Quantitative spectrophotometry of scattering media via frequency-domain and constant-intensity measurements.
The attenuation of light by scattering and absorbing media is nonlinearly dependent upon the absorption coefficient, since detected light has experienced many different flight times. The frequency response of such a sample to modulated light is also nonlinear. We derive an expression for the attenuation that includes both the absorption coefficient and the modulation frequency. Its form is a power series whose coefficients are the cumulants of the temporal point-spread function (TPSF). Recasting this expression in terms of intensity leads to a similar expression with the cumulants replaced by the moments of the TPSF. A means of exploiting this relationship to produce estimates of the absolute concentration of the absorbing species is suggested.
Crowe
John
J
Applied Optics Group, School of Electrical and Electronic Engineering, University of Nottingham, UK. john.crowe@nottingham.ac.uk
Morris
David
D
Woolfson
Malcolm
M
Rodmell
Paul
P
Walker
John
J