Search

The refractive index of blood is a key biophysical parameter, which can reflect the physiological state. We measured the refractive index of whole blood and other components, such as serum, plasma, and hemoglobin, based on internal reflection by using a homemade apparatus in the spectral range of 400 to 750 nm. In addition to the hemoglobin solution, which has a Soret band about 420 nm and two Q-bands between 500 and 600 nm, the measurements of other samples are the normal dispersion curve. The results are approximated by the Cauchy equation and Sellmeier equation, and the correlation coefficients are more than 0.997. [ABSTRACT FROM AUTHOR]

The complex refractive index dispersion (CRID), which contains the information on the refractive index dispersion and extinction coefficient spectra, is an important optical parameter of biotissue. However, it is hard to perform the CRID measurement on biotissues due to their high scattering property. Continuous CRID measurement based on internal reflection (CCRIDM-IR) is introduced. By using a lab-made apparatus, internal reflectance spectra of biotissue samples at multiple incident angles were detected, from which the continuous CRIDs were calculated based on the Fresnel formula. Results showed that in 400- to 750-nm range, hemoglobin solution has complicated dispersion and extinction coefficient spectra, while other biotissues have normal dispersion properties, and their extinction coefficients do not vary much with different wavelengths. The normal dispersion can be accurately described by several coefficients of dispersion equations (Cauchy equation, Cornu equation, and Conrady equation). To our knowledge, this is the first time that the continuous CRID of scattering biotissue over a continuous spectral region is measured, and we hereby have proven that CCRIDM-IR is a good method for continuous CRID research of biotissue. [ABSTRACT FROM AUTHOR]

Traditionally, continuous refractive index dispersion (CRID) measurement of materials with scattering is hard to realize. In this paper, CRID measurement based on the derivative total reflection method (CRIDM-DTRM) is proposed to measure the CRID of both absorption and scattering materials. It effectively determined the CRID of K9 glass, concentrated milk, and 0.5% methyl red solution in the 400-750 nm range with the spectral resolution of about 0.259 nm. For the first time, CRID of a scattering material is measured. CRIDM-DTRM is a useful technique in the field of RID measurement, especially for biotissues and anomalous dispersion materials. [ABSTRACT FROM AUTHOR]

The physical changes of tissue are complicated to evaluate during optical clearing (OC) treatment. Monitoring the changes of optical parameters, including the complex refractive index (CRI), helps people better understand the OC process. From the imaginary part of CRI, we can deduce the extinction coefficient of tissue. Based on the total internal reflection method, the time-dependent CRI of porcine muscle during natural dehydration is well determined. Results show that the real RI increases continuously with the increase of dehydration time, whereas the extinction coefficient initially increases and then decreases. Finally, the extinction coefficient becomesmuch smaller than the initial value, which demonstrates that better tissue optical clarity is obtained. The change tendency of the extinction coefficient of tissue is used to qualitatively explain the dynamic change of transmittance of a natural dehydrated tissue. Consequently, CRI, especially its imaginary part, is a very useful optical parameter by which to evaluate the OC effect. [ABSTRACT FROM AUTHOR]

The refractive-index profile (RIP) of optical fibers is of fundamental significance in determining critical fiber properties. Here, we present the application of a two-dimensional (2-D) scanning focused refractive-index microscopy (SFRIM) to accurately obtain the 2-D RIP of a graded-index optical fiber. Some modifications are made to SFRIM for better 2-D measurement. Quantitative RIP of the fiber is obtained with derivative total reflection method. The refractive-index accuracy is 0.002. The measured result is in good agreement with theoretical expectation. This method is straightforward, simple, repeatable, and free from signal distortion. This technique is suitable for symmetric and asymmetric optical fibers. The results indicate that this technique can be applied to obtain the RIPs of a wide range of materials and has broad application prospect in many fields. [ABSTRACT FROM AUTHOR]

We report the dynamic refractive index (RI) change of tissue under a stepped compression load using a custom-built pressure apparatus. Angle-dependent reflectance profiles of biotissue samples are recorded, and the RI values are resolved using the derivative total reflection method. These results are relevant for understanding the mechanism of mechanical optical clearing, for investigating tissue dynamics under mechanical stimuli, and for other biomedical applications. [ABSTRACT FROM AUTHOR]

Non-homogenous material such as solid composite materials examination using refractive index-sensing remains a challenge for researchers. A derivative total reflection method for simultaneous measurement of the refractive indices of various components of a non-homogeneous solid was developed. Only a measurement of the reflectance from the surface of composite sample is necessary. In our experiments, simulation samples, porcine tissue, and Rosso Levanto marble samples were measured to verify proposed method. [ABSTRACT FROM AUTHOR]