Optical characterization of liquid phantoms in 500–1000 nm using an improved single integrating sphere system

This paper reports on optical characterization (absorption coefficient μa and reduced scattering coefficient μs′) of liquid phantoms in the wavelength range of 500–1000 nm using an improved single integrating sphere system. 54 liquid optical phantoms (18 pure absorption, pure scattering and mixed samples each) with known optical properties were first prepared. The overall performance of a laboratory-established single integrating sphere system was then evaluated, and the results indicated that the system has perfect stability, repeatability, and accuracy in optical property measurement. After that, effect of cuvette size (i.e., optical path and wall thickness) on optical property measurement was investigated. The experimental results showed that the discrepancies of the measured optical properties for the pure absorption and scattering phantoms held by different cuvettes with varying optical paths and wall thicknesses were within 8.76 %. Finally, the effect of different concentrations of absorber and scatterer on optical property determination of mixed liquid phantoms were explored. It was found the measured optical properties of the mixed liquid phantoms had a considerable difference from those of the pure absorption and pure scattering phantoms. We guessed that the addition of the absorber (scatterer) would dilute the concentration level of scatterer (absorber), and also brought about interaction between the two particles, and thus resulting in an offset for the measured optical properties. Future work needs to test our conjecture from the micro level, like monitoring the dynamic change of the absorption and scattering particle distribution and interaction, when optically characterizing the mixed liquid phantoms.