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--- qcl:photon-assisted_transport_and_gain_clamping [2020/11/19 16:22]
thomas.grange
+++ qcl:photon-assisted_transport_and_gain_clamping [2021/04/02 08:29]
thomas.grange
@@ Line 55: / Line 55: @@
 In this case, the electric field in the cavity is adjusted self-consistently so that the gain for this photon energy matchs the specified cavity losses.
+=== Wall plug efficiency ===
+The internal wall plug efficiency (WPE)  is calculated when gain clamping occurs. It is defined as
+$$ \eta_{\text{WPE}}^{internal} = \frac{P_{\text{stimulated emission}} - P_{\text{absorption}}}{UI} $$
+If the front mirror losses are specified, the external WPE is output as
+$$ \eta_{\text{WPE}}^{external} = \eta_{\text{WPE}}^{internal} \frac{\alpha_{\text{fm}}}{\alpha_{\text{tot}}}$$
+where $\alpha_{\text{fm}}$ is the front mirror losses, which can be defined using the command:
+<code>
+    <Gain>
+       ...
+       <Cavity_Losses unit="cm^{-1}">2.76</Cavity_Losses>
+       <FrontMirror_Losses unit="cm^{-1}">2.26</FrontMirror_Losses>
+       ...
+    </Gain>
+</code>
+=== Example: Mid-infrared QCL  ===
+The following animated gifs show the electron density, current density and output as the voltage is swept. Above the threshold bias (around 300 meV), the clamping of the gain to the cavity losses results a rapid increase in the internal electric field in the cavity. The photon-assisted transport results in a discontinuity in the slope of the current-voltage characteristics at the threshold bias/current: above threshold, the current increases much faster as stimulated emission reduces the upper laser level lifetime.
+{{:negf:bai2011_electrondensity.gif?direct&600|}}
+{{:negf:bai2011_current.gif?direct&600|}}
+{{:negf:bai2011_emission.gif?direct&600|}}

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