Vladislav Gerginov

A strontium lattice clock with 3 × 10 −17 inaccuracy and its frequency

We have measured the absolute frequency of the optical lattice clock based on 87Sr at PTB with an uncertainty of 3.9 × 10−16 using two caesium fountain clocks. This is close to the accuracy of todayʼs best realizations of the SI second. The absolute frequency of the 5 s2 1S0 – 5s5p 3P0 transition in 87Sr is 429 228 004 229 873.13(17) Hz. Our result is in excellent agreement with recent measurements performed in different laboratories worldwide. We improved the total systematic uncertainty of our Sr frequency standard by a factor of five and reach 3 × 10−17, opening new prospects for frequency ratio measurements between optical clocks for fundamental research, geodesy or optical clock evaluation.

Atomic vapor cells for chip-scale atomic clocks with improved long-term frequency stability

A novel technique for microfabricating alkali atom vapor cells is described in which alkali atoms are evaporated into a micromachined cell cavity through a glass nozzle. A cell of interior volume 1 mm3, containing 87Rb and a buffer gas, was made in this way and integrated into an atomic clock based on coherent population trapping. A fractional frequency instability of 6 x 10(-12) at 1000 s of integration was measured. The long-term drift of the F=1, mF=0-->F=2, mF=0 hyperfine frequency of atoms in these cells is below 5 x 10(-11)/day.

High resolution spectroscopy with a femtosecond laser frequency comb

The output of a mode-locked femtosecond-laser is used for high resolution spectroscopy of Cs in an atomic beam. The laser is referenced directly to a stable RF signal from the NIST time-scale. By changing the lasers repetition rate, the Cs D/sub 1/ and D/sub 2/ transitions are detected with high resolution.

Direct frequency comb spectroscopy

We summarize recent developments in direct frequency-comb spectroscopy that allowed high-resolution, broad-bandwidth measurements of multiple atomic and molecular resonances using only a phase-stabilized femtosecond laser, opening the way for merging precision spectroscopy with coherent control.

Wafer-level filling of microfabricated atomic vapor cells based on thin-film deposition and photolysis of cesium azide

The thin-film deposition and photodecomposition of cesium azide are demonstrated and used to fill arrays of miniaturized atomic resonance cells with cesium and nitrogen buffer gas for chip-scale atomic-based instruments. Arrays of silicon cells are batch fabricated on wafers into which cesium azide is deposited by vacuum thermal evaporation. After vacuum sealing, the cells are irradiated with ultraviolet radiation, causing the azide to photodissociate into pure cesium and nitrogen in situ. This technology integrates the vapor-cell fabrication and filling procedures into one continuous and wafer-level parallel process, and results in cells that are optically transparent and chemically pure.

Microfabricated atomic frequency references

Using microfabrication processes, we have been able to construct physics packages for vapour cell atomic frequency references 100× smaller than previously existing versions, with a corresponding reduction in power consumption. In addition, the devices offer the potential for wafer-level fabrication and assembly, which would substantially reduce manufacturing costs. It is anticipated that a complete frequency reference could be constructed based on these physics packages with a total volume below 1 cm3, a power dissipation near 30 mW and a fractional frequency instability below 10−11 over time periods from hours to days. Such a device would enable the use of atomically precise timing in applications that require battery operation and portability, such as hand-held global positioning system receivers and wireless communication systems.

Long-term frequency instability of atomic frequency references based on coherent population trapping and microfabricated vapor cells

We present an evaluation of the long-term frequency instability and environmental sensitivity of a chip-scale atomic clock based on coherent population trapping, particularly as affected by the light-source subassembly. The long-term frequency stability of this type of device can be dramatically improved by judicious choice of operating parameters of the light-source subassembly. We find that the clock frequency is influenced by the laser-injection current, the laser temperature, and the rf modulation index. The sensitivity of the clock frequency to changes in the laser-injection current or the substrate temperature can be significantly reduced through adjustment of the rf modulation index. This makes the requirements imposed on the laser-temperature stabilization, in order to achieve a given frequency stability, less severe. The clock-frequency instability due to variations in local oscillator power is shown to be reduced through the choice of an appropriate light intensity inside the cell. The importance of these parameters with regard to the long-term stability of such systems is discussed.

Femtosecond frequency comb measurement of absolute frequencies and hyperfine coupling constants in cesium vapor

We report measurements of absolute transition frequencies and hyperfine coupling constants for the 8S{sub 1/2}, 9S{sub 1/2}, 7D{sub 3/2}, and 7D{sub 5/2} states in {sup 133}Cs vapor. The stepwise excitation through either the 6P{sub 1/2} or 6P{sub 3/2} intermediate state is performed directly with broadband laser light from a stabilized femtosecond laser optical-frequency comb. The laser beam is split, counterpropagated, and focused into a room-temperature Cs vapor cell. The repetition rate of the frequency comb is scanned and we detect the fluorescence on the 7P{sub 1/2,3/2{yields}}6S{sub 1/2} branches of the decay of the excited states. The excitations to the different states are isolated by the introduction of narrow-bandwidth interference filters in the laser beam paths. Using a nonlinear least-squares method we find measurements of transition frequencies and hyperfine coupling constants that are in agreement with other recent measurements for the 8S state and provide improvement by 2 orders of magnitude over previously published results for the 9S and 7D states.

A Local Oscillator for Chip-Scale Atomic Clocks at NIST

We describe the first local oscillator (LO) that demonstrates viability in terms of performance, size, and power, for chip-scale atomic clocks (CSAC) and has been integrated with the physics package at the National Institute of Standards and Technology (NIST) in Boulder, CO. This voltage-controlled oscillator (VCO) achieves the lowest combined size, DC power consumption, phase noise, and thermal frequency drift among those previously reported, while achieving a tuning range large enough to compensate for part tolerances but small enough to permit precision locking to an atomic resonance. We discuss the design of the LO and the integration with the NIST physics package

A microfabricated photonic magnetometer

An integrated optically-controlled sensor, suitable for remote, high-sensitivity detection of magnetic fields, is presented. The sensor head is free of electrical currents or metal parts, which largely eliminates any spurious fields created by the sensor itself. We demonstrate the operation of the sensor by employing a scheme first published by Bell and Bloom and reach a sensitivity of 2.6 pT/Hz1/2 at 30 Hz, limited primarily by the photon shot noise of the detector.