Theoretical Calculations of HfSe₃ Band Characteristics and Its Applications in Pulse Fiber Lasers

Transition metal trichalcogenides (TMTs) are known for their two-dimensional (2D) characteristics and the presence of quasi one-dimensional chains. These materials are less vulnerable to edge defects, which makes them suitable for optical and electronic devices with low-dimensional structures. This study demonstrates the application of HfSe_3 nanomaterial as an emerging ultrafast photonic device capable of producing mode-locked and Q-switched pulses in fiber lasers. The nonlinear optical absorption properties of a HfSe_3-based saturable absorber (SA) were analyzed, revealing a modulation depth of 7% and nonsaturable loss of 35%, respectively. In addition, first principles-based theoretical calculations were performed to explore the optoelectronic properties of bulk HfSe_3. The integration of the HfSe_3-based SA into an Er-doped fiber laser cavity enabled both Q-switched and mode-locked pulse operations. For the mode-locked operation, the pulse duration was 560 fs, accompanied by a signal-to-noise ratio (SNR) of 71.43 dB. In the Q-switched regime, the narrowest pulse width recorded was 757.1 ns with an SNR of 75.45 dB. This study indicates that nanodevices based on 2D TMTs hold promise for efficient ultrafast photonic applications and can be extensively employed in nonlinear optical technologies.