Modified critical angle method for measuring the refractive index of bio-optical materials and its application to bacteriorhodopsin

Abstract

The critical angle technique is modified for the accurate measurement of the refractive index of bio-optical materials. Based on the analysis of reflection from the boundary of the material as a function of incident angle and polarization direction, the critical illumination angle is obtained by numerical differentiation of the reflection curve. As an example, the dispersion curve of bacteriorhodopsin is given. The measurement error and the effect of the host bovine skin gelatin on the results are analyzed.

Application of the critical angle method to refractive index measurement of human skinin vivounder partial contact

“…6,8,9 On the other hand, the reflectance decreases rapidly as the incident angle decreases from the critical angle. This allows the critical angle to be determined easily and precisely, especially for p-waves.…”

“…[3][4][5] The other class of measurements measures the RI of an area close to a surface and utilizes the relationship between the incident angle and the reflectance. [6][7][8][9][10][11][12] In the case of in vivo measurements of skin, the measurement depth is important because the amount of water varies dramatically with depth, and it generates a gradient in the RI with depth. 13,14 In evaluating the behavior of light at the air-skin interface, the latter class of measurements is more appropriate since those measurements are considered to be sensitive to the ratio of surface reflection to interior reflection.…”

“…Theoretically, the profile should be fitted by the Fresnel equation with a complex RI. 6,7,[10][11][12] RIs have been measured in this manner in recent studies. [10][11][12] We also tried this method but found that it did not work well, which is probably due to errors from other sources.…”

Critical-angle refractometer enhanced by periodic multilayer coating

“…Critical-angle refractometers [3,4], such as classical Abbe refractometers, derive the RI of the sample under investigation by measuring the angle of total internal reflection (TIR) Â TIR from this sample. The sample RI n e is then given by n e = n 0 sin(Â TIR ),…”

Measurement of the complex refractive index of tissue-mimicking phantoms and biotissue by extended differential total reflection method

“…[15][16][17][18][19][20] The differential total reflection method (DTRM) is a modified version of TIR. When the sample has weak absorption or little scattering, an inflexion point of the reflectance curve at the critical angle makes it easy to obtain n r .…”