Effects of Fabry-Perot cavity interference on the absorption spectrum of EBT3 radiochromic film

Optical response of the radiochromic film (RCF) has been studied, reporting two main absorption bands centered at 636 nm and 585 nm. However, other bands below 540 nm have been reported for EBT3, which deserve special attention. León-Marroquín et al. (2016) have suggested that these bands behave as an interference pattern of a Fabry-Perot cavity due to the symmetric structure of the EBT3 film. The aim of this work is to generate the absorption spectra of the RCF EBT3 using the model for a Fabry Perot cavity containing poly-DCHD and compare them with the measured net absorption spectra (Nas). Films were irradiated with a 6 MV photon beam from a clinical accelerator using the calibration conditions. Nas of the RCF irradiated in a dose range from 0 to 10 Gy were measured using a double-beam UV-Vis spectrophotometer in a wavelength from 400-800 nm. The theoretical model describing the net absorbance of a Fabry-Perot cavity containing poly-DCHD was used to generate the net absorption spectra of the RCF. Measured and theoretical Nas was compared. The absorption bands centered at 636 and 585 corresponding to the poly-DCHD of the active layer of the RCF were observed in the measured Nas. Additionally, four absorption bands were observed in a spectral range of 400 - 500 nm, positioned at 412, 433, 460, and 492 nm. Through the theoretical model for a Fabry-Perot cavity, four interference bands (fringes) were generated at 414, 436, 458 and 488 nm. The peak position between the measured and theoretical bands is around 5 nm off in all the four bands. These results could be supporting the hypothesis proposed by León-Marroquín et al. (author)