|> Energy band gap > GaAs | AlxGa1-xAs | InxGa1-xAs|
|> Refractive index > GaAs | AlAs | AlxGa1-xAs | InxGa1-xAs|
|> Devices > Bragg mirror | SAM | RSAM | SANOS | SOC | Microchip laser | PCA|
Spectral reflectance of AlAs/GaAs-Bragg mirrors
|>||1. Reflectance of a quarter-wave stack|
The reflectance R of a quarter-wave stack in air or free space with high-index layers outermost on both sides is given by
|optical admittance of a quarter wave stack with (2p + 1) layers|
|In this equation the symbols and constants have the following meaning:|
|nH||high index of refraction|
|nL||low index of refraction|
|nS||index of the substrate|
|(2p + 1)||number of layers in the stack|
If the number (2p + 1) of films in the quarter-wave stack is large and the absorption can be neglected then
|>||3. Spectral width of the high reflectance zone|
The spectral width Dl
of the high reflectance zone increases with increasing
difference of the refractive indices nH - nL.
|spectral width of high reflectance||eq.(4)|
|>||4. Numerical examples for AlAs/GaAs-Bragg mirror|
For the wavelength 1064 nm (photon energy = 1.165 eV) the refractive indices
of the materials GaAs and AlAs are due to
equation (1) given on the page n(AlGaAs) n(GaAs) = 3.49 and n(AlAs) = 2.95 respectively.
Spectral reflectance of Bragg-mirrors consisting of AlAs/GaAs quarter-wave stacks with the center wavelength of l0 = 1064 nm and different numbers of AlAs/GaAs pairs.