Pierre-Yves Bourgeois

Measurement of the Fundamental Thermal Noise Limit in a Cryogenic Sapphire Frequency Standard Using Bimodal Maser Oscillations

We report observations of the Schawlow-Townes noise limit in a cryogenic sapphire secondary frequency standard. The effect causes a fundamental limit to the frequency stability, and was measured through the novel excitation of a bimodal maser oscillation of a Whispering Gallery doublet at 12.04 GHz. The beat frequency of 10 kHz between the oscillations enabled a sensitive probe for this measurement of fractional frequency instability of 10(-14) tau(-1/2) with only 0.5 pW of output power.

Quartz resonator instabilities under cryogenic conditions

The phase noise of a quartz crystal resonator working at liquid helium temperatures is studied. Measurement methods and the device environment are explained. The phase noise is measured for different resonance modes, excitation levels, amount of operating time, device orientations in relation to the cryocooler vibration axis, and temperatures. Stability limits of a frequency source based on such devices are evaluated in the present measurement conditions. The sources of phase flicker and white noises are identified. Finally, the results are compared with previous works.

Unprecedented long-term frequency stability with a microwave resonator oscillator

This article reports on the long-term frequency stability characterization of a new type of cryogenic sapphire oscillator using an autonomous pulse-tube cryocooler as its cold source. This new design enables a relative frequency stability of better than 4.5 × 10-15 over one day of integration. To the best of our knowledge, this represents the best long-term frequency stability ever obtained with a signal source based on a macroscopic resonator.

High power solid-state sapphire Whispering Gallery mode maser

We present new results on a cryogenic solid-state maser frequency standard, which relies on the excitation of Whispering Gallery (WG) modes within a doped monocrystalline sapphire resonator (α-Al2O3). Included substitutively within the highest purity HEMEX-grade sapphire crystal lattice are Fe2+ impurities at a concentration of parts per million, an unavoidable result of the manufacturing process. Mass conversion of Fe2+ to Fe3+ ions was achieved by thermally annealing the sapphire in air. Above-threshold maser oscillation was then excited in the resonator at zero applied DC magnetic field by pumping high-Q WG modes coincident in frequency with the Electron Spin Resonance (ESR) energy levels of the Fe3+ spin population. A two stage annealing process was undertaken, resulting in an improvement of six orders of magnitude in output power over the previous best implementation of this scheme, and giving an output seven orders of magnitude more powerful than a typical commercial hydrogen maser. We estimate the limit on the frequency stability due to the Schawlow-Townes fundamental thermal noise limit on the order of 1×10−17/√τ.

Creating traveling waves from standing waves from the gyrotropic paramagnetic properties of Fe3+ ions in a high-Q whispering gallery mode sapphire resonator

We report observations of the gyrotropic change in magnetic susceptibility of the Fe 3+ electron paramagnetic resonance at 12.037GHz (between spin states|1/2 > and |3/2 >) in sapphire with respect to applied magnetic field. Measurements were made by observing the response of the high-Q Whispering Gallery doublet (WGH±17,0,0) in a Hemex sapphire resonator cooled to 5 K. The doublets initially existed as standing waves at zero field and were transformed to traveling waves due to the gyrotropic response.

ELISA: An ultra-stable oscillator for esa deep space antennas

The technology of the Sapphire Whispering Gallery Mode Resonator allows to surpass the frequency stability of traditional ultra-stable oscillators, and then can be exploited in number of applications requiring a high frequency stability as a frequency standard for the ESA ground station for which the requirement in term of frequency stability is σ<inf>y</inf>(τ) = 3 × 10⁻¹⁵ for integration times 1 ≤ τ ≤ 1000s.

Noise in high-speed digital-to-analog converters

We report on the measurement of phase noise of high speed analog to digital converters in a full digital measurement setup and for various development boards. The tested configurations ensures a Nyquist rate higher than 100 MHz suitable for conventional ultralow noise devices. Several analog to digital converters featuring a SNR higher than 140 dB enable the measurement of AM and PM noise with a background noise of -185 dBc (floor) and -160 dBc (flicker, 10 Hz off the carrier) using cross-correlation technique.

Influence of the electron spin resonance saturation on the power sensitivity of cryogenic sapphire resonators

Here, we study the paramagnetic ions behavior in presence of a strong microwave electromagnetic field sustained inside a cryogenic sapphire whispering gallery mode resonator. The high frequency measurement resolution that can be now achieved by comparing two Cryogenic Sapphire Oscillators (CSOs) permit to observe clearly the non-linearity of the resonator power sensitivity. These observations that, in turn, allow us to optimize the CSO operation are well explained by the electron spin resonance saturation of the paramagnetic impurities contained in the sapphire crystal.

Whispering-gallery mode technique applied to the measurement of the dielectric properties of Langasite between 4 K and 300 K

We report new measurements of dielectric properties of Lanthanum gallium silicate (Langasite or LGS) conducted with the whispering-gallery mode technique at microwave frequencies and between 4.2 K and 300 K. The real part of the permittivity tensor of LGS presents two components having temperature coefficients of opposite sign. This unique property enables the design of a temperature compensated resonator that may be useful in building stable microwave oscillators or filters. We report also the first measurements of the two independent components of the imaginary part of the permittivity tensor. It appears LGS is a relatively high-loss dielectric material compared with sapphire or quartz.

Cryogenic sapphire microwave oscillators for space, metrology and scientific applications

We recently demonstrated a Cryogenic Sapphire Oscillator (CSO) presenting a short term frequency stability better than 3 × 10−15 for 1 s≤ τ < 1000 s and achieving 4.5 × 10−15 for one day integration. This CSO incorporates a pulse-tube cooler instead of a bath cryostat-thus eliminating the need for regular supplies and manual transferring of liquid helium. The advent of reliable and cryocooled CSO open the possibility to implement such an ultra-stable reference not only in metrological laboratories with liquid helium facilities but also in remote sites like base stations for space navigation, VBLI antenna sites, …