I. Galli et al., Phys. Rev. Lett. (2011)

For a date, give me a ring. To determine the age of a sample, the SCAR technique uses a highly stable infrared laser to excite carbon dioxide molecules in a mirrored cavity. When the laser is turned off, trapped light dies away in the cavity (or “rings-down”) at a rate that depends on the amount of carbon-$14$ in the sample.