Measurement of the refractive index at cryogenic temperature of absorptive silver thin films used as reflectors in a Fabry-Perot cavity.

Data on the refractive index of silver thin films are scarce in the literature, and largely dependent on both the deposition method and thickness. We measure the refractive index of silver films at cryogenic temperature with a technique that takes advantage of the absorption of the films and the corresponding peculiar properties of Fabry-Perot cavities: a frequency shift between the reflection and transmission peaks, together with a modified cavity bandwidth. We demonstrate a decrease in the real value of the refractive index, together with a decrease in its imaginary value at 4 K.

Rare Events Detected with a Bulk Acoustic Wave High Frequency Gravitational Wave Antenna.

This work describes the operation of a high frequency gravitational wave detector based on a cryogenic bulk acoustic wave cavity and reports observation of rare events during 153 days of operation over two separate experimental runs (run 1 and run 2). In both run 1 and run 2, two modes were simultaneously monitored. Across both runs, the third overtone of the fast shear mode (3B) operating at 5.

Mitigation of Temperature-Induced Light-Shift Effects in Miniaturized Atomic Clocks.

The demonstration of miniature atomic clocks (MACs) based on coherent population trapping (CPT) with improved mid- and long-term frequency stability benefits from the implementation of additional stabilization loops to reduce temperature-induced light-shift effects. In this article, we report and highlight the individual and combined benefits of such servo loops on the frequency stability of a CPT-based MAC. The first loop stabilizes the actual temperature of the vertical-cavity surface-emitting laser (VCSEL) chip using a compensation method in which the reading of external temperature variations is derived from the atomic vapor output signal.

Frequency-Temperature Compensated Cuts of Crystalline-Quartz Acoustic Cavity Within the Cryogenic Range [4 K, 15 K].

New temperature coefficients of quartz elastic coefficients particularly relevant at liquid-helium temperature have been reported recently. Based on this result, frequency-temperature compensated cuts are predicted by calculation and then demonstrated by experiment. Such compensated cuts can definitely fix the issue of remaining temperature sensitivity of crystalline-quartz acoustic cavities unbeatable for their extremely low mechanical loss, as low as $10^{-9}$ , when operated at liquid-He temperature.

A new method of probing mechanical losses of coatings at cryogenic temperatures.

A new method of probing mechanical losses and comparing the corresponding deposition processes of metallic and dielectric coatings in 1-100 MHz frequency range and cryogenic temperatures is presented. The method is based on the use of high-quality quartz acoustic cavities whose internal losses are orders of magnitude lower than any available coating nowadays. The approach is demonstrated for chromium, chromium/gold, and multilayer tantala/silica coatings.

Quality Factor Measurements of Various Types of Quartz Crystal Resonators Operating Near 4 K.

Quartz crystal resonators can exhibit huge quality factors (in excess of 1 billion) at liquid-helium temperature. However, they must satisfy a set of conditions to meet this high level of performance. With the help of experimentation, the main conditions are identified, such as the material quality, the energy trapping due to the vibrational mode structure, as well as the corresponding influence of the support mechanism and the effects of the electrodes.

Laser light routing in an elongated micromachined vapor cell with diffraction gratings for atomic clock applications.

This paper reports on an original architecture of microfabricated alkali vapor cell designed for miniature atomic clocks. The cell combines diffraction gratings with anisotropically etched single-crystalline silicon sidewalls to route a normally-incident beam in a cavity oriented along the substrate plane. Gratings have been specifically designed to diffract circularly polarized light in the first order, the latter having an angle of diffraction matching the (111) sidewalls orientation.

Computation method for the short-term stability of quartz crystal resonators obtained from passive phase noise measures.

The amplitude-frequency effect is a well-known phenomenon in quartz crystal resonators. It can distort the results of short-term stability measurements. In our case, results are computed from phase noise measurements in passive bridge systems.

Observation of Rayleigh phonon scattering through excitation of extremely high overtones in low-loss cryogenic acoustic cavities for hybrid quantum systems.

The confinement of high frequency phonons approaching 1 GHz is demonstrated in phonon-trapping acoustic cavities at cryogenic temperatures using a low-coupled network approach. The frequency range is extended by nearly an order of magnitude, with excitation at greater than the 200th overtone achieved for the first time. Such a high frequency operation reveals Rayleigh-type phonon scattering losses due to highly diluted lattice impurities and corresponding glasslike behavior, with a maximum Q(L)×f product of 8.

Extremely low loss phonon-trapping cryogenic acoustic cavities for future physical experiments.

Low loss Bulk Acoustic Wave devices are considered from the point of view of the solid state approach as phonon-confining cavities. We demonstrate effective design of such acoustic cavities with phonon-trapping techniques exhibiting extremely high quality factors for trapped longitudinally-polarized phonons of various wavelengths. Quality factors of observed modes exceed 1 billion, with a maximum Q-factor of 8 billion and Q × f product of 1.

A high-performance frequency stability compact CPT clock based on a Cs-Ne microcell.

This paper reports on a compact table-top Cs clock based on coherent population trapping (CPT) with advanced frequency stability performance. The heart of the clock is a single buffer gas Cs-Ne microfabricated cell. Using a distributed feedback (DFB) laser resonant with the Cs D1 line, the contrast of the CPT signal is found to be maximized around 80°C, a value for which the temperature dependence of the Cs clock frequency is canceled.

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.

Oscillator frequency stability improvement by means of negative feedback.

A novel, simple method is proposed to increase the frequency stability of an oscillator. An additional negative feedback is used in combination with the positive loop of the harmonic oscillator to decrease the phase sensitivity to fluctuations of parameters other than the resonator. The main advantage of the proposed correction approach is that it does not require expensive external elements such as mixers or resonators.

Parametric model of the BAW resonator phase-noise.

Excepted for the very short terms the frequency stability of ultra-stable oscillators is mainly limited by the resonator noise. In this work we proposed a parametric model of the bulk acoustic wave (BAW) resonator phase noise based on an equivalent circuit. This model explains phase noise generated by a BAW crystal from a point of view of parametric fluctuations and proves the f(-1) dependences of the crystal noise.

Precision close-to-carrier phase noise simulation of BAW oscillators.

Based on a commercial simulation tool, the influence of BAW resonator noise on the resulting oscillator phase noise is revisited. The parametric model of the resonator uses experimental data, and includes an f(-2) noise not often considered in measurements, in addition to its flicker noise.

Investigations on LGS and LGT crystals to realize BAW resonators.

The LGS family are promising materials for the design of high quality bulk acoustic wave resonators. We have manufactured many plano-convex 10 MHz 5th overtone Y-cut resonators using langasite (LGS, La(3)Ga(5)SiO(14)) and langatate (LGT, La(3)Ga(5.5)Ta(0.

Development of a 10 MHz oscillator working with an LGT crystal resonator: preliminary results.

Presently, to our knowledge, measurement of the noise of langatate (LGT) crystal oscillators has not previously been reported. First results of such a measurement are given in this paper. They have been obtained from 10 MHz resonator prototypes tested with a dedicated electronics.

Predicting phase noise in crystal oscillators.

In order to predict the phase noise in crystal oscillators an enhanced phase-noise model has been built. With this model, the power spectral densities of phase fluctuations can be computed in different points of the oscillator loop. They are calculated from their correlation functions.

A parametric quartz crystal oscillator.

Parametric oscillators have been well studied but currently are not used often. Nevertheless, they could be a low-phase noise solution, at least outside the frequency bandwidth of the resonant circuit. The theoretical aspect of parametric oscillations is briefly reviewed in this paper.

New phase-noise model for crystal oscillators: application to the Clapp oscillator.

Leeson's is the basic model for predicting oscillator noise. A mathematical analysis of this "heuristic" model has been proposed. Both models do not detail the relative importance of the amplifier transfer function associated to its own noise with regard to that of the resonator.