Research On The Improved Double-Integrating-Sphere System Based On Lock-in Amplifier

This paper presents the measurement results of the tissue optical parameters in turbid medium. It is expected that the reactive principle and physical meaning of the light absorption and scattering by the tissue or tissue-like medium could be clarified through quantitative measurement of the optical parameters, and the precise expression of the original information brought by the absorption and scattering parameters could be made.In order to detect the optical parameters of turbid medium, according to the features and the follow-up research, we choose the double-integrating-sphere system to measure the optical parameters. Based on the investigation of the measurement principle, the system composition and technology, we designed an improved double-integrating-sphere system based on the lock-in amplifier. By modulating the light, the system uses the lock-in amplifier to effectively improve the system's SNR. Discussion about the influencing factors on the measurement is also given in this article.With a 1310nm laser diode (LD), the intralipid-10% solution (strong scattering weak absorption medium), copper sulfate solution (net absorption medium) and mixed solution of the above two media were used to validate the system. Results show that the maximal relative measurement error for the scattering medium is less than 5.8% while that for the absorption medium is less than 5.3%. Based on these basic measurements, experiments were also performed on milk. It is found that the variety of the optical parameters can be utilized not only to distinguish the pure milk and powdered milk but also to discern normal milk and the metamorphic one. Measurements on glucose solution verified that absorption variation is affected by the replacement effect and the scattering variation is influenced by the change in refractive index.