Laser wavelength dependence on angular emission dynamics of Nd:YAG laser-produced Sn plasmas

We investigated the laser wavelength effect on angular atomic and ionic emission from laser-produced Sn plasma, since it is regarded as a viable candidate for an EUV lithography source. For producing plasmas, the fundamental, second and fourth harmonics radiation from a Nd : YAG laser were used. The angular variation of atomic and ionic particle analysis was carried out using quartz crystal microbalance and Faraday cups by moving them in a circular path at a constant distance from the target normal. Along with atomic and ionic emission, we also compared the plasma emission features in the visible and EUV spectral regions. Results indicate strong forward bias in atomic and ionic plasma debris at all wavelengths. Shorter wavelength plasmas are found to generate more atomic particles while ion flux showed a similar trend irrespective of the excitation wavelength. (Some figures may appear in colour only in the online journal)