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Title: Investigation into laser self-mixing for accelerator applications
Author: Alexandrova, Alexandra
ISNI:       0000 0004 6422 4660
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2017
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Sensors play an important role in many areas of science, ranging from fundamental research to the automotive industry. These areas are pushing the development of more compact, sensitive and affordable sensors which can provide reliable information on displacement, velocity, density, and other key parameters. In this thesis a compact laser-based sensor, based on the self-mixing effect in semiconductor lasers, was studied and assessed in detail with regards to its use for a number of applications. The work includes the development of the self-mixing sensor itself, studies into its intrinsic limitations from a physics and engineering point of view, and investigations into ways to optimise signal level and quality; of specific interest were studies into the use of the sensor in the context of particle accelerators. The self-mixing phenomenon occurs inside a laser cavity and influences the wavelength of the light and its power fluctuation. The interaction of the backscattered light with the initial light is amplified within the cavity. This means that the sensor is very sensitive to external variation of the coupled back light; hence it does not require high power lasers, and there is no need for a complex optical system. The development of the sensor addresses the choice of laser and light delivery system, the detection system, and the data analysis. The detection system includes a photodiode which is part of a commercially available laser, a custom-built current delivery system to a transimpedance amplifier, and the transimpedance amplifier for converting and amplifying the current into a voltage. The data analysis system consists of a custom-written Matlab code. This thesis contains the combination of a new theory for modelling the self-mixing signal in order to extract the velocity profile, with an experimental study into its limitations. These include velocities, the experimental parameters of the measured target and the environment. Research into the limitations of the self-mixing technique complemented the study. It was shown that the sensor can be applied for numerous applications in a particle accelerator environment, as well as in many other areas. These are highlighted across the thesis. This thesis consists of five chapters which describe the self-mixing sensor in great detail. After a general introduction in Chapter 1, Chapter 2 presented developments of the theory behind the self-mixing technique. The subsequent Chapters 3 and 4 described experiments relating to different applications of the technique. Chapter 5 focused on applications using the sensor in a completely new area of supersonic gaseous targets. Finally, Chapter 6 presents conclusion and outlook.
Supervisor: Welsch, C. P. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral