Absolute Measurement with an Integrating Sphere

In this equation, I, is the integrated emission spectmm of the sphere with the excitation bean hitting the sample, is the integrated emission spectmm of the sphere with the sample with the excitation beam hitting the sphere wall but not the sample, and is the integrated excitation spectmm of the integrating sphere with the sample holder. The absorption coefficient a of the sample is defined as 

is the integrated excitation spectrum of the sphere with the sample with the excitation beam hitting the sphere wall but not the sample and is the integrated excitation 

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