Subcompact hydrogen maser atomic clocks

Article Abstract:

Compact hydrogen maser atomic frequency clocks have been developed based on both active and passive designs that offer frequency drift rates of no more than 1 x 10(superscript -15) per day. Hydrogen masers currently offer the outstanding short-term stability for critical timing applications such as critical timing references for NASA's Deep Space Network, the NIST and US Naval Observatory standard clocks, and for very long baseline interferometry studies. Hughes Research Laboratories has developed a series of subcompact active hydrogen lasers based on a Q-enhanced master oscillator, while the NIST has developed a compact passive hydrogen maser. Both are described at length. Improvements in stability performance, size, and weight of the devices is expected. The history and basic principles of the atomic hydrogen maser are briefly described.

Trends, Scientific Research, Clocks, Oscillators, technical, Timing Circuitry

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Time and frequency in fundamental metrology

Article Abstract:

Modern science and technology are increasing demands on time and frequency measurements in metrology. The International System of Units (SI) is used almost universally. SI embodies seven base units: time, length, mass, quantity of electricity, thermodynamic temperature, amount of substance and luminous intensity. The three time units in the SI are the second, the hertz and the becquerel. The ability to accurately measure the second is far ahead of the other units. It may be important, in the future, to distinguish between a time standard and a frequency standard; the latter does not need to operate continuously. General and special relativity need to be better accounted for. There are probably seven or more orders of magnitude to go before reaching ultimate accuracy limits for frequency measurement; probably by the end of the next century.

Standard, Standardization, Time measurement, Technology, Science, Physics, Technical

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