Layered structured binary alkaline metal phosphide of KP₁₅ as saturable absorbers for ultrashort pulsed laser generation

We demonstrated an all-fiber passively mode-locked 980 nm picosecond laser using KP₁₅ materials as saturable absorbers (SAs). The micron-sized wire-like KP₁₅ crystals were prepared using a vapor-phase transfer method. The material not only shows excellent optoelectronic properties, such as optical anisotropic and large binding energy, but also long-term stability. By inserting the KP₁₅ crystals into the ytterbium-doped all-fiber laser cavity, a mode-locked 980 nm laser with a pulse duration of 30 ps, a repetition rate of 15.65 MHz and spectral width of 5.6 nm was achieved for the first time, to the best of our knowledge. In addition, we investigated the long-term stability of the KP₁₅-based mode-locked 980 nm laser, and the root-mean-square of the output power of the picosecond pulse was only 1.03% when operating for 4 h. The results indicated that the KP₁₅ material prepared using a chemical vapor transport method was a promising SA for ultrafast fiber laser generation. (letter)