Gaetano Mileti

Laser-pumped rubidium frequency standards: new analysis and progress

We have achieved a stability of 3/spl middot/10/sup -13/ /spl tau//sup -1/2/ for 3</spl tau/<30 s with a laser-pumped rubidium gas-cell frequency standard by reducing the effects due to noise in the microwave and laser sources. This result is one order of magnitude better than the best present performance of lamp-pumped devices.

A compact laser head with high-frequency stability for Rb atomic clocks and optical instrumentation

We present a compact and frequency-stabilized laser head based on an extended-cavity diode laser. The laser head occupies a volume of 200cm3 and includes frequency stabilization to Doppler-free saturated absorption resonances on the hyperfine components of the Rb87D2 lines at 780 nm, obtained from a simple and compact spectroscopic setup using a 2cm3 vapor cell. The measured frequency stability is ⩽2×10−12 over integration times from 1 s to 1 day and shows the potential to reach 2×10−13 over 102−105 s. Compact laser sources with these performances are of great interest for applications in gas-cell atomic frequency standards, atomic magnetometers, interferometers and other instruments requiring stable and narrow-band optical sources.

Experimental demonstration of a compact and high-performance laser-pumped rubidium gas cell atomic frequency standard

The authors present a compact high-performance laser-pumped Rubidium atomic frequency standard exploiting the advantages of laser optical pumping for improved stability. The clock is based on an industrial Rb clock with the lamp assembly removed and optically pumped by light from a compact frequency-stabilized laser head. The modification of the buffer gas filling in the clock resonance cell reduces instabilities on medium-term timescales arising from the ac Stark effect and temperature variations. The frequency stability of the demonstrator clock was measured to be better than 4/spl times/10/sup -12//spl tau//sup -1/2/ up to 10/sup 4/ s, limited by the local oscillator (LO) quartz and RF loop electronics. Long-term drifts under atmosphere amount to 2-6/spl times/10/sup -13//day only, comparable to or lower than that for lamp-pumped clocks under similar conditions. Typical signal contrasts lie at around 20%, corresponding to a shot-noise limit for the short-term stability of 2/spl times/10/sup -13//spl tau//sup -1/2/. The results clearly demonstrate the feasibility of a laser-pumped Rb clock reaching <1/spl times/10/sup -12//spl tau//sup -1/2/ in a compact device (< 2 L, 2 kg, 20 W), given the optimization of the implemented techniques. Compact high-performance clocks of this kind are of high interest for space applications such as telecommunications, science missions, and future generations of satellite navigation systems [GPS, global orbiting navigation satellite system (GLONASS), European satellite navigation system (GALILEO)].

Microfabricated rubidium vapour cell with a thick glass core for small-scale atomic clock applications

This paper presents a new fabrication method to manufacture alkali reference cells having dimensions larger than standard micromachined cells and smaller than glass-blown ones, for use in compact atomic devices such as vapour-cell atomic clocks or magnetometers. The technology is based on anodic bonding of silicon and relatively thick glass wafers and fills a gap in cell sizes and technologies available up to now: on one side, microfabrication technologies with typical dimensions <= 2 mm and on the other side, classical glass-blowing technologies for typical dimensions of about 6-10 mm or larger. The fabrication process is described for cells containing atomic Rb and spectroscopic measurements (optical absorption spectrum and double resonance) are reported. The analysis of the bonding strength of our cells was performed and shows that the first anodic bonding steps exhibit higher bonding strengths than the later ones. The spectroscopic results show a good quality of the cells. From the double-resonance signals, we predict a clock stability of approximate to 3 x 10(-11) at 1 s of integration time, which compares well to the performance of compact commercial Rb atomic clocks.

Compact microwave cavity for high performance rubidium frequency standards

The design, realization, and characterization of a compact magnetron-type microwave cavity operating with a TE(011)-like mode are presented. The resonator works at the rubidium hyperfine ground-state frequency (i.e., 6.835 GHz) by accommodating a glass cell of 25 mm diameter containing rubidium vapor. Its design analysis demonstrates the limitation of the loop-gap resonator lumped model when targeting such a large cell, thus numerical optimization was done to obtain the required performances. Microwave characterization of the realized prototype confirmed the expected working behavior. Double-resonance and Zeeman spectroscopy performed with this cavity indicated an excellent microwave magnetic field homogeneity: the performance validation of the cavity was done by achieving an excellent short-term clock stability as low as 2.4 × 10(-13) τ(-1/2). The achieved experimental results and the compact design make this resonator suitable for applications in portable atomic high-performance frequency standards for both terrestrial and space applications.

Pseudoresonance mechanism of all-optical frequency-standard operation

We propose an approach to all-optical frequency standard design, based on a counterintuitive combination of the coherent population trapping effect and signal discrimination at the maximum of absorption for the probe radiation. The short-term stability of such a standard can achieve the level of

Microfabricated alkali vapor cell with anti-relaxation wall coating

{10}^{\ensuremath{-}14}∕\sqrt{\ensuremath{\tau}}

Recent progress in laser-pumped rubidium gas-cell frequency standards

. The physics beyond this approach is a dark resonance splitting caused by the interaction of the nuclear magnetic moment with the external magnetic field.

Demonstration of a high-performance pulsed optically pumped Rb clock based on a compact magnetron-type microwave cavity

We present a microfabricated alkali vapor cell equipped with an anti-relaxation wall coating. The anti-relaxation coating used is octadecyltrichlorosilane and the cell was sealed by thin-film indium-bonding at a low temperature of 140 °C. The cell body is made of silicon and Pyrex and features a double-chamber design. Depolarizing properties due to liquid Rb droplets are avoided by confining the Rb droplets to one chamber only. Optical and microwave spectroscopy performed on this wall-coated cell are used to evaluate the cells relaxation properties and a potential gas contamination. Double-resonance signals obtained from the cell show an intrinsic linewidth that is significantly lower than the linewidth that would be expected in case the cell had no wall coating but only contained a buffer-gas contamination on the level measured by optical spectroscopy. Combined with further experimental evidence this proves the presence of a working anti-relaxation wall coating in the cell. Such cells are of interest for applications in miniature atomic clocks, magnetometers, and other quantum sensors.

Low-temperature indium-bonded alkali vapor cell for chip-scale atomic clocks

This paper presents the current results of our development of a laser-pumped passive rubidium frequency standard. With a vapor cell containing isotopic Rb/sup 87/ and a mixture of buffer gas we obtained a double resonance signal compatible with a short-term stability of 2.10/sup -13/ /spl tau//sup -1/2/ (shot noise limit). Measurements of the effect of the interrogating phase noise demonstrated that our microwave synthesizer did not limit this potential short-term stability. Two types of monochromatic light source lasers have been used: broad-band solitary lasers and extended cavity lasers. We found that their main limitation on the frequency stability was due to the AM noise detected by the photocell. In order to improve the S/N of the clock, an all-electronic AM noise cancellation technique has been successfully employed. Light-shift measurements allowed tuning of the laser frequency to the zero light-shift point. Presently, our clock has a short-term stability of 7.10/sup -13/ /spl tau//sup -1/2/ (2</spl tau/<40 s) with the solitary laser and 5.10/sup -13/ /spl tau//sup -1/2/ (4</spl tau/<40 s) with the extended cavity laser. These are the best reported performances for passive rubidium clocks.