Single-Frequency Pulsed Fiber Laser Enabled by Tantalum Carbide Featuring 2.8 μm Wavelength Tunability

We demonstrate, for the first time, to the best of our knowledge, a single-frequency pulsed fiber laser (SFPFL) operating in the important mid-infrared region. We employed a high precision germanium etalon along with a compound cavity to achieve a single-longitudinal-mode selection and home-synthesized MXene-Ta₄C₃T_x to initiate Q-switching in an Er³⁺-doped ZBLAN fiber laser. The MXene-Ta₄C₃T_x, synthesized through selective etching, exhibits a modulation depth of 14.8% and a saturation optical intensity of 3.62 GW/cm² at 2794.4 nm. The developed SFPFL is centered at 2780.06 nm with a linewidth as narrow as 320 kHz, and has an output power, repetition rate, pulse width, and pulse energy of 121.8 mW, 132.4 kHz, 1.48 μs, and 0.92 μJ, respectively. The high stability of the laser pulses is confirmed by the high radio-frequency signal-to-noise ratio of 50 dB. With the incorporation of a diffraction grating, wavelength tuning from 2753.14 to 2780.26 nm was achieved. Our findings introduce a wavelength-tunable SFPFL source characterized by high coherence, high stability, and low noise. This source effectively addresses the challenges associated with self-modulation-induced temporal instability, elevated noise levels, and reduced coherence typically encountered in conventional multi-longitude-mode Q-switching operations. In addition, our results reveal MXene-Ta₄C₃T_x as a promising all-optical passive modulator for laser pulse generation in the essential mid-infrared spectral region.