Contribution of unbound modes to light absorption in visual photoreceptors

Only a portion of the light incident upon a photoreceptor is transmitted in discrete bound modes (corresponding to rays undergoing total internal reflection). In this paper, we examine the contribution of the remaining unbound modes (corresponding to rays undergoing partial reflection) to total absorption in the photoreceptor. It is found that the unbound mode contribution is generally very small but that in short photoreceptors with dimensionless frequency, V, approximately equal to one (the central rhabdomeres of the fly rhabdom, for example), this radiation component cannot be dismissed.