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Appendix B: Tutorial on PTTI Frequency Standards
Pages 56-71

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From page 56... ... At room temperature isolated atoms are usually in the lowest state, called the ground state. The ground state may be split into a number of substates of small energy separation, called hyperfine splitting, by interactions of the atomic electrons with the nuclear magnetic moment. Read the entire page →
From page 57... ... However, in gas cell microwave standards or other standards in which atomic collisions occur, collisions shorten the relaxation time and determine the linewidth. In isolated atom microwave standards, the linewidth is roughly proportional to the reciprocal of the interaction time of the electromagnetic field with the atoms. Read the entire page →
From page 58... ... Passive Standards ~7 The atomic resonator described above is used to make a microwave frequency standard, as shown in Figure B.2. The goal is to produce a useful output signal the frequency of which is tied to the atomic resonance at vO. Read the entire page →
From page 59... ... s9 z I ~ o ~ Ir Z a ~ ~ Ir ~:L ma e O 1~1W ~� C' ~ O IL _ _ C' ~ ~ O IL he C' I Ill .~ ? Read the entire page →
From page 60... ... Noisier local oscillators require a longer loop time constant, which is often undesirable. The frequency stability, characterized by the Allan deviation and determined by the noise in the atomic resonator, is approximately 1/(S/ZV Quit, where S/ZV is the effective electrical signal-to-noise ratio in a 1 Hz bandwidth centered at the modulation frequency at the output of the resonator, A is the quality factor mentioned above, and ~ is the averaging time of the measurement. Read the entire page →
From page 61... ... 61 A: A: IL ~ at ~ A: ~ ~ o A: o ~ I In 0 ~ ~ Ir Z I In In A: ~ O hi: I O Z At: � a: ~ In Ir o o o Z A: A: ~ 1 O ~ O A: O ,o,0 ~ ~ O ~ o 5 z c, So o (' N ~ I C' ~ Z IL (A o, o A: ~ lo- 0: ~: O (n ~ o ~� C' ~ ~: O IL C' ~ ~: O IL s~ a~ Cq bC o Cq C) Read the entire page →
From page 62... ... MICROWAVE ATOMIC FREQUENCY STANDARDS Laboratory Cesium Beam These standards use a beam of cesium-133 that is state separated and detected either by magnetic deflection or optical pumping. Optically pumped standards give the best performance. Read the entire page →
From page 63... ... This shift can be estimated by varying the helium pressure, observing the frequency changes, and extrapolating to zero pressure. Hydrogen Maser Molecular hydrogen is dissociated into atoms and state separated in a magnetic field so that the higher energy state atoms are directed into a suitably coated bulb inside a high quality-factor (Qc) Read the entire page →
From page 64... ... Rubidium Gas Cell Rubidium-87 atoms, along with a buffer gas in a glass cell surrounded by a microwave cavity, are optically pumped by light from a rubidium lamp/filter combination to perform state selection between the hyperfine levels. The transmitted pumping light is monitored by a photodetector to provide the electrical output signal. Read the entire page →
From page 65... ... It uses laser cooling and trapping to generate and launch balls of cold, state-selected cesium atoms in a way similar to that described above for the cesium fountain. However, in the microgravity environment of space, the balls are in free, unaccelerated motion and are directed through a Ramsey cavity, like that in the beam apparatus described above, to achieve Ramsey interrogation. Read the entire page →
From page 66... ... Calcium NIST is working on an optical frequency standard using trapped calcium atoms. The clock transition frequency is about 4.54 x 10~4 Hz with a narrow natural linewidth of about 400 Hz. Read the entire page →
From page 67... ... Monitoring the fluorescence or the transmission through the cell does the resonance detection for this type of passive microwave standard. If a cavity tuned to the resonance frequency between the ground states surrounds the cell, microwave power radiated by the atoms can be detected. Read the entire page →
From page 69... ... LOCAL OSCILLATORS Quartz, Rubidium, and Hydrogen Relatively simple quartz oscillators as described above can serve as LOs for many of the lowerperforming atomic standards. The best commercial cesium beam standards require a good OCXO. Read the entire page →
From page 70... ... Another effect involves amplitude modulation of the atomic resonator output that is coherent with frequency modulation of the LO. This can occur, for example, in atomic beam standards as a result of changes in the gravitational acceleration direction caused by motion of a vehicle. Read the entire page →
From page 71... ... By locking one of the comb lines to an optical frequency standard, a microwave frequency is generated that has the same accuracy as the optical standard. The technique for measuring and controlling the offset frequency involves broadening the comb spectrum with a nonlinear optical fiber so that it extends over a two-to-one frequency range, an octave. Read the entire page →

From page 56...

... At room temperature isolated atoms are usually in the lowest state, called the ground state. The ground state may be split into a number of substates of small energy separation, called hyperfine splitting, by interactions of the atomic electrons with the nuclear magnetic moment.

Appendix B: Tutorial on PTTI Frequency Standards Pages 56-71

Appendix B: Tutorial on PTTI Frequency Standards
Pages 56-71