Actually, now that you bring it up... it's not conventional for laser (read this as holography) setups to be done on metal, anyway. They're usually done on a granite or composite bed "floating" in a sand tray. Metal is too unstable thermally to suit.
Even the smallest assymetrical temperature changes on the surface of a metal plate would kill his alignment precision. It would only work in a perfectly stabile temperature environment with no moving air.
LLoyd