We demonstrate a vapor cell atomic clock prototype based on continuous-wave (CW) interrogation and double-modulation coherent population trapping (DM-CPT) technique. The DM-CPT technique uses a synchronous modulation of polarization and relative phase of a bi-chromatic laser beam in order to increase the number of atoms trapped in a dark state, i.e. a non-absorbing state. The narrow resonance, observed in transmission of a Cs vapor cell, is used as a narrow frequency discriminator in an atomic clock. A detailed characterization of the CPT resonance versus numerous parameters is reported. A short-term frequency stability of 3.2 × 10 −13 τ −1/2 up to 100 s averaging time is measured. These performances are more than one order of magnitude better than industrial Rb clocks and comparable to those of best laboratory-prototype vapor cell clocks. The noise budget analysis shows that the short and mid-term frequency stability is mainly limited by the power fluctuations of the microwave used to generate the bi-chromatic laser. These preliminary results demonstrate that the DM-CPT technique is well-suited for the development of a high-performance atomic clock, with potential compact and robust setup due to its linear architecture. This clock could find future applications in industry, telecommunications, instrumentation or global navigation satellite systems.

Laser power fluctuations can significantly reduce the device performances in various applications. High frequency fluctuations impact the signal-to-noise ratio, while slow variations can reduce the device repeatability or accuracy. Here we report experimental investigations on the power stabilization of a diode laser with an acousto-optic modulator. In the frequency domain, the relative power noise is reduced at the level of 2.2 × 10−8 Hz−1/2 in the range 1-100 kHz. The slow variations are studied in the time domain. The relative Allan standard deviation is measured at the level of 6 × 10−7 at 100 s averaging time. Above 100 s, the instability increases and reaches 2 × 10−6 at 10 000 s.

In this work we propose, and experimentally demonstrate, the use of a self-oscillating all-optical atomic magnetometer for magnetic induction measurements. Given the potential for miniaturization of atomic magnetometers, and their extreme sensitivity, the present work shows that atomic magnetometers may play a key role in the development of instrumentation for magnetic induction tomography.

First, the root arrangement was studied on each internode considered separately. A x z test showed that roots were not arranged according to a random pattern (Table III). The assumption of a symmetrical arrangement has to be discarded too. On this assumption angles between roots would be equal to 360/1, I being the number of roots. This assumption could be accepted for I = 3 but could not be accepted for I = 2, or 1 = 4. For I = 3 the modal value of angles between roots was 120 degrees (Fig. 5). In this particular case lots of the root arrangements were close to a symmetrical arrangement (Fig. 4). For 1 = 2 very few values were equal to 180 degrees (Fig. 3). For I = 4 the modal classes of angles between roots were [70][71][72][73][74][75][76][77][78][79][80] degrees and [1 00-120J degrees (Fig. 6.a).The relative locations of roots belonging to 2 successive internodes (called E ; and E i+1 ) was also studied. It appeared that the roots of E i+1 occupied the more open angles between the roots of E ; . This result was shown by studying the locations of the roots of E i+1 relative by to the angles between roots of E ; classified by descending order. The following ratio : number of E i+1 roots between 2 roots of E ; /value of the angle between the 2 roots of E ; was constant for angles over 100 degrees but decreased for angles under 100 degrees (Fig. 7). When there was 1 E i+1 root between 2 E ; roots, this root was often close to the bisectrix of the angle (Fig. 8). When there were 2 E ;+ , roots between 2 E i roots, they tended to separate the whole angle into 3 parts equal (Fig. 9). These results showed that the positions of the roots on successive internodes tend to alternate. Possible origins of such arrangements are discussed.root morphology -phyllotaxis -stem -maize

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We report the implementation and performance of a double servo-loop for intensity and phasedifference active stabilization of a dual-frequency vertical external-cavity surface-emitting laser (DF-VECSEL) for coherent population trapping (CPT) of cesium atoms in the framework of compact atomic clocks. In-phase fully correlated pumping of the two laser modes is identified as the best scheme for intensity noise reduction, and an analytical model allows the optimization of the active stabilization strategy. Optical phase-locking the beat-note to a local oscillator leads to a phase noise level below-103 dBc/Hz at 100 Hz from the carrier. The laser contribution to the short-term frequency stability of the clock is predicted to be compatible with a targeted Allan deviation below σy = 5 × 10 −13 over one second.

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Abstract. Toward the next generation of compact devices, atomic clocks based on coherent population trapping (CPT) offer a very interesting alternative. We present a review of our studies on the short and mid term stability of a compact high performance atomic clock based on CPT in view of portable applications.