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Diffuse reflectance spectroscopy relies upon the spectral responsivity of the photon remission to the medium’s property for application. Practically, it is imperative to assess the conditions at which the photon remission becomes illy responsive or unresponsive to the change of an otherwise sensible property of the medium. Such limiting cases may be particularly relevant to single-fiber reflectance (SfR) for minimally invasive sensing and center-illuminatedcentral- acquired (CIC-A) geometry for non-contact sensing. The steady-state photon remission of SfR in the absence of absorption, for example, was shown by Monte Carlo (MC) to be insensitive to the scattering changes as the fiberdiameter scaled dimensionless reduced-scattering reaches μ'darea >10. Similar limiting patterns are observed with steady-state CIC-A known to be scalable over steady-state SfR. To gain insights on the conditions of saturation in CIC-A as projectable to SfR, we revise a model of the steady-state photon remission of CIC-A geometry demonstrated in (Sun & Piao, 2022, App. Opt.), which predicts the onset of saturation as the dimensionless reduced scattering increases. The model-projected saturation-level and the corner-condition of the saturation, both being absorptiondependent, are examined against MC simulations. Experiments in non-contact CIC-A geometry were conducted. Diffuse reflectance was collected from two co-centric areas that differ by ~10 times in diameter when responding to the same centered illumination. The limiting-pattern indicative model was applicable to the diffuse reflectance from aqueous samples of the scattering increased to near-saturation followed by absorption increasing. The scattering-saturation may be useful for simplifications such as implementing differential pathlength factor towards real-time assessment of absorption.
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