Time Crystals in Active Mode-Locked Lasers

Active mode-locking (AML) is a prominent technique for generating ultra-short laser pulses and frequency combs, finding applications in fields such as medicine and laser metrology. AML systems typically utilize ring cavities with either an electro-optic or acousto-optic modulator, see Fig. 1(a). When the modulation frequency matches the spacing between longitudinal modes, sidebands are created, thus resulting in modal interactions that produce pulse trains. A key advantage of AML is its electrical tunability, which allows to control the pulse shape and repetition rate [1].