Influence of laser pulse duration on extreme ultraviolet and ion emission features from tin plasmas

Abstract

We investigated the role of laser pulse duration and intensity on extreme ultraviolet (EUV) generation and ion emission from a laser produced Sn plasma. For producing plasmas, planar slabs of pure Sn were irradiated with 1064 nm Nd:YAG laser pulses with varying pulse duration (5–20 ns) and intensity. Experimental results performed at CMUXE indicate that the conversion efficiency (CE) of the EUV radiation strongly depend on laser pulse width and intensity, with a maximum CE of ∼2.0% measured for the shortest laser pulse width used (5 ns). Faraday Cup ion analysis of Sn plasma showed that the ion flux kinetic profiles are shifted to higher energy side with the reduction in laser pulse duration and narrower ion kinetic profiles are obtained for the longest pulse width used. However, our initial results showed that at a constant laser energy, the ion flux is more or less constant regardless of the excitation laser pulse width. The enhanced EUV emission obtained at shortest laser pulse duration studied is related to efficient laser-plasma reheating supported by presence of higher energy ions at these pulse durations.

Collimation of laser-produced plasmas using axial magnetic field

“…the top magnet (Roy et al, 2014a;2014b). The lateral peak plume expansion velocities measured from the images are 1.2 and 0.75 cm/μs without and with the axial B-field, respectively.…”

“…Details of the experimental setup can be found elsewhere (Roy et al, 2014a;2014b). The laser beam energy was attenuated using a combination of a half-wave plate and a polarizing cube.…”

“…The plasma plume expanded in a direction normal to the target (and parallel to magnetic field). The details of the B-field configuration and distribution obtained using a Gauss meter are given elsewhere (Roy et al, 2014a;2014b). The target was placed in a chamber which was evacuated using a turbomolecular pump to a pressure lower than 10 −5 Torr.…”

“…Laser-produced tin plasma has come up as a most promising and energy-efficient next generation EUV light source for the semiconductor lithography industry (Bakshi, 2009;Roy et al, 2014a;2014b). A high-brightness and debris-free source emitting at 13.5 nm radiation with 2% bandwidth (in-band) is necessary for this purpose.…”

“…In the field of inertial fusion, confinement of the expanding target plasma using a B-field offers a potential means to slow high-energy particles before they implant in the surrounding structures. The B-field is also used for controlling or diverting ion debris in extreme ultraviolet (EUV) lithography laser-produced plasma (LPP) sources (Harilal et al, 2006;Roy et al, 2014a;2014b).…”