Abstract
Recent c axis-polarized infrared measurements in the high-transition temperature (high- T c ) cuprate superconductor (La,Sr) 2 CuO 4 can be interpreted on the basis that the entire condensation energy comes from the interlayer Josephson coupling. This gives a parameter-free determination of penetration depth λ and coherence length ξ for this superconductor that are in agreement with experiment.