software to fit optical spectra - Quantum Materials Group

In ellipsometry the complex ratio ρ = r p / rs
is measured, commonly expressed in terms
i∆
of the two real parameters ψ and ∆ : ρ = tan ψe
. The inversion of this formula gives
ψ = arctan ρ and ∆ = arg ρ .
The pseudo-dielectric function is defined as:
ε pseudo
2
⎡
⎤
2
2 ⎛1
+ ρ ⎞
= sin θ ⎢1
+ tan θ⎜
⎟ ⎥ .
⎢⎣
⎝1
− ρ ⎠ ⎥⎦
In the case of an isotropic sample the ε pseudo coincides with the true dielectric function ε .
One of the possible ellipsometry configurations involves a fixed polarizer (at angle P )
and a rotating analyzer (without a retarder). In this case the Fourier coefficients of the detector
signal as functions of the analyzer angle are:
2
2
tan ψ − tan P 2 tanψ
cos ∆ tan P
α =
, β =
.
2
2
2
2
tan ψ + tan P tan ψ + tan P
The description of the model parameters is given in Table 4-8.
# Wo Wp G
1 DF model for εx θ [degrees] P [degrees]
2 DF model for εy - -
3 DF model for εz - -
Table 4-8 The parameters of the model “Ellipsometry of an orthorhombic sample”.
An example of such a model is shown in Figure 4-9. It is assumed that the “Model2”
containsε x , the “Model3” contains ε y and “Model4” contains ε z . The angle of incidence is
80 o and the polarizer angle is 45 o .
To imitate the isotropic sample, one should assign the dielectric components ε x , ε y and
ε z may to the same model. For a uniaxial crystal two of the three components should refer to
the same “Dielectric function” model.
Figure 4-9 An example of the model “Ellipsometry of an orthorhombic sample”.
Guide to RefFIT Page 67