Frequency Stable Oscillator Research Articles

Searching for Scalar Dark Matter via Coupling to Fundamental Constants with Photonic, Atomic, and Mechanical Oscillators.

We present a way to search for light scalar dark matter (DM), seeking to exploit putative coupling between dark matter scalar fields and fundamental constants, by searching for frequency modulations in direct comparisons between frequency stable oscillators. Specifically we compare a cryogenic sapphire oscillator (CSO), hydrogen maser (HM) atomic oscillator, and a bulk acoustic wave quartz oscillator (OCXO). This work includes the first calculation of the dependence of acoustic oscillators on variations of the fundamental constants, and demonstration that they can be a sensitive tool for scalar DM experiments. Results are presented based on 16days of data in comparisons between the HM and OCXO, and 2days of comparison between the OCXO and CSO. No evidence of oscillating fundamental constants consistent with a coupling to scalar dark matter is found, and instead limits on the strength of these couplings as a function of the dark matter mass are determined. We constrain the dimensionless coupling constant d_{e} and combination |d_{m_{e}}-d_{g}| across the mass band 4.4×10^{-19}≲m_{φ}≲6.8×10^{-14} eV c^{-2}, with most sensitive limits d_{e}≳1.59×10^{-1}, |d_{m_{e}}-dg|≳6.97×10^{-1}. Notably, these limits do not rely on maximum reach analysis (MRA), instead employing the more general coefficient separation technique. This experiment paves the way for future, highly sensitive experiments based on state-of-the-art acoustic oscillators, and we show that these limits can be competitive with the best current MRA-based exclusion limits.

Temperature fluctuations in a solid-nitrogen cooled secondary frequency standard

Liquid helium and liquid nitrogen are commonly used as coolants for highly frequency stable oscillators. In this paper, we present the use of solid nitrogen as an alternative coolant. Solid nitrogen solidifies near 52 K under vacuum and we show that the temperature fluctuations in the solid are an order of magnitude lower than in the liquid. This has the advantage of reducing the temperature control requirements necessary to limit temperature induced frequency fluctuations in cryogenic microwave resonator-oscillators.

Frequency reference in VSAT

A low cost technique of frequency reference distribution within a VSAT network is discussed. This technique allows the use of a modestly frequency stable oscillator as the master frequency reference in the hub of a star-connected VSAT network. The need for extremely frequency stable OCXOs in VSATs is completely avoided. This technique was successfully incorporated In the early commercial VSAT networks. It contributes partially to the low cost nature of some of the VSAT networks available today. >

The phase variations of the solar cycle

It has previously been shown that the statistics of the phase fluctuation of the sunspot cycle are compatible with the assumption that the solar magnetic field is generated deep in the Sun by a frequency stable oscillator and that the observed substantial phase fluctuation in the sunspot cycle is due to variation in the time required for the magnetic field to move to the solar surface (Dicke, 1978, 1979). It was shown that the observed phase shifts are strongly correlated with the amplitude of the solar cycle. It is shown here that of two empirical models for the transport of magnetic flux to the surface, the best fit to the data is obtained with a model for which the magnetic flux is carried to the surface by convection with the convection velocity proportional to a function of the solar cycle amplitude. The best fit of this model to the data is obtained for a 12-yr transit time. The period obtained for the solar cycle is T = 22.219 ± 0.032 yr. It is shown that the great solar anomaly of 1760–1800 is most likely real and not due to poor data.

Improvements in the theory and design of RC oscillators

The general oscillator theory pertinent to frequency stability is presented, and the superiority of the bridge oscillator is demonstrated. The tables provided show the similarity between the transfer functions, and certain other network functions, of the commonly used <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</tex> oscillator networks. These networks are optimized for use in frequency stable oscillators, and some very simple constraints are found for the parallel- <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</tex> network. Contrary to the ideas of previous authors the best network for an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</tex> oscillator cannot be established theoretically. Instead, it is shown that the seven networks given fall into only three groups. Together these groups provide a continuous range of the two major properties required for good frequency stability. These properties must be chosen empirically to match the amplifier used in a particular oscillator.