Solid-state lasers with joule-level pulse energies and kilowatt average powers for industrial applications

• Main Author: Poulter, Michael Jon
• Published: University of Strathclyde 2011
• Subjects: 530
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.665203

The work presented in this thesis is concerned with the development of commercial Nd:YAG laser systems for a number of specific industrial applications. Common to all of these applications is the need to scale toward joule-level pulse energies for adequate light-matter interaction. These applications are unusual in that they also require kilohertz pulse-repetitionfrequencies and therefore kilowatt average powers to enable commercially viable levels of yield and throughput. This thesis begins by defining the specific requirements for each of the target applications. Laser system development begins with the design and characterisation of a laser gain-module, which is continuously-pumped using high-power diode lasers. A number of new and existing engineering design principles are then combined for the optimisation of nanosecond pulse, multi-spatial-mode standing-wave resonators. Pulsing at kilohertz repetition frequency is achieved by acousto-optical Q-switching. A suite of complementary mathematical models is presented that facilitates the design of laser resonators with industrially robust performance. Power-scaling at the fundamental wavelength of 1.064 μm is achieved by implementing a number of master-oscillator power-amplifier arrangements. This leads to average powers of around 1600 W at pulse-repetition-frequencies up to 20 kHz. The industrial laser systems developed produce maximum pulse energies of 0.32 J with 18 ns pulse durations, resulting in peak powers in excess of 18 MW. Unprecedented combinations of pulse energy and average power have also been achieved using intra-cavity second harmonic generation. 520 W average power has been demonstrated at 0.532 μm wavelength with similar pulse durations and repetition frequencies.