Enhancement of laser-plasma EUV conversion efficiency by introduction of prepulses

Summary from only given. Until today laser plasma based EUV sources for lithography are still lacking to provide sufficient EUV output power for industrial use. The straight forward way to get more EUV power is to increase the incident laser energy or repetition rate. However, a tricky method is to modify the laser pulse in a way to improve the EUV conversion efficiency from laser radiation into EUV radiation. One way is to use prepulses to create the right preplasma conditions for optimum absorption of the main pulse. We show that by introducing a prepulse the conversion efficiency can be improved within a factor 6-8.