Add dispersion functions

src/dispersion.jl

@@ -28,7 +28,24 @@ const DispersionARCA = BaileyDispersion(350)
     dp.a0 + dp.a1 * dp.P + x * (dp.a2 + x * (dp.a3 + x * dp.a4))
 end
 
-
 @inline function refractionindexgroup(dp::BaileyDispersion, λ)
-    error("Not implemented yet")
+    n = refractionindexphase(dp, λ)
+    y = dispersionphase(dp, λ)
+    n / (1.0 + y*λ/n)
+end
+
+@inline function dispersionphase(dp::BaileyDispersion, λ)
+    x = 1.0 / λ
+    -(x^2)*(dp.a2 + x*(2.0*dp.a3 + x*3.0*dp.a4))
+end
+
+@inline function dispersiongroup(dp::BaileyDispersion, λ)
+    x = 1.0 / λ
+
+    n   = refractionindexphase(dp, λ)
+    np  = dispersionphase(dp, λ)
+    npp = x^3*(2.0*dp.a2 + x*(6.0*dp.a3 + x*12.0*dp.a4))
+    ng  = n / (1.0 + np*λ/n)
+
+    ng^2 * (2*np^2 - n*npp) * λ / (n^3);
 end

src/parameters.jl

@@ -5,6 +5,7 @@ The parameter set for light detection.
 - `minimum_distance`: the minimum distance [m] between muon track and PMT
 - `lambda_min`: minimum wavelength [ns]
 - `lambda_max`: maximum wavelength [ns]
+- `n`: average index of refraction of medium (default: water) corresponding to the group velocity
 - `legendre_coefficients`: a tuple of two vectors which contain the Legendre coefficients
 - `dispersion_model`: the dispersion model
 - `scattering_model`: the scattering model
@@ -14,6 +15,7 @@ Base.@kwdef struct LMParameters{D<:DispersionModel,S<:ScatteringModel,A<:Absorpt
     minimum_distance::Float64 = 1.0e-1
     lambda_min::Float64 = 300.0
     lambda_max::Float64 = 700.0
+    n::Float64 = 1.3800851282
     legendre_coefficients::Tuple{Vector{Float64},Vector{Float64}} = gausslegendre(5)
     dispersion_model::D = BaileyDispersion()
     scattering_model::S = Kopelevich()