We are pleased to present to you this special issue dedicated to photonics for harsh environments. Photonic technologies for computing, power, and sensing applications play an increasingly important role in modern technology deployed in extreme environments, with stressors such as radiation, high pressures, extreme temperatures, and/or high speeds. Studying photonics in such environments helps us to better understand the performance and reliability of the underlying materials and structures found in applications such as radiation-rich environments (such as outer space and man-made environments), supersonic/hypersonic flight, underground pipelines, and ultra-hot and cold regions.

This feature issue is intended to offer a glimpse of the evolving field that consolidates photonic design with extreme environmental awareness. The state of the art in this subject has been comprehensively covered in a review in the present feature article [1], as well as a recent Ph.D. thesis [2]. To provide a more in-depth snapshot of current research, the other 7 articles provide in-depth examples of current research on this topic [3–9].

Five of these original research articles concern the effects of ionizing radiation on photonic materials and devices - in some cases, combined with temperature effects.

Medvedev et al. show that the thermal damage thresholds of different classes of materials, such as PMMA and diamonds, tend to stay the same or lowers with the increase of the irradiation temperature, while nonthermal damage thresholds may go in either direction, which has implications for materials choice in combined radiation / extreme temperature environments [3].

Jia et al. demonstrate that SiC-based optically transduced microdisk resonators exhibit significant sensitivity to prolonged high-energy proton radiation [4].

On the other hand, Mølster et al. find that periodically-poled Rb:KTP crystals designed for optical parametric amplifiers exhibit remarkly low sensivity to proton irradiation, making them interesting candidates for space-based LIDAR applications [5].

Wang et al. simulate high-energy electron irradiation of LaF₃/MgF₂ multilayers to find that dendritic patterns can form at the interfaces, which predispose such structures typically used in space applications to asymmetric delamination; however, they show that using low-temperature/low-stress deposition conditions can greatly mitigate these risks [6].

In the final radiation environment article, Sayan Roy and Peter Bermel leverage density functional theory to predict that transition metal dichalcogenide-based photovoltaics can yield efficiencies up to 23% with substantially enhanced radiation survivability compared to incumbent silicon materials [7].

Another original research article by Demirbas et al. examines the effects of cryogenic temperatures on rare earth-based Tm:YLF crystals, and shows that it can be effective for as a lasing medium down to liquid nitrogen temperatures (around 78 K) [8].

The final original research article by Oliva et al. shows that typical total solar irradiance radiometers are highly-suceptible to UV radiation, but also proposes a solution in terms of using carbon nanotubes, which have much lower susceptibility to degradation from such a stressor [9].

In conclusion, the study of photonics for harsh environments is an increasingly complex topic, fundamentally driven by the increasing sophistication of the materials and applications where photonics are used. Therefore, this topic will continue to grow in significance and will continue to be revisited often in future research.