Oxygen vacancies based BiOBr nanoflowers saturable absorber and its application in Q-switched mode-locked infrared laser

In this work, BiOBr nanoflowers with oxygen vacancies as saturable absorber are prepared using hydrothermal method. Passively Q-switched mode-locked infrared laser is achieved. The output power reaches the maximum 312 mW. The minimum Q-switched envelope is 242 ns with the maximum repetition rate of 180.5 kHz. Meanwhile, the mode-locked pulse duration within the Q-switched envelope is approximately 315 ps with repetition rate of 232 MHz. The results of X-ray diffraction (XRD), Electron paramagnetic resonance (EPR), UV–Vis–NIR diffuse reflectance spectra, and X-ray photoelectron spectroscopy (XPS) demonstrate the oxygen vacancies introduce intermediate energy levels in the energy band of BiOBr, which enhances the optical absorption in the near-infrared region. Therefore, BiOBr saturable absorber exhibits good saturable absorption characteristics in the near-infrared region and is a promising modulation element in Q-switched mode-locked infrared lasers. •The modulation depth and the saturation intensity of BiOBr nanoflowers saturable absorber is 7.5% and 522 MW/cm2 respectively.•The maximum output power of the laser is 312 mW. The pulse duration and repetition rate are 242 ns and 180.5 kHz respectively, corresponding to single pulse energy of 1.73 μJ and peak power of 7.14 W.•The mode-locked pulse duration within the Q-switched envelope is approximately 315 ps with repetition rate of 232 MHz.