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Figure 10: The optical design of the external DRA.

Integrating sphere

An integrating sphere is an optical device used to collect and measure electromagnetic

radiation. The radiation sampled by the DRA integrating sphere is provided by the

spectrophotometer reference and sample beams present inside the sample compartment.

Upon entering the sphere, the light strikes the sample surface and the highly reflective

walls of the cavity, undergoing many diffuse reflections. Radiation trapped inside the

sphere cavity can dissipate by a combination of three ways. Most of the light eventually

is absorbed into the sphere walls. Some of the light exits the cavity through one of the

empty ports, and a small portion of the trapped radiation strikes the active surface of the

sphere detector. A steady state radiant flux distribution is established almost

instantaneously within the sphere and remains as long as the beam source is active. All

integrating spheres possess one unique property with regard to a steady-state flux: the

radiance all along the wall surface of the sphere is uniform and proportional to the flux of

the source input. The sphere detector samples the radiance at the wall surface and relays

the detector signal to the spectrophotometer for processing.

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