Fig. 1: The working principle of quantum cascade laser and its geometry structure. | Light: Science & Applications

Fig. 1: The working principle of quantum cascade laser and its geometry structure.

From: High-power, high-wall-plug-efficiency quantum cascade lasers with high-brightness in continuous wave operation at 3–300μm

Fig. 1

The vertical axis represents energy and the horizontal axis represents the growth direction of materials. The periodically alternating structure at left side represents quantum wells and barriers. The black dashed lines represent artificial energy levels arising from quantum confinement. The black dots presented electrons. The green arrows represent electron injection to upper energy levels. The red wavy lines represent photon emissions originating from electrons transitions from upper energy levels to lower energy levels. After laser transition in a period, electrons will be transported (injected) from the lower energy level of this period to the upper energy level of the next period in the downstream for further transition and photon emission. This process will be repeated in each period and thus considerably increase the gain of lasers

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