In recent years, optical techniques such as photoacoustic imaging (PAI),1,2 ultrasound-modulated optical tomography,3 fluorescence imaging,4 and diffuse optical tomography (DOT)5 have been employed with great success for imaging deep inside highly scattering biological tissue. Due to the scattering and absorbing nature of biological tissue, the optical fluence decays with the distance from the light source. As a result, the amount of light reaching a point away from the light source becomes unknown. The lack of information about local fluence prevents the above methods from achieving quantification. Currently, methods to estimate the fluence distribution in biological tissue are based on various theoretical models, each with their own respective drawbacks. It is known that the radiative transfer equation (RTE) accurately describes photon propagation in biological tissue.6,7 However, solutions of RTE exist only for simple cases where the medium is infinite and homogeneous.8 In media with dominant scattering compared to absorption, the fluence rate far from optical boundaries and the light source can be approximated using diffusion theory.9 In more complex media, computational models are used to solve RTE under certain approximations,10,11 including the most commonly used method—Monte Carlo simulations.12 To estimate optical fluence in biological tissue using the above-mentioned techniques, exact knowledge of optical properties of the medium is required. Unfortunately, in real biological tissue, neither are the exact optical properties known, nor is the medium homogeneous, which limits the practicality of these methods. An experimental technique that vanquishes the aforementioned needs of a priori knowledge of the medium properties would be more practical.