Enhanced Interband Transition in FeCoNiAlTi High‐Entropy Alloy for Ultrafast Nonlinear Optical Applications

Abstract

High‐entropy alloys (HEAs) possess superior mechanical, thermal, and electronic properties, which attract great interest in the fields of photothermal, electrocatalysis, and magnetic applications. Herein, the nonlinear optical properties of FeCoNiAlTi HEA with a large specific surface area for the first time is investigated. Owing to the strong d–d interaction, the interband transition near the Fermi level could be enhanced in HEAs, leading to broadband optical absorption. Excitation with the picosecond laser source, the FeCoNiAlTi HEA possesses saturable absorption with a large modulation depth of 7.61% and 30.47% at 1 and 1.5 µm, respectively. Furthermore, at the higher excitation level at 1.5 µm, the saturable absorber exhibits a typical reverse saturable absorption property. Subsequently, the FeCoNiAlTi HEA on the tapered fiber first serves as the saturable absorber in the Yb‐doped fiber laser and the Er‐doped fiber laser, leading to the noise‐like pulses at 1 µm, and the stable Q‐switching, conventional soliton, and dissipative soliton resonance mode‐locking operations at 1.5 µm. This work confirms that the enhanced saturable absorption in HEAs can endow the high‐performance ultrashort pulse generation.

Germanene Nanosheets as Saturable Absorbers for Soliton Rains and Large-Energy Pulse Generation in Passively Mode-Locked Fiber Lasers

“…Additionally, CS, Q-switched pulse, and dissipative soliton resonant square pulse outputs were all achieved in an Er-doped fiber laser (EDFL) by them. 12 In 2023, based on the applications of PdTe 2 and MoTe 2 , Zeng et al and Wu et al made significant research breakthroughs in the field of photoelectric detection. 13,14 Besides the above reports, newly discovered 2D materials 15−20 have demonstrated ultrafast saturable absorption properties.…”

“…In the past two years, Dong et al have investigated the broadband nonlinear optical (NLO) properties of Ta 4 C 3 MXene and ZIF-8 in fiber lasers, excellent dissipative soliton as well as conventional soliton (CS) pulse outputs were obtained. , In 2023, based on a new FeCoNiAlTi high-entropy alloy as SA, Liu et al presented the noise-like mode-locked (ML) pulse output in an Yb-doped fiber laser. Additionally, CS, Q-switched pulse, and dissipative soliton resonant square pulse outputs were all achieved in an Er-doped fiber laser (EDFL) by them . In 2023, based on the applications of PdTe 2 and MoTe 2 , Zeng et al and Wu et al made significant research breakthroughs in the field of photoelectric detection. , Besides the above reports, newly discovered 2D materials − have demonstrated ultrafast saturable absorption properties.…”