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qcl:photon-assisted_transport_and_gain_clamping
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qcl:photon-assisted_transport_and_gain_clamping [2021/04/02 08:35] thomas.grange |
qcl:photon-assisted_transport_and_gain_clamping [2022/03/30 17:19] (current) thomas.grange |
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| </code> | </code> | ||
| - | Note that in the current version (2020-11-16), only a single EM mode is supported at a time. | + | Note that in the current version (2022-03-30), only a single EM mode is supported at a time (i.e. multi-mode lasing operation is not supported). |
| The electric field in this EM mode can be either imposed (detection mode) or calculated self-consistently (gain clamping). | The electric field in this EM mode can be either imposed (detection mode) or calculated self-consistently (gain clamping). | ||
| Line 26: | Line 26: | ||
| <ElectricField unit="V.m^-1">1.0e6</ElectricField> | <ElectricField unit="V.m^-1">1.0e6</ElectricField> | ||
| </EMmode> | </EMmode> | ||
| + | </EMfield> | ||
| </code> | </code> | ||
| Line 31: | Line 32: | ||
| The gain feature calculates the linear response to an a.c. incoming field. In this case, the d.c. current is not modified. | The gain feature calculates the linear response to an a.c. incoming field. In this case, the d.c. current is not modified. | ||
| On the other hand, the photon-assisted transport is modeled through the use of a self-energy (self-consistent Born approximation) to describe both absorption and stimulated emission processes, and has an influence on the d.c. transport. | On the other hand, the photon-assisted transport is modeled through the use of a self-energy (self-consistent Born approximation) to describe both absorption and stimulated emission processes, and has an influence on the d.c. transport. | ||
| - | In the case of the electron-photon self-energy, a gain is also calculated at the specified EM mode energy. However, the calculated gain slightly differ from the one calculated using linear response, even for small intensities, as broadening effects are not treated within the same approximations in the two cases. This is all the more the case when going to small photon energy (i.e. long wavelengths). Hence this method can produce unreliable results in terahertz devices where broadening effects are comparable to the photon energy. | + | In the case of the electron-photon self-energy, a gain is also calculated at the specified EM mode energy. However, the calculated gain slightly differ from the one calculated using linear response, even for small intensities, as broadening effects are not treated within the same level of approximations in the two cases. This is all the more the case when going to small photon energy (i.e. long wavelengths). Hence this method can produce unreliable results in terahertz devices where broadening effects are comparable to the photon energy. |
| ==== Gain clamping ==== | ==== Gain clamping ==== | ||
| - | Gain clamping is relevant to the simulation of quantum cascade lasers above threshold. Indeed, when the gain surpasses the cavity losses, lasing starts and the gain is clamped to the cavity losses. | + | Gain clamping is relevant to the simulation of quantum cascade lasers above threshold. Indeed, when the modal gain $g_c$ reaches the cavity losses, lasing starts and the gain is clamped to the cavity losses, that is |
| + | $$ g_c = \alpha$$ | ||
| + | The modal gain (or cross-section gain), is defined as | ||
| + | $$ g_c = \Gamma g$$ | ||
| + | where $g$ is the material gain in the active region and $\Gamma$ the overlap factor between the cavity mode and the active region. | ||
| To simulate gain clamping, the following command should be used: | To simulate gain clamping, the following command should be used: | ||
| Line 42: | Line 47: | ||
| <Cavity_Losses unit="cm^{-1}">2.76</Cavity_Losses> | <Cavity_Losses unit="cm^{-1}">2.76</Cavity_Losses> | ||
| <GainClamping>yes</GainClamping> | <GainClamping>yes</GainClamping> | ||
| + | <OverlapFactor>0.9</OverlapFactor> | ||
| </Gain> | </Gain> | ||
| </code> | </code> | ||
| - | Note that in this case, the EM electric field should be set to zero: | + | If not specified, the default value for the overlap factor $Gamma$ is assumed to be 1.0 (i.e. perfect overlap between the active region and the cavity mode). |
| + | |||
| + | Note that in the case of gain clamping, the EM electric field value should be either not specified or set to zero: | ||
| <code> | <code> | ||
| <EMfield> | <EMfield> | ||
| Line 53: | Line 61: | ||
| </code> | </code> | ||
| - | 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. | + | Indeed, for gain clamping, the electric field in the cavity is adjusted self-consistently so that the modal gain $g_c$ for this photon energy matches the specified cavity losses $\alpha$. |
| === Wall plug efficiency === | === Wall plug efficiency === | ||
| Line 74: | Line 82: | ||
| Note that the relation between the specified cavity losses and the front mirror one reads | Note that the relation between the specified cavity losses and the front mirror one reads | ||
| - | $$ \alpha_{\text{tot}} = \alpha_{\text{fm}} + \alpha_{\text{bm}} + \alpha_{\text{waveguide}} | + | $$ \alpha_{\text{cavity}} = \alpha_{\text{fm}} + \alpha_{\text{bm}} + \alpha_{\text{waveguide}} $$ |
| where $\alpha_{\text{bm}}$ are the losses due to the back mirror and $\alpha_{\text{waveguide}}$ are the waveguide losses. | where $\alpha_{\text{bm}}$ are the losses due to the back mirror and $\alpha_{\text{waveguide}}$ are the waveguide losses. | ||
qcl/photon-assisted_transport_and_gain_clamping.1617352502.txt.gz · Last modified: 2021/04/02 08:35 by thomas.grange
