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Title: Passive Q-switching of 1 micron Nd:YAG lasers for military target designator applications
Author: Smillie, Marc Walker
ISNI:       0000 0004 7960 8798
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2018
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In this research project we assess the potential for a passively Q-switched, diode end pumped 1064 nm Nd:YAG system to be implemented in future generations of military target designators. The main challenges were to achieve a pulse energy above 50 mJ, timing jitter below ± 5 μs, and ensuring operation over a temperature range of -40 to +70 °C. We have addressed these challenges and established a framework for future research into passively Q-switched designators. We found that the limited pulse energy was due largely to a non-uniform pump beam, which was corrected with an engineered diffuser. This enabled us to achieve a single pulse energy of 53.4 mJ, which is the highest reported energy for a diode end pumped, passively Q-switched 1064 nm Nd:YAG laser. Secondly, we identified, through experiment and modelling, that the main causes of timing jitter in our system were mechanical vibrations and pump power fluctuations. We also investigated the presence of satellite pulses, which we experimentally attribute to longitudinal mode competition. We also provide a summary of the Q-switching performance of V:YAG, Cr:YAG and BDN (bis[4-dimethylaminodithiobenzil] nickel) dye saturable absorbers, through experiment and rate equation modelling. From this we can confirm that Cr:YAG is the only commercially viable material suitable for high energy passive Q-switching at 1064 nm. Finally we evaluated the thermal performance of a mechanically robust Nd:YAG laser passively Q-switched with Cr:YAG. The pulse energy, duration, jitter and threshold were measured over the temperature range -40 to +70 °C. Through modelling we propose that the experimentally observed changes in the laser parameters are driven by the temperature dependence of the effective emission cross section (Nd:YAG), pump power and laser mode size.
Supervisor: Kemp, Alan Sponsor: Not available
Qualification Name: Thesis (Eng.D.) Qualification Level: Doctoral