Broadband tunable alexandrite lasers with sub-100 femtosecond pulse widths

A wavelength-tunable mode-locked alexandrite (Cr³⁺: BeAl₂O₄) laser is investigated using two-dimensional (2D) Cu₃Se₂ as the saturable absorber (SA). Broadband wavelength tuning from 745.1 nm to 770.4 nm is achieved with a spectral full width at half maximum (FWHM) consistently exceeding 7.9 nm, while maintaining pulse widths of sub-100 fs. At a central wavelength of 757.0 nm, the mode-locked laser generates 76 fs pulses with a spectral FWHM of 9.0 nm and a maximum average output power of 120 mW. Additionally, this work presents a tunable continuous-wave laser spanning from 710.7 nm to 773.0 nm, delivering a maximum output power of 312 mW at 752.9 nm. To the best of our knowledge, this is the first time that alexandrite has been used to achieve a broadband tunable laser with a pulse width of less than 100 fs.