26 research outputs found
Power Dependent Lineshape Corrections for Quantitative Spectroscopy
The Voigt profile - a convolution of a Gaussian and a Lorentzian - accurately
describes the absorption lines of atomic and molecular gases at low probe
powers. Fitting such to experimental spectra yields both the Lorentzian natural
linewidth and the Gaussian Doppler broadening. However, as the probe power
increases saturation effects introduce spurious power dependence into the
fitted Doppler width. Using a simple atomic model, we calculate power-dependent
corrections to the Voigt profile, which are parametrized by the Gaussian
Doppler width, the Lorentzian natural linewidth, and the optical depth. We show
numerically and experimentally that including the correction term substantially
reduces the spurious power dependence in the fitted Gaussian width.Comment: 4 pages, 3 figure
Nano-Kelvin thermometry and temperature control: beyond the thermal noise limit
We demonstrate thermometry with a resolution of 80 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 (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
Saturation Spectroscopy of Iodine in Hollow-core Optical Fibre
We present high-resolution spectroscopy of Iodine vapour that is loaded and
trapped within the core of a hollow-core photonic crystal fibre (HC-PCF). We
compare the observed spectroscopic features to those seen in a conventional
iodine cell and show that the saturation characteristics differ significantly.
Despite the confined geometry it was still possible to obtain sub-Doppler
features with a spectral width of ~6 MHz with very high contrast. We provide a
simple theory which closely reproduces all the key observations of the
experiment.Comment: 12 pages, 7 figure
Nano-Kelvin thermometry and temperature control: Beyond the thermal noise limit
We demonstrate thermometry with a resolution of 80nK/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 (±0.3ppm). The wavelength and temperature dependence of the refractive index means that the frequency difference between these modes is an ultrasensitive 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
Moderate drinking before the unit: medicine and life assurance in Britain and the US c.1860–1930
This article describes the way in which “Anstie’s Limit” – a particular definition of moderate drinking first defined in Britain in the 1860s by the physician Francis Edmund Anstie (1833–1874) – became established as a useful measure of moderate alcohol consumption. Becoming fairly well-established in mainstream Anglophone medicine by 1900, it was also communicated to the public in Britain, North America and New Zealand through newspaper reports. However, the limit also travelled to less familiar places, including life assurance offices, where a number of different strategies for separating moderate from excessive drinkers emerged from the dialogue between medicine and life assurance. Whilst these ideas of moderation seem to have disappeared into the background for much of the twentieth century, re-emerging as the “J-shaped” curve, these early developments anticipate many of the questions surrounding uses of the “unit” to quantify moderate alcohol consumption in Britain today. The article will therefore conclude by exploring some of the lessons of this story for contemporary discussions of moderation, suggesting that we should pay more attention to whether these metrics work, where they work and why
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