Manipulation and applications of ultrafast all-optical switching based on transient absorption and dispersion in KTN...

Potassium tantalate niobate (KTN) represents a noteworthy category of optical crystals known for their superior nonlinear optical properties. In this study, we conducted measurements of femtosecond time-resolved transient absorption (TA) spectra in KTa_0.57Nb_0.43O₃ crystals. Notably, a rapid and pronounced "plateau" phase, ∼1.5 ps in duration, was detected at the onset of the TA kinetics and succeeded by two distinct decay components, exhibiting lifetimes of ∼140 ps and over 10 ns, respectively. We attribute these observations to a decay process involving two-photon absorption, dispersion characteristics, and excited state absorption. Based on this unique TA characteristic of KTN crystals, an all-optical switching strategy was proposed and utilized to measure the ultrafast lasing dynamics of single-crystal CH₃NH₃PbBr₃ nanowires. This polarization-independent TA gate approach offers an adjustable gate width combining ps and ns time scales and introduces a versatile tool for advanced optical applications.