Signedname plate: H-10 ATOMIC HYDROGEN MASER / HEWLETT PACKARD SERIAL NO.6. stored with 1990-1-0004b on B18-E5.
Inscribedplaque marked SMITHSONIAN INSTITUTION / 89079
FunctionThis is among the first commercial models of atomic clocks, and the first based on atomic hydrogen. It remains one of the most accurate timekeeping systems available.
It works by inducing and amplifying the emission of a very specific radiation frequency by atomic hydrogen (hyperfine transition: 1420.405 GHz). In order to do this, the machine first has to select hydrogen atoms (from the gas cylinder) in the appropriate energy state by passing them through especially designed magnets inside the black cylinder of the rectangular case. The selected atoms are then led into a quartz cavity coated in teflon that would be inside the metallic grey cylinder (now stored separately as 1990-7-0004b). There they are exposed to microwave radiation close to their emission frequency, making them start emitting themselves. The produced radiation has a very definite frequency and is picked up, converted to an electronic signal and made available by a socket on the control panel.
One can easily use this frequency signal as the basis for a very accurate clock.
For a more detailed description of this instrument, see the article by its developer, Norman F. Ramsey, "The Atomic Hydrogen Maser", Metrologia 1 (1965): 7-14.
Historical AttributesThis is the commercial version [one of the first production units] of the hydrogen maser developed at Harvard University by H. M. Goldenberg, D. Kleppner and N. F. Ramsey.
Starting in the 1960s, Robert Vessot, at the Smithsonian Astrophysical Observatory, together with seveal colleagues including Norman Ramsey, the creator of the Maser, developed the atomic clock based on it. This is likely one of the hydrogen masers that was used in the early stages of this development.
Primary SourcesNorman F. Ramsey, "The Atomic Hydrogen Maser", Metrologia 1 (1965): 7-14.
ProvenanceAcquired 12/10/90 from Dr. Robert Vessot's lab, Harvard/Smithsonian Astrophysical Observatory.
Published ReferencesFor an article describing the development of atomic clocks from masers at the Smithsonian Astrophysical Observatory see: Marcia Bartusiak, "The Ultimate Timepiece", in Discover Magazine, May 1981, pp 78-83. Available online here.
A mention of Ramsay's participation in the development of atomic clocks is found on his autobiography, available online here.