The laser beam absorption lengths of CO 2 (10.6μm wavelength) and a high power diode laser (HPDL) (810nm wavelength) radiation for an Al 2 O 3 /SiO 2 -based refractory have been determined through the application of Beer–Lambert’s law. The findings revealed marked differences in the absorption lengths despite the material having similar beam absorption coefficients for both lasers. The absorption lengths for the Al 2 O 3 /SiO 2 -based refractory of CO 2 and a HPDL radiation were calculated as being 345±22 and 198±15μm, respectively. Moreover, this method of laser beam absorption length determination, which has hitherto been used predominantly with lasers operated in the pulsed mode, is shown to be valid for use with lasers operated in the continuous wave (CW) mode, depending upon the material being treated.