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

Accurate lineshape spectroscopy and the Boltzmann constant

Spectroscopy has an illustrious history delivering serendipitous discoveries and providing a stringent testbed for new physical predictions, including applications from trace materials detection, to understanding the atmospheres of stars and planets, and even constraining cosmological models. Reaching fundamental-noise limits permits optimal extraction of spectroscopic information from an absorption measurement. Here, we demonstrate a quantum-limited spectrometer that delivers high-precision measurements of the absorption lineshape. These measurements yield a very accurate measurement of the excited-state (6P1/2) hyperfine splitting in Cs, and reveals a breakdown in the well-known Voigt spectral profile. We develop a theoretical model that accounts for this breakdown, explaining the observations to within the shot-noise limit. Our model enables us to infer the thermal velocity dispersion of the Cs vapour with an uncertainty of 35 p.p.m. within an hour. This allows us to determine a value for Boltzmann's constant with a precision of 6 p.p.m., and an uncertainty of 71 p.p.m

Measuring temperature with atoms and molecules

OSA Technical Digest (online) (Optical Society of America, 2018), paper STu3P.3. From the session Precision Spectroscopy (STu3P)We have developed atomic and molecular spectrometers to deliver quantum-limited measurements of the absorption lineshape. We use this to deduce the temperature of the gas and thereby measure Boltzmann's constant with high precision and uncertainty.G.-W. Truong, S. Scholten, F. Karim, J. D. Anstie, C. Perrella, P. Light, Dong Wei, E. F. May, T. M. Stace, and A. N. Luite

Governing the injecting drug user: Beyond needle fixation

This article offers a critical contribution to the debate on a problematic 'type' of injecting drug use referred to as needle fixation. At the heart of this debate, is a questioning of the existence, prevalence and usefulness of the needle fixation concept for academics and drug treatment practitioners working with injecting drug users. The aim of this article is to extend and develop this discussion by examining the historical conditions of the needle fixation discourse. Drawing upon Michel Foucault's concept of governmentality, it uses primary and secondary sources from the 19th century to the present to trace the historical trajectory of the problematic relationship between the injecting drug user, the syringe and truth. By reconceptualizing needle fixation as a technology of government, this article will argue that needle fixation can be seen to be incompatible with contemporary rationalities found in treatment policy and practice, suggesting that we have moved beyond needle fixation as a way of governing injecting drug use and into the domain of risk management. Beyond revealing this tension, the article highlights new lines that are currently being drawn between the injecting drug user, the syringe and truth from the field of neuroscience and the risk-management potential of psychopharmacology. © The Author(s) 2012