Active light shift stabilization in modulated CPT clocks

Journal of The Optical Society of America B-optical Physics, 2006

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 lasertemperature 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.

IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 2000

We evaluate the influence of 2 types of laser sources with different spectral profiles on the performance of vapor cell atomic clocks based on lin‖lin coherent population trapping (CPT) resonances. We show that a short-term stability of 1 -2 · 10 −11 τ −1/2 may be reached in a compact system using a modulated vertical cavity surface-emitting laser. Here the stability is limited by the detection noise level and can be improved up to a factor of 4 by increasing the lock-in detection frequency to several tens of kilohertz, which is not possible in standard double resonance atomic clocks. We compare these results with CPT prepared under the same experimental conditions, using 2 phase-locked extended cavity diode lasers, with which we predict a challenging short-term stability of 1 -3 · 10 −13 τ −1/2 , comparable to the state-of-the-art laser-pumped Rb-clocks. are with the laboratoire Temps-Fréquence, University of neuchâtel, neuchâtel, switzerland.

Physical Review A, 2003

We report the first direct excitation of the strongly forbidden 5s 2 1 S0 −5s5p 3 P0 transition in 87 Sr. Its frequency is 429 228 004 235 (20) kHz. A resonant laser creates a small leak in a magneto-optical trap (MOT): atoms build up to the metastable 3 P0 state and escape the trapping process, leading to a detectable decrease in the MOT fluorescence. This line has a natural width of 10 −3 Hz and can be used for a new generation of optical frequency standards using atoms trapped in a light shift free dipole trap.

Journal of The Optical Society of America B-optical Physics, 2006

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 lasertemperature 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.

HAL (Le Centre pour la Communication Scientifique Directe), 2015

Nature Photonics, 2019

Physical Review Letters, 2003

An ultrastable optical clock based on neutral atoms trapped in an optical lattice is proposed. Complete control over the light shift is achieved by employing the $5s^2 {}^1S_0 \to 5s5p {}^3P_0$ transition of ${}^{87}{\rm Sr}$ atoms as a "clock transition". Calculations of ac multipole polarizabilities and dipole hyperpolarizabilities for the clock transition indicate that the contribution of the higher-order light shifts can be reduced to less than 1 mHz, allowing for a projected accuracy of better than $ 10^{-17}$.

HAL (Le Centre pour la Communication Scientifique Directe), 2014

Coherent population trapping (CPT) of metalalkali atoms is an interesting technique for the development of compact atomic frequency references; it relies on the excitation of the atoms by two phase-coherent laser fields. We describe the design and operation of an innovating dual-frequency laser source dedicated to Cs CPT atomic clocks, based on the direct dual-frequency and dual-polarization operation of an opticallypumped semiconductor laser at 852 nm. The phase noise of beatnote generated by the laser source is at maximum of -90 dBrad²/Hz with active stabilization, and the relative intensity noise (RIN) has been measured at -115 dB/Hz. It would potentially results in a clock frequency stability of 1.6 .10 -12 at 1 second, limited by the laser RIN. With proper adjustments in the laser and clock set-up, we target a stability of 3.10 -13 at 1 second.

2014