Kareem, Dler Abdulmahdi (2024). Development of far-ir ultrafast time-resolved and polarization dependent techniques for investigation the charge carriers dynamics in topological insulators. University of Birmingham. Ph.D.
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Kareem2024PhD.pdf
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Abstract
This thesis investigates the ultrafast dynamics of photo-excited carriers on the surface of a topological insulator sample Bi2Te3. The work involves two parts. The first part of this work describes the use of time resolved spectroscopy as a technique with an infrared probe
being used in conjunction with a visible pump. An ultrafast laser system was employed in this work and shows the advantage of using an infrared probe to investigate the dynamics of free carriers on the surface. We studied the reflectance of the probe with different pump power and different probe polarization states. It was found that reflectance signals indicated the surface plasma wave generated by a visible pump that excited the surface. A surprising �finding is that the decay time of the surface wave increases as pump fluence increases. The results showed that Bi2Te3 can be employed for high-speed switching in infrared devices and optical communication.
The second part of this work is devoted to the development and application of the time resolved ellipsometry method to investigate how the refractive index of the topological insulator surface evolves in time. We developed an ellipsometry set-up by using a visible pump and an infrared probe. We have demonstrated how the complex refractive index changed following excitation. The results indicate that the refractive index reduced after excitation, while the extinction coefficient increased. In addition, the complex refractive index is recovered in a few picoseconds. From our results, we suggest that, by combining ultrafast surface plasma generated on the metallic surfaces with highly tunable refractive
index in the infrared region, Bi2Te3 thin �films can be used efficiently in optical devices for light control.
| Type of Work: | Thesis (Doctorates > Ph.D.) | |||||||||
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| Award Type: | Doctorates > Ph.D. | |||||||||
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| Licence: | All rights reserved | |||||||||
| College/Faculty: | Colleges (2008 onwards) > College of Engineering & Physical Sciences | |||||||||
| School or Department: | School of Physics and Astronomy | |||||||||
| Funders: | Other | |||||||||
| Other Funders: | Ministry of High Education and Scientific Research in Iraq | |||||||||
| Subjects: | Q Science > QC Physics | |||||||||
| URI: | http://etheses.bham.ac.uk/id/eprint/14503 |
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