# Wavelength shifting in fiber (absorption length)

Dear Geant4 users,

I have a problem which concerns optical wavelength shifting simulation in fiber. I cannot understand how it is rigth to set an absorption length for fiber. I want to set this length to 217 cm for example (let’s assume it does’t depend on wave of comming photons). So when I did the following (below), that works fine, but the absorption length is not right.

Code

G4double PhotonEnergy_PS_ABS[nEntries_PS_1] = {3.539eV, 3.477eV, 3.340eV, 3.321eV, 3.291eV, 3.214eV, 3.162eV, 3.129eV, 3.091eV, 3.086eV, 3.049eV, 3.008eV, 2.982eV, 2.958eV, 2.928eV, 2.905eV, 2.895eV, 2.890eV, 2.858eV, 2.813eV, 2.774eV, 2.765eV, 2.752eV, 2.748eV, 2.739eV, 2.735eV, 2.731eV, 2.723eV, 2.719eV, 2.698eV, 2.674eV, 2.626eV, 2.610eV, 2.583eV, 2.556eV, 2.530eV, 2.505eV, 2.480eV, 2.455eV, 2.431eV, 2.407eV, 2.384eV };

G4double RIndexFiber_PS[nEntries_PS_1] = {1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59, 1.59};

G4double AbsFiber_PS[nEntries_PS_1] = {0.28cm, 0.28cm, 0.26cm, 0.25cm, 0.24cm, 0.21cm, 0.19cm, 0.16cm, 0.13cm, 0.13cm, 0.14cm, 0.11cm, 0.08cm, 0.05cm, 0.02cm, 0.05cm, 0.08cm, 0.10cm, 0.13cm, 0.10cm, 0.08cm, 0.07cm, 0.08cm, 0.11cm, 0.13cm, 0.16cm, 0.19cm, 0.21cm, 0.24cm, 0.27cm, 0.30cm, 2.69cm, 3.49cm, 3.99cm, 5.00cm, 8.6cm, 11.6cm, 23.1cm, 55cm, 93cm, 317cm, 494cm};

G4double PhotonEnergy_PS_EM[nEntries_PS] = {2.69eV, 2.67eV, 2.66eV, 2.64eV, 2.63eV, 2.61eV, 2.58eV, 2.56eV, 2.55eV, 2.53eV, 2.50eV, 2.48eV, 2.46eV, 2.45eV, 2.44eV, 2.43eV, 2.41eV, 2.37eV, 2.33eV, 2.25eV, 2.24eV, 2.19eV, 2.15eV, 2.08eV };

G4double EmissionFiber_PS[nEntries_PS] = {0, 0.02, 0.09, 0.20, 0.29, 0.40, 0.59, 0.70, 0.80, 0.89, 1.00, 0.96, 0.88, 0.79, 0.69, 0.59, 0.50, 0.40, 0.31, 0.22, 0.19, 0.10, 0.06, 0};

But when I change AbsFiber_PS to:

Changed AbsFiber_PS

G4double AbsFiber_PS[nEntries_PS_1] = {217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm, 217cm};

there is no wavelength shigting at all. Don’t understand why? So, could someone please tell how to set absorption length in fiber to 217 cm for example in right way?