Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 23 for “"modulation spectroscopy"”.
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Extending frequency modulation spectroscopy : sensitive and selective high resolution laser absorption in the visible and ultraviolet
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1996.
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High-accuracy and high-precision infrared spectroscopy of fundamental molecular ions using noise immune cavity enhanced optical heterodyne velocity modulation spectroscopy
… can be accomplished by combining heterodyne modulation, cavity enhancement, and velocity modulation in a spectroscopic technique called Noise-Immune Cavity-Enhanced Optical Heterodyne Velocity Modulation Spectroscopy (NICE-OHVMS). This thesis will describe efforts to conduct high-resolution …
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Near infrared tunable diode laser spectroscopy for aero engine related applications
Tunable diode laser spectroscopy is a widely used technique for recovering quantitative gas information in a range of industrial applications. Established methods often use readily available, robust and low cost optoelectronic hardware in the near-infrared, with output wavelengths that coincide …
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Determination of the Band Gap Bowing Parameter of A1xGa1-xN with Contactless Electroreflectance
Contactless electroreflectance (CER), a modulation spectroscopy (MS) technique, has been used to study the A and C exciton transitions in A1xGa1-xN layers for a composition range of 0 ≤ x ≤ 0.48 at room temperature. Taking the entire composition range (0 ≤ x ≤ 1) into account by incorporating a …
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Optical characterization of compound semiconductors using photoconductivity and photoreflectance
Custom photoreflectance modulation spectroscopy and photoconductivity spectroscopy set-ups were constructed and used to characterize semiconductor materials. The ternary Cd1--xZnxTe compound was studied to achieve fine control over its composition to provide lattice-matched substrates for the …
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Optoelectronic processes in polyfluorene ambipolar transistors
This thesis describes the use of charge modulation spectroscopy to investigate the negative and positive charge-induced absorptions in conjugated semiconducting polymers as a way to experimentally compare the wavefunctions of electrons and holes. Interactions between light and charges including …
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Novel techniques for molecular ion spectroscopy in a discharge
Velocity modulation laser spectroscopy has proven to be a successful spectroscopic technique for the study of molecular ions; indeed, it has become the conventional technique. However, there are a number of limitations to velocity modulation in its conventional form. First, there is a background …
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Temperature dependent excitonic effects in silicon
… behaviour. In this project, a wavelength modulation spectroscopy (WMS) instrument is developed for the observation of the exciton-assisted absorption in silicon at various temperatures. The technique enhances weak spectral features that are immersed in a signal background that is generally …
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Application of sensitive spectroscopic techniques to intramolecular dynamics and combustion kinetics
Modifications of Cavity Ringdown Spectroscopy (CRD) for use in the UV region are discussed. These modifications partially overcome the low sensitivity of CRD in the UV (due to lower mirror reflectivity, R - 0.99) by removal of non-exponential contributions to the ringdown decay. We have also …
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Application of the FMCW method to quasi-distributed absorption sensors
… by suitable choice of cell length, proper modulation of the source and appropriate signal processing. In order to improve sensitivity we present the theoretical analysis of a new scheme based on combining the (FMCW) technique with frequency modulation spectroscopy (FMS). Here we arrange for …
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Using saturated absorption spectroscopy on acetylene-filled hollow-core fibers for absolute frequency measurements
… pump power in three different HC-PCFs. Frequency modulation spectroscopy is then implemented on the acetylene-filled HC-PCF to generate sub-Doppler dispersion features that are useful for frequency stabilization using standard servo electronics. Instability and accuracy of this near-IR optical …
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New techniques for sub-Doppler spectroscopy of molecular ions
… for performing high-resolution sub-Doppler spectroscopy of molecular ions in the laboratory. Molecular ions are of interest to a variety of fields, from astrochemistry to fundamental physics to the study of chemical reactive intermediates. The limiting factor in developing a deeper …
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Near-infrared tunable diode laser absorption spectrometer for trace gas detection
… be achieved using second harmonic wavelength modulation spectroscopy in the 50-100k Hz region. Instrument sensitivity was enhanced through the use of a Herriott multipass cell. A computer model of the behaviour of a paraxial ray passing through such a cell has been developed, allowing suitable …
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The NICE-OHVMS technique: realizing the full potential of precision molecular ion spectroscopy
… Cavity Enhanced Optical Heterodyne Velocity Modulation Spectroscopy (NICE-OHVMS) is one of the most sensitive spectroscopic techniques specific to molecular ions. NICE-OHVMS relies on the combination of three separate techniques, each of which is a powerful tool. Cavity enhancement extends …
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Design of an Optical Fiber-Coupled Sensor for Ambient Methane Measurement
… the sweep integration (SI) and wavelength modulation spectroscopy (WMS) detection methods, which inferred the methane volume mixing ratio from an absorption or second-harmonic (2f) feature respectively. Signals controlling the laser injection current were optimized to balance trade-offs …
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Defect engineering of polycrystalline titanium dioxide synthesized by atomic layer deposition
… of undoped TiO2, photoreflectance, a type of modulation spectroscopy, is invoked to examine the degree of fixed charge buildup at buried solid-solid interfaces in metal oxide thin film structures. Lastly, since the method of in-situ doping during ALD is unique in its ability to allow for …
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Sensitive and high-precision rovibrational spectroscopy of molecular ions relevant to astronomical and quantum chemistry
High-precision spectroscopy of molecular ions has enabled new discoveries in astronomy and provided valuable benchmarks for ab initio calculations of molecular structure. Astronomers and theorists require accurate and precise laboratory measurements of rotational and rovibrational transition …
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Electroluminescence in ion gel gated organic polymer semiconductor transistors
… characteristics are observed. By charge modulation spectroscopy (CMS) study we show that there is a prominent electrochemical doping occurring with gate voltages. Further, owing to the movement of ions with voltages, irrespective of the location of electrodes, we show that the ion gel, …
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Activity of methanogenic archaea under simulated Mars analog conditions
… could be proven. Through real-time wavelength modulation spectroscopy measurements the increase in the methane concentration at temperatures down to -5 °C could be detected. The results presented in this thesis contribute to the understanding of the activity potential of methanogenic archaea …
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Design, construction, and characterization of an ultra-sensitive, high-precision fast ion-beam spectrometer for the study of molecular ions
… cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) technique in conjunction with a fast ion beam. Additionally, it is the first work outlining direct electronic spectroscopy in an ion beam. Direct spectroscopy of a fast molecular ion beam offers many advantages over …
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