Near-infrared laser based cavity ringdown spectroscopy for applications in petrochemical industry

A simple, economic diode laser based cavity ringdown system for trace-gas applications in the petrochemical industry is presented. As acetylene (C2H2) is sometimes present as an interfering contaminant in the gas flow of ethylene (ethene, C2H4) in a polyethylene production process, an on-line monitoring of such traces is essential. We investigated C2H2-C2H4 mixtures in a gas-flow configuration in real time. The experimental setup consists of a near-infrared external cavity diode laser with an output power of a few mW, standard telecommunication fibers and a home-made gas cell providing a user-friendly cavity alignment. A noise-equivalent detection sensitivity of 4.5×10-8cm-1 Hz-1/2 was achieved, corresponding to a detection limit of 20ppbV C2H2 in synthetic air at 100mbar. In an actual C2H2-C2H4 gas-flow measurement the minimum detectable concentration of C2H2 added to the C2H4 gas stream (which may already contain an unknown C2H2 contamination) increased to 160ppbV. Moreover, stepwise C2H2 concentration increments of 500ppbV were resolved with a 1-min time resolution and an excellent linear relationship between the absorption coefficient and the concentration was foun

Investigation and optimisation of a multipass resonant photoacoustic cell at high absorption levels

A theoretical and experimental investigation of photoacoustic (PA) signals in a resonant multipass PA cell with high background absorption (up to 29m-1) is presented. An analogous electric transmission line model including discontinuity inductances at cross section changes was used to model the first longitudinal acoustic mode of the multipass PA cell equipped with two buffer volumes. This model was validated with experimentally obtained results and used to predict the behaviour of the PA cell for different multipass arrangements and different buffer volume diameters. The highest PA signal is obtained for high pass number and large buffer radius. Increasing the absorption coefficient of the medium enhances the PA signal until a maximum is reached, leading to a minimum for the PA signal sensitivity. For a given background absorption, the number of passes required to maximise the sensitivity depends on the absorption coefficient. The model allows the determination of the best-suited number of passes for a given absorption coefficient and cell geometr

Trace gas monitoring with infrared laser-based detection schemes

The success of laser-based trace gas sensing techniques crucially depends on the availability and performance of tunable laser sources combined with appropriate detection schemes. Besides near-infrared diode lasers, continuously tunable midinfrared quantum cascade lasers and nonlinear optical laser sources are preferentially employed today. Detection schemes are based on sensitive absorption measurements and comprise direct absorption in multi-pass cells as well as photoacoustic and cavity ringdown techniques in various configurations. We illustrate the performance of several systems implemented in our laboratory. These include time-resolved multicomponent traffic emission measurements with a mobile CO2-laser photoacoustic system, a diode-laser based cavity ringdown device for measurements of impurities in industrial process control, isotope ratio measurements with a difference frequency (DFG) laser source combined with balanced path length detection, detection of methylamines for breath analysis with both a near-IR diode laser and a DFG source, and finally, acetone measurements with a heatable multipass cell intended for vapor phase studies on doping agents in urine sample

Near-infrared laser based cavity ringdown spectroscopy for applications in petrochemical industry

ISSN:0946-2171ISSN:1432-0649ISSN:0721-7269ISSN:0340-379

Investigation and optimisation of a multipass resonant photoacoustic cell at high absorption levels

ISSN:0946-2171ISSN:1432-0649ISSN:0721-7269ISSN:0340-379

Trace gas monitoring with infrared laser-based detection schemes

ISSN:0946-2171ISSN:1432-0649ISSN:0721-7269ISSN:0340-379

A threat to coral reefs multiplied? Four species of crown-of-thorns starfish

In the face of ever-increasing threats to coral reef ecosystems, it is essential to understand the impact of natural predators in order to devise appropriate management strategies. Destructive population explosions of the crown-of-thorns starfish Acanthaster planci have devastated coral reefs throughout the Indo-Pacific for decades. But despite extensive research, the causes of outbreaks are still unclear. An important consideration in this research is that A. planci has been regarded as a single taxonomic entity. Using molecular data from its entire distribution, we find that A. planci is in fact a species complex. This discovery has important consequences for future coral reef research, and might prove critical for successful reef conservation management