Supply of a particle-included droplet as laser plasma target for extreme ultraviolet emission

Many solid state materials, such as tin or boron nitride, which have a high conversion efficiency at specific wavelengths in the range of the extreme ultraviolet, are difficult to supply in a regenerative long life target form. Here we present experimental results of carrying micro-particles with a droplet to supply solid state material for the laser plasma source aiming at nearly infinite operation time. At the initial stage of this research, priority was given to the stable operation of the droplet source since it is crucial to the application of a droplet in the laser plasma EUV source. Several key parameters (droplet velocity, frequency and allowed vibration amplitude range of piezo-actuator) for the generation of stable large size droplets were experimentally investigated. Wide-band EUV emission (with photon energy from about 50 to 100 eV) stability from the water droplet plasma was enhanced from 17.3% to 4.2% (1δ, average standard deviation over 2000 shots) by adopting an improved synchronization approach. The inclusion of BN particles in the water droplet was performed and EUV emission from BN (mainly at 4.86 nm) was generated from the boron nitride particle-included droplet.