Optical absorbers based on strong interference in ultra‐thin films (Laser Photonics Rev. 10(5)/2016)

Structures that enhance the absorption of electromagnetic waves find uses in a variety of applications, including photovoltaic and photochemical cells, photodetectors, optical filters, stealth technology, thermal light sources, and color coatings. Recent efforts have sought to reduce the footprint of optical absorbers by using emerging concepts in plasmonics, metamaterials, and metasurfaces. Unfortunately, these new absorber designs require patterning on subwavelength length scales, and are therefore impractical for many large‐scale optical and optoelectronic devices. The cover article reviews recent progress in the development of optical absorbers based on lossy films with thicknesses significantly smaller than the incident optical wavelength. These absorbers have a small physical footprint and require no nanoscale patterning, making them ideal for large‐area applications. On the cover is a photograph of color images lithographically printed on a glass slide, using ultra‐thin layers of lossy amorphous germanium on top of gold films. The different colors are generated by germanium thickness variations of about four nanometers from one region to another, which dramatically change the absorption spectrum, and hence the color. Photograph courtesy of M. Kats and L. Liu. (Picture: Mikhail A. Kats and Federico Capasso, 10.1002/lpor.201600098 pp. 735–749, in this issue)