Broadband spectral measurements of diffuse optical properties by an integrating sphere instrument at the National Institute of Standards and Technology

Diffuse materials that approximate the optical properties of human tissue are commonly used as phantoms. In order to use the phantoms in a manner that provides consistent results relative to independent measurements, the optical properties need to be tied to a physics based scale. Such a scale is needed for volume scattering of diffuse materials and this is currently being addressed by the development of a sphere based optical scattering reference instrument at the National Institute of Standards and Technology (NIST). Previous work towards that goal was constrained to the use of several laser lines at discrete wavelengths. Current work has expanded the spectral range for contiguous coverage. Here we report measurement results of the optical properties of solid phantoms, using two different base materials, acquired using NISTs diffuse optical properties reference instrument with visible or near infrared broadband illumination. The measurements of diffuse hemispherical reflectance and transmittance are analyzed using a custom inversion algorithm of the adding-doubling routine, and the expanded uncertainties on the results are provided. The broadband diffuse optical properties measured with the improved system agree to within the estimated uncertainty of the discrete measurements from two other institutes using alternative methods. This work expands the capabilities of the facility and can provide services for a wider range of applications.