Demonstration of a fiber-coupled optical cryocooler: a step towards future space applications

We report on the design, fabrication and testing of the first laser cryocooler prototype made in Europe. The proposed architecture is based on a 7.5%-Yb:YLF cooling crystal located at the center of an astigmatic multipass cavity. A 1020 nm, 50 W laser is fiber coupled through the first cavity mirror, allowing the laser source to be located at any distance from the cold head. Encouraging preliminary results show good coupling efficiency of the laser source, stable temperature of the crystal and a minimum achieved temperature below 150 K with only 8.8 W of laser power, leaving margins for further improvements.