Preparation and Optical Properties of Nd:Bi2Ti2O7 Laser Crystal with Disordered Structure and Attractive Multiwavelength Emission Characteristics

Laser crystals with multiwavelength emission characteristics are potential light sources for terahertz radiation. Herein, the pure and Nd-doped Bi2Ti2O7 (BTO) laser crystals with sizes up to 16 × 13 × 5 mm3 were successfully grown using the flux method in the KF-B2O3-CaBi4Ti4O15 growth system. The crystal structure, ideal morphology, chemical, mechanical, and thermal properties, optical transmission and Raman spectra, refractive index, absorption, and fluorescence spectra, as well as fluorescence lifetimes, were systematically studied. Besides, the spectral parameters of Nd3+ ions in the BTO crystal were systematically calculated based on the Judd-Ofelt theory. The Nd:BTO crystal has a wide transmittance range (0.44-7.30 μm), a small coefficient of thermal expansion (5.80 × 10-6 K-1), and a large absorption full width at half-maximum (fwhm) (31.2 nm) at around ∼804 nm, making it more potential for use in high-power laser systems. Moreover, fluorescence spectra show four emission peaks at 1054, 1062, 1104, and 1112 nm. The strong multiwavelength emission property makes Nd:BTO a promising laser crystal, serving as a potential light source for terahertz radiation.

Few-layer Ti3C2Tx (T = O, OH, or F) saturable absorber for a femtosecond bulk laser

Few-layered titanium carbide (Ti₃C₂T_x), a novel two-dimensional (2D) Van der Waals material in the MXene family, was fabricated with a liquid-phase method and applied as a saturable absorber for a continuous-wave mode-locked femtosecond bulk laser. Pulses as short as 316 fs with a repetition rate of 64.06 MHz and maximum output power of 0.77 W were achieved at the central wavelength of 1053.2 nm, demonstrating the first known, to the best of our knowledge, application of MXene in an all-solid-state laser. Considering the flexible band gap for different surface functional groups of Ti₃C₂T_x, these results may promote the development of ultrafast photonics and further applications of 2D optoelectronic layered materials in the infrared and mid-infrared regions.