PRECISE PHOTONIC ENGINES FOR UV PULSED LASER DEPOSITION

摘要

High pulse energy excimer lasers with pulse energies between 300mJ and 1200mJ/pulse and photon energies between 5eV and 7.9eV lend maximum flexibility to the technique of pulsed laser deposition. On account of the high energy densities accessible with the latest generation of excimer lasers, the entire material spectrum including high band-gap metal oxides such as ZnO is amenable to precise and controlled ablation with subsequent stoichiometric transfer to the substrat. Because the transferred material needs time to smoothly deposit and position itself optimally on the substrate, the repetition rate of the ablation laser is typically on the order of only 10Hz. These requirements are best met by pulsed lasers with short wavelengths (248nm as the most common), high pulse energies (100mJ to 1000mJ) and homogeneous spatial energy distribution. Thin film quality is very sensitive to shot-to-shot energy density fluctuations, and because deposition time in a lab takes up to one hour, both spatial (beam profile) and temporal (shot-to-shot) energy stability are essential in order to obtain reproducible results.