High Power Continuous Wave Laser Heating and Damage with Contamination, and Non-Uniform Spectrally Dependent Thermal Photon Statistics
2015-12
Loading...
View/Download File
Persistent link to this item
Statistics
View StatisticsJournal Title
Journal ISSN
Volume Title
Title
High Power Continuous Wave Laser Heating and Damage with Contamination, and Non-Uniform Spectrally Dependent Thermal Photon Statistics
Authors
Published Date
2015-12
Publisher
Type
Thesis or Dissertation
Abstract
A model is presented and confirmed experimentally that explains the anomalous behavior observed in the continuous wave (CW) excitation of thermally-isolated optics. Very low absorption, high reflective optical thin film coatings of HfO2 and SiO2 were prepared. When illuminated with a laser for 30s the coatings survived peak irradiances of 13MW/cm2. The temperature profile of the optical surfaces was measured using a calibrated thermal imaging camera; about the same peak temperatures were recorded regardless of spot size, which ranged between 500μm and 5mm. This phenomenon is explained by solving the heat diffusion equation for an optic of finite dimensions, including the non-idealities of the measurement. An analytical result is also derived showing the transition from millisecond pulses to CW, where the heating is proportional to the laser irradiance (W/m2) for millisecond pulses, and proportional to the beam radius (W/m) for CW. Contamination-induced laser breakdown is often viewed as random and simple physical models are difficult to apply. Under continuous wave illumination conditions, failure appears to be induced by a runaway free-carrier absorption process. High power laser illumination is absorbed by the contaminant particles or regions, which heat rapidly. Some of this heat transfers to the substrate, raising its temperature towards that of the vaporizing particle. This generates free carriers, causing more absorption and more heating. If a certain threshold concentration is created, the process becomes unstable, thermally heating the material to catastrophic breakdown. Contamination-induced breakdown is exponentially bandgap dependent, and this prediction is borne out in experimental data from TiO2, Ta2O5, HfO2, Al2O3, and SiO2. The spectral dependence of blackbody radiation and thermal photon noise is derived analytically for the first time as a function of spectra and mode density. An algorithm by which the analytical expression for the variance can be found for any spectral distribution is also presented. The analytical results of some simple distributions are found and shown to be inaccurately approximated with a uniform spectral distribution highlighting the importance of the finding. Two microcavities are then presented to exemplify enhanced or inhibited photon statistics effects on the cavity.
Description
University of Minnesota Ph.D. dissertation. December 2015. Major: Electrical Engineering. Advisors: Joseph Talghader, Paul Ruden. 1 computer file (PDF); xiii, 98 pages.
Related to
Replaces
License
Collections
Series/Report Number
Funding information
Isbn identifier
Doi identifier
Previously Published Citation
Suggested citation
Olson, Kyle. (2015). High Power Continuous Wave Laser Heating and Damage with Contamination, and Non-Uniform Spectrally Dependent Thermal Photon Statistics. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/177114.
Content distributed via the University Digital Conservancy may be subject to additional license and use restrictions applied by the depositor. By using these files, users agree to the Terms of Use. Materials in the UDC may contain content that is disturbing and/or harmful. For more information, please see our statement on harmful content in digital repositories.