A. Bebeachibuli

The Brazilian time and frequency atomic standards program

Cesium atomic beam clocks have been the workhorse for many demanding applications in science and technology for the past four decades. Tests of the fundamental laws of physics and the search for minute changes in fundamental constants, the synchronization of telecommunication networks, and realization of the satellite-based global positioning system would not be possible without atomic clocks. The adoption of optical cooling and trapping techniques, has produced a major advance in atomic clock precision. Cold-atom fountain and compact cold-atom clocks have also been developed. Measurement precision of a few parts in 10(15) has been demonstrated for a cold-atom fountain clock. We present here an overview of the time and frequency metrology program based on cesium atoms under development at USP São Carlos. This activity consists of construction and characterization of atomic-beam, and several variations of cold-atom clocks. We discuss the basic working principles, construction, evaluation, and important applications of atomic clocks in the Brazilian program.

Comparative short-term stability for a Cs beam and an expanding cold atomic cloud of Cs used as atomic frequency standards

We have compared the stability of two distinct atomic frequency standards. One is based on an atomic cold cloud of 133Cs atoms in free expansion, interrogated by a Rabi resonance. The other standard is based on a thermal Cs beam interrogated by the separated oscillatory field method (Ramsey’s method). The atomic expanding cloud standard shows better stability and technical advances based on its simplicity.

Demonstration and Observation of a Frequency Standard Based on an Expanding Cold Atoms Cloud of Cesium

This work reports the first results obtained in a laboratory system implemented to be a primary standard based on an expanding cloud of cold 133Cs. An atomic sample is prepared through the magneto-optical trapping technique, and after the loading procedure the atomic cloud is left to freely expand. A microwave interrogation signal is applied to the atoms, probing them in the ground state transition 6S1/2(F = 3)- 6S1/2(F = 4). The microwave interrogation was applied either in one or two pulses methods. The system could be also locked in a commercial standard to perform its stability evaluation. The first results showed a stability of 9times10 -11 tau-frac12, promising for such use of simple type of frequency standard

The Brazilian Atomic Fountain Primary Frequency Standard

From some years our group has been investing efforts to develop a Caesium atomic fountain system to operate as a frequency standard. Our most recent results concern the observation of the first Ramsey resonance and we also performed a characterization of it. We discuss the main characteristics of our system and the improvements on planning

Brazilian microwave standards of Time and Frequency

Time and Frequency scientific metrology is a necessary component of many important scientific and technological applications. A few years ago we have started an effort to establish a Brazilian Laboratory for the development of atomic clocks. In this communication a progress report of our activities is described, providing present status and future perspectives. The original goal is the construction and characterization of a Fountain as well as alternative frequency references based on cold atoms. Along the past years such goals were achieved with a Cs Fountain operation, which improvement and characterization is presently under progress. In another experiment, interrogation of a cold atomic cloud in free expansion was demonstrated and the implementation of a new chamber overcoming some limitations is now in course. Finally, a system based on a composition of commercial clocks and a hydrogen maser is being assembled to define a local timescale and to provide a link for future contributions to TAI.

Measurement of the absolute total electron impact cross section on Cs atoms using a magnetooptical trap

Laser cooling and trapping of neutral atoms has been employed for the measurement of the total electron impact cross sections of the ground state 62S1/2 of 133Cs atoms in the energy range from 80 to 500 eV. The total electron impact cross sections of the cold Cs atoms in the MOT were measured by observing the decay of the MOT after the interaction with the electron beam, and were found to depend only on the electron flux and not on the total number of atoms in the MOT. We confirm and extend the existing data on these measurements.

Characterization of the frequency pulling by magnetic field oscillations of the Brazilian /sup 133/Cs atomic-frequency standard

In this work, we present a progress report made on the Brazilian scientific time and frequency program. In the last evaluation comparing our frequency standard with a HP 5061-B we have obtained the Allan standard deviation /spl sigma//sub y/(T=)(1.62/spl plusmn/0.08)x10/sup -11//spl tau//sup -0.5/. We have applied the method described by Makdissi et al. and Shirley et al to determine the major frequency shifts like, the second-order Zeeman shift, magnetic field inhomogeneity along the rf-cavity, Rabi and cavity pulling, in order to characterize our standard.