Dimensionality Crossover in the Organic Superconductor Tetramethyltetraselenafulvalene Hexafluorophosphate [${\mathrm{}\left(\mathrm{TMTSF}\right)\mathrm{}}_2$P${\mathrm{F}}_6$]

Polarized reflectance measurements from the far infrared to the visible are reported for ${\mathrm{}\left(\mathrm{TMTSF}\right)\mathrm{}}_2$P${\mathrm{F}}_6$. At low temperatures, both parallel and perpendicular polarizations show plasma edges in the infrared with metallic reflection below these edges, indicating two- or three-dimensional behavior. The transverse plasma frequency is $\sim \frac{1}{5}$ of the parallel plasma frequency. At higher temperatures, the plasmon in the perpendicular polarization becomes highly overdamped, indicating a crossover to one-dimensional behavior.