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> Energy band gap > GaAs  Al_{x}Ga_{1x}As  In_{x}Ga_{1x}As  
> Refractive index > GaAs  AlAs  Al_{x}Ga_{1x}As  In_{x}Ga_{1x}As  
> Devices > Bragg mirror  SAM  RSAM  SA  SANOS  SOC  Microchip laser  PCA  
Spectral reflectance
of AlAs/GaAsBragg mirrors 

>  Contents  
>  1. Reflectance of a quarterwave stack  
 
The reflectance R of a quarterwave stack in air or free space with highindex layers outermost on both sides is given by  
reflectance  eq.(1)  
with  
optical admittance of a quarter wave stack with (2p + 1) layers  
In this equation the symbols and constants have the following meaning:  
n_{H}  high index of refraction  
n_{L}  low index of refraction  
n_{S}  index of the substrate  
(2p + 1)  number of layers in the stack  
>  2. Approximations  
If the number (2p + 1) of films in the quarterwave stack is large and the absorption can be neglected then  
reflectance  eq.(2)  
transmittance  eq.(3)  
 
 
>  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 n_{H}  n_{L}.  
spectral width of high reflectance  eq.(4)  
 
>  4. Numerical examples for AlAs/GaAsBragg 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 Braggmirrors consisting of AlAs/GaAs quarterwave stacks with the center wavelength of l_{0} = 1064 nm and different numbers of AlAs/GaAs pairs.  