SYSTEM AND METHOD FOR GENERATING AN OPTICAL FREQUENCY STANDARD

摘要

A system for generating an optical frequency standard is described. The system comprises a first laser source for generating a first laser output at a first frequency, a first second harmonic generator receiving as an input the first laser output to generate a frequency-doubled first laser output at a doubled first frequency, a second laser source for generating a second laser output at a second frequency different from the first frequency and a second harmonic generator receiving as an input the second laser output to form a frequency-doubled second laser output at a doubled second frequency. The system further includes a two-colour stabilisation arrangement to stabilise a sum of the doubled first and the doubled second frequencies that includes an interaction region incorporating a laser active material having a two-photon transition from a first energy level to a second energy level which receives as an input the frequency-doubled first laser output and the frequency-doubled second laser output where these outputs are selected to together cause the two-photon transition from the first energy level to the second energy level using an intermediate energy level to enhance the two-photon transition rate. The system also includes a detector to detect an indicator of the two-photon transition occurring in the interaction region which generates a frequency stabilisation signal for modifying either the first laser output or the second laser output to stabilise the sum of the doubled first frequency and the doubled second frequency to the two-photon transition based on the indicator and a stabilised optical output generator that includes a sum frequency generator receiving as an input the first laser output and the second laser output to generate a stabilised optical output with a frequency corresponding to the optical frequency standard.