Measurements of the indium hyperfine structure in an atmospheric-pressure flame by use of diode-laser-induced fluorescence

We report on what we believe is the first demonstration of laser-induced fluorescence (LIF) in flames by use of diode lasers. Indium atoms seeded into an atmospheric-pressure flame at trace concentrations are excited by a blue GaN laser operating near 410 nm. The laser is mounted in an external-cavity configuration, and the hyperfine spectrum of the 5(2)P(1/2) → 6(2)S(1/2) transition is captured at high resolution in single-wavelength sweeps lasting less than one tenth of a second. The research demonstrates the potential of diode-based LIF for practical diagnostics of high-temperature reactive flows

A calibration method for broad-bandwidth cavity enhanced absorption spectroscopy performed with supercontinuum radiation

An efficient calibration method has been developed for broad-bandwidth cavity enhanced absorption spectroscopy. The calibration is performed using phase shift cavity ring-down spectroscopy, which is conveniently implemented through use of an acousto-optic tunable filter (AOTF). The AOTF permits a narrowband portion of the SC spectrum to be scanned over the full high-reflectivity bandwidth of the cavity mirrors. After calibration the AOTF is switched off and broad-bandwidth CEAS can be performed with the same light source without any loss of alignment to the set-up. We demonstrate the merits of the method by probing transitions of oxygen molecules O-2 and collisional pairs of oxygen molecules (O-2)(2) in the visible spectral range

Inflation from non-minimally coupled scalar field in loop quantum cosmology

The FRW model with non-minimally coupled massive scalar field has been investigated in LQC framework. Considered form of the potential and coupling allows applications to Higgs driven inflation. Out of two frames used in the literature to describe such systems: Jordan and Einstein frame, the latter one is applied. Specifically, we explore the idea of the Einstein frame being the natural 'environment' for quantization and the Jordan picture having an emergent nature. The resulting dynamics qualitatively modifies the standard bounce paradigm in LQC in two ways: (i) the bounce point is no longer marked by critical matter energy density, (ii) the Planck scale physics features the 'mexican hat' trajectory with two consecutive bounces and rapid expansion and recollapse between them. Furthermore, for physically viable coupling strength and initial data the subsequent inflation exceeds 60 e-foldings.Comment: Clarity improved. Replaced with revised version accepted in JCA

The evolution of language: a comparative review

For many years the evolution of language has been seen as a disreputable topic, mired in fanciful "just so stories" about language origins. However, in the last decade a new synthesis of modern linguistics, cognitive neuroscience and neo-Darwinian evolutionary theory has begun to make important contributions to our understanding of the biology and evolution of language. I review some of this recent progress, focusing on the value of the comparative method, which uses data from animal species to draw inferences about language evolution. Discussing speech first, I show how data concerning a wide variety of species, from monkeys to birds, can increase our understanding of the anatomical and neural mechanisms underlying human spoken language, and how bird and whale song provide insights into the ultimate evolutionary function of language. I discuss the ‘‘descended larynx’ ’ of humans, a peculiar adaptation for speech that has received much attention in the past, which despite earlier claims is not uniquely human. Then I will turn to the neural mechanisms underlying spoken language, pointing out the difficulties animals apparently experience in perceiving hierarchical structure in sounds, and stressing the importance of vocal imitation in the evolution of a spoken language. Turning to ultimate function, I suggest that communication among kin (especially between parents and offspring) played a crucial but neglected role in driving language evolution. Finally, I briefly discuss phylogeny, discussing hypotheses that offer plausible routes to human language from a non-linguistic chimp-like ancestor. I conclude that comparative data from living animals will be key to developing a richer, more interdisciplinary understanding of our most distinctively human trait: language

Diode laser induced fluorescence for gas-phase diagnostics

We highlight the capabilities and potential of diode laser induced fluorescence for measurements in gas-phase reacting flows. Many applications of diode lasers in practical sensing are based on absorption spectroscopy. Fluorescence-based diagnostics possess similar advantages in terms of practicality and implementation-cost but additionally are capable of achieving excellent spatial resolution. Diode laser fluorescence instruments have been employed for high-sensitivity trace gas monitoring in applications ranging from plasma physics to atmospheric chemistry. This article begins by describing the UV-visible diode laser technology used to perform fluorescence. The principles of diode laser induced fluorescence are then reviewed and a comparison is made with absorption spectroscopy. Examples are given of concentration measurements of both atomic and molecular trace gases. Recent work on using diode laser induced atomic fluorescence for precision measurements of flame temperature is also reviewed. We conclude by a discussion of future opportunities for diode laser fluorescence spectroscopy drawing attention to interesting potential target species as well as novel application areas, such as monitoring of synthesis processes for nanomaterials. Read More: http://www.oldenbourg-link.com/doi/abs/10.1524/zpch.2011.018

Use of Te-130(2) for frequency referencing and active stabilisation of a violet extended cavity diode laser

This paper reports on the use of Te-130(2) absorption lines in active laser-locking, and in frequency referencing, of the emission of a violet extended cavity diode laser with a wavelength of around 410 nm. We note the existence of closely spaced tellurium absorption lines, suitable for referencing purposes in gas sensing applications, at wavelengths below the lower limit (417 nm) of the spectral region covered by the tellurium atlas [J. Cariou, P. Luc, Atlas du spectre d'Absorption de la Molecule de Tellure, CNRS, Paris, 1980]. The absolute positions of the lines in the acquired spectra were estimated by comparison to a simultaneously acquired fluorescence spectrum of atomic indium, and were identified using calculations based on fundamental spectroscopic data. The laser frequency was stabilised within a range of 40 MHz, which is negligible compared to typical transition widths at atmospheric pressure

Two-line atomic fluorescence flame thermometry using diode lasers

This paper reports on the first application of diode laser based LIF for pointwise temperature measurements in flames. The technique is based on two-line atomic fluorescence (TLAF) thermometry of indium atoms seeded at trace levels into the flame. Two novel extended cavity diode laser systems (ECDLs) were developed, providing tunable single-mode radiation around 410 and 451 nm, respectively, to excite the temperature sensitive 5P(1/2)-6S(1/2) and 5P(3/2)-6S(1/2) transitions of indium. The wide tuning range of the ECDLs allowed scans over the entire pressure broadened hyperfine structure of both transitions to be performed with signal-to-noise ratios exceeding 50 on single wavelength sweeps (at 20 Hz). We present a modified TLAF detection scheme that requires only a single detector and obviates the need for detection system calibration. Spatially resolved temperature profiles were obtained from a laminar premixed CH4/air flame and found to be in excellent agreement with temperatures obtained from high-resolution OH LIF scans. The accuracy and spatial resolution of the technique makes this an attractive alternative to traditional, more complex, and expensive, temperature measurement techniques of similar or better precision. Finally, we demonstrate that PLIF imaging of atom distributions in flames is possible using low power diode lasers

Temperature response of an acoustically-forced turbulent lean premixed flame : a quantitative experimental determination

Temperature measurements have been taken on an acoustically-forced lean premixed turbulent bluff-body stabilised flame. The burner used in this study is a test-bed to investigate thermo acoustic instability in gas-turbine engines at the University of Cambridge. Numerous experiments have been performed on the burner, one of which used two-line OH planar laser induced fluorescence to measure temperature. Here, we employ vibrational coherent anti-Stokes Raman scattering (CARS) of nitrogen as an alternative to measure temperature, circumventing the limitations of the former method. The use of nitrogen CARS avoids the problem of probing regions of the flame with low OH concentrations that resulted in erroneous temperature. Such an application of CARS showed that the results from previous efforts were systematically biased up to 47% close to the bluff-body. We also critically review the limitations of CARS used in our experiments, pertaining to spatial resolution and associated biasing further downstream from the bluff-body. Using the more accurate results from this work, more up-to-date CFD models of the burner can be validated, with the aim of improved understanding and prediction of thermo acoustic instability in gas turbines