arXiv subjects

Rodolphe Boudot

Publications and source records attributed to Rodolphe Boudot.

23 records · Page 2Linked to original sources

arXiv2013

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.

physics.atom-ph↗

arXiv2013

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.

physics.atom-ph↗

arXiv2012

Phase Noise in RF and Microwave Amplifiers

Understanding the amplifier phase noise is a critical issue in numerous fields of engineering and physics, like oscillators, frequency synthesis, telecommunications, radars, spectroscopy, in the emerging domain of microwave photonics, and in more exotic domains like radio astronomy, particle accelerators, etc. This article analyzes the two main types of phase noise in amplifiers, white and flicker. White phase noise results from adding white noise to the RF spectrum around the carrier. For a given amount of RF noise added, noise is proportional to the inverse of the carrier power. By contrast, the 1/f coefficient is a constant parameter of the amplifier, in a wide range of carrier power. This fact has amazing consequences on different amplifier topologies. Connecting m equal amplifiers in parallel, flicker is 1/m times that of one device. Cascading m equal amplifiers, flicker is m times that of one amplifier. Recirculating the signal in an amplifier so that the gain increases by a power of m (a factor of m in dB) due to positive feedback (regeneration), which for integer m is similar to the case of m amplifiers, we find that flicker is m^2 times that of the amplifier alone. Starting from the fact that near-dc flicker exists in all electronic devices, although generally not accessible from outside, the simplest model for the 1/f phase noise is that the near-dc 1/f noise phase-modulates the carrier through some parametric effect in the semiconductor. This model predicts the behavior of the (simple) amplifier and of the different amplifier topologies. Numerous measurements on amplifiers from different technologies and frequencies (HF to microwaves), also including some obsolete amplifiers, validate the theory.

physics.ins-det↗

arXiv2011

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.

physics.atom-ph↗

arXiv2006

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.

physics.ins-det↗