The thermo-optical properties, the non-radiative relaxation time, tau(r), and the characteristic diffusion time, tau(beta), of a 0.001 mol% Cr2O3 doped low silica calcium aluminate glass were investigated by photothermal technique and photoacoustic spectroscopy, respectively. The results are interpreted in terms of frequency dependence predicted by the theory of Resencwaig and Gersho, and by the thermoelastic model. In the PA spectra, it is possible to identify two bands centered at 380 and 620 nm, the tau(r) of which is 2.18 and 1.55 ms, respectively, and tau(beta) was found to be 0.53 and 0.49 ms, respectively, for each band. (c) 2008 Elsevier B.V. All rights reserved.