The Two Photon Absorption - Transient Current Technique (TPA-TCT) is a device characterisation technique that enables three-dimensional spatial resolution. Laser light in the quadratic absorption regime is employed to generate excess charge carriers only in a small volume around the focal spot. The drift of the excess charge carriers is studied to obtain information about the device under test. Neutron, proton, and gamma irradiated p-type pad silicon detectors up to equivalent fluences of about 7e15 neq/cm2 and a dose of 186 Mrad are investigated to study irradiation induce effects on the TPA-TCT. Neutron and proton irradiation lead to additional linear absorption, which does not occur in gamma irradiated detectors. The additional absorption is related to cluster damage and the absorption scales according to the non-ionising energy loss. The influence of irradiation on the two photon absorption coefficient is investigated, as well as potential laser beam depletion by the irradiation induced linear absorption. Further, the electric field in neutron and proton irradiated pad detectors at an equivalent fluence of about 7e15 neq/cm2 is investigated, where the space charge of the proton irradiated devices appears inverted compared to the neutron irradiated device.