P. Cerez

Investigation of microwave π transitions in cesium beam clocks operated with U‐shaped H plane waveguide cavities

In this article, we present the characteristics of the ΔF=±1, ΔmF=±1, π microwave transitions which appear in the response of cesium beam resonators operating with U‐shaped waveguide Ramsey cavities bent in the plane of the H field. Such resonances are due to the presence in the cavity of microwave magnetic induction perpendicular to the static field direction. It is shown that the π resonance feature is derived from a pure two‐level atomic system interacting with four spatially separated oscillating fields. Good agreement is found between experimental data and theoretical predictions when we take into account the actual transverse microwave field profile in the cavity obtained with tridimensional electromagnetic field computations.

An 850 nm semiconductor laser tunable over a 300 Å range

Abstract We have designed and realized a compact external cavity semiconductor laser operating around 850 nm. The main characteristics are the following: a 32 nm tuning range, a stable single mode operation always attainable in this range and a linewidth of a few hundred kilohertz. This spectral purity improvement is the result of an increased photon lifetime in the external cavity. The potentiality of this solid state laser source is finally underlined.

Ground state Zeeman coherence effects in an optically pumped cesium beam

Abstract The population trapping in a cesium beam induced at low magnetic field by σ polarized light from a broadband laser diode has been investigated. The dip observed in the fluorescence is interpreted in terms of Zeeman coherences in the ground state which trap the atomic populations. A quantitative description is given through the analysis of the atom light interaction with a rate equation model including Zeeman coherences.

Hyperfine structure in Iodine at the 612-nm and 640-nm helium-neon laser wavelengths

Abstract The hyperfine structure of iodine-127 at 612 nm and 640 nm is observed by saturated absorption in a gas cell placed within a He-Ne laser cavity modified to operate at these wavelengths. At 612 nm, all the 21 components of the strong R 47 9-2 line lie within the laser gain profile, and the resulting saturated absorption peaks have a contrast of 10% at a gas pressure of 3 Pa.

Measurement of the Signal-to-noise Ratio in an Optically Pumped Caesium-beam Frequency Standard

We have measured a figure of merit for a caesiumbeam frequency standard in which optical pumping and optical detection are accomplished by a single semiconductor laser source. The value of this figure of merit is 29, leading to an estimated fractional frequency stability of 2.6 × 10-12 τ-1/2. This result compares very favorably with the frequency stability of the best manufactured caesium-beam frequency standards.

New Absolute Wavenumber Measurement of the D2 Line of Caesium

A new interferometric measurement of the caesium D2 resonance line wavenumber has been performed. The source is a diode laser stabilized on the fluorescence light of a caesium beam. Its wave number is measured with an improved interferometric wavemeter (lambdameter). The σD2 wavenumber is determined with an accuracy of 3.5 × 10-8.

Comparison of pumping a cesium beam tube with D1 and D2 lines

The operation of a cesium beam tube optically pumped with cesium D1 and D2 lines is theoretically and experimentally investigated. In a single laser diode configuration using the D2 line, the most efficient excitation scheme is found to be the 3→3σ(D2) scheme leading to a clock signal‐to‐noise ratio equal to 15 000 in a one‐hertz bandwidth. In the case of the D1 line, the predicted best excitation schemes are the 4→3π(D1) and the 4→3σ(D1) schemes. However, these two configurations lead to an extra fluorescence noise presumably due to unpumped atoms. The 3→4π(D1) scheme is experimentally found to be the best with S/N performances comparable to the 3→3σ(D2) configuration. Nevertheless, in the case of the 3→3σ(D2) scheme, optical pumping efficiency decreases when the magnetic field is too low whereas 3→4π(D1) features are independent of the magnetic‐field amplitude. Moreover, the well‐separated fluorescence lines in the case of the D1 line allow a more accurate locking of the laser frequency on the top of th...

Frequency stability of an optically pumped cesium beam frequency standard

Results obtained in an experimental optically pumped cesium beam frequency standard in which a single semiconductor laser is used for the state selection and the atom detection are reported. The separation between the two interaction regions is equal to 21 cm. This gives a 500 Hz linewidth which is observed with a signal to noise ratio equal to 10,000 in a 1 Hz noise bandwidth. A quartz crystal oscillator is frequency controlled by the atomic transition. The measured short term frequency stability is given by σy(τ)=2×10−12τ−1/2 for 1 s<τ≲500 s. Prospects for improvement of this frequency stability are discussed.

Noise in the optical detection of atoms in a beam

Abstract The noise processes which affect the optical detection of atoms in a beam are identified. A noise factor of the atom to fluorescence photon conversion is defined in the case where the counting statistics of the fluorescence photons can be assumed poissonian. The signal to noise ratio of the atom detection is given in the case where a photomultiplier or a silicon photocell is used. It is shown that the noise added to the actual atomic beam shot noise can be represented in terms of the shot noise of an equivalent fictitious flux of incident atoms. Results given are applied to the optical detection of cesium atoms.

Frequency Locking Of A 850 nm External-Cavity Semiconductor Laser On A Doppler-Free Cs-D 2 Line

Preliminary experimental results concerning frequency stabilization of a 850 nm external-cavity semi-conductor laser on the cesium D2 absorption line using a simple saturated absorption technique are presented. The relative frequency stability reaches 10-12 over a 1 sec. averaging time.