High Conversion Efficentcy for Laser-Produced EUV Plasmas with Longer Pulse Durations

Summary form only given. In the pursuit to find a suitable source for EUV lithography, many people have studied laser-produced plasmas using 1.064 micron lasers with a pulse duration ranging from 1.2 ns up to 15 ns. There is also work that shows that an optimum pulse duration exists for the highest conversion efficiency (CE) from laser light to in-band EUV emission; the value is around 2 ns for Sn on planar targets. We have conducted experiments using a 1.064 micron laser with pulse durations ranging from 1 to 14 ns. Slab tin targets were irradiated with the optimum intensity for maximizing CR depending on the pulse duration. Ion vield, EUV spectral quality, and 2D plasma density measurements were made simultaneously along with CE. Our work has shown that the same CE can be achieved for various pulse durations for planar Sn targets even when the pulse duration is above 10 ns. Maintaining a high CE for longer pulse durations could be important for work being done with CO₂ lasers since it is difficult to produce a short pulse CO₂ laser.