In this study, red light emitting InP/ZnSeS/ZnS quantum dots (QDs) are prepared by thermal injection method. The results show that the InP/ZnSeS/ZnS QDs saturable absorbers (SA) have good nonlinear saturable absorption properties with modulation depth of 24.2% and saturation intensity of 0.08 KW cm−2. Then the QD SAs are applied to the erbium‐doped fiber laser (EDFL) ring cavity system, and a mode‐locked laser pulse with a pulse width of 635 fs is generated. In addition, the pulse width is determined by the carrier recovery time, which is closely related to the defect density in the material. A large number of defects are eliminated in the QDs by hydrogen fluoride (HF) treatment, and the pulse width is reduced from 635 to 450 fs. Results of time‐resolved photoluminescence and ultrafast transient absorption spectroscopy (TAS) show that HF treatment indeed reduces defects in InP/ZnSeS/ZnS QDs, indicated by the decrease of the carrier recovery time. This is different from the reported 2D SA materials, which usually reduce the carrier recovery time by increasing the defect density. This study will inspire new applications of QDs in ultrafast photonics and nonlinear optics.
We have demonstrated spatiotemporal pulses from a Q-switched ytterbium-doped multimode fiber laser, with a pulse energy of up to 16.5 μJ, a pulse repetition rate of 108.7 kHz, and an average output power of 1.80 W. Benefiting from the weakened spectral filtering effect, there is high pulse energy that can be produced from multimode fiber oscillators. We have observed and analyzed the evolution of multimode Q-switching with spatiotemporal correlation. Furthermore, we find that the polarization control in the saturable absorber has a modulation and selective effect on the transverse modes of the multimode fiber laser. Our results help to understand the spatiotemporal characteristics of pulsed fiber lasers and contribute to developing high-pulse energy lasers.
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