| 1. |
- Wang, Junyang, 1983-
(författare)
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Dicke narrowing and speed-dependent effects in dispersion signals : Influence on assessment of concentration and spectral parameters by noise-immune cavity-enhanced optical heterodyne molecular spectrometry
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Laser spectroscopic techniques have, during the last decades, demonstrated an extraordinary capability for sensitive detection of molecular constituents in gas phase. Since spectra from such techniques constitute unique and characteristic signatures for each type of species, these techniques enable investigations of molecular structures as well as detection of the presence of species in a gas mixture. They are therefore used for a variety of application, from fundamental studies to the assessment of gas concentrations. In fact, quantitative assessments of gas concentrations by laser-based techniques are constantly gaining in popularity, primarily due to properties such as high sensitivity and selectivity and an ability to perform non-invasive measurement. Moreover, investigations of isolated molecular transitions under different conditions provide excellent means to obtain a comprehensive understanding of spectral broadening mechanisms, which is of importance for, for example, environmental sciences and remote sensing applications. In fundamental studies, spectroscopic parameters are often retrieved from fits of a model function of the technique used, which in turn is based upon a suitable lineshape function. In order to obtain parameter values with highest possible accuracy, it is of importance to use the lineshape model that most correctly can predict the measured spectra. Even though the Voigt function is the most commonly used lineshape model when both Doppler and collision broadenings are present, it is not always suitable when spectroscopic parameters are to be assessed with high precision.This thesis represents a thorough investigation of Dicke narrowing and speed-dependent effects, which are phenomena that are not accounted for by the conventional Voigt profile. For the first time, it is demonstrated that both these effects take place not only in absorption but also in the dispersion mode of detection. Their dispersion lineshape functions are first theoretically presumed and explicitly given before they are validated experimentally by the noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS). By using the models developed, it is also shown that although the two modes of detection, absorption and dispersion, both can provide good quality of fits, they do not always provide identical spectroscopic parameters. A detailed analysis under which conditions they do so, and subsequent recommendations of their use, are presented.It also describes the instrumental implementation of a distributed-feed-back (DFB) laser-based NICE-OHMS instrumentation, which constitutes an important step towards the further development of this technique. Due to the wide tunability of the DFB laser, the setup is capable of extending the working range of NICE-OHMS into the collision broadening region, which, in turn, allows for precise spectroscopic studies. The use of a fiber-coupled DFB laser also provides a compact NICE-OHMS system. The minimum detectable on-resonance absorption was assessed to 2× 10-10 cm-1 for a 70 s integration time.
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| 2. |
- Westberg, Jonas, 1983-
(författare)
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Faraday modulation spectroscopy : Theoretical description and experimental realization for detection of nitric oxide
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Faraday modulation spectroscopy (FAMOS) is a laser-based spectroscopic dispersion technique for detection of paramagnetic molecules in gas phase. This thesis presents both a new theoretical description of FAMOS and experimental results from the ultra-violet (UV) as well as the mid-infrared (MIR) regions. The theoretical description, which is given in terms of the integrated linestrength and Fourier coefficients of modulated dispersion and absorption lineshape functions, facilitates the description and the use of the technique considerably. It serves as an extension to the existing FAMOS model that thereby incorporates also the effects of lineshape asymmetries primarily originating from polarization imperfections. It is shown how the Fourier coefficients of modulated Lorentzian lineshape functions, applicable to the case with fully collisionally broadened transitions, can be expressed in terms of analytical functions. For the cases where also Doppler broadening needs to be included, resulting in lineshapes of Voigt type, the lineshape functions can be swiftly evaluated (orders of magnitude faster than previous procedures) by a newly developed method for rapid calculation of modulated Voigt lineshapes (the WWA-method). All this makes real-time curve fitting to FAMOS spectra feasible. Two experimental configurations for sensitive detection of nitric oxide (NO) by the FAMOS technique are considered and their optimum conditions are determined. The two configurations target transitions originating from the overlapping Q22(21=2) and QR12(21=2) transitions in the ultra-violet (UV) region (227nm) and the Q3=2(3=2)-transition in the fundamental rotational-vibrational band in the mid-infrared (MIR) region (5.33 µm). It is shown that the implementations of FAMOS in the UV- and MIR-region can provide detection limits in the low ppb range, which opens up the possibility for applications where high detection sensitivities of NO is required.
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| 3. |
- Alrifaiy, Ahmed
(författare)
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Lab on a chip for electrophysiological measurements with control of the oxygen content : optical manipulation and spectroscopic analysis of biological cells
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Stroke affects nearly 20 million people around the world every year. Clinically, stroke is a result of brain damage due to the shortage of oxygen delivered to the nerve cells. To minimize suffering and costs related to the disease, extensive research is performed on different levels. The focus of our research is to achieve fundamental understanding on how the lack of oxygen in brain tissue activates intrinsic biomolecular defense mechanisms that may reduce brain damage. More knowledge may hopefully lead to new therapeutic and preventive strategies on the molecular level for individuals in the risk zone for stroke or those who have just suffered a stroke.The area of study is based on the discovery of a hemoprotein called neuroglobin (Ngb), which is found in various regions in the brain, in the islets of Langerhans, and in the retina. Several studies have shown that Ngb seems to have a protective function against hypoxia-related damage. However, until now, it has not been understood how Ngb affects the nerve system and protects neurons from damage.The well-established patch-clamp technique is routinely used to measure and analyze the electrophysiological activity of individual biological cells. To perform accurate patchclamp experiments, it is important to create well-controlled physiological conditions, i.e. different oxygen levels and fast changes of nutrients and other biochemical substances. A promising approach is to apply lab on a chip technologies combined with optical manipulation techniques. These give optimal control over fast changing environmental conditions and enable multiple readouts.The conventional open patch-clamp configuration cannot provide adequate control of the oxygen content. Therefore, the aim of the thesis was to design and test a multifunctional microfluidic system, lab on a chip (LOC), that can achieve normoxic, anoxic and hypoxic conditions. The conventional patch clamp configuration was substituted by a gas-tight LOC system with an integrated patch-clamp micropipette. The system was combined with optical tweezers, optical sensor and optical spectroscopy.Optical tweezers were used to trap and guide single cells through the LOC microchannels towards the fixed micropipette. Optical spectroscopy was essential to investigate the biochemical composition of the biological samples. The developed, gas-tight LOC acted as a multifunctional system for simultaneous electrophysiological and spectroscopic experiments with good control over the oxygen content in the liquid perifusing the cells. The system was tested in series of experiments: optically trapped cells (red blood cells from human and chicken and nerve cells) were steered to the fixed patch-clamp pipette within the LOC system. The oxygen content within the microfluidic channels was measured to ∼ 1% compared to the usual 4-7% found in open system. The trapping dynamics were monitored in real-time while the spectroscopic measurements were performed simultaneously to acquire absorption spectra of the trapped cell under varying environments. To measure the effect of the laser tweezers on the sample, neurons from rats in a Petri dish were optically trapped and steered towards the patch-clamp micropipette where electrophysiological investigations were performed. The optical tweezers had no effect on the electrophysiological measurements.The future aim is to perform complete protocols of patch-clamp electrophysiological investigations while simultaneously monitoring the biochemical composition of the sample by optical spectroscopy. The straightforwardness and stability of the microfluidic chip have shown excellent potential to be applied for various biomedical applications. The subsequent ambition is to use this system as a mini laboratory that has benefits in cell sorting, patch-clamp and fertilization experiments where the gaseous and the biochemical content is of importance.The long-term goal is to study the response of individual neurons and defense mechanisms under hypoxic conditions that may establish new ways to understand cell behavior related to Ngb for various diseases such as stroke, Alzheimer’s and Parkinson’s.
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| 4. |
- Ehlers, Patrick, 1981-
(författare)
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Further development of NICE-OHMS : – an ultra-sensitive frequency-modulated cavity-enhanced laser-based spectroscopic
technique for detection of molecules in gas phase
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Noise-immune cavity-enhanced optical heterodyne molecular spectroscopy, NICE-OHMS, is a laser-based spectroscopic detection technique that comprises the concepts of frequency modulation (FM, for reduction of 1/f-noise by detecting the signal at a high frequency) and cavity enhancement (CE, for a prolongation of the optical path length) in a unique way. Properly designed, this gives the technique an intrinsic immunity against the frequency-to-noise conversion that limits many other types of CE techniques. All this gives it an exceptionally high sensitivity for detection of molecular species. Although originally developed for frequency standard purposes in the late 1990s, soon thereafter development of the technique towards molecular spectroscopy and trace gas detection was initiated. This thesis focuses on the further development of Doppler- broadened NICE-OHMS towards an ultra-sensitive detection technique. A number of concepts have been addressed. A few of these are: i) The detection sensitivity of fiber-laser-based NICE- OHMS has been improved to the 10−12 cm−1 range, which for detection of C2H2 corresponds to a few ppt (parts-per-trillion, 1:1012) in gas phase, by improving the locking of the laser to a cavity mode by use of an acousto-optic modulator. ii) It is shown that the system can be realized with a more compact footprint by implementation of a fiber-optic circulator. iii) A systematic and thorough investigation of the experimental conditions that provide maximum signals, referred to as the optimum conditions, e.g. modulation and demodulation conditions and cavity length, has been performed. As a part of this, an expression for the NICE-OHMS line shape beyond the conventional triplet formalism has been proposed and verified. iv) To widen the applicability of NICE-OHMS for detection of pressure broadened signals, also a setup based upon a distributed-feedback (DFB) laser has been realized. v) In this regime, the Voigt profile cannot model signals with the accuracy that is needed for a proper assessment of analyte concentrations. Therefore, the thesis demonstrates the first implementations of line profiles encompassing Dicke narrowing and speed-dependent effects to NICE-OHMS. While such profiles are well-known for absorption, there were no expressions available for their dispersion counterparts. Such expressions have been derived and validated by accompanying experiments. vi) The applicability of the technique for elemental detection, then referred to as NICE-AAS, has been prophesied.
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| 5. |
- Lathdavong, Lemthong, 1964-
(författare)
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Development of diode laser-based absorption and dispersion spectroscopic techniques for sensitive and selective detection of gaseous species and temperature
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main aim of this thesis has been to contribute to the ongoing work with development of new diode-laser-based spectroscopic techniques and methodologies for sensitive detection of molecules in gas phase. The techniques under scrutiny are tunable diode laser absorption spectrometry (TDLAS) and Faraday modulation spectrometry (FAMOS). Conventional distributed-feedback (DFB) telecommunication diode lasers working in the near-infrared (NIR) region have been used for detection of carbon monoxide (CO) and temperature in hot humid media whereas a unique frequency-quadrupled external-cavity diode laser producing mW powers of continuous-wave (cw) light in the ultra violet (UV) region have been used for detection of nitric oxide (NO). A methodology for assessment of CO in hot humid media by DFB-TDLAS has been developed. By addressing a particular transition in its 2nd overtone band, and by use of a dual-fitting methodology with a single reference water spectrum for background correction, % concentrations of CO can be detected in media with tens of percent of H2O (≤40%) at T≤1000 °C with an accuracy of a few %. Moreover, using an ordinary DFB laser working in the C-band, a technique for assessment of the temperature in hot humid gases (T≤1000 °C) to within a fraction of a percent has been developed. The technique addresses two groups of lines in H2O that have a favorable temperature dependence and are easily accessed in a single scan, which makes it sturdy and useful for industrial applications. A technique for detection of NO on its strong electronic transitions by direct absorption spectrometry (DAS) using cw UV diode laser light has been developed. Since the electronic transitions are ca. two or several orders of magnitude stronger than of those at various rotational-vibrational bands, the system is capable of detecting NO down to low ppb∙m concentrations solely using DAS. Also the FAMOS technique has been further developed. A new theoretical description expressed in terms of both the integrated line strength of the transition and 1st Fourier coefficients of a magnetic-field-modulated dispersive lineshape functions is presented. The description has been applied to both ro-vib Q-transitions and electronic transitions in NO. Simulations under different pressures and magnetic field conditions have been made that provide the optimum conditions for both cases. A first demonstration and characterization of FAMOS of NO addressing its electronic transitions in the UV-region has been made, resulting in a detection limit of 10 ppb∙m. The characterization indicates that the technique can be significantly improved if optimum conditions can be obtained, which demonstrates the high potential of the UV-FAMOS technique.
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