CW‐Pumped Amplified Spontaneous Emission From Thermally Evaporated CsPbBr 3 Films

Lead halide perovskites are widely reported as promising optical gain media for optoelectronic applications in the short‐pulse regime. However, their operation under continuous‐wave excitation remains severely limited by thermal accumulation and gain instability. Here, we present a systematic study of amplified spontaneous emission under long‐pulse and continuous‐wave excitation in thermally evaporated CsPbBr 3 thin films, providing direct insight into the limits of sustained optical gain in perovskite materials. By correlating excitation pulse duration, substrate thermal conductivity, temperature‐dependent emission properties, and time‐resolved carrier dynamics, we establish a physical framework linking thermal dissipation to gain stability. We identify excitation‐time thresholds and define optimal operating regimes, demonstrating sustained amplified spontaneous emission for pulse widths up to 30 µs in films without encapsulation or additional post‐processing. Our results reveal that light‐induced thermal accumulation is the dominant mechanism limiting amplified spontaneous emission under extended excitation and highlight thermal management as a critical design parameter for steady‐state optical gain. These findings provide practical design rules for perovskite gain media and represent a key step toward electrically pumped, continuous‐wave‐performing perovskite superluminescent and laser diodes.