Controllable epitaxy of CrTe₂ thin films for application as saturable absorbers

1T-CrTe₂ is one of the typical two-dimensional transition metal dichalcogenides (TMDCs) and has attracted great attention in the field of spintronics due to its fascinating magnetic properties. However, the optical properties such as the nonlinear optical characteristics of 1T-CrTe₂ films have rarely been reported. Here, the CrTe₂ thin films were prepared on highly oriented pyrolytic graphite and gold-coated plane mirrors via molecular beam epitaxy. By adjusting the growth temperature and the flux of the source, CrTe₂ thin films with various morphologies were obtained. In addition, the CrTe₂ thin films were used as saturable absorbers (SAs) and incorporated into Er-doped fiber lasers. A modulation depth of 43.5% and mode-locking at 1560 nm with a pulse width of 316 fs were achieved, showing extremely outstanding nonlinear optical response among TMDCs. This work demonstrates the growth of high-quality CrTe₂ films and verifies that CrTe₂ films have enormous prospects in ultrafast optical devices.