Abstract
To accurately determine sample optical properties using single fiber reflectance spectroscopy (SFR), an absolute calibration of the reflectance is required. We investigated two SFR calibration methods, using a calibrated mirror and using the Fresnel reflection at the fiber tip as a reference. We compared these to commonly used calibration methods, using either Intralipid-20% in combination with Monte Carlo simulations or Spectralon as a reference. The Fresnel reflection method demonstrated the best reproducibility and yielded the most reliable result. We therefore recommend the Fresnel reflection method for the measured absolute reflectance calibration of SFR.
Highlights
Broadband fiberoptic spectroscopy is investigated for diagnostic applications, e.g., to noninvasively determine tissue scattering and absorption properties
Using the Fresnel reflection method [Eqs. (4) and (5)], the effective index of the fiber was calculated, which differed from the refractive index of fused silica[12] with 1% to 2% (Fig. 2)
R values based on the Fresnel reflection, the calibrated mirror and the Monte Carlo (MC) simulations with both the phase functions were similar
Summary
Broadband fiberoptic spectroscopy is investigated for diagnostic applications, e.g., to noninvasively determine tissue scattering and absorption properties. Spectroscopic instrumentation requires a calibration to account for wavelength-dependent factors, such as the output from the fiber and detector sensitivity. For some diffuse reflectance spectroscopy[1] techniques, a relative calibration of the reflectance is sufficient. For single fiber reflectance spectroscopy (SFR), the measured absolute reflectance R is related to the sample optical properties[2,3]. Where fðμs[0]; μa; γ; dfibÞ describes the reflectance of the sample as a function of the reduced scattering coefficient μs[0], the absorption coefficient μa, a parameter related to the scattering phase function γ, and the fiber diameter dfib. The expected reflectance spectrum[4] of Intralipid-20% is determined using Monte Carlo (MC) simulations, which requires wavelength-dependent optical properties as input
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