A light filter is a plate of thickness d whose absorption coefficient depends on wavelength , as x() = a(1 / 0)2cm 1, where

A light filter is a plate of thickness d whose absorption coefficient depends on wavelength λ, as x(λ) = a(1 – λ/ λ0)2cm –1, where a and λo are constants. Find the pass band ∆λ, of this light filter, that is the band at whose edge the attenuation of light is η times that at the wavelength Xo. The coefficient of reflection from the surfaces of the light filter is assumed to be the same at all wavelengths.