Fred Baynes

University of Adelaide · Institute for Photonics and Advanced Sensing

We carried out a 26-day comparison of five simultaneously operated optical clocks and six atomic fountain clocks located at INRIM, LNE-SYRTE, NPL and PTB by using two satellite-based frequency comparison techniques: broadband Two-Way Satellite Time and Frequency Transfer (TWSTFT) and Global Positioning System Precise Point Positioning (GPS PPP). Wi...

We demonstrate an optical frequency standard based on the 5S1/2→5D5/2 two-photon transition of rubidium. The transition is interrogated in a Doppler-free arrangement by two lasers at 780 and 776 nm, with the sum frequency of the two lasers locked to the two-photon transition. We measure the fractional frequency stability of the frequency standard t...

We carried out a 26-day comparison of five simultaneously operated optical clocks and six atomic fountain clocks located at INRIM, LNE-SYRTE, NPL and PTB by using two satellite-based frequency comparison techniques: broadband Two-Way Satellite Time and Frequency Transfer (TWSTFT) and Global Positioning System Precise Point Positioning (GPS PPP). Wi...

We discuss the relation between atomic clocks and gravity from two perspectives: gravity potential measurements for optical clock comparisons and contributions to international timescales and, conversely, the measurement of gravity potential differences using optical clocks.

The advent of novel measurement instrumentation can lead to paradigm shifts in scientific research. Optical atomic clocks, due to their unprecedented stability and uncertainty, are already being used to test physical theories and herald a revision of the International System of units (SI). However, to unlock their potential for cross-disciplinary a...

The highly forbidden (Formula presented.) electric octupole transition in (Formula presented.) is a potential candidate for a redefinition of the SI second. We present a measurement of the absolute frequency of this optical transition, performed using a frequency link to International Atomic Time to provide traceability to the SI second. The (Formu...

The highly forbidden $^2$S$_{1/2} \rightarrow ^2$F$_{7/2}$ electric octupole transition in $^{171}$Yb$^+$ is a potential candidate for a redefinition of the SI second. We present a measurement of the absolute frequency of this optical transition, performed using a frequency link to International Atomic Time to provide traceability to the SI second....

Phase compensated optical fiber links enable high accuracy atomic clocks separated by thousands of kilometers to be compared with unprecedented statistical resolution. By searching for a daily variation of the frequency difference between four strontium optical lattice clocks in different locations throughout Europe connected by such links, we impr...

Fundamental science, as well as all communications and navigation systems, are heavily reliant on the phase, timing, and synchronization provided by low-noise and agile frequency sources. Although research into varied photonic and electronic schemes have strived to improve upon the spectral purity of microwave and millimeter-wave signals, the relia...

We demonstrate an ultralow-noise microrod-resonator based laser that oscillates on the gain supplied by the stimulated Brillouin scattering optical nonlinearity. Microresonator Brillouin lasers are known to offer an outstanding frequency noise floor, which is limited by fundamental thermal fluctuations. Here, we show experimental evidence that ther...

Optical resonators provide a powerful tool for testing aspects of Lorentz invariance. Here, we present a reanalysis of an experiment where a path asymmetry was created in an optical ring resonator by introducing a dielectric prism in one arm. The frequency difference of the two fundamental counter-propagating modes was then recorded as the apparatu...

The demand for higher data rates and better synchronization in communication and navigation systems necessitates the development of new wideband and tunable sources with noise performance exceeding that provided by traditional oscillators and synthesizers. Precision synthesis is paramount for providing frequency references and timing in a broad ran...

The most frequency-stable electromagnetic radiation is produced optically, with lasers locked to passive reference cavities reaching a fractional frequency instability of 10 −16 , and optical clock instabilities approaching 10 −18 at 10 4 s. These references can find new utility when their stability is transferred to the electronic domain, such as...

The most frequency-stable sources of electromagnetic radiation are produced optically, and optical frequency combs provide the means for high fidelity frequency transfer across hundreds of terahertz and into the microwave domain. A critical step in this photonic-based synthesis of microwave signals is the optical-to-electrical conversion process. H...

We generate a frequency comb via laser electro-optic modulation. Nonlinear spectral broadening increases the 4nm bandwidth to 1150nm. With this comb, we demonstrate frequency measurements across 140 THz and detection of the comb's offset frequency.

We demonstrate the combination of a tunable Brillouin microcavity laser and a second reference microcavity that together provide a compact 1550 nm laser source with fractional noise < 7.8×10-14 1/√Hz at 10 Hz offset.

Using carefully constructed pulse interleavers, we demonstrate ~10 dB reduction in the quantum noise from optical amplification for short pulse detection, resulting in a phase noise floor on a 10 GHz microwave of -175 dBc/Hz.

We demonstrate thermometry with a resolution of 80 nK/√Hz using an isotropic crystalline whispering-gallery mode resonator based on a dichroic dual-mode technique. We simultaneously excite two modes that have a mode frequency ratio that is very close to two (±0.3 ppm). The wavelength and temperature dependence of the refractive index means that the...

We investigate the impact of pulse interleaving and optical amplification on the spectral purity of microwave signals generated by photodetecting the pulsed output of an Er:fiber-based optical frequency comb. It is shown that the microwave phase noise floor can be extremely sensitive to delay length errors in the interleaver, and the contribution o...

A stable optical frequency is phase-coherently divided to generate ultralow-noise 10 GHz signals having phase noise below -100 dBc/Hz at 1 Hz and a white noise of -177 dBc/Hz at higher offset frequencies. We discuss the technical and fundamental challenges of this approach, along with potential for integration of the components in a portable and ro...

We describe noise limitations associated with Er:fiber-based optical frequency dividers. A low-noise Er:fiber laser combined with optimized photodetection results in 5 GHz signals having phase noise floors of -176 dBc/Hz.

We demonstrate an optical frequency standard based on rubidium vapor loaded within a hollow-core photonic crystal fiber. We use the S_1/25→D_5/25 two-photon transition, excited with two lasers at 780 and 776 nm. The sum-frequency of these lasers is stabilized to this transition using modulation transfer spectroscopy, demonstrati...

We demonstrate a scheme to split an optical frequency comb into four separate frequency combs, each with four times the repetition rate of the original, but which are offset in frequency from each other. These spectrally-rarified “daughter” combs are generated using fiber interferometers that are actively stabilized. We describe how these “daughter...

In this Letter, we present an improved constraint on possible isotropic variations of the speed of light. Within the framework of the standard model extension, we provide a limit on the isotropic, scalar parameter κ˜tr of 3±11×10-10, an improvement by a factor of 6 over previous constraints. This was primarily achieved by modulating the orientation...

We have constructed a compact and robust optical frequency standard based around iodine vapor loaded into the core of a hollow-core photonic crystal fiber (HC-PCF). A 532 nm laser was frequency locked to one hyperfine component of the R(56) 32-0 (127)I(2) transition using modulation transfer spectroscopy. The stabilized laser demonstrated a frequen...

Odd-parity tests of Lorentz Invariance (LI) are ~104 times more sensitive to oddparity and isotropic (scalar) violations of LI than conventional even parity Michelson-Morley type experiments. This experiment is the first odd-parity tests to make use of an asymmetric optical resonator. We propose to sense counter-propagating modes within the resonat...

We present the first experimental test of Lorentz invariance using the frequency difference between counter-propagating modes in an asymmetric odd-parity optical resonator. This type of test is $\sim10^{4}$ more sensitive to odd-parity and isotropic (scalar) violations of Lorentz invariance than equivalent conventional even-parity experiments due t...

Recent experiments utilizing resonant cavities have produced remarkable results that limit the level of any possible violation of Lorentz Invariance. However, within the framework of the Standard Model Extension (SME) one parameter κtr remains significantly under-constrained compared to the other parameters. It has been shown an asymmetric optical...

A significant limiting factor on the sensitivity of interferometric gravitational wave detectors has been identified as thermal noise generated by mechanical loss in the high reflectivity dielectric mirror coatings on the test masses. The development of coatings which maintain high optical performance and minimize mechanical loss is therefore vital...