Effect of temperature on Quantum Cascade Laser emission as a function of cavity length

Quantum Cascade Laser (QCL) is extremely unique in its characteristics due to its narrow bandwidth resulting from unipolar operation, mid-infrared emission, and wavelength tunability by quantum mechanical engineering. While lasing, the change in temperature affects the cavity length of the QCL, which in turn may affect the emission wavelength. In this work, we have studied the tunability of QCL emission when the operating temperature varies. We have found that the temperature-dependent tunability of the emission wavelength is sensitive to the cavity length. The tunability is greater for smaller cavity lengths. However, the emission wavelength may change sharply at different temperatures for larger cavities due to mode hopping. In any case, the overall change in the emission wavelength will not affect the performance if the target molecules do not have absorption peaks separated by less than 2 cm^-1, which makes QCL an outstanding mid-infrared spectroscopy source.