Laser-based Trace Gas Detection Research Articles

Laser-Based Trace Gas Detection inside Hollow-Core Fibers: A Review.

Thanks to the guidance of an optical wave in air, hollow-core fibers may serve as sampling cells in an optical spectroscopic system. This paper reviews applications of hollow-core optical fibers to laser-based gas sensing. Three types of hollow-core fibers are discussed: Hollow capillary waveguides, photonic band-gap fibers, and negative curvature fibers. Their advantages and drawbacks when used for laser-based trace gas detection are analyzed. Various examples of experimental sensing systems demonstrated in the literature over the past 20 years are discussed.

Stress responses of duckweed (Lemna minor L.) and water velvet (Azolla filiculoides Lam.) to anionic surfactant sodium-dodecyl-sulphate (SDS)

Surfactants are used for several purposes and recently they have attracted the attention for their ability to modify the behavior of other preexistent or co-disposed contaminants, although their use or discharge in wastewaters can represent a real or potential risk for the environment. Lemna minor L. and Azolla filiculoides Lam. are floating aquatic macrophytes, very effective in accumulating several pollutants including sodium dodecyl sulphate (SDS). In this work we evaluated the effects of SDS on these species by determining the stress ethylene production via laser-based trace gas detection, and the activities of enzymes involved in stress response, such as guaiacol peroxidase (G-POD), phenylalanine ammonia-lyase (PAL) and polyphenol-oxidase (PPO). Phenolics content was also determined. The macrophytes were treated with different concentrations of SDS for one week. SDS affected duckweed enzymatic activities and phenol content. While in the fern phenolics amount, PAL, G-POD and PPO activities were not affected by SDS except for 100ppm SDS, the only concentration that was taken up and not completely degraded. Stress ethylene production was induced only in the fern treated with 50 and 100ppm SDS.

Cantilever enhanced photoacoustic detection of carbon dioxide using a tunable diode laser source

Recently introduced cantilever enhanced photoacoustic sensing has been applied to the tunable diode laser-based trace gas detection. The pressure variations due to the photoacoustic signal are detected with a miniature silicon cantilever, whose displacement is measured with a compact Michelson type laser interferometer. The system has been used to detect carbon dioxide (CO2) at 1572 nm with a distributed feedback diode laser. With a new photoacoustic cell, that was optimized for the laser sources, a normalized noise equivalent sensitivity of 1.7×10-10 cm-1W/\(\sqrt{Hz}\) at atmospheric pressure was realized. The result obtained in the non-resonant operation mode is at least 10 times better than in previous reports. The future improvements of the technique are also discussed.

Laser-based trace gas detection of ethane as a result of photo-oxidative damage in chilled cucumber leaves (invited)

At low temperatures, high light intensity induces strong photooxidative lipid peroxidation in chilling sensitive cucumber leaves. A sensitive laser-based photoacoustic detector was employed to monitor on-line the evolution of ethane, one of the end products of lipid peroxidation. The Δv=2 CO laser operated in the 2.62–4.06 μm infrared wavelength region with a maximum intracavity power of 11 W. In combination with an intracavity placed photoacoustic cell the laser was able to detect ethane down to 0.5 part per billion. Cucumber leaf disks chilled in the light produce ethane; the rate of ethane production depends on the applied temperature, light intensity, and period of chilling.

Kinetics of Ethanol and Acetaldehyde Production in Fermenting Wheat Dough by Laser-Based Trace Gas Detection

The fermentation process of wheat dough was studied by laser-based trace gas detection. A CO-laser-driven photoacoustic spectrometer was used to monitor simultaneously, in real time, the ethanol and acetaldehyde production rates of two commercial types of active dry yeast ( Saccharomyces cerevisiae) in wheat dough substrates. Both types of yeast, Oand B, produced ethanol for 5 hours. Acetaldehyde was yielded only during 100 minutes by the yeast O, whereas the yeast Bgenerated this compound for 3.5 hours. The total ethanol and acetaldehyde productions amounted to 1.50 mL/g dough and 4.5 µ L/g dough in the Ocase, and 0.84 mL/g dough and 14.75 µ L/g dough, in the Bcase, respectively. The yeasts were also tested for their ability tometabolize mixes consisting of the control wheat dough substrate and extra amounts of glucose or maltose. Both types of yeasts showed a similar ability to consume the added glucose, however, only the yeast Bwas found to possess an adapted enzymatic system to metabolize maltose. This work showed the efficiency of applying photoacoustic trace gas detection to food technology research for on-line monitoring of fermenting wheat dough.

Kinetics of Ethanol and Acetaldehyde Production in Fermenting Wheat Dough by Laser-Based Trace Gas Detection

Kinetics of Ethanol and Acetaldehyde Production in Fermenting Wheat Dough by Laser-Based Trace Gas Detection