Laser cooling of ytterbium-erbium Co-doped nanoparticle with optical tweezers in vacuum

A strongly focused laser beam with high power density employed in optical tweezers typically results in photothermal damage and instability to the trapped nanoparticles or bio-targets. Here, we report an effective laser cooling of trapped Yb3+-Er3+ co-doped rare-earth nanoparticle by employing a new cooling channel provided by Er3+ and utilizing an enhancement of the anti-Stokes emission through energy transfer between Yb3+ and Er3+. Especially in high temperature conditions, the co-doped system demonstrates a high laser cooling performance, that enable the temperature to decrease from 500 K to around room temperature. But for the initial temperature of around room temperature, the cooling temperature does not drop below freezing, which can avoid not only thermal but also cold damage to bio-targets in optical tweezers. This work provides experimental evidence of the Yb3+-Er3+ co-doping rare-earth nanoparticle for laser cooling, which can hold a potential to address the challenge of precise measurements in optical tweezers. The high-power trapping lasers in optical tweezers generate damaging heat. Here, the authors demonstrate efficient laser cooling using an erbium-ytterbium co-doped nanoparticle, which cools targets from high temperatures to near room temperature while avoiding sub-zero cooling from ambient conditions, thus enabling safe trapping of biological specimens.