An interferometer returns parallel beams that are subject to walk-off caused by reflector misalignment for an additional pass through the interferometer optics and thereby eliminates beam walk-off. In a base section of a turbo molecular pump, a bottom portion thereof is sealed by a bottom cover. By virtue of the crystalline metal oxide shells, the core nanoparticle made of metal or semiconductor can ensure excellent chemical and mechanical stability, and the core-shell nanoparticles can show new properties resulting from the interaction between the metal cores and the metal oxide crystal shells. Wavefields can then be analyzed separately in either time or frequency domains and analyzed or integrated with other data. The density of fins is also increased and the heat dissipating efficiency is improved.