Continuous-Wave Mode-Locked 2.85 <i>μ</i> m Er:Lu ₂ O ₃ Crystal Bulk Laser Based on Graphene

The gain medium with high gain and superior spectral performance is essential for generating mid-infrared 3 μm ultrashort lasers, due to its strong phonon absorption and thermal effects in the mid-infrared wavelength region. This study investigates the spectral and ultrashort laser characteristics of Er:Lu<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> crystals, which possess remarkable optical and mechanical properties. The experimental results demonstrate an ultrabroad fluorescence spectrum spanning from 2700 to 2860 nm, along with a broadband tuning range of 2711 to 2848 nm. For the first time, a continuous wave mode-locked (CWML) mid-infrared laser operating at ~3 μm has been achieved using a two-dimensional material saturable absorber. The mode-locked laser produces ultrashort pulses with a pulse width of 19.7 ps at a repetition rate of 71 MHz, delivering a maximum average output power of 52 mW. The central wavelength of the CWML laser is located at 2845 nm, with a full width at half maximum (FWHM) of 1.74 nm. The laser spectrum exhibits a signal-to-noise ratio of 55 dB, confirming excellent stability and validating the Er:Lu<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> crystal as a highly promising gain medium for mid-infrared 3 μm ultrashort lasers.