Demonstration of partially transparent thick metallic sodium in the vacuum ultraviolet spectral range: comment.

In a previous publication [Opt. Express21, 28182 (2013)10.1364/OE.21.028182], Daido et al. reported that solid samples of metallic sodium exhibited high transparency of vacuum ultraviolet light through several millimeter-thick samples. The calculated extinction coefficient associated with these observations was near 7E-7, over 4 orders of magnitude lower than previous measurements. In this paper, we will compare the phenomenon reported by Daido et al. with the existing literature to establish that there is no peer-reviewed support for the observations. Further, this paper will discuss a rigorous experimental campaign that failed to replicate the transmission phenomenon observed by Daido et al.