A Vernier spectrometer is built with a near-infrared mode-locked Er:doped fiber laser, a Fabry-Perot cavity with finesse of 1000, a diffraction grating and a photo detector. The optical cavity provides high sensitivity in absorption detection by enhancing the interaction length of the light with molecular species contained in the cavity. Coupling an optical frequency comb to the cavity provided a broadband spectral bandwidth with high precision to measure the absorption of several molecular species simultaneously. Also, by using the optical cavity as a filter, transmission of some bunch comb lines was achieved. This comb filtering together with a simple grating and a photodiode formed the Vernier detection technique to provide very fast measurements while it kept the setup very simple and compact. The system allows to detect carbon dioxide in the air and water vapor and OH radicals in the flame in a spectrum spanning from 1550 nm to 1590 nm, approximately. The retrieved spectrum has a resolution of 9.3 GHz being acquired in 0.05 s.

A common consequence of protein denaturation is the loss of biological activity. Natural osmolytes such as Trimethylamine N-oxide (TMAO) contribute to protein folding, whereas other osmolytes such as urea act as an agent in the denaturation of proteins. Many studies have shown that denaturation of proteins could occur for certain concentrations of urea, however, this effect could be prevented with the presence of Trimethylamine N-oxide (TMAO) molecules. The aim of the present study is to find out the mechanism of TMAO as a protein stabilizer against urea. Firstly, Molecular Dynamics simulations were carried out for 1, 8, 27 and 64 TMAO molecules. The time-average location of the TMAO molecules during the simulation was studied by the partial density. These simulations examine if TMAO is amphiphilic molecule, i.e contains both hydrophobic and hydrophilic parts. However, these results might not be representative due to bad statistics. Secondly, an experiment ran at BESSY II at Helmholtz-Zentrum Berlin using X-ray Photoelectron Spectroscopy in liquids. In this experiment, Lauryldimethylamine oxide(LDAO) was used instead of Trimethylamine N-oxide (TMAO) due to some practical reasons. The behaviour of urea and LDAO molecule was studied when these molecules were in different and same solutions. The purpose of this experiment is to find out the mechanism of LDAO against urea. Finally, LDAO interacts with urea and a possible mechanism between them is suggested. A common consequence of protein denaturation is the loss of biological activity. Natural osmolytes such as Trimethylamine N-oxide (TMAO) contribute to protein folding, whereas other osmolytes such as urea act as an agent in the denaturation of proteins. Many studies have shown that denaturation of proteins could occur for certain concentrations of urea, however, this effect could be prevented with the presence of the Trimethylamine N-oxide (TMAO) molecules. The aim of the present study is to find out the mechanism of TMAO as a protein stabilizer against urea. Firstly, Molecular Dynamics simulations were carried out for 1, 8, 27 and 64 TMAO molecules. The time-average location of TMAO molecules during the simulation was studied by the partial density. These simulations examine if TMAO is amphiphilic molecule, i.e contains both hydrophobic and hydrophilic parts. However, these results might not be representative due to bad statistics. Secondly, an experiment ran at BESSY II at Helmholtz-Zentrum Berlin using X-ray Photoelectron Spectroscopy in liquids. In this experiment, Lauryldimethylamine oxide (LDAO) was used instead of Trimethylamine N-oxide (TMAO) due to some practical reasons. The behaviour of urea and LDAO molecule was studied when these molecules were in different and same solutions. The purpose of this experiment is to find out the mechanism of LDAO against urea. Finally, LDAO interacts with urea and a possible mechanism between them is suggested. / <p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p>

Since the surprising first detection of small carbon cluster dianions by Compton et al 1990, several studies have been made investigating their structure, fragmentation pathways and stability. As other carbon anions have been found in space, it is likely that these dianions exists as well and their ability to react with other molecules is therefore of interest. Previous studies have shown that they may survive on microsecond timescales, but it is still an open question whether they are metastable or thermodynamically stable. Therefore, this study utilizes the cyrogenic storage ring DESIREE to investigate the lifetime and stability of carbon cluster dianions Cn(2-) (n=7-10) in the new domains. Dianions were produced with a cesium ion sputtering source and their spontaneous decay Cn(2-) -&gt; Cn(-) + e- was monitored for almost 100 ms by detection of the singly charged decay products. Also, the extra electron's tunneling probability through the repulsive coloumb barrier for C8(2-) was calculated and the lifetime for different energy states was estimated. Analyzing the DESIREE data, the lifetime of the dianions could be determined to exceed the previous concluded lifetimes of 10 us by a whole order of magnitude. The only way to detect stable ions after that would be if they collided with rest gas and due to good vacuum, this eventual signal is too low. Probably due to varying structures, an alternating pattern was found, dianions with even n decaying slower than their odd neighbours. The fitting of power laws to the data is consistent with that the dianions were produced with a broad internal energy distribution. Calculations for C8(2-) indicated that its electron affinity had to be at least -1eV in order to agree with the experimental results. Continuing the investigations, future studies could, after sufficient time, use DESIREE in an alternative way, allowing detection of possible stable dianions.

No description available.

Cavity enhanced optical frequency comb spectroscopy is a technique that allows for quick and sensitive measurements of molecular absorption spectra. Locking the comb lines of an optical frequency comb to the cavity modes of an enhancement cavity and then extracting the spectral information with a Fourier transform spectrometer grants easy access to wide segments of absorption spectra. One of the main obstacles complicating the analysis of the measurements is the inevitable dispersion occurring inside the cavity. In this project, absorption measurements of CO2 were performed using an existing and well established setup consisting of a near-infrared optical frequency comb locked to a Fabry- Pérot enhancement cavity using the Pound-Drever-Hall technique, and a Fourier transform spectrometer. The purpose was to improve theoretical models of the measured absorption spectra by creating and verifying a model for the cavity dispersion, stemming mostly from the cavity mirrors but also from the normal dispersion of the intracavity medium. Until now, the cavity dispersion has been treated as an unknown and was included as a fitting parameter together with the CO2 concentration when applying fits to the absorption measurements. The dispersion model was based on previously performed precise measurements of the positions of the cavity modes. The model was found to agree well with measurements. In addition, pre-calculating the dispersion drastically reduced computation time and seemed to improve the overall robustness of the fitting routine. A complicating factor was found to be small discrepancies between the locking frequencies as determined prior to the measurements and the values yielding optimum agreement with the model. These apparent shifts of the locking points were found to have a systematic dependence on the distance between the locking points. The exact cause of this was not determined but the results indicate that with the locking points separated by more than about 10nm the shifts are negligible.

Multilayered interference coatings based on titanium- and zirconium nitride and designed for solar control have been prepared using reactive d c magnetron sputtering. Preparation effects and degradation mechanisms were investigated. It was shown that the quality of the nitride strongly depends on the degree of crystallinity in the underlying oxide. It has been shown that the nitride layer partly oxidizes as the top oxide layer is deposited. The degradation is enhanced with temperature. A thin sacrificial layer of aluminium deposited between successive depositions of nitride and oxide is shown to improve the optical performance of the coating as preparedm as well as after accelerated ageing tests. The optical properties of opaque and semitransparent films of zirconium nitride have been studied. A thorough investigation of the influence of composition, deposition rate, substrate temperature and film thickness on the optical response of the film was performed. Both photometric and ellipsometric methods were used to determine thicknesses and the optical constants at wavelengths ranging from 0.23 to 25 μm. The resulting values of n and k, in the wavelength intervals where these independent methods are applicable, have been shown to agree extremely well. The results so far indicate an even larger potential for zirconium nitride based solar control coatings as compared to the titanium nitride based. Access to optical constants derived from films of zirconium nitride of variable quality made multilayer modelling a powerful tool in the design and analysis of solar control coatings.

Only very few molar polarizabilities are known with high accuracy; and when so, they are in general only known at a given wavelength. There is therefore a need to assess the molar polarizability with high accuracy of various gases, at different wavelengths. The molar polarizability of a gas is a measure of the susceptibility of a molecule to have its charge distribution affected by light. It is also the entity that relates the index of refraction to the (molar) density of a gas in Lorentz-Lorenz equation. Hence, for high precision measurements of the density of a gas, it is important to know the molar polarizability of the gas to high accuracy. In this work a GAMOR system has been used to determine the wavelength-dependent molar polarizability of Ar at 1550 nm.  However, a high accuracy assessment of the molar polarizability of a gas requires that the gas density is known with high accuracy. Since this is not trivial to assess, the molar polarizability of argon has been assessed in terms of that of nitrogen, which is assumed to be known with high accuracy. Hence, to minimise measurement errors, the measurement cavity was alternately filled with nitrogen and argon and the ratio between the signals provided by the GAMOR system represents the ratio of the molar polarizabilities of the two gases. It was found that the molar polarizability of argon was  0.94393(5) times that of nitrogen. Since the latter one has been assessed to 4.34828(3) x 10^-6  m^/mol, the molar polarizability of argon could be assessed to 4.10446(5) x 10^-6 m^3/mol.

In the last decades the scientific development has made it possible to produce pulses with durations below the femtosecond time scale (1 fs = 1015 s), reaching to attoseconds (1 as = 1018 s). This is the time scale of electronic motion inside atoms and molecules. One way to produce isolated attosecond pulses is through high harmonic generation in gases with intense few-cycle laser pulses. This process depends strongly on the electric field shape relative to the pulse envelope, which is characterized by the so called carrier-envelope phase (CEP).The goal of this master’s thesis is to measure and investigate the possibility to improve the CEP stability of sub-two-cycle laser pulses from the laser, Light Wave Synthesizer 20 (LWS-20). The first step of the master’s thesis was to modify a Labview program used to evaluate the CEP change to be able to reevaluate the already acquired raw data. The measurements are done with an f-to-2f interferometer, whichis a spectral interference device, which measures the CEP difference between two pulses. The CEP change of the laser system was measured at three positions: after the multi-pass amplifier of the laser front end (MP), after a hollow-core fiber (HCF), which is used for spectral broadening, and at the end of the laser system. The stability is determined as the RMS error (standard deviation) of the phase change overall shots in one sample (lower RMS is better stability). The measurements show an average stability of 160±20 mrad RMS after the MP, 280±31 mrad RMS after the HCF and 560±53 mrad RMS at the end of the system. The stability at the end of the system could be improved to 475±40 mrad RMS after a scan of the pump energy for one of the amplifier stages. The HCF appears to provide a lower limit in stability and influences it only if it is very good after the MP. The alignment of the HCF does also seem to influence the CEP stability and the best stability appears to coincide with maximum output energy. An acousto-optic modulator (Dazzler) has been used to manipulate the CEP change at the end of the system and can thereby compensate for long-term drifts, but the source of the CEP stability degradation at the end of the system should be further investigated.

This text investigates THz-TDS signals in the time-frequency domain. Addi- tionally this text discusses the prospects of using time-frequency analysis to alleviate distortion in THz spectrographic characterizations induced by back- reflections in the free space electro optic sampling used in the THz time-domain spectroscopy detection scheme. THz time domain spectroscopy is a technique for characterization of materials in the terahertz regime. The THz regime offers interesting properties of materials such as strong phonon-photon interaction and resonances for vibration states of molecules. Three time-frequency representations are compared for the analysis of the time-domain signal, the short-time Fourier transform, the Wigner-Ville transform and the continuous wavelet transform. It is concluded that the Wigner-Ville transform is most suited for analysis of the spectral properties of a single pulse due to the Wigner-Ville transforms inherit high spectral resolution. The continuous wavelet transform is most suited for analysis of the time-domain signal since it has no cross-term interference as compared to the Wigner-Ville transform. By masking the continuous wavelet transform with a Lorentzian time-frequency mask the back-reflections are dampened and the resolution of the characterization is improved.

Potassium (K) is the main ash-forming element released from biomass during thermochemical conversion. A better understanding of K chemistry and monitoring of K species is needed to optimize combustion systems. Since K species are highly reactive and prevailing concentrations depend on the conversion conditions, accurate quantification requires in situ measurement techniques. Tunable diode laser absorption spectroscopy with a single-mode distributed feedback laser is used to probe the D1 transition of atomic potassium, K(g), at 769.9 nm. The large current tuning range of the diode laser (5 cm-1) enables monitoringthe wings of the absorption profile. Fitting to the acquired line shape wings is used as astrategy to enhance the dynamic range of the sensor and measure K(g) concentrations even under optically thick condition. A potassium-rich combustion environment is simulated by converting KOH salt in a premixed methane/air flat flame. Quantitative measurements of K(g) are made at 75 positions in the flame. This yields radial K(g) profiles at three different heightsin the plume above the KOH salt and an axial profile at the burner center. The acquired average K(g) concentrations are corrected for effective plume size, i.e. the absorption pathlength determined from the radial profiles. Knowledge of the K(g) distribution in flames can lead to a better understanding of K release and primary reaction kinetics.