As a relatively novel approach to vibration-free cryocooling, solid state optical refrigeration has advanced a lot since it was first demonstrated in 1995, with low temperatures now reaching a record, below 90 K.
Having reached a point where space-based applications for this new tech can be considered, a recently closed TDE activity with Lumium, in the Netherlands, and the University of Pisa, Italy, made a first step in engineering optical cryocoolers for space applications.
The activity aimed to compare feasible performance for several concepts. These different critical device components were investigated in detail, yielding feasible performance envelope estimates in terms of cooling power and efficiency, for a given set of optical and material property values.
In particular, the activity wanted to investigate the roles of rare-earth ion co-doping, of fluoride crystal hosts, the changes made through impurities, and the effects of active ion concentrations.
Overall, the activity found that optical solid state cryocooling technologies can provide truly vibration-free cooling in a miniaturised and robust format, filling a significant technology gap. In fact, a record cooling temperature of 87 K was recorded during the testing.
On top of this, elemental analysis of trace impurities showed a correlation between iron-ion concentration and cooling performance.
The activity also developed a laser breadboard and software to assess different pumping simulations and computations on optical pumping and cooling medium geometries.
As the future need for vibration-free and active cooling of, amongst others, next generation Earth Observation systems grows, the activity fund it can be uniquely met by optical cooling.
Through the trade-off analysis of a range of potential cooling media, a preferred prototype optical cryocooler was selected for future development and a Demonstration Model is planned for 2020.
TDE activity 4000116795 closed in 2017 but is currently on track to reach TRL 6 by 2023.