Y Zhang, H Yu, H Zhang, A Di Lieto, M Tonelli… - Optics Letters, 2016 - opg.optica.org
… lasers at the wavelengths of 522 nm, 607 nm, 639 nm, and 720 nm have been obtained with
the repetition rates of 2.8 GHz, 3.1 GHz, 3.1 GHz, and 3.0 GHz, … doubled repetition frequency …