Amplitude transmittance
= Amplitude transmittance
{title2=$t=U_{\rm out}/U_{\rm in}$}
<Amplitude transmittance> is the local ratio of transmitted to incident <complex amplitude> in a thin optical-element model. It includes <wave phase> as well as attenuation. For identical incident and transmitted media at normal incidence, the corresponding intensity <transmittance> is $|t|^2$; $t$ itself is not the transmitted <power> fraction. A pure <phase screen> has $|t|=1$.