A method, which makes use of difference of absorption in different stages of excitation process, is introduced to get more information about optical stimulated luminescence (OSL) properties of electron trapping materials (ETM). Absorption spectra of excited ETM contain all absorption of various traps (defects) together. So, the difference between absorption spectra before and after excitation (differential absorption) not only acts as the same as stimulation spectra, but also provides more information, such as holes stimulation, total volume of optical storage, etc. This method is helpful in studying OSL properties.