The electronic structure and optical properties of ternary GaAs:Bi alloy are investigated by first principles calculations. It is found that the band gap of GaAs_1-xBi_x decreases monotonously with the increasing of Bi concentration, resulting in the fundamental absorption edge and main absorption peaks of GaAs_1-xBi_x shifting toward lower energy with the increase of the Bi content. The optical constants of GaAs_1-xBi_x, such as the optical absorption coefficient, refractive index, extinction coefficient and optical conductivity, are greater than those of pure GaAs when x > 3.1%, but less than those of pure GaAs when x < 3.1%, which is primarily decided by the intraband level repulsions between Bi-induced states and host states on the valence bands; the contribution of Bi-6s, Bi-6p orbitals and Ga-4p, Ga-4s orbitals on conduction bands is also crucial. Bi doping plays an important role in the modulation of the static dielectric constant and the static refractive index. These results suggest a promising application of GaAs_1-xBi_x alloy as a semiconductor saturable absorber.

Cupric oxide (CuO), as a transition metal oxide (TMO) semiconductor, has attracted tremendous attention for various applications. In the present work, we synthesize the CuO nanosheets modified by TiO ₂ nanoparticles via a facile, non‐toxic two‐step method. Subsequently, the morphology and the structures of CuO and TiO ₂ /CuO nanocomposites are investigated. By utilizing the common Z‐scan technology, broadband nonlinear optical (NLO) properties of the as‐prepared CuO nanosheets and TiO ₂ /CuO nanocomposites are demonstrated, elucidating the enhancement on the NLO response via the TiO ₂ dopant, which is attributed to the more oxygen vacancies and the formed p‐n junctions. Furthermore, CuO nanosheets and TiO ₂ /CuO nanocomposites are implemented to the passively Q‐switched bulk lasers operating in the near‐infrared (NIR) region, generating broadband ultrastable pulses. Ultimately, TiO ₂ /CuO nanocomposites were intergrated in a passive mode‐locking bulk laser for the first time, achieving stable mode‐locked pulses and verifying its ultrafast optical response potential. Our results illustrate the tremendous prospects of the CuO nanosheets modified by oxygen vacancy engineering as a broadband NLO material in ultrafast photonics field.

Herein, we synthesized and extracted pure semiconducting single-walled carbon nanotubes (s-SWCNTs).

Zeolitic imidazolate frameworks (ZIFs) show extraordinary potential in the domains of fundamental research and miscellaneous technology applications.

We report on the first laser operation of a disordered Tm:CaGdAlO₄ crystal on the ³H₄ → ³H₅ transition. Under direct pumping at 0.79 µm, it generates 264 mW at 2.32 µm with a slope efficiency of 13.9% and 22.5% vs. incident and absorbed pump power, respectively, and a linear polarization (σ). Two strategies to overcome the bottleneck effect of the metastable ³F₄ Tm³⁺ state leading to the ground-state bleaching are exploited: cascade lasing on the ³H₄ → ³H₅ and ³F₄ → ³H₆ transitions and dual-wavelength pumping at 0.79 and 1.05 µm combining the direct and upconversion pumping schemes. The cascade Tm-laser generates a maximum output power of 585 mW at 1.77 µm (³F₄ → ³H₆) and 2.32 µm (³H₄ → ³H₅) with a higher slope efficiency of 28.3% and a lower laser threshold of 1.43 W, out of which 332 mW are achieved at 2.32 µm. Under dual-wavelength pumping, further power scaling to 357 mW at at 2.32 µm is observed at the expense of increased laser threshold. To support the upconversion pumping experiment, excited-state absorption spectra of Tm³⁺ ions for the ³F₄ → ³F_2,3 and ³F₄ → ³H₄ transitions are measured for polarized light. Tm³⁺ ions in CaGdAlO₄ exhibit broadband emission at 2.3 - 2.5 µm making this crystal promising for ultrashort pulse generation.