Nonlinear optical properties of a Ge₂Sb₂Te₅ film saturable absorber for short-pulse solid-state lasers

In this study, we employed a stable Ge₂Sb₂Te₅ (GST) thin film as a saturable absorber (SA) to create near-infrared short-pulse solid-state passively Q-switched and Q-switched mode-locked lasers for the first time. The GST saturable absorber (GST-SA) produced an exceptional nonlinear optical response with a modulation depth of 2.9%, a nonlinear absorption coefficient of −2.21 × 10³ cm GW⁻¹, a fast decay time of 2.31 ps and a slow decay time of 59.6 ps. When integrated into an Nd:YVO₄ laser cavity, the GST-SA achieved stable passively Q-switched pulsed laser output with a pulse width of 260 ns, and a maximum output power of 480 mW. By adjusting the resonant cavity, a Q-switched mode-locked output with a maximum power of 110 mW, a Q-switched pulse envelope repetition frequency of 33 kHz, a pulse width of 1.75 µs, and a pulse energy of 3.33 µJ were obtained. The mode-locked pulse repetition frequency within the Q-switched envelope was 100 MHz, with a pulse width of 1.51 ns. These results underscore the potential of GST as a superior near-infrared nonlinear optical material, making it an ideal candidate for next-generation high-performance pulsed solid-state lasers.