Abstract
We investigated dual wavelength mid-infrared quantum cascade lasers based on heterogeneous cascades. We found that due to gain competition laser action tends to start in higher order lateral modes. The mid-infrared mode with the lower threshold current reduces population inversion for the second laser with the higher threshold current due to stimulated emission. We developed a rate equation model to quantitatively describe mode interactions due to mutual gain depletion.
Highlights
Quantum cascade lasers [1] (QCLs) are semiconductor lasers based on intersubband transitions between electronic states in coupled quantum wells (QWs)
In this paper we study in detail the multimode behavior of dual wavelength QCLs and describe the experimental effects by a rate equation model which includes the interaction of the two lasers
To describe and understand the underlying physics we suggest a rate equation model that includes the mutual interactions of the two laser modes
Summary
Quantum cascade lasers [1] (QCLs) are semiconductor lasers based on intersubband transitions between electronic states in coupled quantum wells (QWs). Integration of coupled QWs with a large nonlinear susceptibility in the active region of QCLs has led to the demonstration of intracavity second harmonic [13,14] and sum-frequency generation [13] in QCLs. Recently, difference frequency generation (DFG) has been demonstrated in dual wavelength mid-IR QCLs [15,16]. Two midIR pump beams sharing the same waveguide generate their difference-frequency in the THz regime by means of intersubband nonlinearities integrated in the active regions of these devices. We found that the two pump lasers tend to operate in different lateral modes, leading to reduced efficiency in nonlinear light generation [17]. In this paper we study in detail the multimode behavior of dual wavelength QCLs and describe the experimental effects by a rate equation model which includes the interaction of the two lasers
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