- About
-
The Global ETD Search service is a free service for researchers
to find electronic theses and dissertations. This service is
provided by the
Networked Digital Library of Theses and Dissertations.
Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
Search results
Showing 1 to 7 of 7 (0.039 seconds)| 1 |
Seeded, Gain-switched Chromium Doped Zinc Selenide AmplifierMcDaniel, Sean A. 21 August 2012 (has links)
No description available.
|
| 2 |
Untersuchungen zur IR-Laser-Ablation in Wasser / A study of mid-IR laser ablation in waterBrendel, Tobias 10 June 2004 (has links)
No description available.
|
| 3 |
The Study and Implementation of Compact Ring Laser for the Generation of Single Frequency IR and Green LasersWeng, Chun-Jen 27 June 2001 (has links)
Abstract
Single frequency laser has the advantages of high stability in frequency and low noise. Therefore, single frequency laser is now widely used in applications, such as high precision measurement, holography and data storage.
Attempts to generate second harmonic radiation using a linear cavity have typically resulted in significant amplitude fluctuations due to longitudinal mode coupling. Various techniques have been proposed for solving the so called ¡§green problem¡¨ to achieve single longitudinal mode operation, such as inserting optical component in the conventional linear cavity or use ring cavity instead of linear cavity. Uni-directional ring cavity has shown to be the most robust method for producing single frequency laser.
The purpose of this study is to develop compact and low-cost single frequency IR and green lasers. A novel symmetrical two-mirror figure ¡§8¡¨ ring cavity is developed. Instead of using several laser mirrors for beam deflection, this ring laser system employs only two spherical mirrors to form the laser cavity for traveling wave oscillation and eliminates ¡§spatial hole burning¡¨ caused by the standing wave operation. In this thesis, we use two-mirror figure ¡§8¡¨ ring cavity for the generation of single frequency IR and green lasers.
The polarization status is crucial for high efficient intracavity frequency doubling. The polarization evaluation in a nonplanar and reentrant ring cavity is characterized by measuring the thermally induced linear and circular birefringence and analyzing the polarization rotation due to cavity configuration.
We have demonstrated a 2-mirror figure ¡§8¡¨ ring cavity which is compact and has few optical elements. The stable single frequency laser output of our ring cavity promises to make the design widely applicable to solid-state lasers.
|
| 4 |
Molecular beam epitaxial growth of rare-earth compounds for semimetal/semiconductor heterostructure optical devicesCrook, Adam Michael 12 July 2012 (has links)
Heterostructures of materials with dramatically different properties are exciting for a variety of devices. In particular, the epitaxial integration of metals with semiconductors is promising for low-loss tunnel junctions, embedded Ohmic contacts, high-conductivity spreading layers, as well as optical devices based on the surface plasmons at metal/semiconductor interfaces. This thesis investigates the structural, electrical, and optical properties of compound (III-V) semiconductors employing rare-earth monopnictide (RE-V) nanostructures. Tunnel junctions employing RE-V nanoparticles are developed to enhance current optical devices, and the epitaxial incorporation of RE-V films is discussed for embedded electrical and plasmonic devices. Leveraging the favorable band alignments of RE-V materials in GaAs and GaSb semiconductors, nanoparticle-enhanced tunnel junctions are investigated for applications of wide-bandgap tunnel junctions and lightly-doped tunnel junctions in optical devices. Through optimization of the growth space, ErAs nanoparticle-enhanced GaAs tunnel junctions exhibit conductivity similar to the best reports on the material system. Additionally, GaSb-based tunnel junctions are developed with low p-type doping that could reduce optical loss in the cladding of a 4 μm laser by ~75%. These tunnel junctions have several advantages over competing approaches, including improved thermal stability, precise control over nanoparticle location, and incorporation of a manifold of states at the tunnel junction interface.
Investigating the integration of RE-V nanostructures into optical devices revealed important details of the RE-V growth, allowing for quantum wells to be grown within 15nm of an ErAs nanoparticle layer with minimal degradation (i.e. 95% of the peak photoluminescence intensity). This investigation into the MBE growth of ErAs provides the foundation for enhancing optical devices with RE-V nanostructures. Additionally, the improved understanding of ErAs growth leads to development of a method to grow full films of RE-V embedded in III-V materials. The growth method overcomes the mismatch in rotational symmetry of RE-V and III-V materials by seeding film growth with epitaxial nanoparticles, and growing the film through a thin III-V spacer. The growth of RE-V films is promising for both embedded electrical devices as well as a potential path towards realization of plasmonic devices with epitaxially integrated metallic films. / text
|
| 5 |
Infrared and photocatalytic studies of model bacterial species for water treatmentEde, Sarah Melinda January 2006 (has links)
The use of a CO2 infrared (IR) laser and photocatalysis for water treatment microorganism disinfection purposes was investigated. During CO2 infrared (IR) laser treatment E. cloacae inactivation was comparable to inactivation via ultraviolet (UV) treatment; however no inactivation of the more resistant B. subtilis endospores occurred. Fourier Transform Infrared-Attenuated Total Reflectance (FTIR-ATR) spectroscopy of the bacterial cells displayed increased polysaccharide contents after IR treatment. FTIR and Raman spectroscopy of simple carbohydrates before and after IR laser treatment displayed no spectral changes, with the exception of N-acetyl-D-glucosamine (NAG), which was partially attributed to sampling techniques. E. cloacae inactivation during IR treatment was attributed to localised and overall temperature increases within the water. Due to the inability to inactivate B. subtilis endospores this technique is not suitable for water treatment purposes. Photocatalytic water treatment using novel TiO2 colloids prepared via a postsynthetic microwave-modification process (MW-treated) was also examined. These colloids were characterised using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) analyses and compared to Degussa P25 and convection hydrothermally-treated (HT-treated) TiO2. Slurry suspensions displayed comparable E. coli inactivation rates, so the colloids were examined in immobilised form using both a model organic degradant, oxalic acid, and E. coli. Oxalic acid degradation studies showed that the MW-treated colloids displayed similar inactivation rates to the HT-treated TiO2, due to their pure anatase composition, while Degussa P25 displayed higher inactivation rates. Investigations into the effect of shortening UV wavelength were also performed. Degussa P25 was the only catalyst which displayed higher apparent quantum yields upon shortening the UV wavelength, which was attributed to its mixed-phase anatase-rutile composition. As E. coli inactivation was observed using distilled water, photocatalysis in natural river water was trailed. It was discovered that the pH had to be lowered from 7.5 to 5.0 and the initial cell concentration must be approximately 1 x 103 colony forming units (CFU) per cm3 or less for inactivation to be observed during a 5 hour treatment period. At a catalyst loading of 1.0 mg per cm2, Degussa P25 absorbed all the applied UVA irradiation; however the MW- and HT-treated TiO2 colloids did not due to their smaller particle size. Therefore sandwich experiments were devised to evaluate the effect of unabsorbed UV irradiation within the system. Small colony variants were identified after photocatalytic and UV treatment, which pose a potential threat to public health. Further investigation of the different TiO2 colloids was performed using in situ FTIR, both with and without an applied potential and compared to a thermally prepared TiO2 catalyst. The latter displayed potential dependent photocatalysis, while the mesoporous TiO2 catalysts displayed potential independent photocatalysis. All catalyst types displayed increased degradation rates upon the application of a positive bias, which was followed in situ via the production of CO2. Sodium oxalate and NAG was examined for photocatalytic degradation, both of which were degraded to CO2, with proposed break-down products identified when using NAG.
|
| 6 |
Raman-Spektroskopie kleiner Moleküle und Molekülaggregate im Überschallstrahl nach thermischer Anregung / Raman spectroscopy of small molecules and clusters in supersonic jets after thermal excitationOtto, Katharina 31 March 2015 (has links)
Mittels spontaner Raman-Streuung im Überschallstrahl wurden kleine Moleküle und Molekülaggregate untersucht. Es wird gezeigt wie Schwingungs- und Rotationstemperaturen im Jet mittels des Stokes/Anti-Stokes-Intensitätsverhältnisses bestimmt werden können. In Studien kleiner Wassercluster konnten Kopplungskonstanten der gebundenen OH-Oszillatoren verschiedener Ringcluster von Trimeren bis Pentameren bestimmt werden, die auch zum Verständnis der Dynamik in kondensierten Phasen relevant sind. Außerdem wird die experimentelle Ermittlung von Enthalpiedifferenzen verschiedener Monomerkonformere zweier isomerisierungsdynamisch sehr unterschiedlicher Systeme vorgestellt.
Des Weiteren wurde die Weiterentwicklung der bestehenden Raman-Technik durch Kopplung mit einer IR-Laseranregung realisiert und erste Tests des neuen Aufbaus durch Studien des Methanol-Dimers durchgeführt.
|
| 7 |
Bildgebung und chemische Analytik mit Laserdesorptions-Massenspektrometrie im Bereich Forensik und Astrophysik / Imaging and Chemical Analysis with Laser Desorption Mass Spectrometry in Forensics and AstrophysicsBeinsen, Alexander 21 June 2011 (has links)
No description available.
|
Page generated in 0.046 seconds