The effect of AM noise on correlation phase noise measurements

We analyze the phase-noise measurement methods in which correlation and averaging is used to reject the background noise of the instrument. All the known methods make use of a mixer, used either as a saturated phase detector or as a linear synchronous detector. Unfortunately, AM noise is taken in through the power-to-dc-offset conversion mechanism that results from the mixer asymmetry. The measurement of some mixers indicates that the unwanted amplitude-to-voltage gain is of the order of 5-50 mV, which is 12-35 dB lower than the phase-to-voltage gain of the mixer. In addition, the trick of setting the mixer at a sweet point -- off the quadrature condition -- where the sensitivity to AM nulls, works only with microwave mixers. The HF-VHF mixers have not this sweet point. Moreover, we prove that if the AM noise comes from the oscillator under test, it can not be rejected by correlation. At least not with the schemes currently used. An example shows that at some critical frequencies the unwanted effect of AM noise is of the same order -- if not greater -- than the phase noise. Thus, experimental mistakes are around the corner.Comment: 16 pages, list of symbols, 8 figures, 27 reference

Temperature Dependence Cancellation of the Cs Clock Frequency in the Presence of Ne Buffer Gas

The temperature dependence of the Cs clock transition frequency in a vapor cell filled with Ne buffer gas has been measured. The experimental setup is based on the coherent population trapping (CPT) technique and a temporal Ramsey interrogation allowing a high resolution. A quadratic dependence of the frequency shift is shown. The temperature of the shift cancellation is evaluated. The actual Ne pressure in the cell is determined from the frequency shift of the 895nm optical transition. We can then determine the Cs-Ne collisional temperature coefficients of the clock frequency. These results can be useful for vapor cell clocks and especially for future micro-clocks

Ramsey spectroscopy of high-contrast CPT resonances with push-pull optical pumping in Cs vapor

We report the detection of high-contrast and narrow Coherent Population Trapping (CPT) Ramsey fringes in a Cs vapor cell using a simple-architecture laser system. The latter allows the combination of push-pull optical pumping (PPOP) and a temporal Ramsey-like pulsed interrogation. An originality of the optics package is the use of a single Mach-Zehnder electro-optic modulator (MZ EOM) both for optical sidebands generation and light switch for pulsed interaction. Typical Ramsey fringes with a linewidth of 166 Hz and a contrast of 33 % are detected in a cm-scale buffer-gas filled Cs vapor cell. This technique could be interesting for the development of high-performance and low power consumption compact vapor cell clocks based on CPT.Comment: 9 pages, 8 figure

Coherent Population Trapping Resonances in Buffer Gas-filled Cs Vapor Cells with Push-Pull Optical Pumping

We report on a theoretical study and experimental characterization of coherent population trapping (CPT) resonances in buffer gas-filled vapor cells with push-pull optical pumping (PPOP) on Cs D1 line. We point out that the push-pull interaction scheme is identical to the so-called lin per lin polarization scheme. Expressions of the relevant dark states, as well as of absorption, are reported. The experimental setup is based on the combination of a distributed feedback (DFB) diode laser, a pigtailed intensity Mach-Zehnder electro-optic modulator (MZ EOM) for optical sidebands generation and a Michelson-like interferometer. A microwave technique to stabilize the transfer function operating point of the MZ EOM is implemented for proper operation. A CPT resonance contrast as high as 78% is reported in a cm-scale cell for the magnetic-field insensitive clock transition. The impact of the laser intensity on the CPT clock signal key parameters (linewidth - contrast - linewidth/contrast ratio) is reported for three different cells with various dimensions and buffer gas contents. The potential of the PPOP technique for the development of high-performance atomic vapor cell clocks is discussed.Comment: 28 pages, 12 figure

Characterization of high-overtone bulk acoustic resonators: applications to ultra-low noise microwave oscillators and miniature atomic clocks

International audienceThe generation of microwave signals with MEMS bulk acoustic wave (BAW) resonators is an exciting challenge. Such resonators allow the development of high-performance microwave sources combining low power consumption, small size, autonomy and ultra-low phase noise performances making them well-suited for applications such as radars, embedded electronics systems, telecommunications or embedded sensors. In the family of MEMS acoustic resonators, high-overtone bulk acoustic (HBAR) resonators [1,2] are valuable candidates by demonstrating a possible direct operation frequency of a few GHz, state-of-the-art Qf products up to 1014 [3,4] and high-potential for wafer-level fabrication

Characterization of Cs vapor cell coated with octadecyltrichlorosilane using coherent population trapping spectroscopy

We report the realization and characterization using coherent population trapping (CPT) spectroscopy of an octadecyltrichlorosilane (OTS)-coated centimeter-scale Cs vapor cell. The dual-structure of the resonance lineshape, with presence of a narrow structure line at the top of a Doppler-broadened structure, is clearly observed. The linewidth of the narrow resonance is compared to the linewidth of an evacuated Cs cell and of a buffer gas Cs cell of similar size. The Cs-OTS adsorption energy is measured to be (0.42 $\pm$ 0.03) eV, leading to a clock frequency shift rate of $2.7\times10^{-9}/$K in fractional unit. A hyperfine population lifetime, $T_1$, and a microwave coherence lifetime, $T_2$, of 1.6 and 0.5 ms are reported, corresponding to about 37 and 12 useful bounces, respectively. Atomic-motion induced Ramsey narrowing of dark resonances is observed in Cs-OTS cells by reducing the optical beam diameter. Ramsey CPT fringes are detected using a pulsed CPT interrogation scheme. Potential applications of the Cs-OTS cell to the development of a vapor cell atomic clock are discussed.Comment: 33 pages, 13 figure

Compact Yb+^+ optical atomic clock project: design principle and current status

We present the design of a compact optical clock based on the $^2S_{1/2} \rightarrow ^2D_{3/2}$ 435.5 nm transition in $^{171}$Yb$^+$. The ion trap will be based on a micro-fabricated circuit, with surface electrodes generating a trapping potential to localize a single Yb ion a few hundred $\mu$m from the electrodes. We present our trap design as well as simulations of the resulting trapping pseudo-potential. We also present a compact, multi-channel wavelength meter that will permit the frequency stabilization of the cooling, repumping and clear-out lasers at 369.5 nm, 935.2 nm and 638.6 nm needed to cool the ion. We use this wavelength meter to characterize and stabilize the frequency of extended cavity diode lasers at 369.5 nm and 638.6 nm.Comment: 7 pages, 5 figures. Proc. of the 8th FSM 2015, Potsdam, Germany. To be published in IOP Journal of Physics: Conference Serie

Investigations for a Miniature Optical Frequency Reference Based on High-Contrast Sub-Doppler Resonance in a MEMS Cesium Vapor Cell

International audienceMany of modern quantum technologies require the development of high-performance and low-power consumption miniaturized devices such as laser systems, atomic clocks, magnetometers and other quantum sensors. These instruments are to date often based on the use of chip-size diode lasers and microfabricated (MEMS) cells filled with alkali atoms [1]. An interesting challenge concerns the development of miniaturized optical frequency references (OFR). Different approaches have been engaged in this direction. One of the most successful example is a rubidium microcell-based OFR, involving the two-photon spectroscopy technique. This approach has recently demonstrated a remarkable frequency stability level of 4.4×10–12 at 1 s [2]. The present study is focused on a simple alternative approach based on sub-Doppler spectroscopy (SDS) with counter-propagating light beams. We propose to use dual-frequency light beams with orthogonal linear polarizations and frequency difference w1–w2 = Dhfs, with Dhfs the frequency of the atom ground-state hyper-fine splitting. First dual-frequency sub-Doppler spectroscopy (DF SDS) experiments have been performed with cmscale cells [3,4]. In the present study, we present preliminary spectroscopy and frequency stability results of alaser stabilized using DF SDS with a Cs vapor microfabricated cell [5] (Fig.1a). An extended-cavity diode laser (ECDL) source and a Mach-Zehnder intensity EOM are used to obtain the dual-frequency light field. A forward beam goes through the cell and is then reflected by a mirror to create the backward beam