Environmentally stable iridium mirror coatings for the infrared spectral range

Thorsten Döhring; Manfred Stollenwerk; Paul Schmitt; Adriana Szeghalmi

doi:10.1117/12.2632057

15 July 2022 Environmentally stable iridium mirror coatings for the infrared spectral range

Thorsten Döhring, Manfred Stollenwerk, Paul Schmitt, Adriana Szeghalmi

Proceedings Volume 12298, Ninth European Seminar on Precision Optics Manufacturing; 122980A (2022) https://doi.org/10.1117/12.2632057
Event: Ninth European Seminar on Precision Optics Manufacturing, 2022, Teisnach, Germany

Abstract

Highly reflective metal coatings are essential for numerous optical elements. Established mirror coatings made of silver (Ag) and gold (Au) offer high and broadband self-reflection in the infrared (IR) spectral range but are susceptible to environmental influences and mechanical stress without suitable protective layers. In the long-wavelength spectral range, in particular, the absorption bands of these protective layers partially reduce the high mirror reflectivity again. However, the noble metal iridium (Ir) is hard, extremely dense, and thermally, mechanically, and chemically stable. Iridium provides a similarly high reflectivity in the mid (MIR) and far-infrared (FIR) spectral range, as silver and gold, and high resistance to environmental influences - even without protective layers. In this paper, the different deposition processes, as well as the optical and structural properties of iridium mirror coatings fabricated by atomic layer deposition (ALD) and by magnetron sputtering (MS), are presented and compared with each other. The complex refractive indices for ALD and MS deposited iridium mirror coatings were determined for wavelengths from 200 nm to 20 μm, complementing the existing literature values. We demonstrate that iridium mirror coatings offer a high and broadband reflectivity from the mid to far-infrared spectral range. In contrast to established – protected – silver and gold mirror coatings, the iridium coatings are environmentally durable and thermally stable up to 600°C, even without protective layers. Therefore, as an interesting mirror coating material, iridium has the potential for special applications in infrared astronomy and probably also for industrial instruments.

Citation Download Citation

Thorsten Döhring, Manfred Stollenwerk, Paul Schmitt, and Adriana Szeghalmi "Environmentally stable iridium mirror coatings for the infrared spectral range", Proc. SPIE 12298, Ninth European Seminar on Precision Optics Manufacturing, 122980A (15 July 2022); https://doi.org/10.1117/12.2632057

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KEYWORDS

Iridium

Reflectivity

Atomic layer deposition

Optical coatings

Mirrors

Infrared coatings

Silver

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