Three-dimensional Dirac semimetal thin-film absorber for broadband pulse generation in the near-infrared.

In this Letter, the transient nonlinear absorption of three-dimensional (3D) topological Dirac semimetal CdAs thin film was characterized in the near-infrared band. By performing broadband pump-probe measurements, we experimentally proved that molecular beam epitaxy (MBE) grown CdAs exhibits strong and tunable saturable absorption effects across 1-2 μm. By further inserting the CdAs film into the cavities of Tm- and Er-doped fiber lasers, we obtained stable mode-locked operations at 1.96 and 1.56 μm. Our results experimentally establish that CdAs is a promising broadband saturable absorber (SA) for pulsed lasers in the infrared range.