The volume absorptions and the interface absorptions of SiO2 and HfO2 single layers are studied using the thermal lens method. Based on the fact that electric field distributions in single layers are different when the films are illuminated from the coating side and substrate side, an equation is given to calculate volume and interface absorptions of single layers. Half wave HfO2 and SiO2 single layers are prepared by electron beam evaporation method. With the absorption data measured by thermal lens technique, we separate the volume absoption from the interface absorption for these two single layers. The results show that interface absorption is non negligible when the absorption of film approaches to a ppm level. Additionally, the HfO2 single layer shows bigger volume and interface absorptions than SiO2 single layer.