TAILORING NONLINEAR TEMPERATURE PROFILE IN LASER-MATERIAL PROCESSING
DENİZHAN KORAY KESİM
Ph.D. Defence in Electrical and Electronics Engineering
Supervisor: ASSOC. PROF. DR. F. ÖMER İLDAY
The seminar will be on Tuesday, March 12, 2019 at 16:00, @EE-314
Ablation cooled material removal opened up great opportunities for understanding nonlinear processes. Especially using lasers as a tool to tailor nonlinear temperature gradient of material and engineering them to achieve unprecedented effects such as high ablation efficiency, speed, and low collateral damage. Numerical simulations showed such engineering of the temperature gradient of material is possible for any repetition rate falling inside the ablation cooling regime. Two temperature model is used to investigate the effects of repetition rate, pulse energy, and burst duration. Simulations suggest ablation can continue indefinitely as burst duration increases. They also suggest there’s a best pulse energy for any repetition rate in terms of efficiency of ablation regarding the material. The results of the simulations are confirmed by experiments using lasers with 1.6 GHz, 1.46 GHz, and 13 GHz repetition rate on organic and non-organic materials. The ablation threshold for a single pulse is lowered 100 times compared to our previous publication.
Finally, related studies that can build upon the shown results are presented. A new thin-disk laser oscillator scheme is proposed that implements mode-locking regimes established in fiber lasers. Dissipative soliton and similariton simulation results were promising for further studies. They can achieve high energy pulses with the help of nonlinear effects instead of limited by it. Then, a new computer generated hologram algorithm is explained where hundreds of layers can be generated from a single hologram. The algorithm utilizes diffusion as a tool to increase the degree of freedom which in turn decreases the cross-talk between layers.