  Halide perovskites are a promising optical gain media with high tunability
and simple solution synthesis. In this study, two gain regimes, namely
amplified spontaneous emission and random lasing, are demonstrated in same
MAPbBr$_3$ halide perovskite single crystal. For this, photoluminescence is
measured at a temperature of 4 K with pulsed femtosecond pumping by UV light
with a 80 MHz repetition rate. Random lasing is observed in areas of the sample
where a random resonator was formed due to cracks and crystal imperfections. In
more homogeneous regions of the sample, the dominant regime is amplified
spontaneous emission. These two regimes are reliably distinguished by the line
width, the mode structure, the growth of the intensity after the threshold, and
the degree of polarization of the radiation. The spectral localization of the
stimulated emission well below the bound exciton resonance raises a question
concerning the origin of the emission in halide perovskite lasers.

Applied Physics;Mesoscale and Nanoscale Physics