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Development and application of photofragmentation laser-induced fluorescence for visualization of hydrogen peroxides

Johansson, Olof LU (2011)
Abstract (Swedish)
Popular Abstract in Swedish

Utveckling och tillämpning av laserfragmentationsteknik för visualisering av väteperoxider

Laserinducerad fluorescens är en etablerad optisk mätmetod för kemiskt specifik detektion och avbildning med tillämpning inom fysik, kemi och biologi. Tekniken bygger på att molekyler ska absorbera laserljus och sedan spontant sända ut ljus som kan detekteras. Det finns dock många molekyler som inte kan detekteras med hjälp av laserinducerad fluorescens. Till exempel kan bindningsenergin mellan vissa atomer i en molekyl vara så pass låg att bindningen bryts då molekylen belyses med laserljus, speciellt UV-ljus. Detta ger upphov till så kallade fotofragment. Trots att många molekyler inte kan... (More)
Popular Abstract in Swedish

Utveckling och tillämpning av laserfragmentationsteknik för visualisering av väteperoxider

Laserinducerad fluorescens är en etablerad optisk mätmetod för kemiskt specifik detektion och avbildning med tillämpning inom fysik, kemi och biologi. Tekniken bygger på att molekyler ska absorbera laserljus och sedan spontant sända ut ljus som kan detekteras. Det finns dock många molekyler som inte kan detekteras med hjälp av laserinducerad fluorescens. Till exempel kan bindningsenergin mellan vissa atomer i en molekyl vara så pass låg att bindningen bryts då molekylen belyses med laserljus, speciellt UV-ljus. Detta ger upphov till så kallade fotofragment. Trots att många molekyler inte kan detekteras med hjälp av laserinducerad fluorescens, utan istället bryts sönder, kan tekniken i vissa fall användas för indirekt detektion genom att detektera de fotofragment som skapas. Väteperoxid och hydroperoxylradikalen är två exempel på molekyler där den svaga bindningen mellan syreatomerna bryts vid belysning med laserljus i det ultravioletta området. De fragment som skapas, dvs OH-radikaler i väteperoxidfallet, är vanligt förekommande inom förbränning och har inom det fältet studerats med hjälp av laserinducerad fluorescens under flera decennier.

Både väteperoxid och hydroperoxylradikalen är extremt viktiga ämnen inom atmosfärskemi och förbränning, men väteperoxid är på grund av sina oxiderande egenskaper även ett ämne av stor betydelse i industriella tillämpningar. Till exempel används väteperoxid för avdödning av mikroorganismer inom livsmedelsindustrin. Det föreliggande doktorandprojektet har haft syftet att utveckla en ny metod baserad på dissociering av väteperoxid och hydroperoxylradikalen följt av fragmentdetektion med hjälp av laserinducerad fluorescens. Förutom möjligheten att detektera specifika ämnen erbjuder laserbaserade mätmetoder möjligheten att mäta med extremt hög tids- och rumsupplösning. Genom att använda korta laserpulser (nanosekund eller pikosekund) kan förlopp som sker på tidsskalor så pass korta som en miljardels sekund upplösas. Hög rumsupplösning kan erhållas genom att laserstrålar fokuseras med hjälp av linser varvid rumskalor i storleksordningen en hundradels mm kan upplösas.

Den utvecklade tekniken har applicerats för mätningar i fria flöden av väteperoxid vid rumstemperatur samt i en industriell testrig avsedd för studier av insprutningsförlopp inom steriliseringsindustrin. Mätmetoden har även utvärderats för mätningar i vissa typer av laboratorieflammor och mätresultaten har jämförts med teoretiska kemimodeller. (Less)
Abstract
The work presented in this thesis is mainly motivated by the need for an optical diagnostic technique which can be used to visualize hydrogen peroxide (H2O2) in its gas phase. Due to the lack of bound electronic states, H2O2 cannot be detected using laser-induced fluorescence based on electronic excitation. Absorption in the ultraviolet leads to photodissociation. Thus a technique called photofragmentation laser-induced fluorescence (PF-LIF) has been developed and applied. It is a pump-probe technique that can be used for indirect detection of some non-fluorescing species. The species of interest is first dissociated using the pump-laser pulse, and the generated fragments are then probed via laser-induced fluorescence (LIF).... (More)
The work presented in this thesis is mainly motivated by the need for an optical diagnostic technique which can be used to visualize hydrogen peroxide (H2O2) in its gas phase. Due to the lack of bound electronic states, H2O2 cannot be detected using laser-induced fluorescence based on electronic excitation. Absorption in the ultraviolet leads to photodissociation. Thus a technique called photofragmentation laser-induced fluorescence (PF-LIF) has been developed and applied. It is a pump-probe technique that can be used for indirect detection of some non-fluorescing species. The species of interest is first dissociated using the pump-laser pulse, and the generated fragments are then probed via laser-induced fluorescence (LIF). Photofragmentation laser-induced fluorescence can be used for imaging, line measurements as well as for point measurements, and it can provide high temporal and spatial resolution.

Experimental investigations have been carried out in free flows of gas phase H2O2/H2O/N2/O2 mixtures, in an industrial test rig as well as in premixed, laminar H2/O2, CH4/O2 and CH4/air flames. Qualitative single-shot imaging during injection of H2O2/H2O/air mixtures into a bottle has been applied to study H2O2 concentration buildup. Quantitative H2O2 concentration measurements have been performed by studying the chemical consumption of OH photofragments following dissociation. In order to be calibration free, the measurements should be carried out with low pump fluence. The chemical consumption of OH photofragments will then be governed by the reaction OH+H2O2→HO2+H2O. This method has been demonstrated for H2O2 number densities in the range 1.16•1016 cm-3 to 3.0•1017 cm-3.

Photofragmentation laser-induced fluorescence is generally subject to the usual difficulties of making LIF quantitative. The main issue is often spatial differences in fluorescence quantum yield. In order to be able to measure the radiative lifetime distribution, which is directly linked to the fluorescence quantum yield, a separate campaign was directed towards development of a new wide-field method for fluorescence lifetime imaging.

Extensive measurement campaigns have been directed towards PF-LIF measurements in laminar, premixed flames. It turned out that the majority of the OH photofragments in the studied flames were stemming from HO2, with smaller contributions from H2O2 and CH3O2. A major challenge with the flame measurements was that OH is naturally present in flames. This signal contribution, which generally was much stronger than the signal from OH photofragments, was subtracted by recording a separate image with the pump laser blocked. This image was then subtracted from the image obtained when both the pump and the probe lasers were used. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Fittschen, Christa, Université des Sciences et Technologies de Lille -Villeneuve d'Ascq Cedex, France
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Flame diagnostics, Fluorescence lifetime imaging, Hydrogen peroxide, Laser diagnostics, Laser-induced fluorescence, Photofragmentation
defense location
Lecture Hall B, Department of Physics, Professorsgatan 1, Lund University Faculty of Engineering
defense date
2011-06-10 10:15
ISSN
1102-8718
language
English
LU publication?
yes
id
ab21f2d3-7717-4015-acf6-be2c39a89cc2 (old id 1963048)
date added to LUP
2011-05-17 10:57:19
date last changed
2016-09-19 08:45:01
@misc{ab21f2d3-7717-4015-acf6-be2c39a89cc2,
  abstract     = {The work presented in this thesis is mainly motivated by the need for an optical diagnostic technique which can be used to visualize hydrogen peroxide (H2O2) in its gas phase. Due to the lack of bound electronic states, H2O2 cannot be detected using laser-induced fluorescence based on electronic excitation. Absorption in the ultraviolet leads to photodissociation. Thus a technique called photofragmentation laser-induced fluorescence (PF-LIF) has been developed and applied. It is a pump-probe technique that can be used for indirect detection of some non-fluorescing species. The species of interest is first dissociated using the pump-laser pulse, and the generated fragments are then probed via laser-induced fluorescence (LIF). Photofragmentation laser-induced fluorescence can be used for imaging, line measurements as well as for point measurements, and it can provide high temporal and spatial resolution.<br/><br>
 Experimental investigations have been carried out in free flows of gas phase H2O2/H2O/N2/O2 mixtures, in an industrial test rig as well as in premixed, laminar H2/O2, CH4/O2 and CH4/air flames. Qualitative single-shot imaging during injection of H2O2/H2O/air mixtures into a bottle has been applied to study H2O2 concentration buildup. Quantitative H2O2 concentration measurements have been performed by studying the chemical consumption of OH photofragments following dissociation. In order to be calibration free, the measurements should be carried out with low pump fluence. The chemical consumption of OH photofragments will then be governed by the reaction OH+H2O2→HO2+H2O. This method has been demonstrated for H2O2 number densities in the range 1.16•1016 cm-3 to 3.0•1017 cm-3. <br/><br>
 Photofragmentation laser-induced fluorescence is generally subject to the usual difficulties of making LIF quantitative. The main issue is often spatial differences in fluorescence quantum yield. In order to be able to measure the radiative lifetime distribution, which is directly linked to the fluorescence quantum yield, a separate campaign was directed towards development of a new wide-field method for fluorescence lifetime imaging. <br/><br>
 Extensive measurement campaigns have been directed towards PF-LIF measurements in laminar, premixed flames. It turned out that the majority of the OH photofragments in the studied flames were stemming from HO2, with smaller contributions from H2O2 and CH3O2. A major challenge with the flame measurements was that OH is naturally present in flames. This signal contribution, which generally was much stronger than the signal from OH photofragments, was subtracted by recording a separate image with the pump laser blocked. This image was then subtracted from the image obtained when both the pump and the probe lasers were used.},
  author       = {Johansson, Olof},
  issn         = {1102-8718},
  keyword      = {Flame diagnostics,Fluorescence lifetime imaging,Hydrogen peroxide,Laser diagnostics,Laser-induced fluorescence,Photofragmentation},
  language     = {eng},
  title        = {Development and application of photofragmentation laser-induced fluorescence for visualization of hydrogen peroxides},
  year         = {2011},
}