Thermally evaporated MAPbBr3 perovskite random laser with improved speckle-free laser imaging

The crystal structure of MAPbBr3:TPPO and pristine MAPbBr3 perovskite films were characterized by XRD (Philips, X’Pert Pro MRD, with Cu Kα radiation, λ = 1.54 Å). Morphology of the perovskite films were measured by SEM (ZEISS Gemini SEM 300 field-emission SEM, with Pt coating). AFM images of the perovskite films were measured by Bruker Multimode 8 AFM. The PL spectra and the steady-state PL measurement were measured by a confocal system (WITec alpha 300R) equipped with a 405 nm continuous wave laser. For ASE experiments, a commercial Ti: sapphire regenerative amplifier (800 nm, 35 fs, 1 kHz) was employed as the two-photon pump source, and 400 nm pulse (one-photon pump source) was obtained through the second harmonic generation (SHG) from a β-barium borate crystal. The excitation beam was focused onto samples through a cylindrical lens, and the stripe length of the spot size was controlled by an adjustable slit. The emission signals were acquired by a fiber spectrometer (Ocean Optics) with a spectral resolution of 1 nm. Optical gain measurements were performed by using the standard VSL method, the stripe length was variable from 0 to 0.3 mm. TA spectroscopy of the samples were measured through a Helios pump-probe system (Ultrafast system LLC), the pump wavelength is 400 nm. For random lasing experiments, the excitation beam was introduced to a confocal system (WITec alpha 300R) and focused onto the samples through an objective (10×) lens.