One major use of the integrating sphere technique is for measurements of diffuse reflectance and diffuse transmittance of turbid samples. In this technique, a sphere with inner surface made of rough and highly reflecting materials or coating is used to redistribute the reflected light (for reflectance measurements) or transmitted light (for transmittance measurements) from a turbid sample homogeneously over the inner spherical surface. This enables the measure of diffusely reflected and diffusely transmitted light with no need to accurately align the sample and detector. For this purpose, three openings or ports are made on the sphere with sample assembled to one port. This port and another opposing port are used to admit an incident light beam and allow the forward component of the transmitted light to escape. The third port is for light detector.
In the Biomedical Laser Laboratory, we has constructed an integrating sphere systems for measurements of diffused reflectance and transmittance of turbid samples, such as intralipid and skin tissue samples, over a wide range of spectrum from 300 to 1700nm with low-power non-coherent light sources. These systems are equipped with multiple light sources and monochromoters to provide the tunable illumination in the wide spectral range and light modulator and lock-in amplifier for extraction weak signals from the light detectors.
