.1,2 until recently, there have been no systematic studies made to determine the optimum performance that can be achieved for a given set of specifications and coating materials. Willey has published two papers with empirical studies of this problem.3,4 He has presented equations which, for a given set of coating materials and for an overall thickness of the multilayers, give an estimate of the lowest achievable reflectance for a normal incidence antireflection. The two equations presented by Willey are valid for a certain range of coating materials, widths of the spectral region and overall thicknesses of the multilayer. They are based on the calculated results obtained for a number of different examples . It will be shown in this paper that, whilst giving a good first estimate of the attainable results, the formulae are not accurate for any one set of coating materials.