Absolute reflectometer for the 0.8-2.5-microm region

Reflectometers for Absolute and Relative Reflectance Measurements in the Mid-IR Region at Vacuum

We demonstrated spectral reflectometers for two types of reflectances, absolute and relative, of diffusely reflecting surfaces in directional-hemispherical geometry. Both are built based on the integrating sphere method with a Fourier-transform infrared spectrometer operating in a vacuum. The third Taylor method is dedicated to the reflectometer for absolute reflectance, by which absolute spectral diffuse reflectance scales of homemade reference plates are realized. With the reflectometer for relative reflectance, we achieved spectral diffuse reflectance scales of various samples including concrete, polystyrene, and salt plates by comparing against the reference standards. We conducted ray-tracing simulations to quantify systematic uncertainties and evaluated the overall standard uncertainty to be 2.18% (k = 1) and 2.99% (k = 1) for the absolute and relative reflectance measurements, respectively.

Optical diffuse reflectance accessory for measurements of skin tissue by near-infrared spectroscopy

An optimized accessory for measuring the diffuse reflectance spectra of human skin tissue in the near-infrared spectral range is presented. The device includes an on-axis ellipsoidal collecting mirror with efficient illumination optics for small sampling areas of bulky body specimens. The optical design is supported by the results of a Monte Carlo simulation study of the reflectance characteristics of skin tissue. Because the results evolved from efforts to measure blood glucose noninvasively, the main emphasis is placed on the long-wavelength near-infrared range where sufficient penetration depth for radiation into tissue is still available. The accessory is applied for in vivo diffuse reflectance measurements.

Absolute measurements of diffuse reflectance in the alpha degrees /d configuration

An improved theory for data reduction of absolute reflectance measurements using the third Taylor method in the alpha degrees / d configuration is presented. A brief description is given of an absolute reflectometer operating in the 0.8-2.5-microm region. The reflectometer is operated according to the improved theory. Experimental data for some widely used samples are given, as well as data showing agreement between the current measurements and those made by the U.S. National Institute of Standards and Technology.

Absolute reflectometer for the mid infrared region

An absolute reflectometer for the 0.8-5.5-mum wavelength region is described. It is based on integrating spheres and uses the third Taylor method in the 7 degrees /d configuration. An improved theory for the reduction of the data is presented, and results for several diffuse gold samples are given.