量子级联laser的本征线宽：超越Schawlow-Townes极限
Observing the intrinsic linewidth of a quantum-cascade laser: beyond the Schawlow-Townes limit
摘要：
首次对自由运转的中红外量子级联激光器的频率噪声谱密度进行了全面的研究。它提供了直接证据，证明这种噪声已降至白噪声平台，对应于几百赫兹的固有线宽。该实验与量子级联激光器中谱线展宽的基本机制的最新理论一致，该理论为Schawlow-Townes公式提供了新的见解，并预测了超过上能级辐射寿命限制的窄化。
英文摘要：
A comprehensive investigation of the frequency-noise spectral density of a free-running mid-infrared quantum-cascade laser is presented for the first time. It provides direct evidence of the leveling of this noise down to a white noise plateau, corresponding to an intrinsic linewidth of a few hundred Hz. The experiment is in agreement with the most recent theory on the fundamental mechanism of line broadening in quantum-cascade lasers, which provides a new insight into the Schawlow-Townes formula and predicts a narrowing beyond the limit set by the radiative lifetime of the upper level.
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