Continuous-wave cavity-ringdown detection of stimulated Raman gain spectra

Cavity ringdown (CRD) spectroscopy, with its high sensitivity, provides a novel way to perform continuouswave (cw) stimulated Raman gain (SRG) spectroscopy, rather than by conventional optically detected coherent Raman techniques. Tunable cw laser light at ∼1544 nm is used to probe ringdown decay from a rapidly-swept, high-finesse optical cavity containing a gas-phase sample of interest and itself located inside the cavity of a cw single-longitudinal-mode Nd:YAG ring laser operating at ∼1064.4 nm. This approach is used to measure cw SRG spectra of the ν1 fundamental rovibrational Raman band of methane gas at ∼ 2916.5 cm−1. The resulting SRG-CRD resonances have ringdown times longer than in the off-resonance case, in contrast to the usual shorter ringdown times arising from absorption and other loss processes. Previously reported noise-equivalent sensitivities have been substantially improved, by using a second ringdown cavity to facilitate subtraction of infrared-absorption background signals. Moreover, by employing a ringdown cavity in the form of a ring, the SRG-pump and CRD-detected Stokes beams can co-propagate uni-directionally, which significantly reduces Doppler broadening.F.V. Englich, Y. He and B.J. Or

Reflections on Place and Place-making in the Cities of China

This article is about the small spaces of the city we call 'places'. Places are shaped by being lived in; they are spaces of encounter where the little histories of the city are played out. They are, of course, also shaped by the state through planning, supervision, ordinances, and so forth. The patterns and rhythms of life in the small spaces of the city are therefore not simply a straightforward projection of civil life. Places are also sites of resistance, contestation, and actions that are often thought to be illegal by the (local) state. After introducing the concept of place, the remainder of this article is a reflection on places and place-making (but also place-breaking) in urban China. Because the patterns and rhythms of urban life have continuity, however, my approach to their study was historical. The story told here is roughly divided into four major periods: Imperial China, Republican China, the People's Republic under Mao Zedong, and the reform period from about 1980 onward. I then return to the concepts of place and place-making with which I began, summarizing my findings and suggesting some topics for further research. Copyright (c) 2007 The Author. Journal Compilation (c) 2007 Joint Editors and Blackwell Publishing Ltd.