It is essential to have a way of comparing the performance of the various atomic clocks installed around the globe, not only to evaluate their metrological precision but also to establish international time scales and contribute to experiments in fundamental physics. Until now, such comparison has mainly been based on the manipulation of radiofrequency signals (GPS and Two-Way Satellite Time and Frequency Transfer - TWSTFT). The T2L2 (Time Transfer by Laser Link) mission will break new ground with the use of optical signals.

CNES has developed the T2L2 experiment in partnership with the GeoAzur Laboratory of the Observatoire de la Côte d'Azur (OCA).

The T2L2 instrument will be carried as a technology passenger on the Jason-2 satellite. It will contribute to the Jason-2 altimetry mission by providing independent characterisation of the onboard Ultra Stable Oscillator (USO) of the DORIS instrument.

With T2L2 it will be possible to synchronise remote clocks located around the globe and to monitor the clock carried by the satellite. T2L2 uses very short pulses of light, propagated between the clocks to be synchronised.

The measurements taken by T2L2 will not only serve to validate its working principle and efficiency but will also contribute to various scientific experiments, mainly in time and frequency metrology and in fundamental physics. T2L2 will provide an opportunity for scientists from various disciplines to work together, namely the fields of Time/Frequency, Fundamental Physics and Laser Ranging.