Theoretical calculations of HfSe₃ band characteristics and its applications in pulse fiber lasers

Transition metal trichalcogenides (TMTs) are known for their two-dimensional (2D) nature and the presence of quasi-one-dimensional (1D) chains. These materials are less vulnerable to edge defects, which improves their suitability for use in optical and electronic devices with low-dimensional structures. This study demonstrates the application of HfSe₃ nanomaterial as an emerging ultrafast photonic device capable of producing mode-locking and Q-switching pulses in a fiber laser. The nonlinear optical absorption properties of the HfSe₃-based saturable absorber (SA) were analyzed, revealing a modulation depth of 7% and a nonsaturable loss of 35%. In addition, first-principle-based theoretical calculations were performed to explore the optoelectronic properties of bulk HfSe₃. The integration of a HfSe₃-based SA in an Er-doped fiber (EDF) laser cavity enabled both Q-switched and mode-locked pulse operations. For the mode-locked operation, the duration of pulse was 560 fs, accompanied by a signal-to-noise ratio (SNR) of 71.43 dB. In the Q-switching regime, the narrowest pulse width recorded was 757.1 ns with a SNR of 75.45 dB. This research indicates that nano-devices based on 2D TMTs hold promise for efficient ultrafast photonic applications and could be extensively employed in nonlinear optical technologies.