Nano-Kelvin thermometry and temperature control: beyond the thermal noise limit

We demonstrate thermometry with a resolution of 80 $\mathrm{nK} / \sqrt{\mathrm{Hz}}$ 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 very close to two ($\pm0.3$ppm). The wavelength- and temperature-dependence of the refractive index means that the frequency difference between these modes is an ultra-sensitive proxy of the resonator temperature. This approach to temperature sensing automatically suppresses sensitivity to thermal expansion and vibrationally induced changes of the resonator. We also demonstrate active suppression of temperature fluctuations in the resonator by controlling the intensity of the driving laser. The residual temperature fluctuations are shown to be below the limits set by fundamental thermodynamic fluctuations of the resonator material

Stabilization of a dynamically unstable opto-thermo-mechanical oscillator

We theoretically and experimentally examine thermal oscillations in a calcium fluoride whispering-gallery-mode resonator that lead to strong mode-frequency oscillations. We show that these oscillations arise from interplay among thermal expansion, the thermo-optic effect, and Kerr effects. In certain regimes we observe chaotic behavior and demonstrate that the threshold for this behavior can be predicted theoretically. We then demonstrate a self-stabilization technique that suppresses the oscillations and delivers high temperature and frequency stability without reference to external standards

Absolute absorption line-shape measurements at the shot-noise limit

Here, we report a measurement scheme for determining an absorption profile with an accuracy imposed solely by photon shot noise. We demonstrate the power of this technique by measuring the absorption of cesium vapor with an uncertainty at the 2-ppm level. This extremely high signal-to-noise ratio allows us to directly observe the homogeneous line-shape component of the spectral profile, even in the presence of Doppler broadening, by measuring the spectral profile at a frequency detuning more than 200 natural linewidths from the line center. We then use this tool to discover an optically induced broadening process that is quite distinct from the well-known power broadening phenomenon

Handheld probe for quantitative micro-elastography

Funding: Australian Research Council (ARC); Department of Health, Western Australia; Cancer Council, Western Australia; OncoRes Medical.Optical coherence elastography (OCE) has been proposed for a range of clinical applications. However, the majority of these studies have been performed using bulks, lab based imaging systems. A compact. handheld imaging probe would accelerate clinical translation, however, to date. tins had been inhibited by the slow scan rates of compact devices and the motion artifact induced by the user's hand. In this paper, we present a proof-of-concept. handheld quantitative micro-elastography (QME) probe capable of scanning a 6 x 6 x 1 mm volume of tissue in 3.4 seconds. This handheld probe is enabled by a novel QME acquisition protocol that incorporates a custom bidirectional scan pattern driving a microelectromechanical system (MEMS) scanner, synchronized with the sample deformation induced by an annular PZT actuator. The custom scan pattern reduces the total acquisition time and the time difference between B-scans used to generate displacement maps. minimizing the impact of motion artifact. We test the feasibility of the handheld QME probe on a tissue-mimicking silicone phantom, demonstrating comparable image quality to a bench-mounted setup. In addition, we present the first handheld QME scans performed on human breast tissue specimens. For each specimen, quantitative micro-elastograms are co-registered with, and validated by, histology, demonstrating the ability-to distinguish stiff cancerous tissue from surrounding soft benign tissue.Publisher PDFPeer reviewe

Precision laser absorption spectroscopy for primary thermometry

There is currently a global effort to refine high-accuracy primary thermometry techniques driven by a call from the Bureau des Internationale de Poid et Measures to remeasure the Boltzmann constant, kB, in preparation for the upcoming redefinition of the kelvin. We have used quantitative laser spectroscopy to precisely measure the Doppler broadening of atomic transitions in rubidium and cesium vapors. By using a conventional platinum resistance thermometer and the Doppler thermometry technique, we were able to determine kB with a relative uncertainty of 1.4 x 10. Our experiment, using an effusive atomic vapor, departs significantly from other Doppler-broadened thermometry (DBT) techniques, which rely on weakly absorbing molecules in a diffusive regime. In these circumstances, the dominant systematic effects strongly differ from those of the molecular experiments and thus can lend further confidence if the outcomes of the experiments are all in agreement

Visualization 1: Self-heterodyne interference spectroscopy using a comb generated by pseudo-random modulation

Time-resolved spectra, 12-µs resolution Originally published in Optics Express on 19 October 2015 (oe-23-21-27806

Visualization 2: Self-heterodyne interference spectroscopy using a comb generated by pseudo-random modulation

Time-resolved spectra, 3-µs resolution Originally published in Optics Express on 19 October 2015 (oe-23-21-27806