Real part of refractive index measurement approach for absorbing liquid

Abstract

An algorithm based on use of a reflected refractometer to measure the real part of the refractive index (RI) for an absorbing liquid is presented. The absorption of liquid will blur the division between bright and dark regions on a Fresnel reflective curve. However, the reflective ratio at some incident angles that are less than the critical angle have little sensitivity to absorbability. Unlike common methods that extract RI from reflectivity in critical angle vicinity, the presented method acquires the real RI from reflective ratio at a subcritical angle. Supported by the theoretical analysis and experimental results on a reflected refractometer, we have achieved accuracy better than 3×10(-4) RIU on ink samples with absorption coefficient around 300 cm(-1). Additional tests on Alizarin yellow GG solutions prove that the subcritical algorithm is feasible and of high accuracy.

Spectral refractive index assessment of turbid samples by combining spatial frequency near-infrared spectroscopy with Kramers–Kronig analysis

“…This phase-shift method has been considered as an essential technique to extract the phase information [Eq. (7)] and employs only simple arithmetic operations. The phase map ϕðx; yÞ calculated by Eq.…”

“…4 In the context of biomedical optics, n is related to the scattering coefficient (μ s ), 5 whereas the imaginary part (k) is connected to absorption coefficient (μ a ) as given by: k ¼ λμ a ∕4π. 6,7 Therefore, exploiting the changes in CRI parameters can provide useful information regarding the sample's physiological properties during diagnostic or treatment procedures. Overall, the independent derivation of n and k values, as well as the determination of scattering and absorption as functions of wavelength, can provide a comprehensive battery of biochemical, morphological, and histochemical parameters of biological tissue.…”

Critical-Angle Differential Refractometry of Lossy Media: A Theoretical Study and Practical Design Issues

“…An indicative yet far from exhaustive list of sensing mechanisms relies on plasmonic [8][9][10][11], photonic crystal [12][13][14][15], micro-cavity [16][17][18][19], optical fiber [20][21][22][23] and wave-guide [24][25][26][27] configurations. Associated with Fresnel reflectance properties at planar interfaces, differential refractometry offers an alternative path to sensing refractive index changes, by exploitation of interference [28], deflection [29] or (more relevant to the present work) critical-angle [30][31][32][33][34][35] effects. Today, differential refractometry is not only a standard analytical tool that operates routinely in many laboratories, but also infiltrates emerging optofluidic and lab-on-chip technologies [36][37][38].…”

Determination of the complex refractive index segments of turbid sample with multispectral spatially modulated structured light and models approximation

“…There are several approaches to derive sample refractive index, including refractometers, optical coherence tomography, total internal reflection, focused scanning microscopy, ellipsometry, etc., each with its own advantages and disadvantages. [31][32][33] However, the extraction of CRI information through spatially modulated illumination differs from the aforementioned methods and grants additional capabilities to this technique by enlarging its measurement range, as elaborated in this work.…”