The goals of the research group EUV Targets are to study, manipulate and enhance the absorption of infrared light by metals, necessary for the creation of a plasma. This requires a deeper understanding of the fundamental processes that play a role in the interaction of high power laser light with metals, processes which typically occur on femtosecond to picosecond time scales.
Under normal circumstances, metals are excellent reflectors of infrared light. By properly nanopattterning the metal surface, surface plasmons can be excited and this is accompanied by strongly enhanced optical absorption. The absorption can be increased by other means as well, for example, by using nano-antennas, metamaterials, and layered structures.
The fundamental processes leading up to the formation of a plasma are investigated using several techniques. For example, when free electrons and ions are formed after excitation with an ultrafast laser, this gives rise to changing currents and electric fields which in turn will give rise to the emission of terahertz electric fields which can be measured. In addition, we are working on measurements of electron emission by the metals, and the use of two-color pump-probe techniques from the near- to the far-infared to study the light absorption and energy decay. For these experiments high power, tunable femtosecond IR pulses in the range from 0.8 micron to 10 micron are available, in addition to high power laser pulses with a duration < 10 fs.